Genomic spectrum of actionable alterations in serial cell free DNA (cfDNA) analysis of patients with metastatic breast cancer

We aimed to study the incidence and genomic spectrum of actionable alterations (AA) detected in serial cfDNA collections from patients with metastatic breast cancer (MBC). Patients with MBC who underwent plasma-based cfDNA testing (Guardant360®) between 2015 and 2021 at an academic institution were included. For patients with serial draws, new pathogenic alterations in each draw were classified as actionable alterations (AA) if they met ESCAT I or II criteria of the ESMO Scale for Clinical Actionability of Molecular Targets (ESCAT). A total of 344 patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) MBC, 95 patients with triple-negative (TN) MBC and 42 patients with HER2-positive (HER2 + ) MBC had a baseline (BL) cfDNA draw. Of these, 139 HR+/HER2-, 33 TN and 13 HER2+ patients underwent subsequent cfDNA draws. In the HR+/HER2- cohort, the proportion of patients with new AA decreased from 63% at BL to 27-33% in the 2nd-4th draws (p < 0.0001). While some of the new AA in subsequent draws from patients with HR+/HER2- MBC were new actionable variants in the same genes that were known to be altered in previous draws, 10-24% of patients had new AA in previously unaltered genes. The incidence of new AA also decreased with subsequent draws in the TN and HER2+ cohorts (TN: 25% to 0-9%, HER2 + : 38% to 14-15%). While the incidence of new AA in serial cfDNA decreased with subsequent draws across all MBC subtypes, new alterations with a potential impact on treatment selection continued to emerge, particularly for patients with HR+/HER2- MBC.

Selection of appropriate biomarkers to monitor effectiveness of ovarian function suppression in pre-menopausal patients with ER+ breast cancer

Use of gonadotropin-releasing hormone (GnRH) agonists has been widely adopted to provide reversible ovarian function suppression for pre-menopausal breast cancer patients who are also receiving aromatase inhibitor or tamoxifen therapy based on results of 25 randomized trials representing almost 15,000 women demonstrating a survival benefit with this approach. Past clinical trials designed to establish the efficacy of GnRH agonists have monitored testosterone in the prostate cancer setting and estradiol in the breast cancer setting. We explore the merits of various biomarkers including estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) and their utility for informing GnRH agonist treatment decisions in breast cancer. Estradiol remains our biomarker of choice in ensuring adequate ovarian function suppression with GnRH agonist therapy among pre-menopausal women with breast cancer. We recommend future trials to continue to focus on estradiol levels as the primary endpoint, as they have in the past.

Glutaminase (GLS1) gene expression in primary breast cancer

BACKGROUND

Tumor growth is mediated in part by glutamine, and glutaminase is an enzyme necessary for glutamine catabolism. We studied glutaminase (GLS1) gene expression in primary breast cancer to determine correlations with clinical and tumor characteristics, and gene associations in publicly available databases. A better understanding of glutaminase gene expression may help guide further exploration of glutaminase inhibitors in breast cancer.

METHODS

GLS1 mRNA levels were evaluated in The Cancer Genome Atlas (n = 817) and METABRIC (n = 1992) datasets. Associations between GLS1 and tumor subtype (ANOVA followed by post-hoc Tukey test for pairwise comparisons) and selected genes involved in the pathogenesis of breast cancer (Pearson's correlations) were determined in both datasets. In METABRIC, associations with overall survival (Cox proportional hazard model) were determined. For all analyses, p < 0.05 was the threshold for statistical significance.

RESULTS

GLS1 expression was significantly higher in triple negative breast cancer (TNBC) than hormone receptor (HR) +/HER2- and HER2+ breast cancer (p < 0.001) and basal versus luminal A, luminal B, and HER2 enriched breast cancer (p < 0.001) in both datasets. In METABRIC, higher GLS1 expression was associated with improved overall survival (HR 0.91, 95% CI: 0.85-0.97, p = 0.005) and this association remained significant in the TNBC subset (HR 0.83, 95% CI: 0.71-0.98, p = 0.032). GLS1 had significant positive gene correlations with immune, proliferative, and basal genes, and inverse correlations with luminal genes and genes involved in metabolism.

CONCLUSION

GLS1 expression is highest in TNBC and basal breast cancer, supporting ongoing clinical investigation of GLS1 inhibition in TNBC. GLS1 may have prognostic implications but further research is needed to validate this finding. GLS1 had significant positive gene correlations with immune genes, which may have implications for potential combinations of glutaminase inhibition and immunotherapy.

Clicking Away to Capture Cancer Staging-The Benefits and Challenges of Completing Standardized Staging Modules

This article by Neelima Vidula and Jeffrey Peppercorn @MGHCancerCenter explores the benefits and challenges of completing standardized modules for cancer staging, and opportunities to improve module compliance while reducing burnout

Utilizing cell-free DNA to predict risk of developing brain metastases in patients with metastatic breast cancer

We compared cell-free DNA (cfDNA) results at MBC diagnosis in patients who developed brain metastases (BM) vs those without (non-BM) to understand genomic predictors of BM. Patients with cfDNA testing at MBC diagnosis (Guardant360®, 73 gene next generation sequencing) were identified. Clinical and genomic features of BM and non-BM were compared (Pearson's/Wilcoxon rank sum tests). Eighteen of 86 patients (21%) with cfDNA at MBC diagnosis developed BM. Comparing BM vs non-BM, a higher prevalence of BRCA2 (22% vs 4.4%, p = 0.01), APC (11% vs 0%, p = 0.005), CDKN2A (11% vs 1.5%, p = 0.05), and SMAD4 (11% vs 1.5%, p = 0.05) was observed. Seven of 18 BM had ≥1 of the following 4 mutations in baseline cfDNA: APC, BRCA2, CDKN2A or SMAD4 vs 5/68 non-BM (p = 0.001). Absence of this genomic pattern had a high negative predictive value (85%) and specificity (93%) in excluding BM development. Baseline genomic profile varies in MBC that develops BM.

Abstract 960: Overlapping expression landscape of antibody drug conjugate targets, trophoblast cell surface antigen 2 (Trop-2) & human epidermal growth factor receptor 2 (HER2), in breast cancer

Background Antibody drug conjugates (ADC) are novel drugs linking potent payloads to antibodies targeting antigen-expressing tumors. Sacituzumab govitecan (SG), targeting Trop-2, is approved for metastatic triple negative breast cancer (TNBC); and trastuzumab deruxtecan, targeting HER2, is approved for HER2-positive and HER2-low metastatic breast cancer. To understand the potentially overlapping clinical landscape of Trop-2 and HER2 antigens, we evaluated RNA expression data in breast cancer from The Cancer Genome Atlas (TCGA) project.

Methods TCGA dataset was assessed for Trop-2 and HER2 expression via processed RNA sequencing (RNA-seq) data of the corresponding genes TACSTD2 and ERBB2. Medium/high gene expression was assessed as &gt;100 transcripts per million (TPM). Samples were classified HER2-low per ASCO/CAP guidelines. Gene expression across clinical parameters was assessed via one-way ANOVA.

Results 1076 patients with primary breast cancer were included. The majority (59%) had both high TACSTD2 expression (TACSTD2hi) and high ERBB2 expression (ERBB2hi) (see Table). Median TACSTD2 expression was 572 TPM (IQR 349-666 TPM); median ERBB2 expression was 122 TPM (IQR 73-192 TPM). No significant difference was observed in TACSTD2 or ERBB2 expression among invasive ductal carcinoma, invasive lobular carcinoma, mixed histology, or other (p = 0.07, 0.23). No significant difference in TACSTD2 expression was noted between HER2-low and HER2-negative subtypes (p=0.34).

Conclusions While SG is approved in TNBC, TACSTD2 is expressed across all breast cancer subtypes, including HER2-low, suggesting a broader population may benefit from Trop-2-targeted ADCs. Furthermore, given that over half of breast cancers have high expression of both TACSTD2 and ERBB2, additional studies are needed to understand the optimal sequencing of ADC-based therapies for patients with breast cancer.

Table Patient subsets(HR = hormone receptor) n TACSTD2hi & ERBB2hi TACSTD2hi & ERBB2low TACSTD2low & ERBB2hi TACSTD2low & ERBB2low All 1,076 632 (59%) 394 (36%) 19 (2%) 31 (3%) Histology 843 Invasive ductal carcinoma 507 267 (32%) 215 (25%) 10 (1%) 15 (2%) Invasive lobular carcinoma 130 103 (12%) 24 (3%) 1 (&lt;1%) 2 (&lt;1%) Mixed 91 63 (7%) 24 (3%) 2 (&lt;1%) 2 (&lt;1%) Other 115 65 (8%) 43 (5%) 2 (&lt;1%) 5 (&lt;1%) HER2 Status 345 HR+/HER2-low 254 170 (49%) 77 (22%) 6 (1%) 1 (&lt;1%) TNBC/HER2-low 55 12 (3%) 39 (11%) 1 (&lt;1%) 3 (&lt;1%) HR+/HER2-negative 24 13 (4%) 11 (3%) 0 0 TNBC/HER2-negative 12 1 (&lt;1%) 10 0 1 (&lt;1%)

Citation Format: Arielle J. Medford, Nicholas J. Haradhvala, Neelima Vidula, Rachel Abelman, Laura M. Spring, Leif W. Ellisen, Gad Getz, Aditya Bardia. Overlapping expression landscape of antibody drug conjugate targets, trophoblast cell surface antigen 2 (Trop-2) & human epidermal growth factor receptor 2 (HER2), in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 960.

Arrhythmogenic Cardiotoxicity Associated With Contemporary Treatments of Lymphoproliferative Disorders

Background There are limited data on risk of arrhythmias among patients with lymphoproliferative disorders. We designed this study to determine the risk of atrial and ventricular arrhythmia during treatment of lymphoma in a real-world setting. Methods and Results The study population comprised 2064 patients included in the University of Rochester Medical Center Lymphoma Database from January 2013 to August 2019. Cardiac arrhythmias-atrial fibrillation/flutter, supraventricular tachycardia, ventricular arrhythmia, and bradyarrhythmia-were identified using International Classification of Diseases, Tenth Revision (ICD-10) codes. Multivariate Cox regression analysis was used to assess the risk of arrhythmic events with treatments categorized as Bruton tyrosine kinase inhibitor (BTKi), mainly ibrutinib/non-BTKi treatment versus no treatment. Median age was 64 (54-72) years, and 42% were women. The overall rate of any arrhythmia at 5 years following the initiation of BTKi was (61%) compared with (18%) without treatment. Atrial fibrillation/flutter was the most common type of arrhythmia accounting for 41%. Multivariate analysis showed that BTKi treatment was associated with a 4.3-fold (P<0.001) increased risk for arrhythmic event (P<0.001) compared with no treatment, whereas non-BTKi treatment was associated with a 2-fold (P<0.001) risk increase. Among subgroups, patients without a history of prior arrhythmia exhibited a pronounced increase in the risk for the development of arrhythmogenic cardiotoxicity (3.2-fold; P<0.001). Conclusions Our study identifies a high burden of arrhythmic events after initiation of treatment, which is most pronounced among patients treated with the BTKi ibrutinib. Patients undergoing treatments for lymphoma may benefit from prospective focused cardiovascular monitoring prior, during, and after treatment regardless of arrhythmia history.

Abstract PD1-10: Impact of Race on Clinical, Socioeconomic, and Genomic Characteristics, Clinical Trial Participation, and Receipt of Genotype-matched Therapy Among Patients with Metastatic Breast Cancer

Background: Clinical outcomes in breast cancer differ across racial and ethnic populations. We have previously demonstrated that receipt of genotype-matched therapy targeted to an actionable mutation may potentially improve patient outcomes (Vidula, CCR, 2021). We evaluated the impact of race on clinical, socioeconomic, and genomic characteristics, clinical trial participation, and receipt of genotype-matched therapy among patients with metastatic breast cancer (MBC). Methods: We conducted a retrospective study of patients with MBC at an academic institution who underwent cell-free DNA testing (cfDNA, Guardant360, 74 gene panel) as part of routine clinical care from 11/29/2016-11/2/2020. Patient demographics (including self-reported race and ethnicity) and clinical trial enrollment (at same institution) were determined by retrospective data collection. Mutations identified in cfDNA were characterized as actionable based on the variant interpretation performed by Guardant360 using vetted genomic databases, and receipt of genotype-matched therapy targeted to an actionable mutation was determined as previously described (Vidula, CCR, 2021). Pearson’s chi-squared and Wilcoxon rank-sum tests were used to compare categorical and continuous variables between groups, with p&lt; 0.05 indicating statistical significance. Results: Four hundred and twenty-five patients with MBC and cfDNA results were identified, of which 369 were White (87%), 27 Black (6.4%), 15 Hispanic (3.5%), and 14 Asian (3.3%). There were no significant differences in median age at MBC diagnosis (p=0.064), disease subtype distribution (p=0.74), proportions of de-novo/recurrent MBC (p=0.95), presence of visceral metastases (p=0.84), Charleston comorbidity index (p=0.93), menopausal status (p=0.3), and level of education (p=0.44) across racial groups. Higher proportions of non-primary English speakers were seen in Hispanic (80%) and Asian (29%) races (p&lt; 0.001). Median distance traveled to the institution also varied based on race, with White patients traveling further (White: 39.1 miles, Black: 21.8 miles, Hispanic 9.4 miles, Asian 9.1 miles, p&lt; 0.001). In addition, type of insurance varied based on race, with White patients having the highest rates of commercial insurance and Medicare, Black patients having the highest rate of state-supported insurance, and Asian patients having the highest uninsured rates (p&lt; 0.001). Clinical trial enrollment rates did not significantly differ by race (White: 44%, Black: 37%, Hispanic: 47%, and Asian 21%, p=0.34), but patients without insurance were significantly less likely to be enrolled on a trial than those with commercial insurance (p=0.03). The proportion of patients with ≥1 actionable mutation in cfDNA did not vary significantly by race (White: 78%, Black: 56%, Hispanic: 73%, Asian 86%, p=0.18) and the median number of actionable mutations found in cfDNA was similar across races (p=0.31). However, receipt of genotype-matched therapy targeted to an actionable mutation varied by race, with the highest rates of matched therapy in White patients (White: 28%, Black: 11%, Hispanic 13%, Asian 14%, p&lt; 0.001). After multivariable logistic regression adjusting for subtype, commercial insurance versus other insurance types, and proximity to the center, White patients remained significantly more likely to receive matched therapy (p=0.029). Conclusions: We observed significant race-based differences in non-English speaking status, insurance type, and median distance traveled to the institution. Racial/ethnic minority patients were less likely to receive genotype-matched therapy than White patients. Further research is needed to identify barriers and reduce disparities in access to precision medicine.

Citation Format: Rupali Sood, Lianne Ryan, Andrzej Niemierko, Laura M. Spring, Dejan Juric, Steven J. Isakoff, Seth A. Wander, Jennifer Shin, Naomi Ko, Leif Ellisen, Beverly Moy, Aditya Bardia, Neelima Vidula. Impact of Race on Clinical, Socioeconomic, and Genomic Characteristics, Clinical Trial Participation, and Receipt of Genotype-matched Therapy Among Patients with Metastatic Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD1-10.

Abstract PD13-07: PD13-07 Combination therapy with the AKT inhibitor, ipatasertib, endocrine therapy, and a CDK4/6 inhibitor for hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC): results from the phase I TAKTIC trial

Background: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) provide significant clinical benefit in patients with HR+/HER2- metastatic breast cancer (MBC) and have become a standard of care treatment. Prior insights from tumor profiling and preclinical analyses suggest that AKT1 activation can induce CDK4/6i resistance. We hypothesized that targeting AKT1 following CDK4/6i progression may be an effective therapeutic strategy and conducted a clinical trial to evaluate both doublet (ET+AKTi) and triplet (ET+AKTIi+CDK 4/6i) therapy in the ≥ 2nd line MBC setting. Methods: TAKTIC is an open-label phase Ib clinical trial (clinicaltrials.gov NCT03959891) evaluating the combination of the AKT inhibitor ipatasertib (ipat) with fulvestrant (Arm A), an aromatase inhibitor (Arm B), or the triplet combination (Arm C) with fulvestrant + palbociclib (palbo). The primary objective is to evaluate the safety (NCI CTCAE 5.0) and tolerability of ipat in combination with endocrine therapy +/- CDK4/6i. Secondary objectives include clinical efficacy, as determined by objective response rate (RECIST v1.1), clinical benefit rate (CBR), progression-free survival (PFS), and overall survival (OS). Key inclusion criteria include unresectable HR+/HER2- MBC; at least 1 prior therapy for MBC including any CDK4/6i; up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). Here, we present an updated interim analysis from all study arms. Results: The trial completed accrual with 77 pts enrolled from June 2019 – February 2022, including 19 on Arm A, 16 on Arm B, and 42 on Arm C. Median age was 62 (range 32-88) and 65/77 pts (84%) received prior CDK4/6i (median no. of prior lines = 3, range 1-13). 56/77 pts (73%) had measurable disease at baseline and 50/77 pts (65%) had visceral metastases in the liver/lung (68% Arm A, 44% Arm B, 71% Arm C). Pts enrolled on Arms A and B received ipat at 400mg in combination with fulvestrant or an aromatase inhibitor, respectively. In Arm C, 27/42 pts enrolled into the dose escalation phase and received ipat + palbo at varying doses in combination with fulvestrant. Two DLTs were observed in the 300mg ipat + 125mg palbo cohort (grade 4 neutropenia ≥ 7 days). ET+400mg ipat + 100mg palbo was determined to be the recommended phase 2 dose (R2PD), and the remaining 15/42 pts on Arm C were treated at this dose level in the expansion phase. Treatment was well tolerated in all arms. Grade 3 and 4 toxicities included neutropenia (39/77, 50.6%), leukopenia (15/77, 19.5%), diarrhea (11/77, 14/3%), transaminitis (7/77, 9.1%), lymphopenia (6/77, 7.8%), rash (6/77, 7.8%), and thrombocytopenia (3/77, 3.9%). As of 6/28/2022, 16/77 pts remain on treatment. The median treatment duration for all pts is estimated at 6 months (range 0.5-39). Among the 56 pts with measurable disease, 11 had partial response (PR) and 32 had stable disease (SD) as the best response. CBR, defined as percentage of pts who achieved PR or SD &gt; 6 months, was 48% across the study (53% Arm A, 31% Arm B, 57% Arm C). The median PFS was 5.5 months (95% confidence interval [CI]: 3.8 – 7.4) and the median OS was 24.5 months (95% CI: 17.1 – 33.9). Conclusions: The combination of ipat with endocrine therapy +/- palbo is well tolerated in heavily pre-treated pts, with preliminary evidence of clinical activity. This trial demonstrates how molecular insights related to CDK4/6i resistance inform potential therapy combinations. Further studies are needed to evaluate AKTi-based combinations in pts with HR+ MBC.

Citation Format: Seth A. Wander, Jennifer C. Keenan, Andrzej Niemierko, Dejan Juric, Laura M. Spring, Jeffrey Supko, Neelima Vidula, Steven J. Isakoff, Lianne Ryan, Sarah Padden, Elizabeth Fisher, Amber Newton, Beverly Moy, Leif Ellisen, Douglas S. Micalizzi, Aditya Bardia. PD13-07 Combination therapy with the AKT inhibitor, ipatasertib, endocrine therapy, and a CDK4/6 inhibitor for hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC): results from the phase I TAKTIC trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD13-07.

Abstract OT1-11-01: Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer identified by cell-free DNA or tumor tissue genotyping

Background: PARP inhibitors are currently approved for the treatment of germline BRCA1/2 mutant metastatic breast cancer (MBC), which accounts for 5-10% of breast cancer. We hypothesize that a PARP inhibitor may also have efficacy in somatic BRCA1/2 mutant MBC, expanding the potential clinical applicability of PARP inhibitors. We previously demonstrated that somatic BRCA1/2 mutations can be identified by both cell-free DNA and tumor tissue genotyping in a subset of patients with MBC who are not germline BRCA1/2 carriers. Furthermore, a PARP inhibitor was demonstrated to induce cell growth inhibition in a circulating tumor cell culture model generated from a patient with pathogenic somatic BRCA1 mutant MBC (Vidula, Dubash, CCR, 2020). In this trial, we are evaluating the efficacy of a PARP inhibitor in somatic BRCA1/2 mutant MBC. Trial Design: This phase II investigator-initiated clinical trial is enrolling 30 patients with somatic BRCA1/2 mutant MBC identified via cell-free DNA or tumor tissue genotyping. Patients are treated with talazoparib, a PARP inhibitor, until disease progression. At baseline and every 3 months, patients undergo CT chest, abdomen, and pelvis, and a bone scan for disease assessment. Patients undergo blood collection at baseline for the Cancer Risk B (CR-B) assay, a novel flow variant assay to assess double-strand break repair mutations in circulating blood cells (Syeda, 2017) and monthly blood collection for cell-free DNA analysis to evaluate changes in the genomic environment. Eligibility Criteria: Patients with MBC with a pathogenic somatic BRCA1/2 mutation identified by cell-free DNA or tumor tissue genotyping are eligible. Both patients with triple-negative breast cancer (≥ 1 prior chemotherapy) or hormone receptor positive/HER2- MBC (≥ 1 prior hormone therapy) are eligible. Patients should not be known germline BRCA1/2 carriers. There is no limit on prior therapies including receipt of a prior platinum (in the absence of disease progression on prior platinum). A prior PARP inhibitor is not allowed. Adequate performance status and organ function are needed. Specific Aims: Primary aim is progression-free survival (PFS) assessed by RECIST 1.1. Secondary aims include objective response rate and toxicity assessed by NCI CTCAE v 5.0. Exploratory aims include assessing impact of BRCA1/2 reversion mutations in cell-free DNA, studying serial changes in BRCA1/2 mutant allelic frequency in cell-free DNA, comparing pre- and post-treatment cell-free DNA results to identify changes in the genomic environment, assessing the CR-B assay positivity rate, and correlating these biomarker analyses with patient response. Statistical Methods: This study uses a two-stage design with 80% power to demonstrate that talazoparib is associated with “success” (PFS &gt; 12 weeks) in 53% patients (4% alpha). Accrual: This study (NCT03990896) is open at Massachusetts General Hospital, MD Anderson, University of California San Francisco, and Emory, with pending activation at Northwestern, Cornell, and Vanderbilt. Five patients are enrolled as of 7/2022. Funding: This study is supported by a Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO–Breast Cancer Research Foundation- Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu

Citation Format: Neelima Vidula, Senthil Damodaran, Erica L. Blouch, Nora Horick, Nathan Royce Ruffle-Deignan, Manali Bhave, Ami N. Shah, Leticia Varella, Vandana Abramson, Joseph Sparano, Leif Ellisen, Ishraq Alim, Harry Ostrer, Hope Rugo, Aditya Bardia. Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer identified by cell-free DNA or tumor tissue genotyping [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT1-11-01.

Abstract P1-13-07: Investigating NF1 Mutations in Circulating Tumor DNA of Patients with Hormone-receptor Positive (HR+) Breast Tumors Resistant to CDK4/6 Inhibition (CDK4/6i): A Retrospective Clinical Analysis

Background: CDK4/6 inhibitors (CDK4/6i) are standard of care for the management of HR+/HER2- metastatic breast cancer (MBC). Genomic alterations that drive resistance to CDK4/6i are diverse, and while the molecular landscape is heterogeneous, several mechanisms of CDK4/6i resistance converge on the RAS/MAPK and PI3K/AKT/mTOR signaling pathways. NF1 downregulates RAS and dampens cellular proliferation. Laboratory-based models demonstrate that loss of NF1 is associated with resistance to endocrine therapy (ET), and emergence of NF1 mutations (NF1m) are correlated with progressive disease (PD) in circulating tumor DNA (ctDNA). While NF1m may diminish CDK4/6i susceptibility, a clear relationship has not been elucidated. The primary objective of this study was to characterize patient (pt) response to CDK4/6i in NF1m HR+/HER2- MBC. Methods: We identified 47 pts with NF1m via a database with one or more ctDNA samples sequenced at variable time-points as part of routine care for MBC. NF1m were categorized as pathogenic (p)NF1m or variants of uncertain significance (VUS) based on their associated Guardant report. We identified 27 pts with HR+/HER2- MBC and NF1m that received at least 1 line of CDK4/6i in the metastatic setting. Intrinsic resistance was defined as PD &lt; 6 months on a CDK4/6i regimen, and acquired resistance was defined as PD &gt;6 months. Pts with intrinsic resistance or acquired resistance and NF1m detected post-PD were categorized as having a resistance phenotype potentially driven by NF1m. Pts with NF1m detected prior to therapy and &gt;6 months clinical response on a CDK4/6i were categorized as having NF1m tumors sensitive to CDK4/6i. Results: The NF1m cohort (n = 27) had 9 pts with pNF1m, while 18 pts expressed VUS. The median age at MBC diagnosis was 54 years, and 67% had visceral metastasis at ctDNA collection. Pts received a median of 1 prior line (range: 0 - 6) of ET or chemotherapy in the metastatic setting before CDK4/6i. Amongst pts with pathogenic variants (n = 9), we found 3 pts with pNF1m were intrinsically resistant to CDK4/6i. Acquired resistance was seen in 1 pt with pNF1m detected post-PD, and 2 pts had evidence of both acquired and subsequent intrinsic resistance to a later line of CDK4/6i. Overall, 67% (6/9) of pNF1m pts demonstrated a CDK4/6i resistance phenotype; mutant allele fraction (AF) ranged from 0.2% - 29.9%, and the mean maximum allele fraction (MAF) was 6.0%. Pre- and post-treatment samples were available on 3 pts with pNF1m, and 1 of these pts had an AF rise from 2.7% to 12.3% when comparing ctDNA pre- and post-CDK4/6i. ctDNA from 4 of 6 resistant tumors harbored other putative drivers including alterations in FGFR, KRAS, PTEN, and RB. We identified 2 counter-examples of pNF1m tumors sensitive to CDK4/6i. These pts expressed relatively low NF1m AF, ranging 0.1% - 0.5% with a mean MAF 0.3%. Another pNF1m pt had intrinsic resistance to initial CDK4/6i but was sensitive to later-line CDK4/6i. In the subgroup of pts with VUS-NF1m (n = 18), a more mixed picture of resistance and sensitivity was seen. 8 pts had intrinsic or acquired resistance, 8 pts had NF1m tumors sensitive to CDK4/6i, and 1 pt had evidence of both; 61% (n = 11) of pts expressed alterations in other resistance mediating genes. 1 pt stopped therapy due to toxicity rather than PD. Conclusions: Our work demonstrates that tumor expression of pNF1m may be associated with CDK4/6i resistance in pts with HR+/HER2- MBC, and allele fraction could be predictive of drug susceptibility. Tumors harboring VUS had varied sensitivity, suggesting that some of these mutations may not be pathogenic, and counter-examples of pNF1m MBC benefiting from CDK4/6i plus ET highlight the complexities in predicting drug response based on single gene alteration. Future effort is warranted to explore the potential impact of NF1 on CDK4/6i resistance, as well as the potential role for therapies targeting the MAPK pathway in this patient population.

Citation Format: Maxwell R. Lloyd, Lianne Ryan, Arielle J. Medford, Jennifer C. Keenan, Laura M. Spring, Neelima Vidula, Beverly Moy, Dejan Juric, Leif Ellisen, Aditya Bardia, Seth A. Wander. Investigating NF1 Mutations in Circulating Tumor DNA of Patients with Hormone-receptor Positive (HR+) Breast Tumors Resistant to CDK4/6 Inhibition (CDK4/6i): A Retrospective Clinical Analysis [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-13-07.

Abstract P5-03-18: Co-occurring alterations in PALB2 germline carriers identified by liquid biopsy in patients with advanced breast cancer

Introduction: PALB2 is a BRCA complex-interacting protein and has an essential role in homologous recombination and repair (HRR). PALB2 germline (gPALB2) mutations are found in 1 – 4% of breast cancer patients and can be incidentally identified by liquid biopsy testing. Recent data has shown the efficacy for PARP inhibitors (PARPi) in breast cancer gPALB2 carriers, highlighting the importance of understanding genomic drivers in this group of patients. Here we present the genomic landscape of patients with advanced breast cancer (aBC) with incidental gPALB2 mutations identified by liquid biopsy testing. Methods: Genomic results were queried for aBC patients who had Guardant360 (G360) testing as part of routine clinical care from October 2020 – March 2022. Eligible patients had must have a diagnosis of breast cancer and an incidental gPALB2 alteration identified on G360, defined by presence of ClinVar loss-of-function single nucleotide variant (SNV)/indel mutation. Co-occurring somatic alterations in these patients were then analyzed after removing synonymous and variants of uncertain significance. Analysis of HRR-related alterations, such as loss of heterozygosity and/or copy number loss, was performed in a subset of patients. Clinical demographics and clinical status (newly diagnosed or progressing at the time of G360 testing), were extracted from test requisition forms. Results: A total of 48 patients had gPALB2 alterations: 60% had indels and 40% SNVs. gPALB2 variant allele frequencies (VAF) were &gt;30% for all patients (median VAF: 49.7, range: 34.1-66.6). All patients were female with a median age of 59 years (range: 31-84); 29 (60%) were tested at progression whereas the rest were tested at diagnosis. 36 (75%) patients with gPALB2 had co-occurring somatic alterations across 23 genes. The most commonly mutated genes were TP53 (47%), ESR1 (23%), and PIK3CA (19%); other mutated genes had less than 7% frequency. Notably, 95% of patients with co-occurring ESR1 alterations and 70% found to harbor PIK3CA co-occurring alterations were tested at progression. Other clinically relevant findings include co-occurring somatic alterations in MTOR (4%) and HRR-related genes ATM, ARID1A, CHEK2, FANCA (4% each; one patient had both ATM and CHEK2 somatic alterations). No somatic BRCA1/BRCA2 alterations were identified in gPALB2 patients. For 33 (69%) patients with gPALB2, additional HRR-related biomarker analysis was performed resulting in identification of 3 (9%) patients with copy number loss, one who had CHEK2 and PALB2 single copy number loss, resulting in PALB2 biallelic loss. In the overall cohort, an additional 33 patients were identified with uniquely somatic PALB2 alterations. Conclusions: Carriers of gPALB2 alterations comprise a rare subset of aBC patients analyzed by liquid biopsy. These patients have co-occurring somatic alterations identified in genes that have been reported in published cohorts of aBC patients without gPALB2 alterations. Assessment of additional somatic HRR-related alterations may identify other patients with PALB2 findings who could benefit from PARPi. Clinical studies are needed to assess how patients with gPALB2 and co-occurring mutations may have altered response and/or resistance to therapies, including standard-of-care regimens and PARPi.

Citation Format: Nan Chen, Rita Nanda, Frederick M. Howard, Neelima Vidula, Jennifer Yen, Leylah M. Drusbosky, Leslie Bucheit. Co-occurring alterations in PALB2 germline carriers identified by liquid biopsy in patients with advanced breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-03-18.

Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer

Purpose

To explore the immunogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in patients with breast cancer based on type of anticancer treatment.

Methods

Patients with breast cancer had anti-spike antibody concentrations measured ⩾14 days after receiving a full SARS-CoV-2 vaccination series. The primary endpoint was IgA/G/M anti-spike antibody concentration. Multiple regression analysis was used to analyze log₁₀-transformed antibody titer concentrations.

Results

Between 29 April and 20 July 2021, 233 patients with breast cancer were enrolled, of whom 212 were eligible for the current analysis. Patients who received mRNA-1273 (Moderna) had the highest antibody concentrations [geometric mean concentration (GMC) in log₁₀: 3.0 U/mL], compared to patients who received BNT162b2 (Pfizer) (GMC: 2.6 U/mL) (multiple regression adjusted p = 0.013) and Ad26.COV2.S (Johnson & Johnson/Janssen) (GMC: 2.6 U/mL) (p = 0.071). Patients receiving cytotoxic therapy had a significantly lower antibody titer GMC (2.5 U/mL) compared to patients on no therapy or endocrine therapy alone (3.0 U/mL) (p = 0.005). Patients on targeted therapies (GMC: 2.7 U/mL) also had a numerically lower GMC compared to patients not receiving therapy/on endocrine therapy alone, although this result was not significant (p = 0.364). Among patients who received an additional dose of vaccine (n = 31), 28 demonstrated an increased antibody response that ranged from 0.2 to >4.4 U/ mL.

Conclusion

Most patients with breast cancer generate detectable anti-spike antibodies following SARS-CoV-2 vaccination, though systemic treatments and vaccine type impact level of response. Further studies are needed to better understand the clinical implications of different antibody levels, the effectiveness of additional SARS-CoV-2 vaccine doses, and the risk of breakthrough infections among patients with breast cancer.

Trophoblast Cell Surface Antigen 2 gene (TACSTD2) expression in primary breast cancer

PURPOSE

Trophoblast Cell Surface Antigen 2 (TROP2) is a glycoprotein expressed in many cancers. A TROP2 antibody-drug conjugate (ADC) was effective in metastatic triple-negative breast cancer (TNBC). We studied TROP2 gene (TACSTD2) expression and associations with tumor and clinical characteristics, as well as selected external genes in primary breast cancer.

METHODS

TACSTD2 gene expression was evaluated using microarray data from I-SPY 1 (n = 149), METABRIC (n = 1992), and TCGA (n = 817). Associations with clinical features (Kruskal-Wallis test, all datasets), chemotherapy response (Wilcoxon rank sum test, I-SPY 1), recurrence free survival (Cox proportional hazard model, I-SPY 1 and METABRIC), and selected genes (Pearson correlations, all datasets) were determined.

RESULTS

TACSTD2 gene expression was detectable in all breast cancer subtypes, with a wide range of expression (all datasets). TACSTD2 gene expression was lower in HER2 + than HR + /HER2- and TNBC (METABRIC: p = 0.03, TCGA p = 0.007), and in HER2 + enriched and luminal B breast cancer (METABRIC: p < 0.001, TCGA: p < 0.001). TACSTD2 expression was higher in grade I vs. II/III tumors (METABRIC: p < 0.001). No association with chemotherapy response (I-SPY 1) or recurrence free survival (I-SPY 1 and METABRIC) was seen. TACSTD2 has significant positive correlations with the expression of epithelial/adhesion genes and proliferative genes, but was inversely correlated with immune genes.

CONCLUSION

TACSTD2 gene expression was seen in all breast cancer subtypes particularly luminal A and TNBC, and correlated with the expression of genes involved in cell epithelial transformation, adhesion, and proliferation, which contribute to tumor growth. These results support the investigation of TROP2 ADC in all subtypes of breast cancer.

Utilizing Natural Language Processing (NLP) to identify breast cancer associated-lung metastases from pathology reports to delineate characteristics and challenges of this common site of breast cancer recurrence

e13592

Background: NLP (artificial intelligence) can automate the identification of records in large datasets. The purpose of this study was to evaluate the feasibility of NLP to identify breast cancer-associated lung metastases to understand clinical characteristics and challenges posed by this common site of breast cancer recurrence. Methods: Patients with pathologically confirmed breast cancer associated-lung metastases seen at a large academic center between 3/2012-5/2019 were identified using NLP of institutional pathology reports, with an IRB approved protocol. Chart review was performed to confirm breast cancer associated-lung metastases and determine clinical and pathological features. Results: Using NLP, 32 patients with pathology reports denoting breast cancer associated-lung metastases were identified, with pathologic confirmation of lung biopsy tissue in the majority of cases (24), and pleural fluid specimens (8) on the remainder. Ten of 32 (31%) were HR+/HER2-, 3/32 (9.3%) HER2+, and 19/32 (59%) TNBC. The majority were invasive ductal carcinoma (21/26) with the remainder invasive lobular carcinoma (2/26) or mixed histology (3/26). Median age at lung metastasis diagnosis was 62 years (range 31-88). The median time to development of lung metastasis following primary breast cancer was 5.6 years (range 0-24.8 years). Fifty six percent of lung metastases were detected on imaging and 44% by symptoms including dyspnea, cough, or pain. Tumor tissue genotyping results on the lung metastases were available for 8 patients showing PI3KCA (5), TP53 (3), SMARCA4 (2), ERBB2 (1), FGFR3 (1), ATM (1), CDK4 (1), MYC (1), and ESR1 (1). Treatment after diagnosis of lung metastases included hormone therapy (61%), chemotherapy (84%), lung irradiation (26%), and surgical resection of lung metastases (6%). Lung metastases were associated with considerable morbidity including pleural effusion (15%), dyspnea (6%), pneumothorax (3%), hemothorax (3%), and atelectasis (3%). Patients diagnosed with lung metastases had brain (32%), bone (35%), renal (6%), skin (3%) and adrenal (3%) metastases during disease course. Conclusions: NLP can help identify organ specific metastases from pathology reports, such as breast cancer associated-lung metastases, which can then facilitate observational, translational, and clinical research to characterize and address challenges posed by this common site of breast cancer recurrence. This cohort of patients highlights the morbidity of breast cancer associated-lung metastases and potential role of NLP for disease characterization and clinical research. (Support from ASCO Medical Student Rotation for Underrepresented Populations Award.)

Abstract OT1-18-08: Randomized phase II trial of pembrolizumab/carboplatin vs. carboplatin alone for breast cancer with chest wall recurrence: TBCRC044

Background: A significant number of patients with breast cancer may develop chest wall recurrence, which can be difficult to treat, and is associated with a poor prognosis. Given the inflammatory nature of chest wall disease, and the association of chest wall disease with lymphovascular invasion, we hypothesized that immunotherapy may be beneficial in this setting. Furthermore, combining immunotherapy and chemotherapy may have a synergistic effect; indeed, the combination of the anti-programmed cell death 1 (PD-1) antibody, pembrolizumab, with chemotherapy has been approved for metastatic triple negative breast cancer (TNBC). Consequently, in this study, we are evaluating the combination of pembrolizumab/carboplatin vs. carboplatin alone for chest wall recurrence. Trial design: This is a phase II study of patients with chest wall disease from breast cancer. Patients are randomized in a 2:1 manner to pembrolizumab/carboplatin x 6 cycles (Arm A) with the option to continue pembrolizumab +/- carboplatin after 6 cycles (Arm Ax) vs. carboplatin alone (Arm B) with the option to cross-over to pembrolizumab +/- carboplatin on progression (Arm Bx). Carboplatin is dosed at AUC 5 IV every 3 weeks, and pembrolizumab at 200 mg IV every 3 weeks. Trastuzumab may be continued with study treatment in patients with HER2 positive disease. Imaging scans (CT chest, abdomen, and pelvis, and bone scan) occur at baseline and every 3 cycles. Chest wall biopsies and peripheral blood is collected at baseline and after completing 2 cycles of treatment for correlative studies. Eligibility criteria: Patients must have chest wall disease from breast cancer. Distant metastases are allowed. TNBC, hormone receptor positive/HER2 negative disease (after 2 prior hormone therapies), and HER2 positive disease (progressed on standard HER2 directed treatment) are eligible. Any number of prior lines of chemotherapy are acceptable, including a prior platinum chemotherapy in the absence of disease progression on the platinum. Specific Aims: Primary aim is to determine disease control rate in the chest wall and other distant sites at 18 weeks of treatment with RECIST 1.1. Secondary aims including determining toxicity, progression-free survival, response based on irRECIST, and response based on tumor PD-L1 expression. Exploratory aims include studying changes in: 1) immune composition of tumor and peripheral blood, 2) peripheral blood cell-free DNA and circulating tumor cells, 3) soluble PD-L1 expression, and 4) association of MYC with PD-1 and immune markers, based on preclinical data demonstrating that MYC upregulates these markers. Statistical Methods: 84 patients (Arm A: 56, Arm B: 28) are being enrolled at 7 sites in the Translational Breast Cancer Research Consortium. The study is powered to identify a 20% difference in disease control rates between Arms A and B (HR 0.52, α= 0.10, ß=0.20). A futility analysis will occur for Arm B after 18 patients are enrolled to allow for early closure if lack of efficacy. Accrual: Present accrual is 57 patients (Arm A: 39, Arm B: 18). (NCT03095352). This trial is partly funded by grants from Merck and University of California San Francisco. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu

Citation Format: Neelima Vidula, Rita Nanda, Kathy Miller, Leisha Emens, Vandana Abramson, Ben Park, Minetta C. Liu, Andrei Goga, Hope Rugo. Randomized phase II trial of pembrolizumab/carboplatin vs. carboplatin alone for breast cancer with chest wall recurrence: TBCRC044 [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT1-18-08.

Abstract P5-13-29: Analytical and clinical validation of a ctDNA assay for detecting copy number loss and structural rearrangement variants contributing to homologous recombination and repair (HRR) deficiency

Background: Inactivating HRR gene mutations can lead to HRR deficiency (HRD) and predict response to PARPi therapy in patients with breast cancer. Copy number loss and large genomic rearrangements (LGR) can result in HRD but are challenging to detect in ctDNA. Here, we present the analytical validation of homozygous deletions, loss of heterozygosity (LoH) and LGR detection on the Guardant360 (G360) liquid biopsy panel, previously validated for detection of small variants, copy number amplifications, and fusions. We present real-world outcomes of BRCA1/2-mutant PARPi-treated patients to demonstrate the clinical validity of the detected variants. Methods: Analytical validation was performed using the G360 83-gene ctDNA panel. Cell line DNA and clinical patient cfDNA were titrated into matched normal cell line DNA or healthy donor cfDNA to establish the limit of detection (LoD) and precision for copy number loss and LGRs, respectively. Accuracy results were compared to those from an orthogonal, externally validated tissue and ctDNA panel. De-identified, longitudinal, claims data were linked to the cancer genomic profiles in Guardant INFORM, a clinical-genomics database. Advanced PARPi treated breast cancer patients with an inactivating or reversion BRCA1/2 mutation detected by G360 were assessed. Results: The analytical sensitivity (95% LoD) for detecting homozygous and LoH deletions for deletion sizes &gt;10MB was established at tumor fractions (TF) of 12.5% and 25%, respectively. The 95% LoD for LGRs was 0.2% variant allele fraction (VAF). The per-sample false positive rate for copy number loss and LGRs was &lt;0.5%. Prevalence of BRCA1/2 homozygous deletions, LoH and LGRs in &gt;1000 advanced breast cancer patients was 1.8%, 16.6% and 0.25% respectively, compared to 2.4%, 56.7% and 0.3% in TCGA. To verify the clinical impact of cfDNA-detected HRR alterations, overall survival was determined for PARPi-treated patients with &gt;1 BRCA1/2 germline or somatic SNV, indel or LGR reversion mutation to be 23.2 months [16.4, 30, CI, n=75] compared to 54.4 [28, NA, CI, n=14] months for BRCA1/2-mutant patients without a reversion (p-value=0.049). Conclusion:. This analytical validation demonstrates that G360 detection of inactivating mutations, including copy number loss and LGRs, is highly sensitive, reliable and robust. Real-world evidence analysis confirmed worse survival outcomes in PARPi treated patients harboring a BRCA1/2 reversion compared to BRCA1/2-mutant patients with no reversion. This data further supports ctDNA as a compelling non-invasive means to identify potential PARPi sensitizing and resistance mutations in patients with advanced breast cancer.

Citation Format: Jennifer Yen, Leylah Drusbosky, Caroline Weipert, Nicole Zhang, David Hanna, Catalin Barbacioru, Hao Wang, Alex Artyomenko, Arielle Yablonovitch, Yu Fu, Aaron Hardin, Nagesh Alla, Robert Foley, Max Maligska, Bhargavi Panchangam, Phil Yen, Jane Meisel, Neelima Vidula, Massimo Cristofanilli, Jeremy Force, Michael Dorschner, Martina Lefterova, Elena Helman, Becky Nagy, Darya Chudova, AmirAli Talasaz. Analytical and clinical validation of a ctDNA assay for detecting copy number loss and structural rearrangement variants contributing to homologous recombination and repair (HRR) deficiency [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-13-29.

Abstract P4-12-04: Healthcare utilization and symptoms among hospitalized patients with breast cancer

Background: Patients with breast cancer generally receive most of their care in an outpatient setting, but unplanned hospitalizations may occur to help manage uncontrolled symptoms. We sought to investigate healthcare utilization and symptoms among patients with breast cancer experiencing an unplanned hospitalization. Methods: We enrolled patients with cancer and unplanned hospitalizations from 9/2014 to 2/2017. The current study focuses on the patients with breast cancer in this cohort. Following hospital admission, we assessed patient-reported symptoms using the Edmonton Symptom Assessment System (ESAS). We reviewed the electronic health record to obtain information about patient demographics, clinical characteristics, healthcare utilization, and reasons for hospital admission (elicited from primary and secondary diagnoses listed on the hospitalization discharge summary). We examined the associations among patients’ symptoms, healthcare utilization (i.e., hospital length of stay and 90-day readmissions), and survival using regression models. Results: We identified 101 patients with breast cancer (median age=60 years [range 22-86]. In this cohort, 74% had metastatic breast cancer. Primary/secondary reasons for hospitalization included fever/infection (34%), pain (18%), dyspnea (12%), gastrointestinal diagnoses (constipation, diarrhea, bowel obstruction, biliary obstruction, ascites, 10%), nausea/vomiting (7%), failure to thrive (6%), pleural effusion (5%), renal failure (4%), blood clot (3%), cardiac diagnoses (atrial fibrillation, cardiomyopathy, 3%), lightheadedness/hypotension (3%), neurologic diagnoses (altered mental status, seizure, subdural hematoma, 3%), fracture (2%), lower extremity swelling (2%), and other (i.e., rash, ptosis, SVC syndrome, fall, 1% each). Table 1 describes the baseline ESAS symptoms collected upon hospital admission. The mean length of hospital stay was 6.2 days and 90-day readmission rates were 28%. Patient disposition post hospitalization included discharge to home (76%), post-acute care facility (12%), hospice (5%), and death in the hospital (6%). We found that patients’ ESAS-physical symptoms were associated with longer hospital length of stay (B=0.08, p=0.029), greater risk of death or readmission within 90-days (OR=1.07, p&lt;0.001), and worse overall survival (HR=1.04, p=0.001). Similarly, patients’ ESAS-total symptoms were associated with longer hospital length of stay (B=0.07, p=0.013), greater risk of death or readmission within 90-days (OR=1.05, p=0.001), and worse overall survival (HR=1.02, p=0.003). Conclusions: In this cohort of hospitalized patients with breast cancer, the majority had metastatic disease and presented with a high symptom burden. Unplanned admissions in these patients with breast cancer commonly occurred for fever/infection, pain, dyspnea, and gastrointestinal reasons. We identified novel associations among patients’ symptoms upon admission with their hospital length of stay, risk of readmissions/death, and overall survival. These findings highlight the need for timely outpatient interventions that address patient symptoms when seeking to enhance health care utilization and survival outcomes in this population.

Table 1.Baseline symptom% of patients with moderate or severe symptomsMedian ESAS scoreTiredness*90%8 (Severe)Pain*78%7 (Severe)Well-being76%5 (Moderate)Drowsiness*71%6 (Moderate)Lack of appetite*68%5 (Moderate)Anxiety61%5 (Moderate)Depression52%4 (Moderate)Nausea*45%2 (Mild)Shortness of breath*45%2 (Mild)Constipation*44%0 (None)Total ESAS scoreMedian score 47 Total ESAS_physical score. . Median score 34*components included in ESAS_physical score

Citation Format: Neelima Vidula, Emilia Kaslow-Zieve, Carolyn Qian, Isabel Neckermann, Eva Gaufberg, Charu Vyas, Richard Newcomb, Patrick C Johnson, Daniel Lage, Jennifer Shin, Ryan Nipp. Healthcare utilization and symptoms among hospitalized patients with breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-12-04.

Abstract P1-18-22: AKT inhibition in combination with endocrine therapy and a CDK4/6 inhibitor (CDK4/6i) in patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) and prior CDK4/6i exposure: A translational investigation

Background: The cyclin-dependent kinase 4/6 inhibitors, with endocrine therapy (ET), have become the standard of care for patients with HR+/HER2- MBC. Prior insight from tumor biopsies and preclinical analyses suggest that AKT1 activation can provoke CDK4/6i resistance, highlighting a potential therapeutic role for AKT inhibition (AKTi) in this setting. However, combinatorial inhibition can be associated with significant toxicity and identification of the optimal biological dose is often challenging. In this translational co-clinical study, we evaluated escalating doses of AKTi combination with CDK 4/6i in parallel patient-derived pre-clinical models as well as a phase 1b clinical trial. Methods: In an open-label phase Ib dose-escalation clinical trial (TAKTIC, NCT03959891), we evaluated the safety, tolerability and efficacy of escalating doses of the AKT1 inhibitor ipatasertib (ipat) in combination with palbociclib (palbo) and fulvestrant (fulv) for patients with HR+/HER2- MBC. Inclusion criteria include unresectable or metastatic disease, at least 1 prior therapy for MBC including any CDK4/6i, and up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). In addition, response to escalating doses of ipat and palbo (with fulv) were explored in vitro via an ATP-based viability assay in tumor cell lines derived from circulating tumor cells (CTC) isolated from patients with endocrine-refractory HR+ MBC. Results: In the dose-escalation portion of the phase 1b clinical trial, 23 patients received the triplet combination of ipat, palbo, and fulv (median number of prior lines = 4.3, range 1-7; 100% with prior CDK4/6i): 3 pts received ipat at 200mg + 125mg palbo, 15 pts received 300mg + 125mg palbo, and 5 pts received 400mg + 100mg palbo, all with fulv (500 mg). Among the 23 patients, 20 patients (86.9%) had disease control (4 partial response and 16 stable disease) as the best response, per RECIST. Grade 3/4 toxicities included neutropenia (n=20), lymphopenia (n=3), diarrhea (n=3), thrombocytopenia (n=2), transaminitis (n=2), and rash (n=2). Two DLTs were observed in the 300mg ipat + 125mg palbo cohort (grade 4 neutropenia ≥ 7 days), but none at 400mg + 100mg palbo. The combination of ipat and palbo demonstrated an additive effect in vitro, with increased sensitivity to lower doses of palbo in the presence of ipat. Based on the totality of data, 400mg ipat + 100mg palbo + fulv 500 mg was selected as the recommended phase II dose (RP2D) in the post-CDK4/6i setting. Conclusions: The triplet combination of endocrine therapy with AKTi and lower dose CDK4/6i appears to be well tolerated in heavily pre-treated pts, with preliminary evidence of clinical activity. Further study is needed to evaluate biomarkers associated with higher AKTi benefit in order to guide rational development of combination therapy for patients with HR+/HER2- MBC in the post-CDK4/6i setting. Overall, this translational study demonstrates how insight into the molecular mechanisms of CDK4/6i resistance and combinatorial modeling can be leveraged to develop actionable therapeutic regimens for patients with MBC.

Citation Format: Seth A. Wander, Douglas S. Micalizzi, Taronish Dubash, Dejan Juric, Laura M. Spring, Neelima Vidula, Jennifer Keenan, Maureen Beeler, Elene Viscosi, Dante Che, Elizabeth L. Fisher, Rachel A. Hepp, Beverly Moy, Steven J. Isakoff, Leif W. Ellisen, Jeffrey G. Supko, Shyamala Maheswaran, Daniel A. Haber, Aditya Bardia. AKT inhibition in combination with endocrine therapy and a CDK4/6 inhibitor (CDK4/6i) in patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) and prior CDK4/6i exposure: A translational investigation [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-18-22.

Abstract OT2-24-03: Phase II study of a PARP inhibitor in metastatic breast cancer with somaticBRCA1/2mutations identified by cell-free DNA: Genotyping based clinical trial

Background: Two PARP inhibitors are approved for germline BRCA1/2 mutant metastatic breast cancer (MBC), based on clinical trials demonstrating an improvement in patient outcomes and quality of life. However, germline BRCA1/2 mutations are identified in 5-10% of breast cancer, limiting their potential applicability. Our prior work demonstrated that somatic BRCA1/2 mutations can be detected in cell-free DNA (cfDNA) in a proportion of patients with MBC who are not germline BRCA1/2 carriers, and that a PARP inhibitor caused growth inhibition in a circulating tumor cell line generated from a patient with MBC and a pathogenic somatic BRCA1 mutation (Vidula, Dubash, CCR, 2020). Thus, we hypothesize that a PARP inhibitor may have efficacy in somatic BRCA1/2 mutant MBC identified by cfDNA. Trial Design: This phase II investigator initiated open label clinical trial is enrolling 30 patients who have pathogenic somatic BRCA1/2 mutations found in cfDNA. Patients must not be known germline BRCA1/2 carriers. Patients receive treatment with the PARP inhibitor, talazoparib, until disease progression. Serial imaging (CT chest, abdomen, pelvis, and bone scan) occurs every 3 months, and cfDNA is collected monthly to evaluate changes in the genomic environment. Patients will also have blood collected at baseline for the Cancer Risk B assay (CR-B), a novel flow variant assay to assess double strand break repair mutations in circulating blood cells (Syeda, Genetics, 2017). Eligibility criteria: Patients with MBC (TNBC with ≥ 1 prior chemotherapy or HR+/HER2- with ≥ 1 prior hormone therapy or ineligible for hormone therapy) with a somatic BRCA1/2 mutation identified in cfDNA (established pathogenic variant) are being enrolled. Patients should not be known germline BRCA1/2 carriers (genetic testing is not required but can be obtained per physician discretion) and may not have previously received a PARP inhibitor. There is no limit on the number of prior therapies, and a prior platinum chemotherapy is allowed in the absence of disease progression on the platinum. Patients must have adequate performance status and organ function. Specific Aims: The primary endpoint is progression-free survival (PFS) using RECIST 1.1. Secondary endpoints include objective response rate and toxicity (NCI CTCAE v 5.0). Exploratory objectives include evaluating serial changes in BRCA1/2 mutant allelic frequency in cfDNA, evaluating the impact of BRCA1/2 reversion mutations, comparing pre- and post-treatment cfDNA results to identify markers of resistance, evaluating the CR-B assay positivity rate, and ultimately correlating these analyses with treatment response. Statistical Methods: A two-stage design with 80% power to demonstrate that talazoparib is associated with “success” (PFS &gt; 12 weeks) in ≥53% patients (4% alpha) is being used. Accrual: This study (NCT03990896) is currently open at Massachusetts General Hospital, where 4 patients are completing screening for enrollment. This study will be activated soon at the University of California San Francisco, MD Anderson, Mayo Clinic Rochester and Jacksonville, Northwestern, and Emory (7 academic centers). Funding: Support for this study is provided by a Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO–Breast Cancer Research Foundation- Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu

Citation Format: Neelima Vidula, Erica Blouch, Erin Basile, Nathan Royce Ruffle-Deignan, Nora Horick, Senthil Damodaran, Alvaro Moreno Aspitia, Manali Bhave, Ami Shah, Minetta C. Liu, Joseph Sparano, Harry Ostrer, Hope Rugo, Leif W. Ellisen, Aditya Bardia. Phase II study of a PARP inhibitor in metastatic breast cancer with somaticBRCA1/2mutations identified by cell-free DNA: Genotyping based clinical trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-24-03.

Evaluation of disseminated tumor cells and circulating tumor cells in patients with breast cancer receiving adjuvant zoledronic acid

We evaluated disseminated tumor cells (DTCs) and circulating tumor cells (CTCs) in patients with stage I-III breast cancer with >4 MM/mL DTC at baseline who received adjuvant zoledronic acid (ZOL). ZOL was administered every 4 weeks for 24 months, and patients underwent bone marrow aspiration at baseline, and 12 and 24 months of ZOL. Complete DTC response (<4 DTC/mL), serial CTCs, survival, recurrence, and toxicity were determined. Forty-five patients received ZOL. Median baseline DTC was 13.3/mL. Significant reduction in median DTC occurred from baseline to 12 months, and 24 months. Complete DTC response was seen in 32% at 12 months, and 26% at 24 months. Nine patients developed recurrence. Baseline DTC > 30/mL and CTC > 0.8/mL were significantly associated with recurrence and death. Serial reduction in DTCs occurred. Higher baseline DTC > 30/mL and CTC > 0.8/mL correlated with recurrence and death.

NTRK1 Fusions identified by non-invasive plasma next-generation sequencing (NGS) across 9 cancer types

BACKGROUND

Activating fusions of the NTRK1, NTRK2 and NTRK3 genes are drivers of carcinogenesis and proliferation across a broad range of tumour types in both adult and paediatric patients. Recently, the FDA granted tumour-agnostic approvals of TRK inhibitors, larotrectinib and entrectinib, based on significant and durable responses in multiple primary tumour types. Unfortunately, testing rates in clinical practice remain quite low. Adding plasma next-generation sequencing of circulating tumour DNA (ctDNA) to tissue-based testing increases the detection rate of oncogenic drivers and demonstrates high concordance with tissue genotyping. However, the clinical potential of ctDNA analysis to identify NTRK fusion-positive tumours has been largely unexplored.

METHODS

We retrospectively reviewed a ctDNA database in advanced stage solid tumours for NTRK1 fusions.

RESULTS

NTRK1 fusion events, with nine unique fusion partners, were identified in 37 patients. Of the cases for which clinical data were available, 44% had tissue testing for NTRK1 fusions; the NTRK1 fusion detected by ctDNA was confirmed in tissue in 88% of cases. Here, we report for the first time that minimally-invasive plasma NGS can detect NTRK fusions with a high positive predictive value.

CONCLUSION

Plasma ctDNA represents a rapid, non-invasive screening method for this rare genomic target that may improve identification of patients who can benefit from TRK-targeted therapy and potentially identify subsequent on- and off-target resistance mechanisms.

A First-in-Human Phase 1 Study of a Novel Selective Androgen Receptor Modulator (SARM), RAD140, in ER+/HER2- Metastatic Breast Cancer

INTRODUCTION/BACKGROUND

This first-in-human, phase 1 study aimed to characterize the safety, tolerability, maximum tolerated dose (MTD), pharmacokinetic (PK) profile, and antitumor activity of RAD140, an oral selective androgen receptor (AR) modulator (SARM).

PATIENTS AND METHODS

This dose-escalation study with a 3 + 3 design and PK expansion cohort enrolled postmenopausal women with ER+/HER2- metastatic breast cancer (mBC). Serum sex hormone-binding globulin (SHBG) and prostate-specific antigen (PSA) were used as surrogate markers of AR engagement.

RESULTS

Twenty-two (21 AR+) heavily pretreated mBC patients were enrolled. Dose levels included 50 mg (n = 6), 100 mg (n = 13), and 150 mg (n = 3) once daily (QD). Most frequent (> 10%) treatment-emergent adverse events (TEAEs) were elevated AST (59.1%), ALT (45.5%), and total blood bilirubin (27.3%), and vomiting, dehydration, and decreased appetite and weight (27.3% each). Grade 3/4 TEAEs occurred in 16 (72.7%) patients and included elevations in AST/ALT and hypophosphatemia (22.7% each). Treatment-related TEAEs occurred in 17 per 22 patients (77.3%); 7 (31.8%) were Grade 3; none were Grade 4. The half-life (t_1/2) of 44.7 hours supported QD dosing. At the MTD of 100 mg/day, 1 patient with an ESR1 mutation at baseline had a partial response. Overall, clinical benefit rate at 24 weeks was 18.2%, and median progression-free survival was 2.3 months. SHBG decreased in 18 per 18 patients, and PSA increased in 16 per 20 patients. Paired baseline and on-treatment tumor biopsies demonstrated AR engagement.

CONCLUSION

RAD140 is a novel oral AR-targeted agent for the treatment of AR+/ER+/HER2- mBC with an acceptable safety profile and preliminary evidence of target engagement and antitumor activity.

Tumor Tissue- versus Plasma-based Genotyping for Selection of Matched Therapy and Impact on Clinical Outcomes in Patients with Metastatic Breast Cancer

PURPOSE

Actionable mutations can guide genotype-directed matched therapy. We evaluated the utility of tissue-based and plasma-based genotyping for the identification of actionable mutations and selection of matched therapy in patients with metastatic breast cancer (MBC).

EXPERIMENTAL DESIGN

Patients with MBC who underwent tissue genotyping (institutional platform, 91-gene assay) or plasma-based cell-free DNA (cfDNA, Guardant360, 73-gene assay) between January 2016 and December 2017 were included. A chart review of records to identify subtype, demographics, treatment, outcomes, and tissue genotyping or cfDNA results was performed. The incidence of actionable mutations and the selection of matched therapy in tissue genotyping or cfDNA cohorts was determined. The impact of matched therapy status on overall survival (OS) in tissue genotyping or cfDNA subgroups was determined with Cox regression analysis.

RESULTS

Of 252 patients who underwent cfDNA testing, 232 (92%) had detectable mutations, 196 (78%) had actionable mutations, and 86 (34%) received matched therapy. Of 118 patients who underwent tissue genotyping, 90 (76%) had detectable mutations, 59 (50%) had actionable mutations, and 13 (11%) received matched therapy. For cfDNA patients with actionable mutations, matched versus nonmatched therapy was associated with better OS [HR 0.41, 95% confidence interval (CI): 0.23-0.73, P = 0.002], and this remained significant in a multivariable analysis correcting for age, subtype, visceral metastases, and brain metastases (HR = 0.46, 95% CI: 0.26-0.83, P = 0.010).

CONCLUSIONS

Plasma-based genotyping identified high rates of actionable mutations, which was associated with significant application of matched therapy and better OS in patients with MBC.See related commentary by Rugo and Huppert, p. 3275.

Phase II multicenter study of talazoparib for somatic BRCA1/2 mutant metastatic breast cancer

TPS1110

Background: PARP inhibitors are approved for the treatment of HER2 negative metastatic breast cancer (MBC) with germline BRCA1/2 mutations, based on phase III studies demonstrating an improvement in progression-free survival (PFS) compared to chemotherapy in this population and better patient reported outcomes (Robson, NEJM, 2017; Litton, NEJM, 2018). However, germline BRCA1/2 mutations account for only 5-10% of breast cancer, limiting the current clinical applicability of PARP inhibitors. Somatic BRCA1/2 mutations are detectable in circulating cell-free DNA (cfDNA) in ̃13.5% of patients with MBC; in pre-clinical models, pathogenic somatic BRCA1/2 mutations have been shown to respond to PARP inhibition (Vidula, CCR, 2020). The purpose of this study is to evaluate the efficacy of talazoparib, a PARP inhibitor, in patients with MBC who have somatic BRCA1/2 mutations detectable in cfDNA, in the absence of a germline BRCA1/2 mutation, which we hypothesize will be effective in this setting. This study may help expand the population of patients with MBC who benefit from PARP inhibitors. Methods: This is an investigator initiated multicenter, single arm, phase II clinical trial studying the efficacy of talazoparib in 30 patients with MBC who have pathogenic somatic BRCA1/2 mutations detected in cfDNA. Patients with MBC who are found to have pathogenic somatic BRCA1/2 mutations detected in cfDNA in the absence of a germline BRCA1/2 mutation are eligible. Patients may have triple negative (with ≥ 1 prior chemotherapy), or hormone receptor positive/HER2 negative breast cancer (with ≥ 1 prior hormone therapy). Patients may have received any number of prior lines of chemotherapy, including a prior platinum (in the absence of progression). They must have adequate organ function and ECOG performance status ≤2, and should not have previously received a PARP inhibitor. Patients are treated with talazoparib 1 mg daily until disease progression or intolerability, with serial imaging using CT chest/abdomen/pelvis and bone scan performed at baseline and every 12 weeks, and cfDNA collection every 4 weeks. Primary endpoint is PFS by RECIST 1.1. Patients are being enrolled in a two-stage design with 80% power to demonstrate that the treatment is associated with “success” (PFS > 12 weeks) in ≥53% patients (4% alpha). Secondary endpoints include objective response rate and safety (NCI CTCAE v 5.0). Exploratory analyses include studying serial changes in cfDNA BRCA1/2 mutant allelic frequency and comparing pre-and post-treatment cfDNA for the emergence of BRCA1/2 reversion and resistance mutations. This study is activated and open at Massachusetts General Hospital, where 2 patients are completing screening. It is also opening soon at 6 other academic centers (NCT03990896). Grant support includes a Pfizer ASPIRE award and 2020 Conquer Cancer Foundation of ASCO – Breast Cancer Research Foundation – Career Development Award. Clinical trial information: NCT03990896 .

Multi-center randomized study of pembrolizumab/carboplatin versus carboplatin alone in patients with chest wall disease from breast cancer: TBCRC 044

TPS1111

Background: Chest wall recurrence is a subtype of breast cancer that is challenging to treat, and associated with a short duration of response to treatment and an increased risk of development of distant metastases. Given the inflammatory nature of this disease and the association of chest wall disease with lymphovascular invasion, which is correlated with higher programmed cell death 1 (PD-1) expression, we hypothesized that immunotherapy may be beneficial as treatment. Combinations of immunotherapy and chemotherapy have a synergistic effect and demonstrated efficacy in the treatment of metastatic triple negative breast cancer (TNBC). This study is evaluating the efficacy of pembrolizumab, an anti-PD-1 antibody, in combination with carboplatin, in patients with chest wall infiltration from breast cancer. This drug combination has shown efficacy in advanced lung cancer. Methods: This is a multicenter, 2:1 randomized phase II study of pembrolizumab/carboplatin (Arm A, 56 patients) vs. carboplatin (Arm B, 28 patients) in 84 patients with chest wall disease from breast cancer, with or without distant metastases. Patients may have TNBC, hormone receptor positive/HER2 negative (following receipt of 2 prior hormone therapies), or HER2 positive breast cancer (with option to continue trastuzumab on study). Pembrolizumab is administered as 200 mg IV every 3 weeks, and carboplatin as AUC 5 IV every 3 weeks. Patients on Arm A may continue pembrolizumab +/- carboplatin (Arm Ax) after completion of 6 cycles of treatment, while patients in Arm B can cross-over to pembrolizumab (+/- carboplatin) on progression (Arm Bx). Patients must have adequate organ function, performance status ≤ 2, and may have received any number of lines of prior chemotherapy. Patients undergo serial chest wall photography and imaging (CT chest, abdomen, and pelvis, and bone scan) at baseline and every 6 weeks, as well as blood collection for correlative studies and chest wall biopsies at baseline and after 2 cycles of treatment. The primary endpoint is disease control rate (RECIST 1.1) at 18 weeks of treatment, and the study is powered to determine a 20% difference in disease control rates between arms (HR 0.52, a = 0.10, ß = 0.20). An interim analysis will occur for Arm B after 18 patients are enrolled, with a stopping rule for futility. Secondary endpoints include progression-free survival, toxicity (NCI CTCAE), and response based on irRECIST and tumor programmed death ligand 1 (PD-L1) expression. Exploratory objectives include evaluating changes in soluble PD-L1, tumor and peripheral blood immune composition, circulating tumor cells and cell-free DNA, and MYC oncogene expression. This study (NCT03095352) is open at 7 sites in the Translational Breast Cancer Research Consortium (TBCRC). 52 patients are enrolled. Grant funding is provided by Merck and UCSF. Clinical trial information: NCT03095352 .

Novel Therapies for Metastatic Triple-Negative Breast Cancer: Spotlight on Immunotherapy and Antibody-Drug Conjugates

Background: Triple-negative breast cancer (TNBC) is a biologically heterogeneous disease that is often associated with worse outcomes compared with other subtypes such as hormone receptor-positive tumors and HER2-positive tumors. While chemotherapy remains the mainstay of standard therapy for metastatic TNBC (mTNBC), several novel treatments have been developed over the past few years. In this review article, we review the major developments in the management of patients with mTNBC. Summary: The combination of chemotherapy and immunotherapy is a potential therapeutic option for PD-L1-positive mTNBC, as the FDA recently approved atezolizumab (Tecentriq) and pembrolizumab (Keytruda) in combination with chemotherapy. Also, 2 targeted therapies-olaparib (Lynparza) and talazoparib (Talzenna)-are FDA approved for the management of mTNBC with germline BRCA mutations, and sacituzumab govitecan, an anti-Trop2 antibody-drug conjugate (ADC), was recently approved for previously treated mTNBC. A number of promising therapies are on the horizon, including AKT inhibitors for PI3K-altered TNBC as well as other ADCs. Key Message: The successful clinical development of immunotherapies, PARP inhibitors, and ADCs for the management of mTNBC has improved the survival outcome of patients. Over the coming years, the therapeutic developments in precision medicine will likely change the mTNBC landscape, and might make the current definition of TNBC as breast cancer that is estrogen receptor negative, progesterone receptor negative, and HER2 negative obsolete.

Programmed cell death 1 (PD-1) receptor and programmed death ligand 1 (PD-L1) gene expression in primary breast cancer

PURPOSE

The interaction of the programmed cell death 1 (PD-1) receptor on tumor-infiltrating lymphocytes with programmed death ligand 1 (PD-L1) on tumor cells downregulates anti-tumor immunity. This study evaluated associations between PD-1 and PD-L1 expression in primary breast cancer, clinical characteristics, and patient outcomes.

METHODS

Microarray data from the Investigation of Serial Studies to predict your therapeutic response with imaging and molecular analysis (I-SPY 1) study (n = 149) was used to evaluate PD-1 and PD-L1 expression. Associations with clinical features and chemotherapy response were determined using Kruskal-Wallis and Wilcoxon rank sum tests, respectively. Recurrence-free survival (RFS) associations were determined with the Cox proportional hazard model. Associations of PD-1 and PD-L1 and selected genes associated with breast cancer, as well as a predictor of olaparib response (PARPi-7), were determined in I-SPY 1 and 2 other datasets: METABRIC (n = 1992) and TCGA (n = 817), using Pearson correlations.

RESULTS

In I-SPY 1, PD-1 expression was higher in triple-negative breast cancer (TNBC) and HER2 + breast cancer (p = 0.003), and grade 2/3 tumors (p = 0.043), and was associated with pathologic complete response (p = 0.006). PD-L1 expression in the lowest quintile was associated with worse RFS, even after subtype adjustment (HR 2.33, p = 0.01). PD-1 and PD-L1 gene expression correlated with the expression of immune-related genes and PARPi-7.

CONCLUSIONS

PD-1 expression is higher in breast cancers with aggressive features such as TNBC. Low PD-L1 expression may be an adverse prognostic factor. PD-1 and PD-L1 gene expression correlates with the expression of immune-related and DNA damage repair genes.

Clinical Outcomes With Abemaciclib After Prior CDK4/6 Inhibitor Progression in Breast Cancer: A Multicenter Experience

BACKGROUND

Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) are widely used as first-line therapy for hormone receptor-positive metastatic breast cancer (HR+ MBC). Although abemaciclib monotherapy is also FDA-approved for treatment of disease progression on endocrine therapy, there is limited insight into the clinical activity of abemaciclib after progression on prior CDK4/6i.

PATIENTS AND METHODS

We identified patients with HR+ MBC from 6 cancer centers in the United States who received abemaciclib after disease progression on prior CDK4/6i, and abstracted clinical features, outcomes, toxicity, and predictive biomarkers.

RESULTS

In the multicenter cohort, abemaciclib was well tolerated after a prior course of CDK4/6i (palbociclib)-based therapy; a minority of patients discontinued abemaciclib because of toxicity without progression (9.2%). After progression on palbociclib, most patients (71.3%) received nonsequential therapy with abemaciclib (with ≥1 intervening non-CDK4/6i regimens), with most receiving abemaciclib with an antiestrogen agent (fulvestrant, 47.1%; aromatase inhibitor, 27.6%), and the remainder receiving abemaciclib monotherapy (19.5%). Median progression-free survival for abemaciclib in this population was 5.3 months and median overall survival was 17.2 months, notably similar to results obtained in the MONARCH-1 study of abemaciclib monotherapy in heavily pretreated HR+/HER2-negative CDK4/6i-naïve patients. A total of 36.8% of patients received abemaciclib for ≥6 months. There was no relationship between the duration of clinical benefit while on palbociclib and the subsequent duration of treatment with abemaciclib. RB1, ERBB2, and CCNE1 alterations were noted among patients with rapid progression on abemaciclib.

CONCLUSIONS

A subset of patients with HR+ MBC continue to derive clinical benefit from abemaciclib after progression on prior palbociclib. These results highlight the need for future studies to confirm molecular predictors of cross-resistance to CDK4/6i therapy and to better characterize the utility of abemaciclib after disease progression on prior CDK4/6i.

Abstract OT-30-02: Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer

Background: PARP inhibitors are currently approved for the treatment of germline BRCA1/2 mutant metastatic breast cancer, and have been shown to improve outcomes and patient quality of life. However, germline BRCA1/2 mutations are observed in 5-10% of breast cancer, limiting the applicability of this well-tolerated therapy. We previously identified that a proportion of patients have somatic BRCA1/2 mutations detected by cell-free DNA (cfDNA), in the absence of germline BRCA1/2 mutations, and have demonstrated that a PARP inhibitor has therapeutic efficacy in a circulating tumor cell-line developed from a patient with a somatic BRCA1 mutation (Vidula, CCR, 2020). We hypothesize that PARP inhibitors may be effective in somatic BRCA1/2 mutant metastatic breast cancer identified via cfDNA.

Trial Design: In this phase II investigator initiated single-arm clinical trial, 30 patients with pathogenic somatic BRCA1/2 mutations detected by cfDNA in the absence of a known germline BRCA1/2 mutation will be treated with talazoparib, a PARP inhibitor, until development of disease progression or unacceptable toxicity. Patients will undergo serial imaging with CT chest, abdomen, and pelvis and bone scan every 12 weeks, and cfDNA collection every 4 weeks.

Eligibility criteria: Patients with metastatic breast cancer that is triple-negative (with receipt of at least 1 prior line of chemotherapy) or hormone receptor positive, HER2 negative (with receipt of at least 1 prior line of hormone therapy or considered inappropriate for hormone therapy) are eligible. Patients must not have received a PARP inhibitor and must not have a germline BRCA1/2 mutation. Any number of prior lines of therapy are allowed. The somatic BRCA1/2 mutation detected in cfDNA must be an established pathogenic variant. Adequate organ function is also required.

Specific Aims: 1. To determine progression-free survival (PFS) by RECIST 1.1 (Primary endpoint), 2. Objective response rate, 3. Safety and tolerability by NCI CTCAE v 5.0, 4. Serial changes in BRCA1/2 mutant allelic frequency in cfDNA, and compare pre- and post-treatment cfDNA results with treatment (Exploratory aim).

Statistical Methods: Patients are being enrolled in a two-stage design, which provides 80% power to demonstrate that the study treatment is associated with “success” (PFS &gt; 12 weeks) in ≥53% patients (4% alpha).

Accrual: Patients are being screened for enrollment at the Massachusetts General Hospital. This study is also opening at other sites in the U.S. including the University of California San Francisco. (NCT03990896)

Funding: This study is funded by Pfizer ASPIRE award and Conquer Cancer Foundation of ASCO Career Development Award. Contact information: Neelima Vidula, MD, Massachusetts General Hospital, nvidula@mgh.harvard.edu

Citation Format: Neelima Vidula, Nora Horick, Erin Basile, Erica Blouch, Leif W. Ellisen, Hope S. Rugo, Aditya Bardia. Phase II study of talazoparib, a PARP inhibitor, in somatic BRCA1/2 mutant metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr OT-30-02.

Abstract PS17-02: Molecular alterations in the androgen receptor and associated clinical outcomes in hormone receptor-positive/HER2- metastatic breast cancer

Background: Although the androgen receptor (AR) is frequently co-expressed with ER and PR in hormone receptor-positive (HR+)/HER2- breast cancer, the biological significance of detectable AR alterations (ARalt) in metastatic disease (MBC) remains poorly understood. The primary objective of this study was to evaluate the association of ARalt status with clinical outcomes among women with HR+/HER2- MBC.

Methods: Retrospective review was performed on patients with HR+/HER2- MBC treated at an academic institution, for whom genotyping information was available. ARalt status was determined using Guardant360, a 73-gene next-generation sequencing assay that detects both AR mutations and amplifications in circulating tumor DNA. Women with positive or unknown HER2 status and triple-negative breast cancer were excluded from analysis, as were cases of male breast cancer. Time-to-progression on the therapy initiated immediately following Guardant testing was compared based on ARalt status, excluding patients treated with androgen-directed therapies given potential for confounding. Cumulative incidence plots were generated and analyzed by Gray’s test, and propensity score-adjusted competing risk models were generated with the probability of treatment as a function of age at metastatic diagnosis, presence of visceral metastasis, presence of de novo metastases, as well as number of prior therapies. Additional analysis was performed to assess progression stratified by treatment type (endocrine or non-endocrine based).

Results: Among women with HR+/HER2- MBC (n=222), 16 patients (7%) had detectable ARalt (12 point mutations, 4 amplifications). No baseline differences were observed between women with ARalt and those without AR alterations (ARwt), with respect to age at primary or metastatic diagnosis, menopause status, time to onset of metastasis or de novo metastatic disease, presence of visceral metastases, or number of endocrine/chemotherapies received prior to Guardant testing. ARalt tumors had a higher frequency of detected mutations (14% vs. 5%, p&lt;0.01), and frequently co-altered genes included TP53, PIK3CA, ERBB2, SMAD4, and NF1. Genes with a tendency towards co-alteration in ARalt but not in ARwt included MAP2K2, ARAF1, MAPK1, SMAD4, MYC, ROS1, TERT, and NRAS. In a multivariable model adjusting for age, de novo metastases, visceral metastases, and number of prior therapies, ARalt status was associated with a higher rate of progression (HR 2.5; 95% CI 1.2-5.0, p=0.01), particularly among patients treated with endocrine-based therapies following Guardant testing (HR 4.2, 95% CI 2.4-7.2, p&lt;0.0005) but was not statistically different in women treated with non-endocrine based therapies (HR 1.6; 95% CI 0.5-4.9, p=0.4).

Conclusions: ARalt tumors demonstrate a higher rate of progression on endocrine-based therapy as compared to ARwt tumors, highlighting a potential role of AR in mediating resistance to endocrine therapy in HR+/HER2- disease. Further translational investigations are warranted to determine whether ARalt/HR+/HER2- disease represents a unique biological subtype that predominantly relies on AR signaling and may thus benefit from blockade with AR antagonists.

Table 1. Multivariable competing risks model for endocrine progression.CovariatePFSMultivariableHR95% CIP-valuePositive ARalt status4.172.43-7.17&lt;0.01Age at metastatic dx1.000.97-1.020.89De novo metastasesYes1.770.96-3.260.07No[ref]Visceral metastasesYes1.250.72-2.160.43No[ref]No. of prior therapies1.060.93-1.210.98

Citation Format: Charles Dai, Andrzej Niemierko, Neelima Vidula, Laura M Spring, Seth A Wander, Arielle J Medford, Katherine A Hesler, Giuliana Malvarosa, Jeffrey Peppercorn, Dejan Juric, Steven J Isakoff, Beverly Moy, Leif W Ellisen, Aditya Bardia. Molecular alterations in the androgen receptor and associated clinical outcomes in hormone receptor-positive/HER2- metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-02.

Abstract PS18-19: Comparison of metastatic genomic profile in patients ≤45 years and patients &gt;45 years with triple-negative breast cancer

Background: Metastatic triple negative breast cancer (mTNBC) is often associated with aggressive biology, particularly in younger women. We hypothesized that the tumor genomic profile might vary based on age. The primary objective of this study was to compare the genomic profile, utilizing plasma-based targeted sequencing of common cancer related genes, in patients ≤45 years and &gt;45 years with mTNBC. The age cut-off of ≤ 45 was selected based on prior literature in TNBC using a similar cut-off for younger age stratification (Dolle, 2009).

Methods: A retrospective review of patients with mTNBC who had cell-free DNA (cfDNA) analysis (next generation sequencing, Guardant360®, 73 gene panel) collected at an academic institution after mTNBC diagnosis as part of clinical care from 1/2016-10/2019 was conducted. Patient age, demographics, and genotyping results were collected. Clinical and genomic characteristics were compared for patients ≤45 and &gt;45 using the Wilcoxon rank-sum test (continuous variables) and Pearson’s chi-squared test (categorical variables). Results:Of 74 patients with mTNBC and cfDNA results available, 17 were ≤45 years (median age 39 at mTNBC diagnosis), and 57 were &gt; 45 years (median age 58). In comparing patients ≤45 years with those &gt; 45 years, similar rates of de novo disease (≤45: 24%, &gt;45: 9%, p=0.10), visceral disease (≤45: 65%, &gt;45: 67%, p=0.88), and median number of prior lines of chemotherapy (≤45: 2, &gt; 45: 1, p=0.49) were observed. The percentage of patients with more than 1 detectable mutation (≤45: 94%, &gt;45: 93%, p=0.87), and median number of detected mutations (≤45: 5, &gt;45: 4, p=0.67) was similar between groups. However, the median mutant allele fraction (MAF; maximum) was significantly higher in patients ≤45 (≤45: median 29.8%; &gt;45: median 4.6%, p=0.006), and this finding remained significant after correcting for number of prior therapies. Table 1 depicts the mutation spectrum. While TP53 mutations were commonly seen in both cohorts, the median TP53 MAF was significantly higher in patients ≤45 years (≤45: 29.8%, &gt;45: 4.0%, p=0.015). PTEN mutations were found in a portion of patients &gt;45, but not identified in those ≤45 years. Amplifications in MYC, BRAF, PI3KCA, AR, CDK6, EGFR, MET, KIT, and CCND2 were seen more often in those ≤45 years, although these findings did not reach statistical significance. Survival outcomes will be presented at the meeting.

Conclusions:Patients with mTNBC diagnosed at ≤45 years had a significantly higher cfDNA MAF than those &gt;45, likely reflecting higher detectable tumor genomic burden. Mutations often associated with aggressive biology such as MYC, MET, and EGFR were more commonly found in patients ≤45, but the small sample size and limited statistical power makes it difficult to draw strong conclusions about differences in individual genes in this study. Further research with a larger multi-center cohort is ongoing to validate these findings.

Table 1.MutationAge ≤45Age &gt;45p-valueTP5376%75%0.93AR18%7%0.19BRCA118%12%0.57APC12%9%0.71NF112%7%0.53ERBB212%11%0.89BRCA26%9%0.70PTEN0%11%0.16AmplificationMYC29%19%0.37CCNE129%21%0.47BRAF29%14%0.14PI3KCA29%12%0.093AR24%7%0.054CDK624%12%0.25EGFR24%12%0.25MET24%11%0.17KIT18%7%0.19FGFR118%21%0.76CCND218%5%0.10PDGFRA12%7%0.53RAF112%7%0.53KRAS12%11%0.89CCND16%7%0.87

Citation Format: Neelima Vidula, Andrzej Niemierko, Katherine Hesler, Steven Isakoff, Dejan Juric, Jennifer Shin, Laura Spring, Jeffrey Peppercorn, Jerry Younger, Irene Kuter, Beverly Moy, Leif W. Ellisen, Aditya Bardia. Comparison of metastatic genomic profile in patients ≤45 years and patients &gt;45 years with triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-19.

Abstract PS13-16: Pharmacokinetic evaluation of an oral paclitaxel DHP107 (Liporaxel®) in patients with recurrent or metastatic breast cancer (MBC): Phase II study (OPERA, NCT03326102)

Background: Paclitaxel is a microtubule stabilizing anticancer therapy used to treat multiple cancers including breast cancer. DHP107 is an oral paclitaxel solubilized in lipid components using DaeHwa-Lipid bAsed Self-Emulsifying Drug delivery system (DH-LASED) technology. It demonstrated comparable efficacy and safety to IV paclitaxel in a phase 3 study for patients with advanced gastric cancer (Ann Oncol 2018) leading to regulatory approval in Korea, and also met the primary endpoint (ORR 54.5%) as first-line therapy (ESMO 2019) in the OPTIMAL Phase II study in patients with HER2 negative metastatic breast cancer (MBC). The confirmatory OPTIMAL Phase III study is ongoing in Asia and Europe. The OPERA Phase II study was designed as multinational, multicenter, randomized, open-label study to establish pharmacokinetic (PK) profile and efficacy of DHP107 in patients with MBC in the U.S. Method: A total of 72 patients with metastatic HER2 negative (HR+/HER2- or triple-negative breast cancer (TNBC)) will be randomized in a 2:1 fashion to receive DHP107 (200mg/m2 orally twice a day on Days 1, 8, and 15 in a 28-day cycle) or IV paclitaxel (80 mg/m2 on Days 1, 8, and 15 in a 28-day cycle) until disease progression or unacceptable toxicity. Tumor assessments are performed every 8 weeks. PK analyses were performed in a subset of patients receiving DHP107. A total of 103 blood samples were collected on Day 1 of Cycle 1 at predose and 1, 2, 3, 4, 6, and 10 hours post dose (before the 2nd dose administration on Day 1), and at predose on Day 8 of Cycle 1. All PK parameters were calculated by non-compartmental analysis using Phoenix WinNonlin version® 8.1. Results: A total of 13 subjects were enrolled in the PK substudy, All 13 patients were female and of Caucasian, non-Hispanic, ethnicity. Median Tmax was 2.17 h (range 1.92-4.08). Mean Cmax and AUC0-10h and their coefficient of variations (CV) were 330 ng/mL (31.1%) and 1233 ng·h/mL (30.3%), respectively (Table 1). The PK parameters of DHP107 were similar to those in a previous Phase I study in Korean cancer patients where Cmax and AUC0-48h were 235 ng/mL (43.9%) and 1348 ng·h/mL (19.7%) (Invest New Drugs 2012).

Conclusion: PK profiles were well characterized from plasma concentrations in 13 Caucasian patients with MBC up to 10 hours after oral 200mg/m2 BID administration. DHP107 was rapidly absorbed and eliminated and inter-individual variability in exposure such as Cmax and AUClast was considered low. Compared to previous phase I PK results in Korean patients, Cmax and AUC parameters were similar after dosing with DHP107, demonstrating no clinically significant differences between Asian and Caucasian patients. Safety and efficacy will be evaluated in the ongoing OPERA and OPTIMAL studies.

Table 1StatisticTmax(h)Cmax(ng/mL)AUClast, 0-10h(ngh/mL)AUCinf(ngh/mL)N13131311Mean(SD)330(103)1233(374)1462(411)CV%31.130.328.1Median[Min-Max]2.17[1.92-4.08]

Citation Format: Hope S Rugo, Timothy J Pluard, Priyanka Sharma, Michelle Melisko, Ghassan Al-Jazayrly, Neelima Vidula, Yan Ji, David Weng, Hyeong-Seok Lim, Koung Eun Yoon, Hyun Ju Cho. Pharmacokinetic evaluation of an oral paclitaxel DHP107 (Liporaxel®) in patients with recurrent or metastatic breast cancer (MBC): Phase II study (OPERA, NCT03326102) [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS13-16.

Abstract PS18-18: Microsatellite instability high (MSI-H) detection utilizing targeted plasma based genotyping in metastatic breast cancer

Background: Microsatellite instability (MSI) occurs in some tumors from defects in mismatch repair genes. Immune checkpoint inhibition is approved for treatment of MSI-high (MSI-H) tumors. Plasma-based genotyping assays are being used more commonly in breast cancer to identify targetable mutations. The objective of this study was to evaluate MSI-H detection by plasma-based genotyping in metastatic breast cancer (MBC) and understand the co-existing genomic landscape. In selected cases, correlations of MSI-H with clinical characteristics were determined.

Methods:Patients who had MSI-H detected by cell-free DNA (cfDNA) analysis via Guardant360™ testing (next-generation sequencing (NGS), up to 74 gene panel) between 9/27/2018 and 3/12/2020 with a diagnosis of breast cancer reported on the test requisition form were identified from a de-identified database. MSI detection is based on plasma NGS of 90 microsatellite sites and combining observed read sequences and molecular barcoding information in a probabilistic model (Willis, 2019). A retrospective review was conducted to identify demographic and genomic characteristics of patients with MSI-H findings. For 11 patients, clinical data was provided by the treating physician for evaluation of demographics and response to immunotherapy.

Results:Of 7824 patients with breast cancer with alterations in plasma NGS, 40 (0.5%) were MSI-H. Of these 40 patients, 40 (100%) were female. The median age was 61 (range 39-92). The median number of genomic alterations per sample was 13 (range 4-69), and the median maximum allelic fraction (MAF) was 15.9% (range 0.92-54.2), compared to 4 and 2.7%, respectively, in all breast cancer samples reported in this time period. Table 1 depicts the most common co-existing non-synonymous mutations, which included DNA damage repair genes (ATM and BRCA2).

Clinical data was available for 11/40 MSI-H patients with MBC. Of these 11 patients, 4 (36%) had triple-negative MBC (mTNBC), and 7 (64%) had hormone receptor positive (HR+)/HER2- MBC. None had known Lynch syndrome. Seven patients received treatment with an immune checkpoint inhibitor (2 atezolizumab/nab-paclitaxel, 3 pembrolizumab, 1 pembrolizumab/capecitabine followed by pembrolizumab/eribulin, and 1 nivolumab). Treatment duration was available for 5 patients, and the median duration of treatment was 108 days (range 65-273 days). Two patients had durable benefit (1 with stable disease for 10 cycles, and another on treatment for &gt; 152 days), both of whom had mTNBC and were treated in the first-line setting with atezolizumab/nab-paclitaxel.

Conclusions:Plasma-based genotyping assays can identify the presence of MSI-H in breast cancer, including in patients with mTNBC and HR+/HER2- MBC. MSI-H breast cancers had a higher number of somatic alterations and MAF, suggesting higher tumor burden and genomic instability. The co-existing genomic landscape is heterogeneous, and mutations in TP53, PI3KCA, ESR1, RB1, NOTCH1, and ARID1A, and DNA damage repair genes (ATM and BRCA2) may be present. Since plasma based genotyping is increasingly being utilized to identify actionable mutations including PI3KCA, the ability to detect additional genomic alterations such as MSI-H extends the potential clinical application. However, the clinical utility of MSI detection by cfDNA needs to be determined and further prospective research is needed to validate the use of immunotherapy in cfDNA detected MSI-H MBC.

Table 1.GeneNumber (%) of MSI-H patients with ≥ 1 mutationTP5331 (78)PI3KCA25 (63)ESR120 (50)RB116 (40)NOTCH115 (38)ARID1A15 (38)ATM14 (35)BRAF14 (35)EGFR13 (33)PDGFRA11 (28)PTEN11 (28)APC11 (28)MET10 (25)KIT10 (25)FGFR210 (25)BRCA210 (25)

Citation Format: Neelima Vidula, Katherine Hesler, Kristin Price, Andrew Lipman, Georges Azzi, Ahmed Elkhanany, Tarek Sabagh, Dejan Juric, Estelamari Rodriguez, Shumei Kato, Joyce O'Shaughnessy, Aditya Bardia. Microsatellite instability high (MSI-H) detection utilizing targeted plasma based genotyping in metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-18.

Rising Circulating Tumor DNA As a Molecular Biomarker of Early Disease Progression in Metastatic Breast Cancer

PURPOSE

Accurate monitoring of therapeutic response remains an important unmet need for patients with metastatic breast cancer (MBC). Analysis of tumor genomics obtained via circulating tumor DNA (ctDNA) can provide a comprehensive overview of tumor evolution. Here, we evaluated ctDNA change as an early prognostic biomarker of subsequent radiologic progression and survival in MBC.

PATIENTS AND METHODS

Paired blood samples from patients with MBC were analyzed for levels of ctDNA, carcinoembryonic antigen, and cancer antigen 15-3 at baseline and during treatment. A Clinical Laboratory Improvement Amendments–certified sequencing panel of 73 genes was used to quantify tumor-specific point mutations in ctDNA. Multivariable logistic regression analysis was conducted to evaluate the association between ctDNA rise from baseline to during-treatment (genomic progression) and subsequent radiologic progression and progression-free survival (PFS).

RESULTS

Somatic mutations were detected in 76 baseline samples (90.5%) and 71 during-treatment samples (84.5%). Patients with genomic progression were more than twice as likely to have subsequent radiologic progression (odds ratio, 2.04; 95% CI, 1.74 to 2.41; P < .0001), with a mean lead time of 5.8 weeks. Genomic assessment provided a high positive predictive value of 81.8% and a negative predictive value of 89.7%. The subset of patients with genomic progression also had shorter PFS (median, 4.2 v 8.3 months; hazard ratio, 2.97; 95% CI, 1.75 to 5.04; log-rank P < .0001) compared with those without genomic progression.

CONCLUSION

Genomic progression, as assessed by early rise in ctDNA, is an independent biomarker of disease progression before overt radiologic or clinical progression becomes evident in patients with MBC.

Novel Agents for Metastatic Triple-Negative Breast Cancer: Finding the Positive in the Negative

Metastatic triple-negative breast cancer (TNBC) is associated with a poor prognosis, and the development of better therapeutics represents a major unmet clinical need. Although the mainstay of treatment of metastatic TNBC is chemotherapy, advances in genomics and molecular profiling have helped better define subtypes of TNBC with distinct biologic drivers to guide the therapeutic development of targeted therapies, including AKT inhibitors for PI3K/AKT-altered TNBC, checkpoint inhibitors for PD-L1-positive TNBC, and PARP inhibitors for BRCA1/2 mutant TNBC. This progress may ultimately convert TNBC from a disease traditionally defined by the absence of therapeutically actionable receptors to one that is defined by the presence of discrete molecular targets with therapeutic implications. Furthermore, antibody drug conjugates have emerged as an important therapeutic strategy to target genomically complex tumors that lack actionable oncogenes but have overexpressed actionable surface receptors such as trop-2. In this article, we discuss promising novel agents for advanced TNBC, some of which have been incorporated into current clinical practice, and others that will likely change the therapeutic landscape and redefine the TNBC terminology in the near future.

Identification of Somatically Acquired BRCA1/2 Mutations by cfDNA Analysis in Patients with Metastatic Breast Cancer

PURPOSE

Plasma genotyping may identify mutations in potentially "actionable" cancer genes, such as BRCA1/2, but their clinical significance is not well-defined. We evaluated the characteristics of somatically acquired BRCA1/2 mutations in patients with metastatic breast cancer (MBC).

EXPERIMENTAL DESIGN

Patients with MBC undergoing routine cell-free DNA (cfDNA) next-generation sequencing (73-gene panel) before starting a new therapy were included. Somatic BRCA1/2 mutations were classified as known germline pathogenic mutations or novel variants, and linked to clinicopathologic characteristics. The effect of the PARP inhibitor, olaparib, was assessed in vitro, using cultured circulating tumor cells (CTCs) from a patient with a somatically acquired BRCA1 mutation and a second patient with an acquired BRCA2 mutation.

RESULTS

Among 215 patients with MBC, 29 (13.5%) had somatic cfDNA BRCA1/2 mutations [nine (4%) known germline pathogenic and rest (9%) novel variants]. Known germline pathogenic BRCA1/2 mutations were common in younger patients (P = 0.008), those with triple-negative disease (P = 0.022), and they were more likely to be protein-truncating alterations and be associated with TP53 mutations. Functional analysis of a CTC culture harboring a somatic BRCA1 mutation demonstrated high sensitivity to PARP inhibition, while another CTC culture harboring a somatic BRCA2 mutation showed no differential sensitivity. Across the entire cohort, APOBEC mutational signatures (COSMIC Signatures 2 and 13) and the "BRCA" mutational signature (COSMIC Signature 3) were present in BRCA1/2-mutant and wild-type cases, demonstrating the high mutational burden associated with advanced MBC.

CONCLUSIONS

Somatic BRCA1/2 mutations are readily detectable in MBC by cfDNA analysis, and may be present as both known germline pathogenic and novel variants.

Comparison of the cell-free DNA genomics in patients with metastatic breast cancer (MBC) who develop brain metastases versus those without brain metastases

1094

Background: The genomics of patients with metastatic breast cancer (MBC) who develop brain metastases (BM) is not well understood given the difficulty in obtaining brain tumor for genotyping. We compared tumor genotyping results via cell-free DNA (cfDNA) collected at MBC diagnosis in patients who developed BM after MBC diagnosis with those who did not develop BM (non-BM). Methods: Patients at an academic institution who had cfDNA testing (Guardant 360/Next generation sequencing, 73 gene assay) at MBC diagnosis between 1/2016-12/2017, with ≥ 6 months of follow-up post testing, were identified. A chart review was done to identify tumor subtype, demographics, cfDNA results, and development of BM at or after MBC diagnosis. Pearson’s chi-squared and Wilcoxon rank sum tests were used to determine differences in clinical and cfDNA characteristics in BM vs. non-BM (p<0.05 for statistical significance). Results: CfDNA results were available for 49 patients, of whom 13 (27%) developed BM (4 with BM at MBC diagnosis). The median time to BM development was 11 months. While patients with BM were younger at MBC diagnosis than non-BM (median age BM 53 vs. non-BM 61, p=0.05), they had similar subtype (BM vs. non-BM: HR+/HER2- 62% vs. 69%, HER2+ 8% vs. 14%, TNBC 23% vs. 17%, unknown 8% vs. 0%, p=0.3), de-novo vs. recurrent disease (BM vs. non-BM: de-novo 8% vs. 14%, recurrent 92% vs. 86%, p=0.6), and visceral disease (BM vs. non-BM: 77% vs. 56%, p=0.2) distributions. All patients with BM had ≥1 detectable cfDNA mutation vs. 88% of non-BM. While the median mutant allele frequency of the most common mutation was similar in BM vs. non-BM (2.4% vs. 3.7%, p=0.5), the mutation pattern varied. Patients with BM more often had mutations in BRCA1 (15% vs. 3%, p=0.1), APC (15% vs. 0%, p=0.02), and CDKN2A (15% vs. 0%, p=0.02), compared to non-BM. In 4 patients with BM at MBC diagnosis, mutations in APC (50%), CDKN2A (50%), and BRCA 1/2 (25%) were noted; 1 had coexisting APC and BRCA1/2 mutations and another had coexisting APC and CDKN2A mutations. Conclusions: Patients with MBC who develop BM may have different cfDNA genomics, particularly BRCA1, APC, and CDKN2A mutations. Further research is needed to determine the predictive value of cfDNA at MBC diagnosis in the identification of patients at higher risk of developing BM. [Table: see text]

Phase II trial of a PARP inhibitor in somatic BRCA mutant metastatic breast cancer

TPS1113

Background: Poly(ADP-ribose) polymerase (PARP) inhibitors are now approved for patients with germline BRCA1/2 mutated HER2 negative metastatic breast cancer (MBC). However, germline BRCA1/2 mutations only account for 5-10% of breast cancer. We previously demonstrated that a subset of MBC may harbor somatic BRCA1/2 mutations detectable by cell-free DNA (cfDNA) (Vidula, SABCS, 2017). We hypothesize that somatic BRCA1/2 mutant MBC may also respond to PARP inhibition, similar to ovarian cancer, where PARP inhibition is efficacious in both somatic and germline tumors (Oza, 2017). Methods: This single arm, open label, phase II clinical trial is evaluating the efficacy of talazoparib, a PARP inhibitor, in 30 patients with somatic pathogenic BRCA1/2 mutant MBC identified by cfDNA. Patients may have triple-negative disease with receipt of at least 1 prior chemotherapy regimen, or hormone receptor positive, HER2 negative disease with at least 1 prior hormone therapy for MBC. Patients may have received a prior platinum, in the absence of progression on platinum chemotherapy. Patients must not have a known germline BRCA1/2 mutation. Patients will be treated with talazoparib 1 mg daily until progression, unacceptable toxicity, or withdrawal of consent, with clinical exams monthly, scans (CT chest, abdomen, and pelvis, and bone scan as appropriate) every 3 months, and serial cfDNA collected monthly. The primary endpoint is progression-free survival, as defined by RECIST 1.1. Subjects are enrolled in a 2-stage design, which provides 80% power to demonstrate that treatment is associated with “success” (PFS > 12 weeks) in ³ 53% patients (4% alpha). Additional endpoints include objective response rate and toxicity (per NCI CTCAE version 5.0). Correlative endpoints include determining changes in BRCA1/2 mutant allele fraction, genomic evolution including emergence of BRCA reversion mutations, and the impact of biomarker changes on outcomes. This trial is currently enrolling patients at the Massachusetts General Hospital. Successful completion of this study may help expand the patient population that is able to benefit from PARP inhibition. Clinical trial information: NCT03990896 .

Immunotherapy and chemotherapy combination for chest wall disease: TBCRC 044 trial

TPS1114

Background: Immunotherapy combined with chemotherapy is being studied in metastatic breast cancer, and may have durable outcomes. Chest wall recurrence represents a difficult to treat subtype of breast cancer with a poor prognosis, with lymphovascular invasion in the primary tumor a significant risk factor. Given the inflammatory nature of this disease and the association of programmed cell death 1 (PD-1) expression with lymphovascular invasion, we hypothesized that the combination of pembrolizumab, an anti-PD-1 antibody, with carboplatin may be effective as treatment for breast cancer chest wall recurrences. Methods: This randomized phase II study is enrolling 84 patients with breast cancer involving the chest wall, who may also have distant metastases. Patients receive treatment with pembrolizumab 200 mg and carboplatin AUC 5 every 3 weeks for 6 cycles (Arm A, n = 56) followed by maintenance pembrolizumab +/- carboplatin (Arm Ax), or carboplatin AUC 5 every 3 weeks for 6 cycles (Arm B, n = 28) with an option to cross-over to pembrolizumab +/- carboplatin on progression (Arm Bx). Patients with all disease subtypes, triple-negative, hormone receptor positive/HER2- after 2 prior lines of hormone therapy, and HER2+ disease (with the option to continue trastuzumab) are eligible, with no limit on the number of prior therapies. Prior platinum chemotherapy is allowed in the absence of overt disease progression. Patients undergo clinical assessment with every cycle of treatment including chest wall photography, scans (CT chest, abdomen, and pelvis) every 2 cycles, and have peripheral blood and chest wall biopsies collected at baseline and the start of cycle 3 for correlative studies. The primary endpoint is the disease control rate in the chest wall and distant sites at 18 weeks of treatment based on RECIST 1.1. The study is powered to determine a 20% difference in disease control between arms (hazard ratio 0.52, α = 0.10, β = 0.20). Additional endpoints include response by tumor programmed death ligand 1 (PD-L1) status and irRECIST, progression-free survival, and toxicity. Chest wall tumor samples will be analyzed for changes in tumor immune composition, and PD-L1 and MYC oncogene expression, based on preclinical data to suggest that PD-L1 may be upregulated by MYC. Peripheral blood samples will be evaluated for changes in PD-L1 expression, cell-free DNA, and circulating tumor cells with treatment. The study is enrolling patients at 7 sites within the Translational Breast Cancer Research Consortium (TBCRC), with current enrollment of 38/84 patients. Clinical trial information: NCT03095352 .

Phase Ib trial to evaluate safety and anti-tumor activity of the AKT inhibitor, ipatasertib, in combination with endocrine therapy and a CDK4/6 inhibitor for patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) (TAKTIC)

1066

Background: The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), with an anti-estrogen, are the standard of care for HR+/HER2- MBC. Insights from patient biopsies and preclinical analysis suggest that AKT1 activation can provoke CDK4/6i resistance. We hypothesized that targeting AKT1 following CDK4/6i progression may provide clinical benefit. Methods: TAKTIC is an open-label phase Ib trial exploring the combination of the AKT1 inhibitor, ipatasertib (ipat), with an aromatase inhibitor (Arm A), fulvestrant (Arm B), or the triplet combination (Arm C) of fulvestrant + ipat + palbociclib (palbo). The primary objective is to evaluate the safety and tolerability of ipat in combination with endocrine therapy +/- CDK4/6i. Key inclusion criteria include unresectable HR+/HER2- MBC; at least 1 prior therapy for MBC including any CDK4/6i; up to 2 prior lines of chemotherapy for MBC (no limit on prior endocrine therapy). Here, we present an interim analysis from the triplet combination (Arm C). Results: As of 1/31/2020, 25 pts have enrolled, including 12 on Arm C, all of whom received prior CDK4/6i (median no of prior lines = 5.5, range 2-7). Along with fulvestrant, 3 pts received ipat at 200mg + 125mg palbo, 7 pts received 300mg + 125mg palbo, and 2 pts received 400mg + 100mg palbo. To date, 8/12 pts remain on treatment including 2 with partial response, 3 with stable disease, 3 with restaging studies pending and 4 with progressive disease. The triplet combination was well tolerated. Grade 3 toxicities included reduced WBC (8/12), reduced neutrophil count (11/12), reduced lymphocyte count (2/12) and single instances of transaminitis, rash, and reduced platelet count. The only grade 4 toxicity was reduced neutrophil count (4/12). There were no DLTs observed and no discontinuations due to toxicity. Mean steady state pharmacokinetic parameters for ipat were similar to historical data from single agent trials suggesting that combined treatment with palbo + fulvestrant did not affect the pharmacokinetics of ipat. Updated analysis will be presented at the meeting. Conclusions: The triplet combination of endocrine therapy with CDK 4/6i and AKTi appears to be well tolerated in heavily pre-treated pts, with a subset demonstrating signs of clinical benefit. The trial demonstrates how insights into the molecular mechanisms of CDK4/6i resistance could be leveraged into actionable therapeutic regimens for HR+/HER2- MBC. Clinical trial information: NCT03959891 .

Novel antibody-drug conjugates for triple negative breast cancer

Triple negative breast cancer (TNBC) is a heterogenous subtype of breast cancer often associated with an aggressive phenotype and poor prognosis. Antibody–drug conjugate (ADC), comprising of a monoclonal antibody linked to a cytotoxic payload by a linker, is gaining increasing traction as an anti-cancer therapeutic. Emerging ADC drugs such as sacituzumab govitecan (IMMU-132) and trastuzumab deruxtecan (DS-8201a) are in late stages of clinical development for patients with metastatic breast cancer, including TNBC. In this article, we review and discuss the development and clinical application of ADCs in patients with advanced TNBC.

Abstract OT2-08-01: A phase 1b trial to evaluate safety and anti-tumor activity of the AKT inhibitor, ipatasertib, in combination with endocrine therapy with/without CDK 4/6 inhibitor for patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) (TAKTIC)

Background: The cyclin-dependent 4/6 inhibitors (CDK4/6i), in combination with an anti-estrogen, have emerged as the standard of care for patients with HR+/HER2- MBC. While only limited insight exists into the molecular factors that drive progression, emerging evidence suggests that activation of AKT1 may provoke resistance in a subset of patients. Overexpression of AKT1 also conveys resistance in HR+/HER2- breast cancer cells in vitro. AKT1 plays a well-established role in promoting tumor progression and metastasis. Targeting AKT1 following progression on CDK4/6i may provide durable clinical benefit in HR+/HER2- MBC.

Trial Design: This is an open-label phase Ib trial with three arms - Arm A includes fulvestrant + ipatasertib and Arm B includes an aromatase inhibitor (AI) + ipatasertib. Arm C includes fulvestrant + ipatasertib + palbociclib. Arm A and B are dose-expansion cohorts while Arm C is a dose-escalation (standard 3+3 design) followed by subsequent dose-expansion.

Eligibility Criteria: Key inclusion criteria include the presence of locally advanced/unresectable and metastatic HR+/HER2- breast cancer; postmenopausal status or pre/peri-menopausal status s/p oophrectomy or GNRH agonist; at least one prior therapy for MBC including any CDK4/6i; adequate performance status (ECOG 0-2); and adequate bone marrow and hepatic function. Stable CNS metastatic disease and up to two prior lines of chemotherapy for MBC are allowed (no limit on number of prior lines of endocrine therapy). Key exclusion criteria include prior use of fulvestrant (for Arm A); any prior intolerable toxicity with CDK4/6i (for Arm C); prior exposure to an AKT inhibitor in any setting; active CNS disease; concurrent use of specific CYP3A4 inhibitors or inducers; poorly controlled intercurrent illness; and pregnancy or active child-bearing potential.

Specific Aims: The primary objective of this study is to evaluate the safety and tolerability of ipatasertib in combination with endocrine therapy (aromatase inhibitor or fulvestrant) with or without CDK4/6i in patients with HR+/HER2- MBC who have received prior CDK 4/6i. Secondary objectives include assessment of objective response rate (ORR), clinical benefit rate (CBR), and progression free survival (PFS). Exploratory objectives include next generation sequencing of solid tumor biopsies and cfDNA along with immunohistochemical analysis of tumor biopsies to identify genomic and protein-based predictors of response and resistance.

Statistical Methods: Arms A and B constitute dose-expansion cohorts to confirm the safety/tolerability of ipatasertib use with anti-estrogens and evaluate preliminary efficacy. A dose-limiting toxicity (DLT) rate of &lt;33% will constitute success for future doublet development. There will be an initial enrollment phase (n=6); if ≤ 2 DLTs occur, total enrollment will be pursued (n=15 for each arm). Arm C is a standard 3+3 phase I trial design to establish a recommended phase II dose (RP2D) and maximum tolerated dose (MTD). Once the doses are established, an expansion cohort will be pursued (n=15) to confirm safety of the triplet and evaluate preliminary evidence of efficacy.

Present and Target Accrual: Anticipated accrual for Arms A+B will be n=15 (each). Arm C enrollment will be n=15-30 pending establishment of RP2D/MTD prior to dose expansion. Current enrollment n=4, since study activation in May 2019.

Citation Format: Seth A. Wander, Dejan Juric, Laura M. Spring, Neelima Vidula, Maureen Beeler, Karleen Habin, Elene Viscosi, Lauren Scarpetti, Elizabeth Tripp, Rachel Hepp, Beverly Moy, Steven J. Isakoff, Leif W. Ellisen, Aditya Bardia. A phase 1b trial to evaluate safety and anti-tumor activity of the AKT inhibitor, ipatasertib, in combination with endocrine therapy with/without CDK 4/6 inhibitor for patients with hormone receptor positive (HR+)/HER2 negative metastatic breast cancer (MBC) (TAKTIC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT2-08-01.

Abstract OT1-05-02: A phase II study to evaluate the efficacy, safety and pharmacokinetics of DHP107 (Liporaxel®, oral paclitaxel) compared to IV paclitaxel in patients with recurrent or metastatic breast cancer: OPERA (NCT03326102)

Background: Paclitaxel is a commonly used anticancer drug worldwide for various cancers including breast cancer. DHP107 is a novel oral formulation of lipid based components and paclitaxel. DHP107 showed comparable efficacy and safety to IV paclitaxel in a phase 3 study for patients with advanced gastric cancer (DREAM study, Ann Oncol 2018). DHP107, Liporaxel® was approved as the first oral paclitaxel in 2016 for gastric cancer in Korea. Currently the OPTIMAL Phase III study is ongoing in Korea and China to evaluate the efficacy of Liporaxel® as first-line therapy in recurrent or metastatic breast cancer. The OPERA Phase II study aims to evaluate the efficacy, safety and pharmacokinetics of DHP107 compared to IV Paclitaxel in non-Asian American patients in U.S. with recurrent or metastatic breast cancer. Trial Design: The OPERA study is a multi-center, randomized, open-label phase II trial enrolling HER2 negative (HR+/HER2- or triple-negative breast cancer (TNBC)) recurrent or metastatic breast cancer patients. Seventy two eligible subjects are being randomized in a 2:1 fashion to receive DHP107(200mg/m2 orally twice daily) or IV paclitaxel 80 mg/m2 on Days 1, 8, and 15 in a 28-day cycle) until disease progression, intolerable toxicity, or withdrawal from this study. Stratification factors include ‘TNBC vs. non-TNBC’ and ‘disease-free interval (DFI) ≤ 12 months vs. DFI &gt; 12 months’. A subset of the first 12 eligible subjects receiving DHP107, blood samples for PK analysis are collected on Day 1 of Cycle 1 at predose(0) and 1, 2, 3, 4, 6, and 10 hours post dose (before the 2nd dose administration on Day 1), and on Day 8 of Cycle 1 at predose (before the 1st dose on Day 8). Tumor assessments are performed every 8 weeks ± 7 days from C1D1 until disease progression or initiation of subsequent chemotherapy. Eligibility Criteria: Subjects must have confirmed HER2 negative breast cancer by immunohistochemistry (IHC) or in situ hybridization (ISH). HR positive (&gt;1%) or negative patients are eligible. Subjects can have received up to 3 lines of therapy for advanced disease, without prior exposure to taxane in the advanced stage setting. Subjects must have performance status of ≤2 on the Eastern Cooperative Oncology Group (ECOG) scale and measurable disease according to the Response Evaluation Criteria in Solid Tumors Version 1.1 (by RECIST version 1.1). Subjects with treated CNS metastases that are documented to be stable by CT or MRI imaging ≥4 weeks after completion of radiation and who do not require systemic corticosteroids are eligible. Subjects with neuropathy grade ≥2 based on CTCAE v4.03 are excluded. Specific Aims: The primary endpoint is objective response rate (ORR). Secondary endpoints include progression free survival (PFS), overall survival (OS), time-to-treatment failure (TTF), duration of response (DOR), disease control rate (DCR), quality-of-life (QoL) and safety. Statistical Design: Seventy two subjects are being enrolled, with an estimated drop-out rate of 10%. This sample size is sufficient to ensure that the lower one-sided 95% confidence limit for the true difference in response rates extends no more than 20% from the observed difference; this calculation assumes that the observed ORR is 60% in both groups. Target Accrual: The first subject was enrolled in July 2018 and recruitment is ongoing. Enrollment of 72 evaluable subjects is expected to complete in Q2 2020.

Citation Format: Timothy J Pluard, Priyanka Sharma, Michelle E. Melisko, Neelima Vidula, David E Weng, Jane D Skelton, Koung Eun Yoon, Hyun Ju Cho, Hope S Rugo. A phase II study to evaluate the efficacy, safety and pharmacokinetics of DHP107 (Liporaxel®, oral paclitaxel) compared to IV paclitaxel in patients with recurrent or metastatic breast cancer: OPERA (NCT03326102) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT1-05-02.

Abstract OT2-03-03: Evaluation of talazoparib, a PARP inhibitor, in patients with somatic BRCA mutant metastatic breast cancer: Genotyping based clinical trial

Background: Metastatic breast cancer (MBC) accounts for most breast cancer deaths. In 2018, two Poly(ADP-ribose) polymerase (PARP) inhibitors, olaparib and talazoparib, were approved for the treatment of MBC patients with germline BRCA1 or 2 mutations based on the OlympiAD and EMBRACA trials (Robson, NEJM, 2017 and Litton, NEJM, 2018), which demonstrated improvement in progression-free survival (PFS) with PARP inhibitors compared to chemotherapy. These landmark findings have triggered much interest in studying PARP inhibitors in MBC, but germline BRCA mutations only account for 5-10% of breast cancer patients. A critical question is whether PARP inhibitors may also be beneficial in MBC with somatic BRCA1 or 2 mutations, similar to somatic BRCA mutant ovarian cancer where they are effective(George, Oncotarget, 2017). Liquid biopsies via circulating cell-free DNA (cfDNA) may unveil somatic mutations. We previously demonstrated (Vidula, SABCS, PD1-13, 2017) that a subset of MBC patients have detectable somatic cfDNA BRCA1 or 2 mutations, in the absence of germline BRCA mutations, highlighting the role of liquid biopsies for detection of somatic BRCA mutations in MBC. Based on our preliminary data, we hypothesize that we can utilize liquid biopsies to detect somatic BRCA1 or 2 mutations and guide therapy selection with a PARP inhibitor in patients with MBC.

Methods: In this single arm phase II clinical trial we will evaluate the efficacy and safety of a PARP inhibitor, talazoparib, in patients with somatic BRCA mutant MBC (N=30). Patients will undergo cfDNA screening to identify cfDNA somatic BRCA1 or 2 deleterious mutations. Patients without known BRCA germline mutations who have cfDNA BRCA1 or 2 mutations will be enrolled at the Massachusetts General Hospital and University of California San Francisco. The study will enroll both patients with hormone receptor positive/HER2 negative breast cancer and triple-negative breast cancer whose disease has progressed on at least 1 prior line of endocrine therapy and at least 1 prior line of chemotherapy for MBC, respectively. Patients may have received any number of prior lines of therapy.

Eligible patients will be treated with talazoparib 1 mg daily until progression (evaluated with serial CT chest/abdomen/pelvis and bone scan) or unacceptable toxicity. The primary endpoint is to determine PFS by RECIST 1.1. Patients will be enrolled in a two-stage design, providing 80% power to demonstrate that the treatment is associated with “success” (PFS &gt; 12 weeks) in ≥53% patients (4% alpha). Secondary endpoints include objective response rate and safety/tolerability (NCI CTCAE v5.0). Serial cfDNA will be collected at baseline and during treatment to evaluate for changes in the BRCA cfDNA mutant allelic fraction in response to therapy. The impact of pre-existing resistance mutations in baseline cfDNA, particularly BRCA reversion mutations that can occur with prior platinum exposure (Weigelt, CCR, 2017), on outcomes will be studied. Paired liquid biopsies (pre- and post-treatment) will be compared to generate hypotheses about potential novel targets for future combination studies with talazoparib to improve response(exploratory objective). This study may help expand the applicability of talazoparib in MBC. This study was activated in July 2019. Funding support for the clinical trial is provided by a Pfizer ASPIRE award. (NCT03990896).

Citation Format: Neelima Vidula, Nora Horick, Erin Basile, Sara Sutherland, Ruth Fax, Daniel Haber, Leif Ellisen, Hope S. Rugo, Aditya Bardia. Evaluation of talazoparib, a PARP inhibitor, in patients with somatic BRCA mutant metastatic breast cancer: Genotyping based clinical trial [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT2-03-03.

Abstract P4-09-06: Brain metastases (BM) in patients with metastatic breast cancer (MBC) and circulating cell-free DNA (cfDNA) somatic BRCA mutations

Background: BM in MBC patients cause significant morbidity and mortality. BRCA1 germline mutations have previously been shown to be associated with an increased risk of developing BM (Lee et al, 2011), with an incidence as high as 15% (Zavitsanos et al, 2016). We previously reported that a subset of MBC patients may have somatic BRCA mutations in the absence of germline BRCA mutations (Vidula N, SABCS, 2017). In this study, we evaluated the incidence and clinical characteristics of BM in MBC patients with somatic BRCA mutations detected by cfDNA.

Methods: MBC patients with somatic BRCA1 or 2 mutations detected by cfDNA (Guardant360TM, next generation sequencing, 73 gene panel; mutations classified as somatic by Guardant360TM) with at least 4 months of follow-up post-testing at an academic institution were identified. From this cohort, we identified patients who developed BM post cfDNA testing. A retrospective review of medical records and Guardant360TM reports was conducted to identify demographics, tumor subtype, type of cfDNA BRCA mutation, whether the BRCA mutation was known to be pathogenic, germline BRCA mutation status, mutant allele fraction (MAF), clonality (MAF ratio of BRCA mutation/gene mutation with highest MAF ≥ 0.25 for clonal, and &lt;0.25 for subclonal) and the coexisting genomic environment. Clinical and genomic features of BM and non-BM patients (patients without BM) were compared using a chi-squared test for categorical variables and Wilcoxon rank-sum test for continuous variables. Brain tumor tissue from available cases of BM patients was used to evaluate somatic BRCA mutation status on the tumor tissue and correlated with cfDNA results.

Results: Of 36 MBC patients with somatic BRCA mutations, 9 (25%) developed BM and 27 (75%) did not have BM (non-BM). The median time to development of BM was 6.7 months after cfDNA testing. Of the BM patients, 5 (56%) had triple-negative (TN) and 4 (44%) had hormone receptor positive (HR+)/HER2- MBC in comparison with the non-BM cases where 5 (19%) had TN, 19 (70%) had HR+/HER2-, and 3 (11%) had HER2+ MBC. Very few patients (1 BM and 2 non-BM) had known co-existing separate germline BRCA mutations (rest not known BRCA carriers confirmed by negative germline testing and/or absence of family history suggestive of a germline BRCA phenotype). The median age at MBC diagnosis was similar for BM and non-BM patients (57 years). PIK3CA and TP53 mutations were commonly seen in both BM and non-BM cases. Additionally, MYC, EGFR, and CCNE1 mutations were commonly seen in BM cases. As outlined in Table 1, among patients with BM, the somatic BRCA mutations were commonly BRCA1, clonal, known to be pathogenic (56%), and present at a higher MAF, but these findings did not reach statistical significance possibly due to the small sample size. Brain tumor tissue mutation status in BM patients and correlation with cfDNA results will be presented at the meeting.

Conclusions: We observed a relatively high incidence (25%) of BM in MBC patients with somatic BRCA mutations detectable by cfDNA, which were often known to be pathogenic mutations (56%), and often associated with co-existing MYC, EGFR, and CCNE1 mutations. Further research using a larger cohort with adequate statistical power is needed to validate these findings, and may help identify MBC patients at risk for BM using a liquid biopsy.

Table 1.Characteristic BMNon-BMPrior anthracycline and/or platinum6 (67%)16 (59%)Type of somatic BRCA mutationBRCA16 (67%)11 (41%)BRCA22 (22%)15 (56%)BRCA1 and 21 (11%)1 (4%)Median BRCA MAF0.40.17ClonalityClonal6 (67%)13 (48%)Subclonal3 (33%)14 (52%)Mutation known to be pathogenic5 (56%)7 (26%)Common co-existing mutationsPIK3CA5 (56%)12 (44%)TP535 (56%)15 (56%)MYC5 (56%)8 (30%)EGFR5 (56%)8 (30%)CCNE15 (56%)6 (22%)KIT3 (33%)5 (19%)

Citation Format: Neelima Vidula, Andrzej Niemierko, Giuliana Malvarosa, Priscilla Brastianos, Erica Blouch, Kristen Shannon, Steven Isakoff, Seth Wander, Laura Spring, Jerry Younger, Kristin Price, Beverly Moy, Dejan Juric, Leif Ellisen, Aditya Bardia. Brain metastases (BM) in patients with metastatic breast cancer (MBC) and circulating cell-free DNA (cfDNA) somatic BRCA mutations [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-09-06.

Abstract P5-11-01 : Phase 1 dose escalation study of a novel selective androgen receptor modulator (SARM), RAD140, in estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-), metastatic breast cancer

Introduction: The androgen receptor (AR) is expressed in ~90% of ER+ BC. Androgen-based therapies have demonstrated response rates from 20-25% in advanced/metastatic breast cancer (mBC). RAD140 is an oral nonsteroidal SARM with tissue-selective AR agonist activity in BC cells but attenuated activity in other androgen-responsive tissues. In in vivo and in vitro models recapitulating various stages of AR/ER+ BCs, RAD140 exhibited potent anti-tumor activity as a single agent and in combination with inhibitors (i) of CDK4/6 or mTOR. Methods: This is a first-in-human, phase 1 dose escalation study with a 3+3 design and pharmacokinetic (PK) expansion cohort. The primary endpoint is safety, tolerability, and to establish the maximum tolerated dose (MTD) and/or recommended dose (RD). Secondary endpoints are PK and antitumor activity by RECIST. In the dose escalation phase, patients (pts) were treated with RAD140 once daily (QD) in 28-day cycles. In the subsequent PK expansion (PKE) cohort, pts were treated with a single dose of 100 mg followed by 1 wk of PK sampling before entering continuous 28-day treatment cycles with 100 mg QD dosing. Dose-limiting toxicity (DLT) was assessed during the first 28-day cycle. Key eligibility criteria included: ER+/HER2- and inoperable/mBC, post-menopausal, and ineligible for standard therapy. Archival tumor samples within 2 years or fresh tumor biopsies collected at the time of enrollment were analyzed retrospectively by immunohistochemistry (IHC) for AR, ER, progesterone receptor (PR), HER2 and Ki67. Serum sex hormone-binding globulin (SHBG) and prostate specific antigen (PSA) were used to assess AR engagement. Results: Dose escalation and PKE enrollment (n=22) is complete. Median age = 60 years, 100% stage IV, 86% visceral disease, 95% AR+, 91% AR+/ER+, and 82% AR+/ER+/HER2-. Median number of prior lines of therapy for mBC = 4; prior fulvestrant 86%, aromatase inhibitor 96%, CDK4/6i 91%, mTORi/PI3Ki 46%, chemotherapy 91%. Starting dose levels were 50 mg (n=6), 100 mg (n=13), and 150 mg (n=3) QD. Median time on treatment = 9 wk (range &lt;1-32+ wk). Most frequent (&gt;30%) treatment-emergent adverse events were elevated AST (27% grade [G] 1; 9% G2; 18% G3; 5% G4) and elevated ALT (18% G1; 23% G3). DLTs at 150 mg were hypophosphatemia (n=2). DLTs at 100 mg were hypophosphatemia (n=1), elevated ALT (n=3), and elevated AST (n=1). All DLTs were grade 3 and reversible. No drug-related deaths occurred. PK samples collected for 144 hrs after the 100 mg single dose showed variable absorption with a half-life of approximately 60 hrs. The observed human steady-state PK exposure at 100 mg exceeds the PK exposure of the efficacious dose in mouse of 10 mg/kg. Of 9 evaluable pts at the MTD of 100 mg, there was 1 partial response (PR; ORR=11%) and 3 pts (33%) with stable disease ≥12 wk. Time to PR was 15.9 wk with duration 18.6+ wk. Three pts remain on treatment. SHBG decreased in 18/18 pts and PSA increased in 15/20 pts with paired samples available, indicative of AR target engagement, most notably in the pt with PR. In 1 pt with paired pre- and on-treatment tumor biopsies, a strong induction of AR by IHC, predominantly in the nucleus was seen, further suggesting AR activation by RAD140 at the tissue level. Conclusions: The MTD and recommended dose for RAD140 is 100 mg QD. RAD140 is a novel oral AR-targeted agent for the treatment of AR+/ER+ mBC with an acceptable safety profile and preliminary evidence of target engagement and antitumor activity. This study is ongoing. NCT03088527

Citation Format: Erika Hamilton, Patricia LoRusso, Cynthia Ma, Neelima Vidula, Rebecca G Bagley, Steven Troy, Miriam Annett, Ziyang Yu, Aaron Weitzman, Maureen G Conlan, Amy Weise. Phase 1 dose escalation study of a novel selective androgen receptor modulator (SARM), RAD140, in estrogen receptor positive (ER+), human epidermal growth factor receptor 2 negative (HER2-), metastatic breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-11-01.