Abstract PS5-10: Esr1 mutation as a potential predictor of abemaciclib benefit following prior cdk4/6 inhibitor (cdk4/6i) progression in hormone receptor-positive (hr+) metastatic breast cancer (mbc): A translational investigation

Background: CDK4/6 inhibitors have emerged as the standard of care for HR+ MBC. However, there is limited insight into the potential benefit of abemaciclib following prior progression on palbociclib or ribociclib. Based on a multi-center cohort of patients with HR+ MBC who had received abemaciclib after prior palbociclib progression (Wander SA et al ASCO 2019), we have previously reported that abemaciclib after prior CDK4/6i progression was well tolerated and that a subset of patients derived durable clinical benefit. Identifying molecular predictors of sensitivity to abemaciclib after prior CDK4/6i progression constitutes an important area of research. Given the high frequency of ESR1 mutations in HR+ MBC with antiestrogen resistance, we evaluated the translational impact of ESR1 mutations in mediating response to abemaciclib in this setting.

Methods: To evaluate abemaciclib sensitivity in ESR1 mutant cell lines, T47D HR+ breast cancer cells were modified to over-express multiple mutant ESR1 isoforms via lentiviral infection and antibiotic selection. These isoforms included ESR1 Y537S, Y537N, and D538G. In an additional T47D cell line, RB1 expression was knocked down via CRISPR. The resulting derivative cell lines were grown in the absence of estrogen (via charcoal-stripped serum, CSS) or in escalating doses of abemaciclib. Cell viability was measured via cell-titer-glo assay. For clinical validation, we identified patients with MBC who had ESR1 mutations detected by targeted sequencing of cell-free DNA (cfDNA), via CLIA certified Guardant assay, and had abemaciclib exposure following prior progression on palbociclib or ribociclib in the existing multi-center cohort from six US institutions.

Results: All ESR1 mutant derivative cells demonstrated enhanced growth in estrogen deprivation compared to GFP controls, as expected, and were similarly sensitive to escalating doses of abemaciclib monotherapy in vitro, suggesting that ESR1 mutations do not confer resistance to abemaciclib. Interestingly, two patients with ESR1 mutations (in the absence of concurrent driver alterations in RB1, FGFR, CCNE2, and ERBB2) demonstrated progression on palbociclib and sensitivity to abemaciclib. In one patient, cfDNA obtained prior to palbociclib and fulvestrant exposure failed to reveal any ESR1 alteration. Following progression on palbociclib, and prior to sequential exposure to abemaciclib, an ESR1 Y537N alteration was identified. The patient went on to receive 16 months of abemaciclib monotherapy. In a second patient, an ESR1 D538G alteration was identified following progression on palbociclib and fulvestrant. The patient had several intervening regimens, and subsequently went on to receive abemaciclib and fulvestrant for 16 months. RB1-null T47D cells were resistant to abemaciclib monotherapy in vitro, as expected and, in the clinical dataset, the presence of alterations in previously identified genomic mediators of CDK4/6i resistance, such as RB1, were associated with progression on both palbociclib and abemaciclib.

Conclusions: HR+ breast cancer cells expressing mutant ESR1 isoforms were resistant to estrogen deprivation but retained sensitivity to abemaciclib in vitro. Furthermore, patients harboring ESR1 mutations via targeted sequencing of cfDNA, in the absence of other known mediators of CDK4/6i resistance, were shown to derive clinical benefit from abemaciclib following prior progression on palbociclib. These results suggest that patients with HR+ MBC, ESR1 mutation, and clinical resistance to anti-estrogen treatment and palbociclib may be candidates for abemaciclib treatment. Further research is warranted to confirm these novel translational observations.

Citation Format: Seth A. Wander, Hyo S. Han, Gabriela N. Johnson, Maxwell R. Lloyd, Pingping Mao, Utthara Nayar, Kailey Kowalski, Casey R. Stein, Veronica Mariotti, Leslie SL Kim, Maren Levin, Jing Xi, Apurva Pandey, Siobhan Dunne, Azadeh Nasrazadani, Adam Brufsky, Kevin Kalinsky, Cynthia X Ma, Joyce O’Shaughnessy, Nikhil Wagle, Aditya Bardia. Esr1 mutation as a potential predictor of abemaciclib benefit following prior cdk4/6 inhibitor (cdk4/6i) progression in hormone receptor-positive (hr+) metastatic breast cancer (mbc): A translational investigation [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 PS5-10.

Abstract PS5-12: Preliminary correlative analysis of clinical outcomes with PIK3CA mutation (mut) status from a phase I/Ib study of GDC-0077 in patients (pts) with hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC)

Background

Mutations in p110α, encoded by PIK3CA, are present in ~40% of HR+/HER2- BCs. GDC-0077, a PI3Kα-selective inhibitor and mutant PI3Kα degrader, elicits antitumor activity in PIK3CAmut preclinical models as a single agent and when combined with endocrine therapy (ET). New evidence suggests BCs harboring multiple PIK3CAmut exhibit increased signaling through the PI3K/AKT pathway and are more sensitive to PI3Kα inhibitors compared with BCs with a single PIK3CAmut. We report a preliminary analysis of PIK3CAmut status with clinical outcomes from an ongoing study of GDC-0077 alone or with ET (letrozole/fulvestrant) ± palbociclib (palbo) in pts with PIK3CAmut HR+/HER2- mBC (NCT03006172).

Methods

Detectable PIK3CAmut from local tumor tissue/blood-based assay or tumor tissue by cobas PIK3CA assay were required to enroll. Plasma-derived circulating tumor (ct) DNA was collected at baseline (BL), cycle 1 day 15 (C1D15), and C2D1 (in the cohort where GDC-0077 starts at C1D15) to detect PIK3CAmut. Paired tumor samples were analyzed for Ki67 and pAKT/pS6 expression by immunohistochemistry. Single vs multiple PIK3CAmut was correlated with the percentage of pharmacodynamic (PD) inhibition of Ki67/pAKT/pS6 expression; with the PIK3CAmut allele frequency ratio between BL and C1D15 or C2D1 (MAFr15); with best overall response (BOR, RECIST v1.1); and with time on treatment (TOT) in days. Statistical analyses: Kruskal-Wallis and Mann-Whitney-Wilcoxon for group and pairwise comparisons, respectively, and two-sample proportion testing for categorical comparisons.

Results

Data cutoff was 03/20/2020. PIK3CAmut were detected in 87/103 (84.5%) pts with BL ctDNA available for sequencing. Multiple PIK3CAmut were detected in 21/87 (24.1%) BL ctDNA samples: 9 from pts treated with single-agent GDC-0077; 8 from pts treated with GDC-0077 + letrozole/fulvestrant; and 4 from pts treated with GDC-0077 + letrozole/fulvestrant + palbo. The median number of lines of prior therapy for metastatic disease was not different between pts with multiple (3.0 lines) vs single (2.5 lines) PIK3CAmut detected at BL (p = 0.205). Median percentage inhibition of Ki67/pAKT/pS6 expression was greater in pts with multiple (-65.8, -70.3, -66.8%, respectively) vs single (-42.1, -34.1, -29.5%) PIK3CAmut detected at BL (p = 0.095, 0.002, 0.056). Median MAFr15 was lower in pts with multiple (MAFr15 0.01) vs single PIK3CAmut (MAFr15 0.15) detected at BL (p = 0.004). Of 73 pts with both BL ctDNA-detected PIK3CAmut and BOR data, 16/16 (100%) with multiple PIK3CAmut experienced BOR of partial response (PR) or stable disease (SD) while 42/57 (73.7%) with single PIK3CAmut experienced BOR of PR or SD (p = 0.051). No pts with multiple PIK3CAmut detected experienced a BOR of progressive disease. Median TOT was greater in pts with multiple PIK3CAmut (196 days) vs single PIK3CAmut (140.5 days) detected at BL, but this was not significant (p = 0.1804).

Conclusions

The fraction of pts in which multiple PIK3CAmut were identified from BL ctDNA in this HR+/HER2- mBC dataset (24.1%) was slightly higher than reported elsewhere. This may be due to the method of detection (blood vs tissue) and/or the definition of multiple PIK3CAmut used. Pts in which multiple PIK3CAmut were detected by ctDNA exhibited greater depth of PD biomarker inhibition in tumors and experienced PR/SD more often compared with pts in which only one PIK3CAmut was detected. However, no significant associations were observed with the number of prior lines of therapy for metastatic disease or TOT. The dataset is currently too small to assess the impact of different treatment regimens in this study but will be re-evaluated as the data mature.

Citation Format: Komal Jhaveri, Dejan Juric, Andrea Varga, Nicolas Turner, Peter Schmid, Cristina Saura, Mafalda Oliveira, Ian E Krop, Kevin Kalinsky, Antoine Italiano, Erika Hamilton, Valentina Gambardella, Andrés Cervantes, Philippe L Bedard, Bonnie P Liu, Jessica W Chen, Junko Aimi, Stephanie Royer-Joo, Jennifer L Schutzman, Katherine E Hutchinson. Preliminary correlative analysis of clinical outcomes with PIK3CA mutation (mut) status from a phase I/Ib study of GDC-0077 in patients (pts) with hormone receptor-positive/HER2-negative metastatic breast cancer (HR+/HER2- mBC) [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 PS5-12.

Abstract GS3-06: Biomarker evaluation in the phase 3 ASCENT study of sacituzumab govitecan versus chemotherapy in patients with metastatic triple-negative breast cancer

Background: Trophoblast cell-surface antigen-2 (Trop-2) is highly expressed in many epithelial tumors, including triple-negative breast cancer (TNBC). Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2 antibody coupled to SN-38, an active metabolite of irinotecan, via a unique hydrolyzable linker that allows for SN-38 release intracellularly and in the tumor microenvironment (bystander effect). Preclinical studies have shown a great range of efficacy with SG in mice bearing tumors with low, moderate, and high Trop-2 expression levels. We report subgroup analyses by Trop-2 expression from ASCENT, a randomized, phase 3 confirmatory study of SG versus standard-of-care chemotherapy in patients with metastatic TNBC (mTNBC). Methods: In the global, multicenter, open-label, phase 3 ASCENT study (NCT02574455), 529 patients with mTNBC refractory to or relapsing after at least 2 prior chemotherapies were randomized 1:1 to receive SG (10 mg/kg intravenously on days 1 and 8 every 21 days) or single-agent treatment of physician’s choice (capecitabine, eribulin, vinorelbine, or gemcitabine) until disease progression or unacceptable toxicity. The primary endpoint was progression-free survival (PFS) measured by central independent review per RECIST v1.1. Secondary endpoints included objective response rate (ORR) per RECIST v1.1, duration of response, overall survival (OS), and safety. Exploratory endpoints included biomarker assessments, including Trop-2 and BRCA1/2. Trop-2 expression was assessed using a validated immunohistochemistry assay. Results: Subgroup analyses by biomarker expression including Trop-2 and BRCA1/2 were performed, and outcomes by PFS, OS, ORR, and safety results will be reported. Conclusions: These analyses will provide further insights into the relationship of Trop-2 expression and the activity of SG in previously treated patients with mTNBC.

Citation Format: Sara A. Hurvitz, Sara M. Tolaney, Kevin Punie, Delphine Loirat, Mafalda Oliveira, Kevin Kalinsky, Amelia Zelnak, Philippe Aftimos, Florence Dalenc, Sagar Sardesai, Erika Hamiltion, Priyanka Sharma, Sabela Recalde, Eva Ciruelos Gil, Tiffany Traina, Joyce O'Shaughnessy, Javier Cortés, Michaela Tsai, Linda Vahdat, Véronique Diéras, Lisa Carey, Hope S. Rugo, David M. Goldenberg, Quan Hong, Martin Olivo, Loretta M. Itri, Aditya Bardia. Biomarker evaluation in the phase 3 ASCENT study of sacituzumab govitecan versus chemotherapy in patients with metastatic 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 GS3-06.

Abstract SP012: Convergent evolution of resistance pathways during early stage breast cancer treatment with combination cell cycle (CDK) and endocrine signaling inhibitors

Combining cyclin-dependent kinase (CDK) inhibitors with endocrine therapy improves outcomes for metastatic estrogen receptor positive (ER+), HER2 negative, breast cancer patients. However, the value of this combination in potentially curable earlier stage patients is not clear. Using single cell transcriptomic profiling, we examined the evolutionary trajectories of early stage breast cancer tumors using serial tumor biopsies from a clinical trial of preoperative endocrine therapy alone (letrozole) or in combination with the cell cycle inhibitor ribociclib. Applying hierarchical regression and Gaussian process mathematical modelling, we classified each tumor by whether it shrinks or persists with therapy and determined cancer phenotypes related to evolution of resistance and cell cycle transcriptional rewiring. We found that all patients’ tumors undergo subclonal evolution during therapy, irrespective of the clinical response. However, tumors subjected to endocrine therapy alone showed reduced diversity over time, those facing combination therapy exhibited increased diversity. Despite different diversity, single nuclei RNA sequencing uncovered common phenotypic changes in tumor cells that persist following treatment. In these tumors, accelerated loss of estrogen signaling is convergent with up-regulation of the JNK pathway, while persistent tumors that maintain estrogen signaling during therapy show potentiation of CDK4/6 activation consistent with ERBB4 and ERK signaling up-regulation. Cell cycle reconstruction identified that these tumors can rebound during combination therapy treatment, indicating stronger selection and promotion of a proliferative state. These results indicate that combination therapy in early stage ER+ breast cancers with ER and CDK inhibition drives rapid evolution of resistance via a shift from estrogen signaling to alternative growth factor receptor mediated proliferation and JNK signaling activation, concordant with a bypass in the G1 checkpoint.

Citation Format: JI Griffiths, J Chen, PA Cosgrove, A O'Dea, P Sharma, CX Ma, M Trivedi, K Kalinsky, KB Wisinski, R O'Reagan, I Makhoul, LM Spring, A Bardia, FR Adler, AL Cohen, JT Chang, QJ Khan, AH Bild. Convergent evolution of resistance pathways during early stage breast cancer treatment with combination cell cycle (CDK) and endocrine signaling inhibitors [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 SP012.

Effect of Capivasertib in Patients With an AKT1 E17K-Mutated Tumor: NCI-MATCH Subprotocol EAY131-Y Nonrandomized Trial

Importance

In the National Cancer Institute Molecular Analysis for Therapy Choice (NCI-MATCH) trial, agents targeting genetic tumor abnormalities are administered to patients. In the NCI-MATCH subprotocol EAY131-Y trial, patients with an AKT1 E17K-mutated metastatic tumor received the pan-AKT inhibitor capivasertib.

Objective

To assess the objective response rate (ORR) of capivasertib in patients with an AKT1 E17K-mutated tumor.

Design, Setting, and Participants

Between July 13, 2016, and August 10, 2017, patients in the NCI-MATCH trial were enrolled and assigned to the subprotocol EAY131-Y nonrandomized trial. Patients included adults with an AKT1 E17K-mutated metastatic tumor that had progressed with standard treatment, and these patients were assigned to receive capivasertib. Tumor assessments were repeated every 2 cycles. Data analysis of this evaluable population was performed from November 8, 2019, to March 12, 2020.

Interventions

The study treatment was capivasertib, 480 mg, orally twice daily for 4 days on and 3 days off weekly in 28-day cycles until disease progression or unacceptable toxic effect. If patients continued hormone therapy for metastatic breast cancer, the capivasertib dose was 400 mg.

Main Outcomes and Measures

The primary end point was the ORR (ie, complete response [CR] and partial response) according to the Response Evaluation Criteria in Solid Tumors criteria, version 1.1. Secondary end points included progression-free survival (PFS), 6-month PFS, overall survival, and safety.

Results

In total, 35 evaluable and analyzable patients were included, of whom 30 were women (86%), and the median (range) age was 61 (32-73) years. The most prevalent cancers were breast (18 [51%]), including 15 patients with hormone receptor (HR)-positive/ERBB2-negative and 3 with triple-negative disease, and gynecologic (11 [31%]) cancers. The ORR rate was 28.6% (95% CI, 15%-46%). One patient with endometrioid endometrial adenocarcinoma achieved a CR and remained on therapy at 35.6 months. Patients with confirmed partial response had the following tumor types: 7 had HR-positive/ERBB2-negative breast cancer, 1 had uterine leiomyosarcoma, and 1 had oncocytic parotid gland carcinoma and continued receiving treatment at 28.8 months. Sixteen patients (46%) had stable disease as the best response, 2 (6%) had progressive disease, and 7 (20%) were not evaluable. With a median follow-up of 28.4 months, the overall 6-month PFS rate was 50% (95% CI, 35%-71%). Capivasertib was discontinued because of adverse events in 11 of 35 patients (31%). Grade 3 treatment-related adverse events included hyperglycemia (8 [23%]) and rash (4 [11%]). One grade 4 hyperglycemic adverse event was reported.

Conclusions and Relevance

This nonrandomized trial found that, in patients with an AKT1 E17K-mutated tumor treated with capivasertib, a clinically significant ORR was achieved, including 1 CR. Clinically meaningful activity with single-agent capivasertib was demonstrated in refractory malignant neoplasms, including rare cancers.

Trial Registration

ClinicalTrials.gov Identifier: NCT00700882.

Advances in Therapeutic Approaches for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC), defined as breast cancer lacking expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2), accounts for up to 20% of all breast cancer, and it occurs at a higher frequency in younger, African American, and Hispanic women. Compared to breast cancers that are hormone receptor and/or HER2 positive, TNBC has an aggressive clinical course and worse prognosis. Because TNBC is by definition unresponsive to endocrine therapy (eg, tamoxifen, aromatase inhibitors) and HER2-directed therapies (eg, trastuzumab), chemotherapy continues to play an important role. TNBC constitutes a molecularly heterogeneous group of tumors that can vary in response to treatment, and clinical management can be challenging, particularly for the practicing community oncologist, for whom breast cancer may be only one of many tumor types encountered. In January 2020, the Breast Cancer Therapy Expert Group (BCTEG) convened a roundtable discussion on the topic of advances in the treatment of TNBC. Topics discussed included histopathologic classification/definition of TNBC, neoadjuvant strategies, adjuvant chemotherapy (with special emphasis on management of patients who do not experience a pathologic complete response), and treatment of metastatic disease. Also reviewed was the wide range of emerging pathways and therapies currently under investigation to expand TNBC treatment options, including immunotherapies and poly(ADP-ribose) polymerase (PARP) inhibitors. This article summarizes the BCTEG discussion and highlights the key opinions relating to the treatment of patients with TNBC.

Antibody-drug conjugates in metastatic triple negative breast cancer: a spotlight on sacituzumab govitecan, ladiratuzumab vedotin, and trastuzumab deruxtecan

INTRODUCTION

Metastatic triple-negative breast cancers (mTNBC) are characterized by aggressive behavior and worse clinical outcomes than other breast cancer subtypes, as well as poor response to cytotoxic chemotherapies. The use of antibody-drug conjugates (ADCs) has been investigated as a potential treatment strategy, particularly in heavily pretreated disease.

AREAS COVERED

This article reviews the preclinical and clinical data supporting the use of the ADCs sacituzumab govitecan (SG), ladiratuzumab vedotin (LV), and trastuzumab deruxtecan (T-DXd) in mTNBC, and highlights ongoing clinical trials and future clinical applications.

EXPERT OPINION

SG, LV, and T-DXd have demonstrated their potential to meaningfully improve clinical outcomes in patients with pretreated mTNBC, as demonstrated by notable response rates in phase I/II and, for SG, phase III clinical trials. Investigation of their use in combination with other agents, including PARP inhibitors and checkpoint inhibitors, is ongoing in the metastatic setting, and their application in early-stage TNBCs are under investigation. ADCs are therefore expected to redefine treatment paradigms in TNBC.

The COVID-19 pandemic impact on breast cancer care delivery at an academic center in New York City

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Background: The coronavirus disease 2019 (COVID-19) pandemic has altered healthcare delivery. To save resources and reduce patient exposure, non-urgent care has been postponed. Previous work has focused on cancer patients with COVID-19, but little has been reported on the impact on patients without COVID-19. We aimed to characterize breast cancer (BC) patients without COVID-19 whose care was impacted by the COVID-19 pandemic at an academic center in New York City. Methods: We performed a retrospective cohort study of BC patients treated at a medical oncology practice between 2/1/2020-4/30/2020. Patients were included if they were scheduled to receive intravenous or injectable therapy or were scheduled as a new patient. Patients were excluded if they tested positive for COVID-19 or transferred care during the study period. Demographic and treatment information were obtained by chart review. Delays/changes in systemic therapy, imaging, interventional radiology procedures, radiation, and surgery were tracked. Delays were defined as postponements of scheduled care. Changes were defined as care alterations without postponements. Care impact was defined as any change/delay in any of the above oncologic care a patient was scheduled for. We conducted a univariate analysis to compare demographics and care impact using χ2 analyses. Results: Of 351 eligible patients, the majority had stage 0-III BC (71.9%) and hormone receptor-positive HER2-negative BC (69.5%). Less than half were Caucasian (43.9%). Care was impacted due to the pandemic in 149 (42.5%) of patients. Surgery changes/delays were most frequent (37 of 84 patients, 44.0%), followed by changes/delays in systemic therapy (90 of 351 patients, 25.6%) and imaging (58 of 282 patients, 20.6%). Patients of Asian, Black, and other non-reported races were more likely to experience a care impact vs. Caucasian patients (47.1% vs. 44.4% vs. 55.6% vs. 31.2%, p = 0.001). Hispanic patients were more frequently impacted vs. non-Hispanic patients (47.6% vs. 35.9%, p = 0.06). Medicaid and Medicare patients were also more frequently impacted vs. commercially insured patients (54.7% vs. 41.4% vs. 36.2%, p = 0.02). BC stage and hormone receptor status were not significantly associated with care impacts. Conclusions: We found that nearly half of our BC patients experienced a change/delay in workup or treatment during the COVID-19 pandemic. We also found significant racial and socioeconomic disparities in the likelihood of care impact. Ongoing studies will determine the impact of alterations in care on cancer outcomes.

Sacituzumab govitecan in previously treated hormone receptor-positive/HER2-negative metastatic breast cancer: final results from a phase I/II, single-arm, basket trial

BACKGROUND

Trophoblast cell-surface antigen-2 (Trop-2) is expressed in epithelial cancers, including hormone receptor-positive (HR+) metastatic breast cancer (mBC). Sacituzumab govitecan (SG; Trodelvy®) is an antibody-drug conjugate composed of a humanized anti-Trop-2 monoclonal antibody coupled to SN-38 at a high drug-to-antibody ratio via a unique hydrolyzable linker that delivers SN-38 intracellularly and in the tumor microenvironment. SG was granted accelerated FDA approval for metastatic triple-negative BC treatment in April 2020.

PATIENTS AND METHODS

We analyzed a prespecified subpopulation of patients with HR+/human epidermal growth factor receptor 2-negative (HER2-) HR+/HER2- mBC from the phase I/II, single-arm trial (NCT01631552), who received intravenous SG (10 mg/kg) and whose disease progressed on endocrine-based therapy and at least one prior chemotherapy for mBC. End points included objective response rate (ORR; RECIST version 1.1) assessed locally, duration of response (DOR), clinical benefit rate, progression-free survival (PFS), overall survival (OS), and safety.

RESULTS

Fifty-four women were enrolled between 13 February 2015 and 1 June 2017. Median (range) age was 54 (33-79) years and all received at least two prior lines of therapy for mBC. At data cut-off (1 March 2019), 12 patients were still alive. Key grade ≥3 treatment-related toxicities included neutropenia (50.0%), anemia (11.1%), and diarrhea (7.4%). Two patients discontinued treatment due to treatment-related adverse events. No treatment-related deaths occurred. At a median follow-up of 11.5 months, the ORR was 31.5% [95% confidence interval (CI), 19.5%-45.6%; 17 partial responses]; median DOR was 8.7 months (95% CI 3.7-12.7), median PFS was 5.5 months (95% CI 3.6-7.6), and median OS was 12 months (95% CI 9.0-18.2).

CONCLUSIONS

SG shows encouraging activity in patients with pretreated HR+/HER2- mBC and a predictable, manageable safety profile. Further evaluation in a randomized phase III trial (TROPiCS-02) is ongoing (NCT03901339).

TRIAL REGISTRATION

ClinicalTrials.gov NCT01631552; https://clinicaltrials.gov/ct2/show/NCT01631552.

Abstract CT109: A phase I/Ib study evaluating GDC-0077 plus fulvestrant in patients with PIK3CA-mutant, hormone receptor-positive/HER2-negative breast cancer

Background: PIK3CA encodes the PI3K p110α subunit, and dysregulating mutations are widely seen in breast cancer (BC) and other solid tumors. GDC-0077 (G) is a potent p110α-selective inhibitor that degrades mutant p110α and demonstrates antitumor activity in PIK3CA-mutant BC xenograft models, either as a single agent, or combined with anti-estrogen therapy. From an ongoing, open-label, phase I/Ib dose-escalation study of G alone and combined with endocrine + targeted therapies (NCT03006172), we present data of G + fulvestrant (F) in postmenopausal patients (pts) with PIK3CA-mutant, hormone receptor-positive/HER2-negative BC, including a food-effect assessment on the pharmacokinetics (PK) of G. Methods: Safety (NCI-CTCAE v4), PK, and preliminary antitumor activity (clinical benefit rate [CBR]: RECIST v1.1 stable disease for ≥24 weeks, partial response [PR], or complete response) of 9 mg oral once-daily G + 500 mg intramuscular F on Day 1 (and Day 15 of Cycle 1) of 28-day cycles were assessed until intolerable toxicity/disease progression. The effect of a standard high-fat meal on the PK of G was evaluated after a single dose and at steady state. Relevant signaling and pharmacodynamic (PD) biomarkers were assessed using circulating tumor (ct) DNA samples. Results: At clinical cutoff (Jul 19, 2019), 20 pts were enrolled in the food-effect portion of the G + F arm. Fifteen (75%) had received ≥2 prior lines of therapy for metastatic BC. Median G treatment duration was 5.9 months (range 1.7-17.8); cumulative dose intensity, 98%. Adverse events (AEs) led to dose reduction in 3 pts (15%). The most common treatment-related (TR) AEs (≥4 pts, 20%) were hyperglycemia (11, 55%), diarrhea (10, 50%), stomatitis (grouped term; 9, 45%), nausea (8, 40%), decreased appetite (7, 35%), dysgeusia, fatigue, and muscle spasms (4 each, 20%). Grade ≥3 TRAEs were hyperglycemia, nausea, lymphopenia, hyperamylasemia, and hyperlipasemia (1 each, 5%). The PK of G in combination with F was similar to single-agent PK. Comparable G exposures (Cmax and AUC0-24) were observed following administration in fasted or fed states. Seventeen pts (85%) discontinued treatment, all due to radiographic/clinical disease progression. Overall, 5/14 pts with measurable disease had a PR (36%; 2 received prior F; 4, prior CDK4/6i), of whom 2 pts (14%) had a confirmed PR. CBR was 60% (12/20 pts). Most pts showed decreased ctDNA PIK3CA-mutant allele frequency during treatment. Conclusion: G + F demonstrated a manageable safety profile, similar PK to G alone, preliminary antitumor activity, and PD modulation of PIK3CA-mutant allele frequency in ctDNA. The presence of food did not significantly impact the rate or extent of G absorption following single or multiple doses. Additional pts are being enrolled in the G + F arm to further inform the safety and efficacy of this combination.

Citation Format: Kevin Kalinsky, Dejan Juric, Philippe L. Bedard, Mafalda Oliveira, Andres Cervantes, Erika Hamilton, Ian E. Krop, Nick Turner, Peter Schmid, Andrea Varga, Antoine Italiano, Zachary Veitch, Cristina Saura, Valentina Gambardella, Sravanthi Cheeti, Naoki Kotani, Guiyuan Lei, Katherine E. Hutchinson, Stephanie Royer-Joo, Anjali Vaze, Jennifer L. Schutzman, Komal Jhaveri. A phase I/Ib study evaluating GDC-0077 plus fulvestrant in patients with PIK3CA-mutant, hormone receptor-positive/HER2-negative breast cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT109.

Akt Inhibition Is Associated With Favorable Immune Profile Changes Within the Tumor Microenvironment of Hormone Receptor Positive, HER2 Negative Breast Cancer

Background: The PI3K/Akt/mTOR pathway in part impacts tumorigenesis through modulation of host immune activity. To assess the effects of Akt inhibition on the tumor micro-environment (TME), we analyzed tumor tissue from patients with operable hormone receptor positive, HER2 negative breast cancer (BC) treated on a presurgical trial with the Akt inhibitor MK-2206. Methods: Quantitative multiplex immunofluorescence (qmIF) was performed using CD3, CD8, CD4, FOXP3, CD68, and pancytokeratin on biopsy and surgical specimens of MK-2206 and untreated, control patients. nanoString was performed on surgical specimens to assess mRNA expression from MK-2206-treated vs. control patients. Results: Increased CD3+CD8+ density was observed in post vs. pre-treatment tissue in the MK-2206-treated vs. control patients (87 vs. 0.2%, p < 0.05). MK-2206 was associated with greater expression of interferon signaling genes (e.g., IFI6, p < 0.05) and lower expression of myeloid genes (CD163, p < 0.05) on differential expression and gene set enrichment analyses. Greater expression of pro-apoptotic genes (e.g., BAD) were associated with MK-2206 treatment (p < 0.05). Conclusion: Akt inhibition in operable BC was associated with a favorable immune profile in the TME, including increased CD3+CD8+ density and greater expression of interferon genes. Additional studies are warranted, as this may provide rationale for combining Akt inhibition with immunotherapy.

A phase Ib/II study of eribulin (ERI) plus pembrolizumab (PEMBRO) in metastatic triple-negative breast cancer (mTNBC) (ENHANCE 1)

1015

Background: As monotherapies, both ERI (a chemotherapeutic microtubule inhibitor) and PEMBRO (a programmed death [PD]-1 blocking immunotherapy) have shown promising antitumor activity in mTNBC. Emerging data suggest that the addition of immunotherapy to traditional chemotherapy holds promise for mTNBC. This open-label, single-arm, phase 1b/2 study evaluated the safety and efficacy of ERI + PEMBRO in mTNBC. Methods: Patients (pts) with mTNBC and ≤2 prior systemic anticancer therapies for metastatic disease were enrolled and stratified by prior number of therapy (Stratum 1, 0; Stratum 2, 1–2). Pts received IV ERI 1.4 mg/m2 on day (d)1 and d8 and IV PEMBRO 200 mg on d1 of a 21-d cycle. The primary objectives were safety and objective response rate (ORR per RECIST 1.1 by independent imaging review). Assessments also included efficacy outcomes by PD ligand-1 (PD-L1) expression status; PD-L1+ was defined as a combined positive score ≥1 using the PD-L1 IHC 22C3 pharmDx. Results: As of data cutoff (July 31, 2019), 167 pts (Stratum 1, n=66; Stratum 2, n=101) were enrolled and treated. No dose-limiting toxicities were observed. The most common treatment-emergent adverse events were fatigue (66%), nausea (57%), peripheral sensory neuropathy (41%), alopecia (40%), and constipation (37%). No deaths were considered treatment related. The overall ORR was 23.4% (95% CI: 17.2–30.5). Efficacy outcomes by PD-L1 status (PD-L1+, n=74; PD-L1-, n=75) and stratum are presented (table). Conclusions: ERI + PEMBRO has activity in pts with mTNBC. There was a trend toward more robust activity for the combination among patients with PD-L1+ tumors compared to PD-L1- tumors in the first-line setting (Stratum 1); whereas, in the later-line setting (Stratum 2) similar survival outcomes were observed among the PD-L1+ and PD-L1- pts. ERI + PEMBRO shows promise for mTNBC with efficacy that appears greater than historical reports of either agent alone. Clinical trial information: NCT02513472 . [Table: see text]

SGNLVA-001: A phase I open-label dose escalation and expansion study of SGN-LIV1A administered weekly in breast cancer

TPS1104

Background: LIV-1 is a highly prevalent transmembrane protein in breast cancer cells. Ladiratuzumab vedotin (LV), SGN-LIV1A, is an investigational antibody-drug conjugate (ADC) that targets LIV-1 via a humanized IgG1 monoclonal antibody conjugated to monomethyl auristatin E (MMAE) by a protease-cleavable linker. LV is internalized when it binds LIV-1 on cell surfaces and MMAE is released, which binds tubulin and induces apoptosis. LV has been shown to be active and tolerable in metastatic breast cancer (mBC) at a recommended dose of 2.5 mg/kg every 21 days (Modi 2017). More frequent, fractionated dosing has improved the activity and/or safety of other ADCs. Thus, this study is actively accruing subjects with metastatic triple negative breast cancer (mTNBC; estrogen receptor (ER)/progesterone receptor (PR)/human epidermal growth factor receptor 2 (HER2) receptor-negative) and endocrine-resistant ER+ or PR+ (hormone receptor [HR+])/HER2-negative mBC to test weekly dosing of LV (Days 1, 8, and 15 of every 3-week cycle). Methods: This study is enrolling up to 82 subjects (42 HR+/HER2-negative and 40 mTNBC) into dose escalation and dose expansion cohorts (NCT01969643). Eligible subjects are females ≥18 years old with pathologically and radiologically confirmed metastatic HR+/HER2-negative or mTNBC with at least 1 measurable lesion per RECIST v1.1. Subjects with HR+/HER2-negative disease must have received no more than 1 prior line of cytotoxic chemotherapy in the locally advanced (LA)/mBC setting, either as single agent or combination therapy. Subjects with mTNBC must have received 1 prior line of cytotoxic chemotherapy in the LA/mBC setting. Progression within 6 months of completion of neoadjuvant or adjuvant therapy is considered an LA/mBC regimen. Subjects must have adequate organ function, ECOG status of ≤1, and no ≥ Grade 2 peripheral neuropathy. Subjects with brain lesions must have received definitive treatment of the lesions. Prior therapy with MMAE-containing agents is not allowed. Dose escalation follows the modified toxicity probability interval method (Ji 2010). Dose expansion cohorts will provide data about activity and tolerability. Tumor assessments will be conducted every 2 cycles per RECIST v1.1 and all subjects will be followed for safety. Pharmacokinetics and markers of pharmacodynamics will be assessed. Primary safety endpoint is the incidence of adverse events and dose-limiting toxicities. Key efficacy endpoints include confirmed overall response rate, duration of response, and progression-free survival. Clinical trial information: NCT01969643 .

Letrozole + ribociclib versus letrozole + placebo as neoadjuvant therapy for ER+ breast cancer (FELINE trial)

505

Background: Ribociclib (R) + letrozole (L) is superior to L in metastatic breast cancer (BC). Preoperative endocrine prognostic index (PEPI) score 0 after neoadjuvant endocrine therapy (NET) is associated with low risk of relapse without chemotherapy in ER+ BC. On-therapy change in Ki-67 predicts adjuvant recurrence. FELINE is a biomarker-based multicenter randomized trial comparing changes in Ki-67 and PEPI between L+ Placebo (P) & L+R. Methods: Postmenopausal women with >2 cm or node+ ER+ HER2- BC were randomized 1:1:1 between L+P, L+R 400 mg continuous dose (Rc) and L+R 600 mg, 3 weeks on/1 week off - intermittent dose (Ri). Treatment was continued for six 28-day cycles. Core biopsies, blood samples were obtained at baseline, Day 14 cycle 1 (D14C1), and surgery. Clinical measurement, mammogram and US were obtained at baseline, surgery; MRI at baseline, week 8. Primary endpoint was rate of PEPI score 0 between L+P and L+R (i+c combined). Other endpoints were change in centrally performed Ki-67, complete cell cycle arrest (CCCA): Ki-67 <2.7%, clinical/imaging response, and difference in response & toxicity between the two R (Rc and Ri) arms. Results: From 2/2016 to 8/2018, 120 women were enrolled at 9 US centers. Thirty-eight were randomized to L+P and 82 to L+R groups (41 in Ri and Rc). Treatment groups were balanced at baseline. PEPI score of 0 was equal (25%) in L+P & L+R groups. CCCA at D14C1 was observed in 52% vs. 92% in L+P, L+R respectively (p < 0.0001). CCCA at surgery was observed in 63.3% vs. 71.4% in L+P, L+R respectively (p = NS). A significant increase in Ki-67 was observed between D14C1 and surgery in 66% vs. 33% in L+R, L+P respectively (p = 0.006). There was no difference in clinical, mammographic, US or MRI response between L+P and L+R. CCCA at D14C1 and surgery was similar in Ri & Rc arms. Grade >3 AEs were observed in 4 (10%) patients in L+P, 23 (56%) in L+Ri, 19 (46%) in L+Rc arms. Conclusions: Addition of R to L as NET did not result in more women with a PEPI score of 0. At D14C1 twice as many women on L+R had CCCA compared to L+P (92% vs 52%). However, significantly more women on L+R had increased proliferation between D14C1 and surgery , resulting in similar CCCA at surgery. Correlative studies are being performed to determine mechanisms of on-therapy acquired resistance to ribociclib. Continuous and intermittent doses of R have similar efficacy, toxicity. Clinical trial information: NCT02712723 . [Table: see text]

Diagnosis of leptomeningeal metastasis (LM) through identification of circulating tumor cells (CTCs) in cerebrospinal fluid (CSF)

3567

Background: Diagnosis of LM from solid tumors can be challenging. The TargetSelector (TS) CTC detection assay has demonstrated highly specific and sensitive CTC capture both for epithelial (CK+) and non-epithelial (CK-) subsets. The assay utilizes a ten-antibody (ab) capture cocktail followed by biotinylated secondary abs that bind to CTCs, enriched in a microfluidic device. TS targeted next-generation sequencing (NGS) assay detects somatic mutations in 12 breast cancer-related genes. The aim was to determine whether TS can improve sensitivity in the diagnosis of LM compared to CSF cytology by lumbar puncture (LP). Methods: CSF was collected prospectively from patients (pts) with a prior solid tumor diagnosis and suspicion of LM. CTCs were isolated from CSF using the TS platform. Cells were stained with cytokeratin (CK), CD45, streptavidin and DAPI. CTCs captured in a microchannel were classified as CK + or -. Peripheral blood samples obtained at time of LP underwent similar CTC analysis. Cell-free total nucleic acids (cfTNA) were extracted from plasma and CSF followed by NGS. Data analysis used the Ion Torrent Suite with annotation and report curation by Ion Reporter and Oncomine Knowledgebase Reporter software respectively. Results: There were 14 pts (13 women and 1 man), median age 56 years (range 32-75) with cancers of the breast (10), lung (1), colon (1), CNS lymphoma (1) or glioma (1). Pts had received a median of 2.5 lines of systemic metastatic therapy (range 0-8). CSF cytology was not sent for 1 pt and TS was not performed for 1 pt. TS and standard cytology had 89% agreement in pts with metastatic breast cancer (MBC, 8/9). Of the 6 pts for whom CTCs were detected in CSF by TS, 3 pts had + cytology (all MBC), 2 pts had - cytology and 1 pt with MBC was not tested by cytology. Of the 3 pts with + CSF by cytology (all MBC), all were detected by TS (Table). Among 5 MBC pts with CTCs present in CSF, ER status was concordant in 2 of 5 (40%). HER2 status was concordant in 3 of 4 (75%) evaluable pts and not determined in 1 pt. Analysis of cfDNA from CSF identified somatic mutations in 3 pts (TP53, PIK3CA, CCND1, respectively). In 1 of 3 pts, the mutation identified in the CSF (PIK3CA) in HR+/HER2- MBC was also identified in the blood. Conclusions: TargetSelector is a viable platform for the detection of breast cancer CTCs in the CSF. NGS performed on CSF samples can identify potentially actionable mutations. [Table: see text]

Abstract P3-11-02: Evaluation of patritumab/paclitaxel/trastuzumab over standard paclitaxel/trastuzumab in early stage, high-risk HER2 positive breast cancer: Results from the neoadjuvant I-SPY 2 trial

Background: I-SPY2 is a multicenter, phase 2 trial using response-adaptive randomization within biomarker subtypes to evaluate novel agents as neoadjuvant therapy for high-risk breast cancer. The primary endpoint is pathologic complete response (pCR) at surgery. The goal is to identify (graduate) regimens with ≥ 85% Bayesian predictive probability of success (i.e., demonstrating superiority to control) in a future 300-patient phase 3 1:1 randomized neoadjuvant trial with pCR endpoint within signatures defined by hormone-receptor (HR), HER2, and MammaPrint (MP) status. Regimens may leave the trial for futility (&lt; 10% probability of success), maximum sample size accrual (with probability of success ≥ 10% and &lt; 85%), or safety concerns as recommended by the independent DSMB. For HER2+ patients, the I-SPY2 control arm was 12 weekly cycles of paclitaxel+trastuzumab (TH, control) followed by doxorubicin/cyclophosphamide (AC) q2-3 weeks x4 and surgery. Patritumab is a fully human monoclonal antibody that inhibits HER3. In this experimental arm for HER2+ patients, patritumab was given q3w x 4 cycles (18mg/kg loading dose followed by 9mg/kg/dose) concurrent with paclitaxel and trastuzumab q1w x 12 weeks (PTH, treatment), followed by AC q2-3w.

Methods: Women with tumors ≥ 2.5cm were eligible for screening. MP low/HR+ tumors were ineligible. MRI scans (baseline, 3 weeks after start of therapy, prior to AC, and prior to surgery) were used in a longitudinal statistical model to predict pCR for individual patients. Analysis was intention to treat. Patients who switched to non-protocol therapy count as non-pCR. Patients on treatment arm therapy at the time of arm closure are non-evaluable. Graduation potential was in 3 of 10 pre-defined signatures: all HER2+, HR-/HER2+, and HR+/HER2+.

Results: The PTH regimen was stopped at the recommendation of the Safety Working Group and DSMB based on a safety event (bilateral sensorineural hearing loss, Gr 3) observed in one patient. At the time of arm closure, N=31 patients had received PTH treatment; 4 patients receiving PTH were changed to non-protocol therapy and removed from the analysis. The final estimated pCR report will consider 27 PTH and 31 TH as evaluable patients. Accrual was insufficient to assess graduation, however, there appears to be good signal in the HER2+HR- but not HER2+HR+ signatures.

I-SPY 2 TRIAL Est. pCR at time of arm closureSignaturesPTH (Treatment)N= 31TH (Control)N = 31All (HER2+)0.40 (0.22 - 0.59), n=310.23 (0.09 - 0.37), n=31HR-/HER2+0.64 (0.36 - 0.91), n=110.30 (0.12 - 0.47), n=12HR+/HER2+0.28 (0.08 - 0.48), n=200.20 (0.06 - 0.34), n=19

HR+/HER2+0.28 (0.08 - 0.48), n=200.20 (0.06 - 0.34), n=19The patient who developed Gr3 sensorineural hearing loss 6 days after the 2nd patritumab (and 4th paclitaxel/trastuzumab) treatment, did not recover her hearing after patritumab was stopped, and also reported Gr3 vulvovaginal pain, vulvitis, and vaginal inflammation. Other gynecological symptoms in the PTH arm include: 1 pt with Gr1 vaginal hemorrhage, and 1 pt with Gr2 dyspareunia. There was a higher frequency of Gr3 hypokalaemia (12.5% vs. 3.2%). One pt in the PTH arm reported Gr3 small intestinal obstruction which resolved with conservative management.

Conclusion: The I-SPY 2 study aims to assess the probability that investigational regimens will be successful in a phase 3 neoadjuvant trial; PTH was stopped due to safety concerns, although there was activity in the HER2+ HR- signature. This is the first report of Gr3 hearing loss associated with patritumab/paclitaxel/trastuzumab, and thus attribution is uncertain.

Citation Format: Teresa L Helsten, Shelly S Lo, Christina Yau, Kevin Kalinsky, Anthony D Elias, Anne M Wallace, A. Jo Chien, Janice Lu, Julie E Lang, Kathy S Albain, Erica Stringer-Reasor, Amy S Clark, Judy C Boughey, Erin D Ellis, Douglas Yee, Angela DeMichele, Claudine Isaacs, Jane Perlmutter, Hope S Rugo, Richard Schwab, Nola M. Hylton, W. Fraser Symmans, Michelle E Melisko, Laura J van't Veer, Amy Wilson, Ruby Singhrao, Smita M Asare, Ashish Sanil, Donald A Berry, Laura J Esserman. Evaluation of patritumab/paclitaxel/trastuzumab over standard paclitaxel/trastuzumab in early stage, high-risk HER2 positive breast cancer: Results from the neoadjuvant I-SPY 2 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 P3-11-02.

Abstract P3-09-02: Evaluation of a novel agent plus standard neoadjuvant therapy in early stage, high-risk HER2 negative breast cancer: Results from the I-SPY 2 TRIAL

Background: I-SPY2 is a multicenter, response-adaptive randomization phase 2 trial to evaluate novel agents when added to standard neoadjuvant therapy for women with high-risk stage II/III breast cancer - weekly paclitaxel + investigational treatment x 12 wks followed by doxorubicin & cyclophosphamide(AC) q3 wks x 4 vs. weekly paclitaxel/AC (control). The primary endpoint is pathologic complete response (pCR). The goal for all investigational arms is to identify/graduate regimens with ≥85% Bayesian predictive probability of success (i.e. demonstrating superiority to control) in a future 300-patient phase 3 1:1 randomized neoadjuvant trial with a pCR endpoint within signatures defined by hormone-receptor (HR) & HER2 status & MammaPrint (MP). Findings from the graduated, previously reported Pembro4 arm (Nanda et al, ASCO 2017) supported investigation of de-escalating therapy, and determining if pembrolizumab (an anti-PD-1 antibody) alone q3 wks x 4 after weekly paclitaxel x 12 wks + pembrolizumab q3 wks x 4 was sufficient to sustain response without AC.

Methods: Women with tumors ≥2.5cm were eligible for screening. MP low/HR+ were ineligible. MRI scans (at baseline, 3 wks, 12 wks, and prior to surgery) were used in a longitudinal statistical model to predict pCR for individual patients (pts). Pts who receive non-protocol therapy (e.g., carboplatin or AC for the Pembro8-noAC arm) count as non-pCR. Pembro8-noAC was open to HER2- pts for evaluation in 3 of 10 pre-defined signatures: HER2-, HR+/HER2-, and HR-/HER2-. Regimens exit the trial for futility (&lt;10% probability of success), maximum sample size accrual (10% &lt;probability of success &lt;85%), or safety as recommended by the independent DSMB.

Results: Pembro8-noAC was randomized to 73 pts, 3 of whom progressed while receiving pembrolizumab alone on study. Randomization to this arm continued after the first report because the rate of progression during AC over the course of the trial was estimated to be 6.5% based on serial MRI studies. However, notification of the third case prompted the study team to ask the DSMB for the summary response for this arm. Although it did not meet formal stopping rules for either graduation or futility, Pembro8-noAC was not near the target threshold pCR rates of 60% for HR-/HER2- and 30% for HR+/HER2+. As a result of this information, combined with the on-treatment progressions, assignment to Pembro8-noAC was discontinued. Treatment with pembrolizumab alone was no longer allowed due to the potential concern for progression, and investigators were given the option to administer AC with pembrolizumab or proceed with definitive surgery following the 12 weeks of paclitaxel + pembrolizumab. 34 pts had surgery results at the time the study was closed. Of the remaining 39 pts, 34 pts have on-therapy MRI assessments. Estimated pCR rates were based on all pts with information at the time (see table). Immune-related adverse events included grade 3 colitis (n=2), grade 3 pneumonitis (n=1), grade 3 transaminitis (n=1), grade 3 hypothyroidism (n=1), and grade 1-2 adrenal insufficiency (n=5).

Conclusion: Although Pembro8-noAC is performing at least as well as standard paclitaxel/AC, the likelihood is very low that the regimen would be successful in a phase 3 trial. Pembrolizumab alone following 12 weeks of paclitaxel + pembrolizumab was not sufficient to sustain a response. This was quickly assessed with a small number of patients.

Estimated pCR rateSignature(95% prob interval)Pembro8-noACControlHER2-0.210.2(0.09-0.32)(0.15-0.25)HR-/HER2-0.270.27(0.09-0.45)(0.19-0.35)HR+/HER2-0.150.15(0.01-0.29)(0.09-0.20)

Citation Format: Minetta C. Liu, Patricia A Robinson, Christina Yau, Anne M Wallace, A. Jo Chien, Erica Stringer-Reasor, Rita Nanda, Douglas Yee, Kathy S Albain, Judy C Boughey, Heather S Han, Anthony D Elias, Kevin Kalinsky, Amy S Clark, Kathleen Kemmer, Claudine Isaacs, Julie E Lang, Janice Lu, Tara Sanft, Angela DeMichele, Nola M Hylton, Michelle E Melisko, Jane Perlmutter, Hope S Rugo, Richard Schwab, W. Fraser Symmans, Laura J van't Veer, Patricia K Haugen, Amy Wilson, Ruby Singhrao, Smita Asare, Ashish Sanil, Donald A Berry, Laura J Esserman. Evaluation of a novel agent plus standard neoadjuvant therapy in early stage, high-risk HER2 negative breast cancer: Results from the I-SPY 2 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 P3-09-02.

Abstract P1-19-27: Phase IB trial of ACY-1215 (ricolinostat) combined with nab-paclitaxel in metastatic breast cancer (MBC)

Background:HDAC6, a cytoplasmic histone deacetylase, impacts cell viability by influencing protein metabolism, microtubule dynamics, and chaperone function. ACY-1215 is an orally active, selective HDAC6 inhibitor. Preclinical studies have demonstrated ACY-1215 to have synergistic activity with taxanes. We have developed an algorithm (HDAC6 score) based on mRNA expression profiling to evaluate the HDAC6 activity of individual tumor samples. Methods: In this open-label phase Ib trial, patients (pts) received ACY-1215 PO daily for 21 days of each 28-day cycle with nab-paclitaxel 100 mg/m2 on days 1, 8, and 15 until progression of disease or unacceptable toxicity. Entry criteria included men or women with any MBC subtypes. Measurable diseae was not required. The primary objective was to establish the maximum tolerated dose (MTD) of ACY-1215 with nab-paclitaxel. Dose escalation employed a time-to-event continual reassessment method (TITE-CRM) and the MTD was defined as the dose combination associated with a target probability of dose limiting toxicity (DLT) of 0.25.The TITE-CRM used an empirical dose-toxicity model (n=16 evaluable pts), starting at 120 mg to a maximum dose of 240 mg daily (qd). HDAC score was performed retrospectively on primary and/or metastatic tissue.Results:Seventeen pts were accrued between March 2016-Feb 2018; 16 were evaluable. Of evaluable pts, the median age was 57.5 years (range: 41-78), 14 were female (87.5%), 3 had triple negative MBC, and 13 hormone receptor (HR)+/HER2- MBC. The mean number of prior lines was 4 (range: 0-9). The first pt started at 120 mg qd, the second at 180 mg qd, and the rest at 240 mg qd. No DLTs were seen in the DLT window, and thus the MTD was not reached. Grade III events related to nab-paclitaxel included neutropenia (n=1), peripheral neuropathy (n=1), and 1 grade IV neutropenia. Grade III syncope related to ACY-1215 was observed in 2 pts. In the 16 evaluable pts, the following were best responses: 1 partial response (PR), 11 stable disease (SD), and 4 progressive disease (PD: 2 TNBC, 2 HR+/HER2-). One patient with SD remains on treatment since Feb 2018 (17 months). Median progression free survival (PFS) was 5.3 months [95% confidence interval (CI): 4.45-11.0]. In evaluable pts with accessible tissue (n=9), pts with high HDAC6 score (n=6: cutoff &gt; -0.1) had a significantly improved PFS compared to low HDAC6 score (n=3, HR: 1.2-115, 6.6 months vs. 2.0 months, respectively p=0.01). Conclusions: ACY-1215 240 mg qd is safe and tolerable with weekly nab-paclitaxel. Clinical activity has been observed, with the majority of pts demonstrating SD and 1 with a PR. In this phase 1b trial, high HDAC6 score associates with longer PFS. HDAC6 score should be evaluated in larger trials as a predictor of response to HDAC6 inhibition.

Citation Format: Kevin Kalinsky, Cody Chiuzan, Maika Onishi, Meghna S Trivedi, Melissa Accordino, Tizita Zeleke, Qingfei Pan, Sean Kelly, Erin Honan, Ruby Wu, Kathleen Fenn, Katherin D Crew, Dawn L Hershman, Matthew Maurer, Jiyang Yu, Jose Silva. Phase IB trial of ACY-1215 (ricolinostat) combined with nab-paclitaxel in metastatic breast cancer (MBC) [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 P1-19-27.

Abstract P6-10-25: Characterization of the tumor immune microenvironment (TME) in early stage HR-positive HER2-positive breast cancer

Background: In patients (pts) with early stage HER2-positive breast cancer (BC) who are treated with combination neoadjuvant chemotherapy (NAC) and HER2-targeted therapy, recent studies report that increased tumor infiltrating lymphocyte (TIL) density is associated with higher rates of pathologic complete response (pCR) and improved overall survival. However, in the subset of HER2-positive pts who are hormone receptor (HR)-positive, less is known about the relationship between the composition of the tumor immune infiltrate and clinical outcomes. In this study, we sought to characterize the TME of pts with early stage HR+ HER2+ BC using H&E-based TIL scoring and multiplex immunohistochemistry to assess for characteristics associated with achievement of pCR after neoadjuvant therapy.

Patients & Methods: We identified 25 pts with HR+ HER2+ early stage BC who were treated with NAC at our institution between 2005 and 2016 for whom pretreatment tissue was available for analysis. Twenty-two pts (88%) received neoadjuvant HER2 antibody therapy along with NAC. Twelve pts (48%) received neoadjuvant pertuzumab in addition to trastuzumab. At the time of surgery, 11 pts achieved pCR and 14 had residual carcinoma (RC). H&E slides from pretreatment biopsy samples were scored for both stromal and intratumoral TILs by a BC pathologist using established guidelines. Additionally, quantitative immunofluorescence (qmIF) was performed on pretreatment biopsy samples for 20 pts (9 with pCR, 11 with RC) using an OPAL antibody panel targeting CD3, CD8, CD68, HLADR, FOXP3, and pancytokeratin. Images were analyzed with the Vectra/inForm software platform (Perkin Elmer) to allow for multiparameter phenotyping. Nearest neighbor analysis to assess median distance between immune cell subtypes and tumor cells was performed using phenoptr software.

Results: Per TIL scoring, mean stromal TIL (sTIL) density was 28% in the pCR group and 17% in the RC group (p=0.05). Using a cutoff of ≥10% sTIL density, high sTILs were seen in pretreatment samples in 100% (11/11) of pCR pts and in 57% (8/14) of RC pts (p=0.05). Intraepithelial TIL density was not significantly associated with pCR (p=0.12). Per qmIF analysis, there was a numerical but not statistically significant increase in mean stromal CD3+CD8+ cell density (18% vs 11%) and decrease in stromal CD68+ cell density (10% vs 14%) in the pCR group compared to the RC group. Nearest neighbor analysis revealed that the median distance from tumor cells to CD68+ cells was significantly higher in pts with pCR vs. RC (p=0.02). No significant differences in median distance between CD3+CD8+ cells and tumor or CD3+CD8+ cells and CD68+ cells were detected among the two groups.

Conclusions: In a population of early stage HR+ HER2+ breast cancer pts who received neoadjuvant therapy, sTIL density by pathology assessment was associated with increased rates of pCR, supporting the hypothesis that the nature of the TME is biologically significant in the subset of HER2+ pts who are also HR+. qmIF is a useful tool to further characterize the density of specific immune cell subtypes and spatial relationships between cell types in the TME. Further studies in larger cohorts are needed to determine more specific immune biomarkers that predict response to combined chemotherapy and HER2-targeted therapy in pts with HR+ HER2+ BC.

Citation Format: Kathleen M. Fenn, Douglas K Marks, Rami Vanguri, Shuobo Boboila, Hua Guo, Hanina Hibshoosh, Kevin Kalinsky, Eileen Connolly. Characterization of the tumor immune microenvironment (TME) in early stage HR-positive HER2-positive 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 P6-10-25.

Abstract P1-01-02: Early changes in diffuse optical tomography predicts pathologic complete response to neoadjuvant chemotherapy in triple-negative breast cancer

Background: Optical based imaging modalities have shown promise for monitoring tumor response to neoadjuvant chemotherapy (NAC) in patients with breast cancer (BC). Patients with triple negative BC (TNBC) who achieve a pathologic complete response (pCR) have improved disease free and overall survival after NAC. In this study, we evaluated whether early changes in diffuse optical tomography breast imaging system (DOTBIS) parameters can predict a pCR. In particular, we studied total hemoglobin concentration (ctHbT) in the tumor region.

Methods: This is a retrospective evaluation of 105 stage II-III BC patients enrolled in a prospective cohort study between 2011 and 2019. All patients received standard taxane-based chemotherapy in the neoadjuvant setting and pCR was defined as no invasive tumor cells from the breast and axillary tissue at surgery (ypT0 ypN0). Residual Cancer Burden (RCB) score was also calculated. By imaging the whole breast volume using low intensity near infrared light, we measured tissue concentration of oxy-hemoglobin (ctO2Hb) and deoxy-hemoglobin (ctHHb). After tumor volume segmentation, the mean ctHbT (ctO2Hb+ ctHHb) extracted from the region of interest was normalized by the non-tumor region ctHbT mean value. We conducted an independent-samples t-test to determine if there was a difference in changes in the normalized ctHbT levels at week 4 (w4) between patients with a pCR and non-pCR. A Pearson's correlation assessed for correlation between RCB score and changes in the normalized ctHbT level at w4 compared to baseline.

Results: In total, 77 patients had complete data for the analysis. Of these, TNBC accounted for 18% (14/77) of BC cases. DOTBIS data was acquired at baseline for all patients. Twelve patients received weekly paclitaxel x 12, followed by dose-dense adriamycin/cyclophosphamide every 2 weeks x 4, and two received docetaxel/cyclophosphamide every 3 weeks x 6. Ten of 14 TNBC patients were imaged after four weeks of taxane-based NAC (w4). Of the 14 TNBC patients, 6 (43%) achieved pCR. Two patients were classified as RCB-I, 5 as RCB-II, and 1 non-pCR patient without an available RCB. After comparing normalized ctHbT levels at w4 to baseline, NAC was associated with an overall decrease of 28% for the pCR group (n=5) as opposed to an increase of 67% for non-pCR (n=5). The normalized ratio between ctHbT levels measured at w4 and baseline was statistically lower in the pCR group (0.72 ± 0.28) than non-pCR (1.67 ± 0.83) (95% CI, 0.17 to 2.09), p = .043. Changes in the normalized ctHbT levels after 4 weeks of NAC were strongly correlated to RCB score (r = .833, p = .005).

Conclusions: This study demonstrates that changes as early as 4 weeks in DOTBIS-measured ctHbT levels in patients with TNBC receiving NAC correlate strongly with pathologic response. If further validated on a larger set, these data could potentially be used to optimize treatment outcomes or improve personalized therapeutic strategies.

Citation Format: Mirella L Altoe, Kevin Kalinsky, Hua Guo, Hanina Hibshoosh, Mariella Tejada, Katherine D Crew, Melissa K Accordino, Meghna S Trivedi, Alessandro Marone, Hyun K Kim, Andreas H Hielscher, Dawn L Hershman. Early changes in diffuse optical tomography predicts pathologic complete response to neoadjuvant chemotherapy in triple-negative 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 P1-01-02.

Propranolol: What is BLOCKing Its Clinical Investigation in Breast Cancer?

Presurgical propranolol modulates biomarkers associated with breast cancer progression. β-adrenergic signaling promotes invasion, epithelial-to-mesenchymal transition phenotype, and immune cell infiltration into the tumor microenvironment. Blockade of the β-adrenergic receptor signaling with propranolol, along with potential future combinatorial strategies, holds promise for reducing breast cancer progression and metastasis.See related article by Hiller et al., p. 1803.