Lasofoxifene versus fulvestrant for ER+/HER2- metastatic breast cancer with an ESR1 mutation: results from the randomized, phase II ELAINE 1 trial

BACKGROUND

Acquired estrogen receptor alpha (ER/ESR1) mutations commonly cause endocrine resistance in ER+ metastatic breast cancer (mBC). Lasofoxifene, a novel selective ER modulator, stabilizes an antagonist conformation of wild-type and ESR1-mutated ER-ligand binding domains, and has antitumor activity in ESR1-mutated xenografts.

PATIENTS AND METHODS

In this open-label, randomized, phase II, multicenter, ELAINE 1 study (NCT03781063), we randomized women with ESR1-mutated, ER+/human epidermal growth factor receptor 2 negative (HER2-) mBC that had progressed on an aromatase inhibitor (AI) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) to oral lasofoxifene 5 mg daily or IM fulvestrant 500 mg (days 1, 15, and 29, and then every 4 weeks) until disease progression/toxicity. The primary endpoint was progression-free survival (PFS); secondary endpoints were safety/tolerability.

RESULTS

A total of 103 patients received lasofoxifene (n = 52) or fulvestrant (n = 51). The most current efficacy analysis showed that lasofoxifene did not significantly prolong median PFS compared with fulvestrant: 24.2 weeks (∼5.6 months) versus 16.2 weeks (∼3.7 months; P = 0.138); hazard ratio 0.699 (95% confidence interval 0.434-1.125). However, PFS and other clinical endpoints numerically favored lasofoxifene: clinical benefit rate (36.5% versus 21.6%; P = 0.117), objective response rate [13.2% (including a complete response in one lasofoxifene-treated patient) versus 2.9%; P = 0.124], and 6-month (53.4% versus 37.9%) and 12-month (30.7% versus 14.1%) PFS rates. Most common treatment-emergent adverse events with lasofoxifene were nausea, fatigue, arthralgia, and hot flushes. One death occurred in the fulvestrant arm. Circulating tumor DNA ESR1 mutant allele fraction (MAF) decreased from baseline to week 8 in 82.9% of evaluable lasofoxifene-treated versus 61.5% of fulvestrant-treated patients.

CONCLUSIONS

Lasofoxifene demonstrated encouraging antitumor activity versus fulvestrant and was well tolerated in patients with ESR1-mutated, endocrine-resistant mBC following progression on AI plus CDK4/6i. Consistent with target engagement, lasofoxifene reduced ESR1 MAF, and to a greater extent than fulvestrant. Lasofoxifene may be a promising targeted treatment for patients with ESR1-mutated mBC and warrants further investigation.

Genetic Alterations Detected by Circulating Tumor DNA in HER2-Low Metastatic Breast Cancer

PURPOSE

About 50% of breast cancers are defined as HER2-low and may benefit from HER2-directed antibody-drug conjugates. While tissue sequencing has evaluated potential differences in genomic profiles for patients with HER2-low breast cancer, genetic alterations in circulating tumor DNA (ctDNA) have not been well described.

EXPERIMENTAL DESIGN

We retrospectively analyzed 749 patients with metastatic breast cancer (MBC) and ctDNA evaluation by Guardant360 from three academic medical centers. Tumors were classified as HER2-low, HER2-0 (IHC 0) or HER2-positive. Single-nucleotide variants, copy-number variants, and oncogenic pathways were compared across the spectrum of HER2 expression. Overall survival (OS) was evaluated by HER2 status and according to oncogenic pathways.

RESULTS

Patients with HER2-low had higher rates of PIK3CA mutations [relative risk ratio (RRR), 1.57; P = 0.024] compared with HER2-0 MBC. There were no differences in ERBB2 alterations or oncogenic pathways between HER2-low and HER2-0 MBC. Patients with HER2-positive MBC had more ERBB2 alterations (RRR, 12.43; P = 0.002 for amplification; RRR, 3.22; P = 0.047 for mutations, in the hormone receptor-positive cohort), fewer ERS1 mutations (RRR, 0.458; P = 0.029), and fewer ER pathway alterations (RRR, 0.321; P < 0.001). There was no difference in OS for HER2-low and HER2-0 MBC [HR, 1.01; 95% confidence interval (CI), 0.79-1.29], while OS was improved in HER2-positive MBC (HR, 0.32; 95% CI, 0.21-0.49; P < 0.001).

CONCLUSIONS

We observed a higher rate of PIK3CA mutations, but no significant difference in ERBB2 alterations, oncogenic pathways, or prognosis, between patients with HER2-low and HER2-0 MBC. If validated, our findings support the conclusion that HER2-low MBC does not represent a unique biological subtype.

Abstract P3-05-08: Prevalence and prognosis of ER-loss in advanced invasive lobular carcinoma

Introduction: Estrogen receptor (ER) loss occurs in about 20% of recurrent breast cancers (BC) and is associated with unresponsiveness to endocrine therapy (ET) and poor prognosis. Prior studies evaluating ER-loss included predominately patients with invasive ductal carcinoma (IDC), and therefore the impact of ER-loss in invasive lobular carcinoma (ILC) is unknown. In this retrospective analysis, using real-world data, we aimed to determine the prevalence and clinical significance of ER-loss in ILC. Methods: Advanced BC were molecularly profiled at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing of DNA (592-gene panel or whole-exome sequencing), RNA (whole transcriptome sequencing, WTS) and immunohistochemistry (IHC) of select markers. A large real-world evidence (RWE) database combining Caris’ molecular data with clinical information obtained from insurance claims data (CODEai) was interrogated and overall survival (OS) was calculated from time of tissue collection to last patient contact. A tumor was considered to have ER-loss if therapies approved only for ER-positive BC were prescribed prior to obtaining a negative ER IHC result. OS was compared using Kaplan-Meier estimates for defined patient cohorts; significance was determined as p values &lt; 0.05. For molecular analyses, Fisher-Exact or Chi-Square tests were used to determine p values. Correction for multiple comparisons was performed using Benjamini-Hochberg to calculate q values. Results: The RWE database included 24,824 patients with advanced BC. At the time of tissue collection for molecular profiling, 6,786 advanced BC patients had been previously treated with ET (with or without mTOR or CDK4/6 inhibitors), of whom 1,338 had data available on histologic classification and ER IHC. The final analytical cohort included 263 patients with ILC and 1,075 with IDC. ER-loss was identified in 11.4% of ILC (n=30/263) and 19.6% (n=210/1075) of IDC (p=0.0017). In ILC, ER-loss was associated with significantly worse OS (HR: 1.75, 95%CI: 1.10-2.79, p=0.016) compared with no ER-loss. In the cohort of patients with ER-loss, patients with ILC had significantly worse OS compared with IDC (HR=2.03, 95% CI: 1.267-3.251, p=0.003). Further, when 1,016 tumors with ER-loss (regardless of histology) were stratified by the median OS (mOS=11mo), positive PD-L1 expression (34% vs. 22%, p=0.04, q=0.22), HER2 IHC positivity (16% vs. 7.8%, p=0.003, q=0.08) and HER2 amplification (16% vs. 4.7%, p=0.0006, q=0.04) were enriched in patients with longer mOS; while amplification of TEFB (0.38% vs. 2.6%, p=0.047, q=0.23) and MYB (0.38% vs. 2.6%, p=0.047, q=0.23) were enriched in patients with shorter mOS. WTS identified 197 differentially expressed genes, the majority of which were enriched in patients with longer mOS (q&lt; 0.05). Conclusions: In this large real-word dataset, ER-loss likely occurred in 11.4% of ILC and was associated with worse OS compared to both patients with IDC and ER-loss and ILC without ER-loss. Our analysis had several limitations; notably, our definition of ER-loss was based on prior treatment, we could not distinguish between de novo or recurrent metastatic disease and time of tissue collection was not standardized during the course of treatment. Thus, additional studies are needed to confirm these findings. However, this study does suggest that ER-loss occurs in a subset of patients with ILC and has poor prognostic implications.

Citation Format: Whitney L. Hensing, Joanne Xiu, W. Michael Korn, Stephanie L. Graff, Irene Kang, Evanthia T. Roussos Torres, Arielle L. Heeke, Andrew A. Davis, Nusayba A. Bagegni, Katherine K. Clifton, Ron Bose, Cynthia Ma, Foluso O. Ademuyiwa. Prevalence and prognosis of ER-loss in advanced invasive lobular carcinoma [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 P3-05-08.

Abstract OT3-11-01: TK IMPACT: Treatment Monitoring of Hormone Receptor Positive (HR+), HER2 Negative (HER2-) Metastatic Breast Cancer (MBC) Patients Receiving CDK 4/6 Inhibitors (CDK4/6i) with DiviTum® Thymidine Kinase 1 Activity

Background: CDK 4/6i have altered the therapeutic landscape of HR+, HER2- MBC, improving progression free and overall survival (PFS and OS) compared to endocrine therapy (ET) alone. Despite durable responses to CDK 4/6i in a large majority of patients, treatment response monitoring in this population has historically included numerous serial blood-based and imaging studies at frequent time points. There is a growing global interest in utilizing novel non-invasive biomarker-driven disease monitoring assessments to improve patient outcomes and reduce health care costs. Thymidine kinase 1 (TK1), a key cell-cycle regulated enzyme important for nucleotide metabolism during DNA synthesis, is regulated by the E2F pathway, downstream of CDK 4/6. Studies have shown that DiviTum® TK1 activity (TKa) may serve as both a prognostic and predictive biomarker of CDK 4/6i treatment response (McCartney et al, Clin Canc Res, 2020; Malorni et al, Eur J Cancer, 2022; Bagegni et al, Breast Cancer Res, 2017). Early TKa suppression within 2 weeks (wk) post CDK 4/6i therapy initiation is associated with improved PFS, suggesting a subgroup of patients who may be able to de-escalate imaging frequency. Elevated TKa at baseline and post CDK 4/6i may identify patients with CDK 4/6i-resistant disease and disease progression (PD) requiring early therapy modification. TK IMPACT is a prospective, single-arm trial designed to assess the impact of incorporation of DiviTum® TKa on a physician’s decision regarding subsequent timing of routine disease monitoring modalities in patients with advanced HR+, HER2- MBC receiving ET plus CDK 4/6i (NCT04968964). Methods: Blood sample collections will be analyzed using DiviTum® TKa at baseline (bl), wk 2, 4, 6, 8, and Q 4 wks thereafter beginning at wk 8 during the first 24-wk time period of study enrollment (+/- 3 days); followed by Q 12 wks thereafter, until PD or 36 months, whichever occurs first. Optional repeat TKa within 2-4 wks (+/-3 days) is permitted in case of rising TKa. Research blood (bl, wk 2, 12, 24, 48, and PD) and optional archival tumor tissue collection at diagnosis and PD will be obtained for correlatives. The investigator will record intended imaging modalities and timing prior to receipt of TKa, followed by documentation of any changes in imaging testing interval after receipt of TKa. Key eligibility criteria include postmenopausal women age ≥18 years with HR+, HER2- MBC, to initiate (Cohort 1) or are currently receiving (≤24 months, Cohort 2) any FDA approved first line ET plus CDK 4/6i with a life expectancy &gt; 6 months. The primary endpoint is any physician-reported intended change in imaging testing interval post TKa by study cohort, within the first 48-wk period of study participation. Key secondary endpoints are concordance rate between TKa values and progression status at first on-study imaging and longitudinal TKa dynamics. Key exploratory endpoints include plasma and tumor tissue-based biomarkers of CDK 4/6i response and resistance. A total of 40 patients will be enrolled (n=20/Cohort). The expected change rate is 20% with a 95% Wilson confidence interval of 0.105~0.248 across all patients and if within each cohort, with a 95% Wilson confidence interval of 0.081~0.416 for N=20. N=40 allows the lower limit of the 95% CI &gt; 10% and that of the N=20 in Cohort 1 to be ~10%, indicating some clinically meaningful influence of TKa progression on patient management. The study is open to accrual and has presently enrolled 5 patients.

Citation Format: Nusayba A. Bagegni, Isabella Grigsby, Leslie Nehring, Jingqin Luo, Jennifer Powers Carson, David W. Gibson, Meghan Horvath, Katherine K. Clifton, Foluso O. Ademuyiwa, Rama Suresh, Ashley Frith, Andrew A. Davis, Lindsay L. Peterson, Ron Bose, Amy Williams, Mattias Bergqvist, Cynthia Ma. TK IMPACT: Treatment Monitoring of Hormone Receptor Positive (HR+), HER2 Negative (HER2-) Metastatic Breast Cancer (MBC) Patients Receiving CDK 4/6 Inhibitors (CDK4/6i) with DiviTum® Thymidine Kinase 1 Activity [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 OT3-11-01.

Abstract P3-06-06: Real-world analysis of adverse events of patients with triple negative breast cancer receiving therapy per KEYNOTE-522

Background: KEYNOTE-522 was a randomized, double-blind, placebo-controlled phase 3 trial which resulted in the FDA approval of pembrolizumab with neoadjuvant chemotherapy for patients (pts) with newly diagnosed, high-risk, early-stage triple negative breast cancer (TNBC). Given the improvement in pathological complete response (pCR) and event-free survival rates, this regimen has emerged as standard-of-care (SOC) therapy. Adverse events in pts on this treatment regimen in clinical practice is unknown and understanding the real-world toxicity of this regimen is critical.

Methods: In this IRB approved retrospective, single-center study we examined pts with early-stage TNBC who received planned treatment per KEYNOTE-522 per SOC from 2021-present. This regimen includes a year of pembrolizumab combined with 4 cycles of neoadjuvant carboplatin/paclitaxel followed by 4 cycles of doxorubicin/cyclophosphamide. Number and length of treatment delays, treatment related toxicities of all grades, and pCR rate were collected from the electronic medical record.

Results: Of the 87 identified pts, 2 were excluded due to locally recurrent or metastatic disease and 6 did not receive immunotherapy due to concerns for toxicity or patient preference. Of the 79 pts who initiated treatment with chemotherapy and immunotherapy, median age of the cohort was 52 (27-77). 9 pts had a BRCA1 mutation and 1 pt had a BRCA2 mutation. 41 (51.9%) had T1-2 disease and 38 (48.1%) had T3-4 disease. 37 (46.8%) pts had N0 disease and 42 (53.2%) had N1-3 disease. 15 pts had baseline comorbidities, including heart disease, kidney disease, type II DM, and/or peripheral neuropathy. 68 pts (86.1%) had baseline ECOG 0, 9 (11.4%) had ECOG 1, and 2 (2.5%) had ECOG 2. At the time of analysis, 70 pts (88.6%) were receiving active treatment, of which 47 (67.1%) had completed ≥50% of the planned neoadjuvant therapy. Of pts completing ≥50% of planned neoadjuvant therapy and pts off therapy (N=56), 31 (55.4%) had 1 or more hospitalizations and 23 (41.1%) had 1 or more emergency room visits. 30 pts had treatment delays (53.6%) and 21 pts (37.5%) had dose reductions. Rates of adverse events are presented in Table 1. Of the 79 analyzed pts, 35 have undergone surgery. pCR rate was 45.7% (N=16). 8 (22.9%) pts had RCB-I, 4 (11.4%) pts had RCB-II, 3 (8.6%) pts had RCB-III, and 4 (11.4%) pts had residual disease without RCB calculation. Updated analysis will be included at time of presentation.

Conclusions: In this single-center retrospective study of pts receiving chemoimmunotherapy for TNBC, we found higher rates of grade 3 toxicity, including nausea, fatigue, neutropenia, diarrhea, peripheral neuropathy, and hypothyroidism, and lower pCR rate than was reported in the KEYNOTE-522 trial. This may reflect a more heterogeneous population of pts treated in routine clinical practice who are typically less fit than pts on clinical trials. Additionally, pts in this study had higher T stages (48.1% with T3-4 disease vs 26.0% in trial) and node positive disease (53.7% with N1-3 disease vs 48.8% in trial). Limitations include immaturity of data and small sample size; however, these data warrant validation through longer-term follow-up and multicenter validation.

Adverse Events in pts receiving Keynote-522 regimen as SOC and on clinical trial

Citation Format: Mara Hofherr, Jennifer Hedgecorth, Foluso O. Ademuyiwa, Lindsay L. Peterson, Nusayba A. Bagegni, Rama Suresh, Ashley Frith, Ron Bose, Katherine Weilbaecher, Cynthia Ma, Andrew A. Davis, Katherine K. Clifton. Real-world analysis of adverse events of patients with triple negative breast cancer receiving therapy per KEYNOTE-522 [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 P3-06-06.

Abstract PD13-09: PD13-09 Clinical outcomes of patients with HR+ HER2- advanced breast cancer with early progression on CDK4/6 inhibitors

Background: CDK4/6 inhibitors (CDK4/6i) paired with endocrine therapy (ET) are considered first-line (1L) therapy for patients (pts) with HR+ HER2- advanced breast cancer (aBC). A minority of pts will demonstrate primary resistance to CDK4/6i, as characterized by early progression. Thymidine kinase 1 (TK1) is a cell-cycle regulated enzyme downstream of CDK4/6 and involved in nucleotide metabolism during DNA synthesis. Prior studies have shown TK1 may serve as a biomarker of response to CDK4/6i, with early TK1 activity (TK1a) suppression after initiation of CDK 4/6i therapy associated with improved PFS. Lack of TK1a suppression may be associated with primary resistance to CDK4/6i. In this study, we aim to analyze response to subsequent lines of therapy and overall survival (OS) of pts with early progression on 1L CDK4/6i. Methods: Pts with HR+ HER2- aBC from a phase II trial of an alternative schedule of palbociclib (palbo alt dosing trial NCT 3007979) and from a retrospective palbociclib study were included in this analysis. Pts in the palbo alt dosing trial underwent baseline and C1D15 TK1a analysis after initiation on CDK4/6i. C1D15 TK1a suppression was defined at TK1a &lt; 30 Du/L. Pts in the retrospective palbociclib study included pts receiving palbo as part of their standard of care 1L therapy for HR+ HER2- aBC at Washington University in Saint Louis from 2016 to 2021. Clinical information, including treatment start and stop dates on each of the next-line therapies, were collected from the electronic medical record. PFS was estimated by the treatment duration on a specified treatment regimen. Early progression on CDK4/6i was defined as PFS &lt; 6 mo. Best response was defined as next line of therapy with the numerically longest PFS. OS was defined as time to death from the initiation of CDK4/6i. Results: Of the 54 pts enrolled on the palbo alt dosing trial, 51 pts were evaluable for clinical benefit and 46 pts were evaluable for TK1a suppression rate at C1D15. 7 pts (15.2%) were found without TK1a suppression at C1D15. This lack of TK1a suppression on palbo was associated with a significantly shorter PFS (median PFS=3.1 mo) compared to not reached in pts with TK1a suppression at C1D15. We conducted clinical analysis on N=26 pts who exhibited early progression on CDK4/6i which included 10 pts from the palbo alt dosing trial and 16 from the retrospective study. The average subsequent line of therapies in this cohort was 3, with the most common second line (2L) therapy being chemotherapy (N=17, 65.4%) and ET (N=8, 30.8%). The median PFS for pts receiving 2L chemotherapy and ET was 4.09 mo and 3.64 mo, respectively. 10 pts received both chemotherapy and ET with 7 (70.0%) achieving best response with chemotherapy compared to 3 pts (30.0%) who achieved best response with ET. The median OS for the cohort was 14.6 mo. Conclusions: Early progression on CDK4/6i is associated with a particularly poor prognosis. In our cohort, the median OS was far below the expected median OS for pts receiving 1L palbo as reported in the PALOMA-2 trial (14.6 mo vs 53.9 mo). Early progression on CDK4/6i is associated with more aggressive disease which may respond more favorably to chemotherapy, as demonstrated by best response to therapy. Further prospective studies are warranted to explore this treatment approach.

Citation Format: Katherine K. Clifton, Shana N. Thomas, Jingqin Luo, Jing Xi, Nusayba A. Bagegni, Foluso O. Ademuyiwa, Rama Suresh, Ashley Frith, Andrew A. Davis, Ron Bose, Katherine Weilbaecher, Whitney L. Hensing, Timothy Pluard, Massimo Cristofanilli, Hyo S. Han, Adam M. Brufsky, Kevin Kalinsky, Shom Goel, Seth A. Wander, Lindsay L. Peterson, Cynthia Ma. PD13-09 Clinical outcomes of patients with HR+ HER2- advanced breast cancer with early progression on CDK4/6 inhibitors [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 PD13-09.

Abstract P3-06-07: Phase Ib/II study to evaluate safety and tolerability of cabiralizumab in combination with nivolumab and neoadjuvant chemotherapy in patients with localized triple-negative breast cancer

Background: Neoadjuvant immune checkpoint inhibition (ICI) in combination with chemotherapy is approved for patients with high-risk, early-stage triple-negative breast cancer (TNBC) based on improved outcomes in the KEYNOTE-522 trial. However, some patients have primary resistant disease and do not achieve a pathological complete response (pCR), while others experience significant toxicity. Tumor-associated macrophages (TAMs) are a potential resistance mechanism for ICIs and are dependent on colony-stimulating factor 1 receptor (CSF1R). Therefore, we examined the addition of cabiralizumab, a CSF1R inhibitor, to neoadjuvant paclitaxel, carboplatin, and nivolumab to assess the safety, tolerability, and changes in the tumor microenvironment (TME) in patients with early-stage TNBC. Methods: This is a phase Ib/II, single-institution, randomized controlled clinical trial (NCT04331067) in patients with newly diagnosed Stage II-III TNBC. The primary endpoints include: (1) to determine the safety of a 12-week neoadjuvant regimen of paclitaxel (80 mg/m2 IV q week) + carboplatin (AUC5 IV q3 weeks) + nivolumab (240 mg IV q2 weeks) with or without cabiralizumab (4 mg/kg IV q2 weeks) and (2) to evaluate the effect of cabiralizumab on TAMs and changes in tumor infiltrating lymphocytes (TILs) in the TME between baseline and an on-treatment biopsy after 4 weeks of therapy. Adjuvant treatment is per investigator’s choice. Secondary objectives include evaluation of pCR rate and recurrence-free survival. Paired tissue and bone marrow biopsies are collected for evaluation of the TME and disseminated tumor cells, respectively. The study was designed to enroll 50 patients, including a 12-patient safety lead-in cohort. Here, we report the planned interim analysis of the safety lead-in cohort. Results: Between December 2020 and May 2022, we enrolled 12 patients to the safety lead-in, including 6 patients in each arm. 5 of 12 patients (41.7%) enrolled are underrepresented minorities, including 4 Black patients and 1 Hispanic patient. 2 of 6 patients in the nivolumab arm experienced grade 3 severe toxicity, including 1 patient who developed sepsis and 1 who developed peripheral neuropathy. 3 of 6 patients in the nivolumab + cabiralizumab arm developed grade 3 severe toxicity including 2 patients who experienced myositis and 1 patient who developed periorbital edema. Of the first 10 patients enrolled, 5 had a pCR (2 pCR in cabiralizumab arm, 3 pCR in non-cabiralizumab arm) and 3 had non-pCR (1 RCB-1 and 1 RCB-3 in cabiralizumab arm, 1 RCB-1 in non-cabiralizumab arm). 2 patients came off study prior to surgery (1 due to toxicity and 1 due to missing study visits). Data from the final 2 patients still on treatment will be available at the time of presentation. Discussion: Full safety, pathologic, and clinical response data in the safety lead-in cohort for patients with early-stage TNBC receiving neoadjuvant chemotherapy + nivolumab with or without cabiralizumab, will be presented.

Citation Format: Andrew A. Davis, Leonel Hernandez-Aya, Jingqin Luo, Mateusz Opyrchal, Foluso O. Ademuyiwa, Nusayba A. Bagegni, Katherine K. Clifton, Jill Anderson, Trish Hammerschmidt, Leslie Nehring, David DeNardo, Mark Watson, Rebecca Aft, Cynthia Ma, Katherine Weilbaecher. Phase Ib/II study to evaluate safety and tolerability of cabiralizumab in combination with nivolumab and neoadjuvant chemotherapy in patients with localized triple-negative 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 P3-06-07.

Targeted Treatment for High-Risk Early-Stage Triple-Negative Breast Cancer: Spotlight on Pembrolizumab

Triple-negative breast cancer (TNBC) is a biologically aggressive yet heterogeneous disease that disproportionately affects younger women and women of color compared to other breast cancer subtypes. The paucity of effective targeted therapies and the prevalence of chemotherapeutic resistance in high-risk, early-stage TNBC pose significant clinical challenges. Deeper insights into the genomic and immune landscape have revealed key features of TNBC, including intrinsic genomic instability, DNA repair deficiency, and potentially an immunogenic tumor microenvironment. These advances led to landmark trials with immune checkpoint inhibitors in the advanced-stage setting, which subsequently translated into immunotherapy-based clinical trials in the early-stage setting and recent promising results. Pembrolizumab, an anti-programmed death 1 (PD-1) monoclonal antibody, was investigated in combination with platinum-, taxane- and anthracycline-based neoadjuvant chemotherapy followed by adjuvant pembrolizumab monotherapy for patients with high-risk, early-stage TNBC in the randomized, double-blind, placebo-controlled phase 3 KEYNOTE-522 trial. In July 2021, the US Food and Drug Administration (FDA) granted approval for pembrolizumab based on marked improvement in pathologic complete response rate and 3-year event-free survival compared to neoadjuvant chemotherapy alone. This advance immediately altered the longstanding treatment paradigm. Here, we review the impact of pembrolizumab plus chemotherapy for the treatment of patients with high-risk, early-stage TNBC, and discuss immunotherapy-related toxicity considerations, key immunomodulatory biomarkers under active investigation, and remaining clinical questions for future research directions.

Phase 1b trial of anti-VEGF/PDGFR vorolanib combined with immune checkpoint inhibitors in patients with advanced solid tumors

Purpose

Vorolanib is a multi-target tyrosine kinase inhibitor with anti-angiogenic properties. This study aimed to evaluate the tolerability, safety and efficacy of vorolanib when added to checkpoint inhibitors (CPIs) in patients with advanced solid tumors.

Methods

We conducted a phase 1b study of vorolanib (300 or 400 mg orally once daily) plus pembrolizumab or nivolumab using a standard 3 + 3 design to determine the dose-limiting toxicity (DLT), maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D). The endpoints included safety, toxicity and objective response rate, according to Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST 1.1).

Results

Sixteen patients (9 in pembrolizumab arm, 7 in nivolumab arm) with gastrointestinal or lung cancers were enrolled. All patients had at least 1 treatment-related adverse event (TRAE). The most common TRAEs across all cohorts were lymphopenia (n = 7), leukopenia (n = 5), fatigue (n = 5), and alanine aminotransferase elevation (n = 5); most toxicities were grade (G) 1–2. DLTs were reported in 3 patients at vorolanib 400 mg dose level, with G3 aspartate aminotransferase elevation, G3 rectal hemorrhage, and G3 rash. Of 13 total response-evaluable patients, 2 patients had confirmed partial responses (1 rectal squamous cell cancer and 1 small cell lung cancer). Two patients achieved prolonged stable disease. Vorolanib 300 mg daily was determined to be the RP2D for either pembrolizumab or nivolumab.

Conclusion

Combination vorolanib 300 mg orally once daily plus CPI appears to be a feasible regimen with manageable toxicity and promising efficacy in select tumor types. NCT03511222. Date of Registration: April 18, 2018.

Abstract PD14-04: Circulating tumor DNA characterization of invasive lobular carcinoma in patients with metastatic breast cancer

Background:Invasive lobular carcinoma (ILC) is the second most common histology of breast cancer, accounting for approximately 10-15% of cases. Prior studies have demonstrated that loss of E-cadherin, as well as alterations in tissue including CDH1, FOXA1, TBX3 and PTEN loss, that were more commonly observed in Luminal A ILC, while GATA3 was more commonly observed in invasive ductal carcinoma (IDC) (Ciriello et al., Cell 2015). However, data regarding the characterization of circulating tumor DNA (ctDNA) in patients (pts) with metastatic ILC are limited. We hypothesized that there would be distinct mutational profiles between pts with metastatic ILC and IDC that could be characterized using ctDNA. Methods:This retrospective cohort study included de-identified clinical, pathological, and ctDNA data from pts with metastatic breast cancer (MBC) combined under a data use agreement and approved by the institutional review boards of three sites: Washington University in St. Louis (MO), Northwestern University (Chicago, IL), and Massachusetts General Hospital (Boston, MA). All pts included in the study had ctDNA testing per standard of care with plasma-based genotyping performed by Guardant360 (Redwood City, CA) between 2015-2020. Histological classification (ILC vs. IDC) was defined based on review of pathology reports from the primary tumor or from breast biopsies of de novo MBC, and additional clinical and pathological variables were obtained via electronic medical record review. Single nucleotide variants (SNVs) were annotated using OncoKB and ClinVar and only pathogenic variants were included. Mutational profiles were compared across histologic subtypes using Fisher’s exact test to assess differences in alteration frequency across subtypes. Multivariable analysis was performed. Results:A total of 994 pts with MBC underwent ctDNA testing and were included in the analysis. 10.7% of pts had ILC (N=106) and 89.3% had IDC (N=888). 89.4% of ILC cases were categorized as hormone-receptor positive (HR+) compared with 67.1% of IDC cases. Pts with ILC had a lower frequency of triple-negative (6.7% vs. 17.7%) and HER2 positive (3.9% vs. 15.2%) breast cancer compared with IDC. Pts with ILC had a significantly higher number of pathogenic SNVs compared with IDC (mean 4.45 vs. 2.77; P=0.0037). In contrast, pts with ILC had a significantly lower number of copy number alterations as compared to pts with IDC (mean 0.40 vs. 1.03; P=0.0017). No differences were observed in mutant allele frequency between pts with ILC and IDC. The 5 most common alterations observed in pts with ILC were the following: PIK3CA, TP53, ESR1, ERBB2, and ARID1A. Alterations in AR, BRAF, CDH1, ERBB2, FGFR2, IDH2, KRAS, NF1, PIK3CA, SMAD4, and TERT were significantly higher in ILC than IDC (all P&lt;0.05). In contrast, mutations in GATA3, and amplifications in ERBB2 and MYC were significantly more common in pts with IDC (all P&lt;0.05). In multivariable analysis, mutations in BRAF, CDH1, ERBB2, IDH2, TERT remained significantly higher in ILC, while amplification of MYC was significantly higher in IDC (all P&lt;0.05). After restricting the analysis to pts with HR+ HER2 negative MBC, the following genes were significant in multivariate analysis: CDH1 and ERBB2 for pts with ILC and MYC amplification for pts with IDC (all P&lt;0.05). Discussion:In this large, multi-institutional dataset, pts with metastatic ILC were characterized by a significantly higher number of SNVs in ctDNA compared to pts with IDC, suggesting higher mutational burden. We report several alterations that were significantly different in ILC vs. IDC. These results demonstrate the ctDNA profile of pts with ILC, and future studies should explore serial plasma-based genotyping to track ILC evolution to develop targeted precision medicine based therapeutic approaches for this unique subset of pts with MBC.

Citation Format: Andrew A Davis, Lorenzo Gerratana, Katherine Clifton, Marko Velimirovic, Whitney L Hensing, Ami N Shah, Paolo D’Amico, Carolina Reduzzi, Qiang Zhang, Charles S Dai, Elyssa N Denault, Nusayba A Bagegni, Mateusz Opyrchal, Foluso O Ademuyiwa, Ron Bose, William J Gradishar, Amir Behdad, Cynthia X Ma, Aditya Bardia, Massimo Cristofanilli. Circulating tumor DNA characterization of invasive lobular carcinoma in patients with metastatic 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 PD14-04.

Abstract P2-01-01: Genetic alterations detected by circulating tumor DNA (ctDNA) in HER2-low metastatic breast cancer (MBC)

Introduction: Approximately 40-50% of breast cancers are characterized by low HER2 expression (HER2-low), defined as immunohistochemistry (IHC) 1+ or 2+ and HER2 fluorescence in situ hybridization (FISH) unamplified, encompassing a large and heterogeneous subgroup that may confer benefit from novel HER2 directed therapies. Circulating tumor DNA (ctDNA) has emerged as a minimally invasive technique to detect cancer-specific gene aberrations. Genetic alterations in ctDNA of HER2-low MBC have not been well described, and we hypothesized that HER2-low MBC may have a distinct genomic profile, beyond standard histopathologic features. Methods: This retrospective cohort study included patients with MBC treated at Washington University in St. Louis, Northwestern University (Chicago, IL) and Massachusetts General Hospital (Boston, MA) who had undergone ctDNA analysis during the course of treatment using the commercially available Guardant360® assay. HER2 expression was evaluated by IHC/FISH according to ASCO/CAP guidelines on metastatic tissue biopsies (or primary breast tumor tissue if a metastatic site biopsy was not available). Tumors were classified as HER2-low (IHC 1+ or 2+/FISH negative), HER2-0 (IHC 0) or HER2-positive (IHC 3+ or IHC 2+/FISH amplified). Clinicopathologic characteristics and ctDNA genetic alterations for HER2-low MBC were described and compared with the HER2-0 and HER2-positive subgroups. Chi-square and Fisher’s exact tests were used for categorical variables. Logistical regression was performed for multivariable analyses. Results: A total of 991 patients with MBC were analyzed, including 160 (16.1%) HER2-positive, 351 (35.4%) HER2-0, and 480 (48.4%) HER2-low MBC. The majority (89.2%) of HER2-low MBC were estrogen-receptor positive (ER+). Compared with HER2-0 MBC, HER2-low MBC had a significantly higher incidence of PIK3CA mutations (OR 1.54, p=0.027). PDGFRA and MYC amplifications were also more common among HER2-low MBC (2.3% vs 0.28% and 8.1% vs 4.6%, respectively), although not significantly associated with this subtype in multivariable analysis. Within the ER+ MBC cohort, those with HER2-low also had higher rates of PIK3CA mutations (OR 1.66, p=0.012) and MYC amplification (OR 2.29, p=0.034), as compared to HER2-0. Compared with HER2-positive, HER2-low MBC had significantly lower rates of ERBB2 alterations (OR 0.26, p=0.0076 for ERBB2 mutations and OR 0.022, p&lt;0.001 for ERBB2 amplification). ESR1, AKT1, and RB1 mutations were more common in HER2-low compared with HER2-positive MBC (14.0% vs 6.9%; 3.1% vs none; 3.1% vs none, respectively), but were not significant in multivariable analysis. Conclusions: Among patients with ER+ MBC, HER-low had a higher incidence of PIK3CA mutations and MYC amplification compared to HER2-0 MBC, and both of these alterations have been implicated as mechanisms of endocrine resistance. We did not demonstrate a high incidence of ERBB2 alterations in patients with HER2-low MBC. To our knowledge, this is the first study to describe genetic alterations detected by ctDNA in patients with HER2-low MBC. Given the emergence of novel HER2-targeted antibody drug conjugates with clinical activity in HER2-low MBC, these findings may guide combination treatment strategies and patient selection for future studies. Further studies are needed to confirm whether HER2-low MBC represents a truly unique biologic subtype.

Citation Format: Whitney L Hensing, Lorenzo Gerratana, Katherine Clifton, Marko Velimirovic, Ami Shah, Paolo D'Amico, Carolina Reduzzi, Qiang Zhang, Charles S Dai, Nusayba A Bagegni, Mateusz Opyrchal, Foluso O Ademuyiwa, Bose Ron, Amir Behdad, Cynthia X Ma, Aditya Bardia, Massimo Cristofanilli, Andrew A Davis. Genetic alterations detected by circulating tumor DNA (ctDNA) in HER2-low metastatic breast cancer (MBC) [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 P2-01-01.

Radiation-Induced Brachial Plexopathy in Patients With Breast Cancer Treated With Comprehensive Adjuvant Radiation Therapy

Purpose

Our purpose was to describe the risk of radiation-induced brachial plexopathy (RIBP) in patients with breast cancer who received comprehensive adjuvant radiation therapy (RT).

Methods and Materials

Records for 498 patients who received comprehensive adjuvant RT (treatment of any residual breast tissue, the underlying chest wall, and regional nodes) between 2004 and 2012 were retrospectively reviewed. All patients were treated with conventional 3 to 5 field technique (CRT) until 2008, after which intensity modulated RT (IMRT) was introduced. RIBP events were determined by reviewing follow-up documentation from oncologic care providers. Patients with RIBP were matched (1:2) with a control group of patients who received CRT and a group of patients who received IMRT. Dosimetric analyses were performed in these patients to determine whether there were differences in ipsilateral brachial plexus dose distribution between RIBP and control groups.

Results

Median study follow-up was 88 months for the overall cohort and 92 months for the IMRT cohort. RIBP occurred in 4 CRT patients (1.6%) and 1 IMRT patient (0.4%) (P = .20). All patients with RIBP in the CRT cohort received a posterior axillary boost. Maximum dose to the brachial plexus in RIBP, CRT control, and IMRT control patients had median values of 56.0 Gy (range, 49.7-65.1), 54.8 Gy (47.4-60.5), and 54.8 Gy (54.2-57.3), respectively.

Conclusions

RIBP remains a rare complication of comprehensive adjuvant breast radiation and no clear dosimetric predictors for RIBP were identified in this study. The IMRT technique does not appear to adversely affect the development of this late toxicity.

Age-related disparities in older women with breast cancer

Improvements in breast cancer (BC) mortality rates have not been seen in the older adult community, and the fact that older adults are more likely to die from their cancer than younger women establishes a major health disparity. Studies have identified that despite typically presenting with more favorable histology, older women present with more advanced disease, which may be related in part to delayed diagnosis. This is supported by examination of screening practices in older adults. Older women have a worse prognosis than younger women in both early stage disease, and more advanced and metastatic disease. Focus on the treatment of older adults has often concentrated on avoiding overtreatment, but in fact undertreatment may be one reason for the age-related differences in outcomes, and treatments need to be individualized for every older adult, and take into account patient preferences and functional status and not chronologic age alone. Given the aging population in the US, identifying methods to improve early diagnosis in this population and identify additional factors will be important to reducing this age-related disparity.

Clinical outcomes with neoadjuvant versus adjuvant chemotherapy for triple negative breast cancer: A report from the National Cancer Database

Purpose

Triple negative breast cancer (TNBC) patients frequently receive neoadjuvant chemotherapy (NAC). Only 50% will achieve pathological complete response (pCR). In this retrospective study, we evaluated TNBC outcomes with NAC vs. AC.

Methods

Patients with stages II and III TNBC treated with NAC or AC between 2010 and 2013 were identified from the National Cancer Database. Baseline characteristics were compared with χ2 and two sample t tests. Kaplan-Meier survival analyses were computed in patients treated with NAC or AC, and log-rank tests used to examine differences. Unadjusted analyses of trends in proportions over time were performed using Cochran–Armitage tests. Log-binomial models were applied to estimate relative risks of non-pCR following NAC.

Results

Of 19,151 patients, 5,621 (29.4%) received NAC, 13,530 (70.6%) received AC. NAC treated patients had worse OS compared to AC treated patients (73.4% vs. 76.8%; p<0.0001). pCR rate following NAC was 47.4%, and was associated with improved 5 year OS compared to non-pCR (86.2% vs. 62.3%; p<0.0001). In patients who received NAC, age, black race, clinical stage, diagnosis year, and Charlson-Deyo comorbidity score predicted non-pCR status. Use of NAC increased over the study period from 2010 to 2013 (27.8% - 31.2%; p = 0.0002).

Conclusions

NAC may be inferior to AC in TNBC, likely related to the high frequency of non-pCR following NAC. It is unclear if removing the primary tumor prior to chemotherapy will have a beneficial biologic impact on therapeutic efficacy. These data should be considered hypothesis-generating as it is possible that the findings are due to selection bias, as physicians may use NAC for TNBC patients with more advanced local disease. Although, NAC still has a role in TNBC, developing biomarkers to identify patients likely to achieve pCR and benefit from NAC is an urgent need.

Solution structure of inhibitor-free human metalloelastase (MMP-12) indicates an internal conformational adjustment

Macrophage metalloelastase or matrix metalloproteinase-12 (MMP-12) appears to exacerbate atherosclerosis, emphysema, aortic aneurysm, rheumatoid arthritis, and inflammatory bowel disease. An inactivating E219A mutation, validated by crystallography and NMR spectra, prevents autolysis of MMP-12 and allows us to determine its NMR structure without an inhibitor. The structural ensemble of the catalytic domain without an inhibitor is based on 2813 nuclear Overhauser effects (NOEs) and has an average RMSD to the mean structure of 0.25 A for the backbone and 0.61 A for all heavy atoms for residues Trp109-Gly263. Compared to crystal structures of MMP-12, helix B (hB) at the active site is unexpectedly more deeply recessed under the beta-sheet. This opens a pocket between hB and beta-strand IV in the active-site cleft. Both hB and an internal cavity are shifted toward beta-strand I, beta-strand III, and helix A on the back side of the protease. About 25 internal NOE contacts distinguish the inhibitor-free solution structure and indicate hB's greater depth and proximity to the sheet and helix A. Line broadening and multiplicity of amide proton NMR peaks from hB are consistent with hB undergoing a slow conformational exchange among subtly different environments. Inhibitor-binding-induced perturbations of the NMR spectra of MMP-1 and MMP-3 map to similar locations across MMP-12 and encompass the internal conformational adjustments. Evolutionary trace analysis suggests a functionally important network of residues that encompasses most of the locations adjusting in conformation, including 18 residues with NOE contacts unique to inhibitor-free MMP-12. The conformational change, sequence analysis, and inhibitor perturbations of NMR spectra agree on the network they identify between structural scaffold and the active site of MMPs.