Evaluation of Alisertib Alone or Combined With Fulvestrant in Patients With Endocrine-Resistant Advanced Breast Cancer: The Phase 2 TBCRC041 Randomized Clinical Trial

Importance

Aurora A kinase (AURKA) activation, related in part to AURKA amplification and variants, is associated with downregulation of estrogen receptor (ER) α expression, endocrine resistance, and implicated in cyclin-dependent kinase 4/6 inhibitor (CDK 4/6i) resistance. Alisertib, a selective AURKA inhibitor, upregulates ERα and restores endocrine sensitivity in preclinical metastatic breast cancer (MBC) models. The safety and preliminary efficacy of alisertib was demonstrated in early-phase trials; however, its activity in CDK 4/6i-resistant MBC is unknown.

Objective

To assess the effect of adding fulvestrant to alisertib on objective tumor response rates (ORRs) in endocrine-resistant MBC.

Design, Setting, and Participants

This phase 2 randomized clinical trial was conducted through the Translational Breast Cancer Research Consortium, which enrolled participants from July 2017 to November 2019. Postmenopausal women with endocrine-resistant, ERBB2 (formerly HER2)-negative MBC who were previously treated with fulvestrant were eligible. Stratification factors included prior treatment with CDK 4/6i, baseline metastatic tumor ERα level measurement (<10%, ≥10%), and primary or secondary endocrine resistance. Among 114 preregistered patients, 96 (84.2%) registered and 91 (79.8%) were evaluable for the primary end point. Data analysis began after January 10, 2022.

Interventions

Alisertib, 50 mg, oral, daily on days 1 to 3, 8 to 10, and 15 to 17 of a 28-day cycle (arm 1) or alisertib same dose/schedule with standard-dose fulvestrant (arm 2).

Main Outcomes and Measures

Improvement in ORR in arm 2 of at least 20% greater than arm 1 when the expected ORR for arm 1 was 20%.

Results

All 91 evaluable patients (mean [SD] age, 58.5 [11.3] years; 1 American Indian/Alaskan Native [1.1%], 2 Asian [2.2%], 6 Black/African American [6.6%], 5 Hispanic [5.5%], and 79 [86.8%] White individuals; arm 1, 46 [50.5%]; arm 2, 45 [49.5%]) had received prior treatment with CDK 4/6i. The ORR was 19.6%; (90% CI, 10.6%-31.7%) for arm 1 and 20.0% (90% CI, 10.9%-32.3%) for arm 2. In arm 1, the 24-week clinical benefit rate and median progression-free survival time were 41.3% (90% CI, 29.0%-54.5%) and 5.6 months (95% CI, 3.9-10.0), respectively, and in arm 2 they were 28.9% (90% CI, 18.0%-42.0%) and 5.4 months (95% CI, 3.9-7.8), respectively. The most common grade 3 or higher adverse events attributed to alisertib were neutropenia (41.8%) and anemia (13.2%). Reasons for discontinuing treatment were disease progression (arm 1, 38 [82.6%]; arm 2, 31 [68.9%]) and toxic effects or refusal (arm 1, 5 [10.9%]; arm 2, 12 [26.7%]).

Conclusions and Relevance

This randomized clinical trial found that adding fulvestrant to treatment with alisertib did not increase ORR or PFS; however, promising clinical activity was observed with alisertib monotherapy among patients with endocrine-resistant and CDK 4/6i-resistant MBC. The overall safety profile was tolerable.

Trial Registration

ClinicalTrials.gov Identifier: NCT02860000.

NCCN Guidelines® Insights: Breast Cancer, Version 4.2023

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Breast Cancer address all aspects of management for breast cancer. The treatment landscape of metastatic breast cancer is evolving constantly. The therapeutic strategy takes into consideration tumor biology, biomarkers, and other clinical factors. Due to the growing number of treatment options, if one option fails, there is usually another line of therapy available, providing meaningful improvements in survival. This NCCN Guidelines Insights report focuses on recent updates specific to systemic therapy recommendations for patients with stage IV (M1) disease.

Advances in systemic therapies for triple negative breast cancer

Triple negative breast cancer (TNBC) continues to be the subtype of breast cancer with the highest rates of recurrence and mortality. The lack of expression of targetable proteins such as the estrogen receptor and absence of HER2 amplification have made relying on cytotoxic chemotherapy necessary for decades. In the operable setting, efforts to improve outcomes have focused on escalation of systemic therapy and a shift toward preoperative delivery followed by a response adapted approach to postoperative systemic therapy. An improved understanding of tumor biology has resulted in the identification of subsets of patients with specific molecular features, leading to testing and approval of multiple new targeted therapies for this disease. Furthermore, advances in drug development have led to the approval of antibody-drug conjugates that are redefining classification schemes for breast cancer. This review focuses on the modern management of TNBC, with particular focus on recent updates in the treatment of operable disease, and an overview of the most recent promising advances in the therapeutic landscape of metastatic disease. It discusses the practical challenges and unanswered questions resulting from the approval of neoadjuvant immunotherapy and shares an approach in the clinic on topics for which evidence is lacking. In addition, it provides a glimpse into the future, highlighting challenges and opportunities for biomarker based right-sizing of preoperative therapy, refining evaluation of response to preoperative therapy after surgery, early diagnosis and detection of relapse, and areas of needed research for metastatic TNBC.

Integration of multiomics data shows down regulation of mismatch repair and tubulin pathways in triple-negative chemotherapy-resistant breast tumors

BACKGROUND

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype. Patients with TNBC are primarily treated with neoadjuvant chemotherapy (NAC). The response to NAC is prognostic, with reductions in overall survival and disease-free survival rates in those patients who do not achieve a pathological complete response (pCR). Based on this premise, we hypothesized that paired analysis of primary and residual TNBC tumors following NAC could identify unique biomarkers associated with post-NAC recurrence.

METHODS AND RESULTS

We investigated 24 samples from 12 non-LAR TNBC patients with paired pre- and post-NAC data, including four patients with recurrence shortly after surgery (< 24 months) and eight who remained recurrence-free (> 48 months). These tumors were collected from a prospective NAC breast cancer study (BEAUTY) conducted at the Mayo Clinic. Differential expression analysis of pre-NAC biopsies showed minimal gene expression differences between early recurrent and nonrecurrent TNBC tumors; however, post-NAC samples demonstrated significant alterations in expression patterns in response to intervention. Topological-level differences associated with early recurrence were implicated in 251 gene sets, and an independent assessment of microarray gene expression data from the 9 paired non-LAR samples available in the NAC I-SPY1 trial confirmed 56 gene sets. Within these 56 gene sets, 113 genes were observed to be differentially expressed in the I-SPY1 and BEAUTY post-NAC studies. An independent (n = 392) breast cancer dataset with relapse-free survival (RFS) data was used to refine our gene list to a 17-gene signature. A threefold cross-validation analysis of the gene signature with the combined BEAUTY and I-SPY1 data yielded an average AUC of 0.88 for six machine-learning models. Due to the limited number of studies with pre- and post-NAC TNBC tumor data, further validation of the signature is needed.

CONCLUSION

Analysis of multiomics data from post-NAC TNBC chemoresistant tumors showed down regulation of mismatch repair and tubulin pathways. Additionally, we identified a 17-gene signature in TNBC associated with post-NAC recurrence enriched with down-regulated immune genes.

Distinct spatial immune microlandscapes are independently associated with outcomes in triple-negative breast cancer

The utility of spatial immunobiomarker quantitation in prognostication and therapeutic prediction is actively being investigated in triple-negative breast cancer (TNBC). Here, with high-plex quantitative digital spatial profiling, we map and quantitate intraepithelial and adjacent stromal tumor immune protein microenvironments in systemic treatment-naïve (female only) TNBC to assess the spatial context in immunobiomarker-based prediction of outcome. Immune protein profiles of CD45-rich and CD68-rich stromal microenvironments differ significantly. While they typically mirror adjacent, intraepithelial microenvironments, this is not uniformly true. In two TNBC cohorts, intraepithelial CD40 or HLA-DR enrichment associates with better outcomes, independently of stromal immune protein profiles or stromal TILs and other established prognostic variables. In contrast, intraepithelial or stromal microenvironment enrichment with IDO1 associates with improved survival irrespective of its spatial location. Antigen-presenting and T-cell activation states are inferred from eigenprotein scores. Such scores within the intraepithelial compartment interact with PD-L1 and IDO1 in ways that suggest prognostic and/or therapeutic potential. This characterization of the intrinsic spatial immunobiology of treatment-naïve TNBC highlights the importance of spatial microenvironments for biomarker quantitation to resolve intrinsic prognostic and predictive immune features and ultimately inform therapeutic strategies for clinically actionable immune biomarkers.

Development and validation of a liquid chromatography-mass spectrometry assay for quantification of Z- and E- isomers of endoxifen and its metabolites in plasma from women with estrogen receptor positive breast cancer

The selective estrogen receptor modifier tamoxifen (TAM) is widely used for the treatment of women with estrogen receptor positive (ER+ ) breast cancer. Endoxifen (ENDX) is a potent, active metabolite of TAM and is important for TAM's clinical activity. While multiple papers have been published regarding TAM metabolism, few studies have examined or quantified the metabolism of ENDX. To quantify ENDX and its metabolites in patient plasma samples, we have developed and validated a rapid, sensitive, and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitative determination of the E- and Z-isomers of ENDX (0.5-500 ng/ml) and the ENDX metabolites norendoxifen (1-500 and 0.5-500 ng/ml E and Z, respectfully), ENDX catechol (3.075-307.5 and 1.92-192 ng/ml E and Z, respectfully), 4'-hydroxy ENDX (0.33-166.5 and 0.33-333.5 ng/ml E and Z, respectfully), ENDX methoxycatechol (0.3-300 and 0.2-200 ng/ml E and Z, respectfully), and ENDX glucuronide (2-200 and 3-300 ng/ml E and Z, respectfully) in human plasma. Chromatographic separation was accomplished on a HSS T3 precolumn attached to an Poroshell 120 EC-C18 analytical column using 0.1 % formic acid/water and 0.1 % formic acid/methanol as eluents followed by MS/MS detection. The analytical run time was 6.5 min. Standard curves were linear (R2 ≥ 0.98) over the concentration ranges. The intra- and inter-day precision and accuracy, determined at high-, middle-, and low-quality control concentrations for all analytes, were within the acceptable range of 85 % and 115 %. The average percent recoveries were all above 90 %. The method was successfully applied to clinical plasma samples from a Phase I study of daily oral Z-ENDX.

Abstract 1689: The role of circular RNAs in triple negative breast cancer and chemotherapy resistance

Background: Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer-related death among women worldwide. Triple negative breast cancer (TNBC) represents 15-20% of all breast cancers and is an aggressive subtype. Chemotherapy-based treatments remain the standard of care for TNBC. Unfortunately, chemotherapy resistance is common, and for these patients, outcomes are poor and alternative treatment strategies remain an unmet need. circRNAs are a newly identified class of noncoding RNA molecules with covalently closed circular structures. An increasing number of recent studies including ours have indicated that circRNAs play crucial roles in regulating tumor development and chemoresistance. However, the role of circRNAs in the process of chemotherapy resistance and TNBC progression is not clear.

Materials and Methods: As a first step towards identifying circRNAs that participate in the development of chemoresistance in TNBC cells, and to determine if targeting such circRNAs is a novel and efficacious therapeutic strategy, doxorubicin-resistant (Doxo-R), paclitaxel-resistant (PTX-R), and double-resistant (DP-R) cell lines were generated from MDA-MB-231. Human circRNA microarrays were utilized to profile the expression of approximately 14,000 known circRNAs in normal breast tissue, matched patient-derived xenografts (PDX) generated prior to and following neoadjuvant chemotherapy (NAC), and TNBC chemosensitive and chemoresistant cell lines. Top hits were validated using RT-PCR.

Results: circRNA microarray profiling identified 429 and 310 transcripts differentially expressed in doxorubicin and paclitaxel resistant cells, respectively, compared to parental chemosensitive cell lines (|FC| ≥ 1.5; p value &lt; 0.05). In comparison to pre-NAC derived xenografts, 1,396 circRNAs were dysregulated among post-NAC PDX models. Further, three circRNAs (hsa_circ_001388, hsa_circ_104652, and hsa_circ_061260) were upregulated in Doxo-R, PTX-R, and post-NAC PDX samples compared to their respective controls. Among these three circRNAs, hsa_circ_001388 (also known as circNSD2) was the only transcript also predicted to be translated into a novel and uncharacterized protein given the presence of a high confidence translation initiation site and IRES sequence. Ongoing studies are aimed at determining the role of circNSD2 protein in breast cancer carcinogenesis, progression, and response to standard of care chemotherapeutics and the mechanistic process by which this protein functions. Additionally, the efficacy of specifically targeting this circRNA as a novel therapeutic approach is being explored.

Conclusions: Increasing knowledge of the important functions of circRNAs underlying drug resistance will provide new opportunities for developing efficacious therapeutic strategies and prognostic/predictive biomarkers for TNBC.

Citation Format: Xiyin Wang, Michael J. Emch, Xiaojia Tang, Jia Yu, Krishna R. Kalari, Liewei Wang, Matthew P. Goetz, John R. Hawse. The role of circular RNAs in triple negative breast cancer and chemotherapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1689.

Clinical Outcomes and Prognostic Factors in Triple-Negative Invasive Lobular Carcinoma of the Breast

Purpose: Triple-negative invasive lobular carcinoma (TN-ILC) of breast cancer is a rare disease and the clinical outcomes and prognostic factors are not well-defined. Methods: Women with stage I-III TN-ILC or triple-negative invasive ductal carcinoma (TN-IDC) of the breast undergoing mastectomy or breast-conserving surgery between 2010 and 2018 in the National Cancer Database were included. Kaplan-Meier curves and multivariate Cox proportional hazard regression were used to compare overall survival (OS) and evaluate prognostic factors. Multivariate logistic regression was performed to analyze the factors associated with pathological response to neoadjuvant chemotherapy. Results: The median age at diagnosis for women with TN-ILC was 67 years compared to 58 years in TN-IDC (p<0.001). There was no significant difference in the OS between TN-ILC and TN-IDC in multivariate analysis (HR 0.96, p=0.44). Black race and higher TNM stage were associated with worse OS, whereas receipt of chemotherapy or radiation was associated with better OS in TN-ILC. Among women with TN-ILC receiving neoadjuvant chemotherapy, the 5-year OS was 77.3% in women with a complete pathological response (pCR) compared to 39.8% in women without any response. The odds of achieving pCR following neoadjuvant chemotherapy were significantly lower in women with TN-ILC compared to TN-IDC (OR 0.53, p<0.001). Conclusion: Women with TN-ILC are older at diagnosis but have similar OS compared to TN-IDC after adjusting for tumor and demographic characteristics. Administration of chemotherapy was associated with improved OS in TN-ILC, but women with TN-ILC were less likely to achieve complete response to neoadjuvant therapy compared to TN-IDC.

Abstract P2-11-34: Mitotic spindle hotspot counting using deep learning networks is highly associated with clinical outcomes in patients with early-stage triple-negative breast cancer who did not receive systemic therapy

Background: Triple-negative breast cancers (TNBC) exhibit high rates of recurrence and mortality. However, recent studies suggest that a subset of patients (pts) with early-stage TNBC enriched in tumor-infiltrating lymphocytes (TILs) have excellent clinical outcomes even in the absence of systemic therapy. Additional histological biomarkers that could identify pts for future systemic therapy escalation/de-escalation strategies are of great interest. TNBC are frequently highly proliferative with abundant mitoses. However, classic markers of proliferation (manual mitosis counting and Ki-67) appear to offer no prognostic value. Here, we evaluated the prognostic effects of automated mitotic spindle hotspot (AMSH) counting on RFS in independent cohorts of systemically untreated early-stage TNBC.

Methods: AMSH counting was conducted with a state-of-the-art deep learning algorithm trained on the detection of mitoses within 2 mm2 areas with the highest mitotic density (i.e. hotspots) in digital H&E images. Details of the development, training and validation of the algorithm were published previously [1] in a cohort of unselected TNBC. We obtained AMSH counts in a centrally confirmed TNBC cohort from Mayo Clinic [2] and focused our analysis on pts who received locoregional therapy but no systemic therapy. Using a fractional polynomial analysis with a multivariable proportional hazards regression model, we confirmed the assumption of linearity in the log hazard for the continuous variable AMSH and evaluated whether AMSH counts were prognostic of RFS. We corroborated our findings in an independent cohort of systemically untreated TNBC pts from the Radboud University Medical Center in the Netherlands (Radboud Cohort). Results are reported at a median follow-up of 8.1 and 6.7 years for the Mayo and Netherlands cohorts, respectively.

Results: Among 182 pts with who did not receive systemic therapy in the Mayo Cohort, 140 (77%) with available AMSH counts were included. The mean age was 61 (range: 31-94), 71% were postmenopausal, 67% had tumors ≤ 2cm, and 83% were node-negative. As expected, most tumors were Nottingham grade 3 (84%) and had a high Ki-67 proliferation index (54% with Ki-67 &gt;30%). Most tumors (73%) had stromal TILs ≤ 30%. The median AMSH count was 18 (IQR: 8, 42). AMSH counts were linearly associated with grade and tumor size, with the proportion of pts with grade 3 tumors and size &gt; 2 cm increasing as the AMSH counts increased (p=0.007 and p=0.059, respectively). In a multivariate model controlling for nodal status, tumor size, and stromal TILs, AMSH counts were independently associated with RFS (p&lt; 0.0001). For every 10-point increase in the AMSH count, we observed a 17% increase in the risk of experiencing an RFS event (HR 1.17, 95% CI 1.08-1.26). We corroborated our findings in the Radboud Cohort (n=126). The mean age was 68 (range: 40-96), and 81% were node-negative. While the median AMSH count was 36 (IQR: 16-63), higher than in the Mayo Cohort (p=0.004), the prognostic impact was similar, with a significant association between AMSH count and RFS (p=0.028) in a multivariate model corrected for nodal status, tumor size, and stromal TILs. For every 10-point increase in the AMSH count in the Netherlands cohort, we observed a 9% increase in the risk of experiencing an RFS event (HR 1.09, 95% CI 1.01-1.17). RFS rates according to AMSH counts for both cohorts are shown in the Table.

Conclusions: AMSH counting is a new proliferation biomarker that provides prognostic value independent of nodal status, tumor size, and stromal TILs in systemically untreated early-stage TNBC. Plans are underway to evaluate AMSH counts in additional cohorts of systemically untreated TNBC, and in other disease settings such as prior to neoadjuvant systemic therapy. If validated, this biomarker should be prospectively evaluated as a potential selection biomarker in clinical trials of systemic therapy de-escalation.

References:

1. PMID: 29994086

2. PMID: 28913760

Table RFS according to AMSH counts in the Mayo and Radboud Cohorts

Citation Format: Roberto A. Leon-Ferre, Jodi M. Carter, David Zahrieh, Jason P. Sinnwell, Roberto Salgado, Vera Suman, David Hillman, Judy C. Boughey, Krishna R. Kalari, Fergus J. Couch, James N. Ingle, Maschenka Balkenkohl, Francesco Ciompi, Jeroen van der Laak, Matthew P. Goetz. Mitotic spindle hotspot counting using deep learning networks is highly associated with clinical outcomes in patients with early-stage triple-negative breast cancer who did not receive systemic therapy [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 P2-11-34.

Abstract P2-03-12: Impact of adjuvant endocrine therapy (ET) omission in ER+ breast cancer (BC) treated with neoadjuvant chemotherapy (NAC)

Background: Adjuvant endocrine therapy (ET) in ER+ breast cancer (BC) reduces local, distant, and contralateral BC events and improves overall survival (OS). Furthermore, decreased adherence or omission of ET increases the risk of death. However, in ER+ pts with early-stage BC treated with NAC who have a pathologic complete response (pCR), the importance of adjuvant ET may be called into question. We sought to examine the impact of ET omission on the survival of pts with ER+ BC treated with NAC, according to pCR vs residual disease.

Methods: We queried the National Cancer Database (NCDB) 2010-2018 for female pts with stage I-III ER+ BC treated with NAC followed by surgery. pCR was defined as ypT0/ypTis, ypN0. The percent receiving adjuvant ET and the impact of adjuvant ET omission on overall survival (OS) in patients with and without pCR were assessed separately based on HER2 expression. OS was analyzed with adjuvant ET as a time-dependent covariate using Cox proportional hazards regression.

Results: We identified 34,394 pts treated with NAC for ER+ BC (28,434 ER+/HER2-, 5960 ER+/HER2+). Pts with ER+/HER2+ BC were less likely than pts with ER+/HER2- BC to have received adjuvant ET (61.6% vs 88.8%, p&lt; 0.001). Overall, 4505 (13.1%) had pCR (9.1% of ER+/HER2- and 32.0% of ER+/HER2+). Within each subtype, pts with pCR were significantly less likely to start adjuvant ET after surgery than pts with residual disease (78.4% vs 89.8% for ER+/HER2- and 46.5% vs 68.7% for ER+/HER2+, each p&lt; 0.001), Table 1. Regarding those with residual disease, pts with ER+/HER2+ BC were less likely than ER+/HER2- BC to receive adjuvant ET (68.7% vs 89.8%, p&lt; 0.001). Median follow-up was 4.4 years. Among pts with pCR, 5-year OS was 93.2% (95% CI: 92.1-94.4%) for ER+/HER2- BC and 94.3% (95% CI: 93.1-95.5%) for ER+/HER2+ BC (p=0.08), while among patients with residual disease 5-year OS was 81.7% (95% CI: 81.1-82.2%) and 85.7% (95% CI: 84.5-86.9%) for the two subtypes respectively (p&lt; 0.001). On multivariable analysis, omission of adjuvant ET was significantly associated with poorer OS in patients with residual disease for both ER+/HER2- BC (adjusted HR 1.72, p&lt; 0.001) and ER+/HER2+ BC (adjusted HR 1.63, p&lt; 0.001). In contrast, omission of adjuvant ET was not significantly associated with OS in patients with pCR, regardless of HER2 status (ER+/HER2- adjusted HR 1.28, p=0.20; ER+/HER2+ adjusted HR 1.13, p=0.54), Table 1.

Conclusions: In pts receiving NAC for ER+ BC, those with ER+/HER2+ disease were less likely to have received adjuvant ET compared to ER+/HER2- patients, regardless of pCR. In pts with residual disease after NAC, omission of adjuvant ET was associated with significantly higher risk of death. These data provide strong support for interventions to increase utilization of ET, especially for patients with residual disease following NAC. The observation that ET omission did not impact OS in pts with ER+ BC who achieve pCR following NAC is hypothesis generating and may have implications for future de-escalation trials for this subset of patients.

Table 1. Differential use of adjuvant endocrine therapy by subtype and pCR and the impact on overall survival

Citation Format: Grace M. Choong, Judy C. Boughey, Tanya L. Hoskin, Courtney N. Day, Matthew P. Goetz. Impact of adjuvant endocrine therapy (ET) omission in ER+ breast cancer (BC) treated with neoadjuvant chemotherapy (NAC) [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 P2-03-12.

Abstract PD9-05: Stromal tumor-infiltrating lymphocytes identify early-stage triple-negative breast cancer patients with favorable outcomes at 10-year follow-up in the absence of systemic therapy: a pooled analysis of 1835 patients

Background: The prognostic value of stromal tumor-infiltrating lymphocytes (TILs) as a biomarker for triple-negative breast cancer (TNBC) has been extensively demonstrated in patients (pts) receiving (neo)adjuvant systemic therapy. In addition, several small studies suggest that a subset of pts with early-stage TNBC and high TILs have excellent long-term outcomes, even in the absence of systemic therapy [1-3]. However, data on the absolute risk of TNBC recurrence according to TIL levels in the absence of systemic therapy are limited and critical to inform the design of future systemic therapy de-escalation clinical trials.

Methods: We conducted an individual patient data pooled analysis of 12 international cohorts of pts with TNBC treated with locoregional therapy but no systemic therapy. TNBC was defined as tumors with estrogen and progesterone receptor of &lt; 1% and HER2 negative (IHC 0, 1+ or IHC 2+ and FISH negative) per local evaluation. TILs were locally assessed in hematoxylin & eosin-stained slides according to the International Immuno-Oncology Biomarker Working Group guidelines (www.tilsinbreastcancer.org). We used the Kaplan-Meier method to assess survival outcomes according to prespecified TIL thresholds: 30% and 50%. Confidence intervals (CI) for survival probabilities were calculated using a percentile bootstrap method. The primary endpoint was invasive disease-free survival (iDFS, STEEP 2.0 definition). Key secondary outcomes included recurrence-free survival (RFS), distant disease-free survival (DDFS) and overall survival (OS).

Results: 1,835 pts diagnosed with TNBC between 1982 and 2017 who did not receive systemic therapy were included. The median age at diagnosis was 56 (IQR 38-71). Menopausal status was known in 1,184 women, of whom 78% were post-menopausal. The median tumor size was 2.0 cm (IQR 1.2-2.6). Most pts (87%) had no axillary lymph node involvement (N0). Most tumors were invasive ductal carcinoma (74%) and grade 3 (70%). The median level of TILs was 15% (IQR 5-40). The median duration of follow-up was 30.4 years (95% CI 29.9, 31.1). A total of 950 (52%) iDFS, 828 (45%) RFS, 767 (42%) DDFS events, and 604 (33%) deaths were observed. In multivariable analyses, higher TILs were independently associated with improved iDFS, RFS, DDFS, and OS beyond clinicopathological factors (likelihood ratio p&lt; 10e-6). Each 10% increment in stromal TILs was associated with an 8% (95% CI: 6-11), 10% (95% CI: 7-13), and 13% (95% CI: 10-15) reduction in the risk of experiencing an iDFS, RFS or DDFS event, and with a 12% (95% CI: 9-15) reduction in the risk of death. iDFS, RFS, DDFS and OS rates according to different TIL thresholds and nodal status are shown in the Table. Of note, the RFS estimates (which exclude second non-breast primaries and contralateral breast cancers) were consistently higher than the iDFS counterparts (which include both), consistent with a high rate of contralateral breast cancers and second primary tumors in this cohort. Notably, patients with node-negative—and especially stage I—TNBC with high TILs had excellent survival rates at 10-year follow-up.

Conclusion: TILs are highly prognostic in pts with systemically untreated early-stage TNBC. Pts with pN0 (and especially stage I) TNBC with high TILs exhibited very favorable long-term outcomes even in the absence of systemic therapy. These data define the natural history of TIL-rich TNBC pts and are crucial to identifying the optimal patient population for future chemotherapy and immunotherapy de-escalation clinical trials.

References:

[1] Leon-Ferre et al, 2017, PMID: 28913760

[2] Park et al, 2019, PMID: 31566659

[3] de Jong et al, 2022, PMID: 35353548

Table 5 and 10-year survival endpoints according TIL level, nodal status, and stage

Citation Format: Roberto A. Leon-Ferre, Sarah Flora Jonas, Roberto Salgado, Sherene Loi, Vincent De Jong, Jodi M. Carter, Torsten Nielson, Samuel Leung, Nazia Riaz, Giuseppe Curigliano, Carmen Criscitiello, Vincent Cockenpot, Matteo Lambertini, Vera Suman, Barbro Linderholm, John WM Martens, Carolien HM van Deurzen, Mieke Timmermans, Tatsunori Shimoi, Shu Yazaki, Masayuki Yoshida, Sung-Bae Kim, Hee Jin Lee, Maria Vittoria Dieci, Guillaume Bataillon, Anne Salomon, Fabrice Andre, Marleen Kok, Sabine Linn, Matthew P. Goetz, Stefan Michiels. Stromal tumor-infiltrating lymphocytes identify early-stage triple-negative breast cancer patients with favorable outcomes at 10-year follow-up in the absence of systemic therapy: a pooled analysis of 1835 patients [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 PD9-05.

Abstract GS1-05: Trial Assigning Individualized Options for Treatment (TAILORx): An Update Including 12-Year Event Rates

Background: Late recurrence of breast cancer after 5 years accounts for about 50% of recurrences in hormone receptor (HR)-positive early breast cancer (EBC). TAILORx established non-inferiority of adjuvant endocrine therapy (ET) given for at least 5 years to chemotherapy plus ET (CET) in EBC and a 21-gene recurrence score (RS) of 11-25, although there was some chemotherapy benefit in women

Methods: Eligibility criteria included women 18-75 years with HR-positive, HER2-negative, T1b-T2N0 EBC who agreed to have CT assigned or randomized based on the RS assay. The primary endpoint was invasive disease-free survival (iDFS) in the RS 11-25 group. The “primary analysis” refers to the original prespecified analysis for the primary IDFS endpoint (836 IDFS events at full information in the RS 11-25 group) after a median of 7.5 years. The “updated analysis” was performed after a median followup of 11.0 and 10.4 years in the randomized and overall populations, respectively.

Results:10,253 eligible women enrolled between 4/7/06-10/6/10.The updated analysis includes substantially more events that the primary analysis, including IDFS events (1819 vs. 1210), distant recurrences (561 vs. 384), locoregional +/- distant recurrences (764 vs. 543), and deaths (910 vs. 499). The table provides 5 and 12-year event rates (and standard errors) for all arms, and comparisons of the randomized arms. The primary trial conclusions remain unchanged: ET was non-inferior to CET in the randomized group with a RS 11-25. Although recurrence occurred in &lt; 10% by 12 years for a RS 0-25, late recurrence events beyond 5 years exceeded earlier recurrence. Non-recurrence events occurred in about 13% at 12 years (~1%/year), contributing substantially to the IDFS rates. For women

Conclusions: The current updated analysis confirms findings from the original primary analysis that ET is non-inferior to CET in HR-positive, HER2-negative, node-negative EBC and a RS 11-25. As in the original primary analysis, the subgroup of women

Abstract GS1-07: Results from a phase III randomized, placebo-controlled clinical trial evaluating adjuvant endocrine therapy +/- 1 year of everolimus in patients with high-risk hormone receptor-positive, HER2-negative breast cancer: SWOG S1207

BACKGROUND: Abnormalities of the PI3kinase/AKT/mTOR signaling network are common in breast cancer (BC) and are associated with endocrine resistance. Everolimus, an mTOR-inhibitor increased PFS when combined with endocrine therapy (ET) in the metastatic setting and is thought to revert endocrine resistance. S1207 is a phase III randomized, placebo-controlled trial evaluating the role of everolimus in combination with ET in the adjuvant setting among patients with high-risk hormone receptor-positive, HER2-negative BC (NCT01674140). METHODS: Eligible patients were &gt;18 years of age with histologically confirmed invasive hormone receptor-positive and HER2-negative high-risk BC. Four risk groups were defined as: 1) &gt; 2cm node-negative disease (or pN1mi), and either an Oncotype DX® Recurrence Score (RS) &gt; 25 or MammaPrint® high-risk category (MP high); 2) 1-3 positive nodes and either RS &gt;25, MP high or a pathological grade 3 tumor; 3) &gt;4 positive lymph nodes. Patients treated with neoadjuvant chemotherapy were eligible if: 4) after surgery had &gt;1 lymph node involvement. Patients were randomized 1:1 to physician’s choice adjuvant ET in combination with one year of everolimus (10 mg PO daily) or ET plus placebo stratified by risk group. The primary endpoint was invasive disease-free survival (IDFS) evaluated by a stratified log-rank test. Secondary endpoints included overall survival (OS) and safety. The hazard ratio (HR) for treatment efficacy was estimated using Cox regression with stratification by risk groups. Subset analyses included preplanned evaluation within risk group and exploratory analyses of menopausal status and age. RESULTS: 1,939 patients were randomized between September 2013 and May 2019, of them 1,792 were eligible and included in the analysis (896 per arm). Primary reason for ineligibility was timing after chemotherapy/radiation or not high risk. Median age was 54 years (22-85) and 32% were premenopausal. With a median follow-up of 50.5 months, there were 389 IDFS events as of May 2022 (data cutoff). 5-year IDFS was 74.8% among patients treated with everolimus and 73.9% among patients treated with placebo, HR=0.93 (95% CI 0.76-1.14). However, the proportional hazards assumption was violated (p=0.02) suggesting differential treatment effect over time. The HR during the one year of treatment was 0.72 (95% CI 0.47-1.10) while after one year it was 1.00 (95% CI 0.80-1.26). The 5-year OS was 87.6% in the everolimus arm and 85.5% in the placebo arm, HR=0.98 (95% CI 0.75-1.28). Analysis by risk group did not show higher everolimus benefit as risk increased. No difference in IDFS or OS was seen among postmenopausal patients (IDFS HR=1.08 [95% CI 0.85-1.36], OS HR=1.19 [95% CI 0.87-1.61]). Among premenopausal patients, everolimus was associated with improved IDFS (HR=0.63 [95% CI 0.43-0.93]) and OS (HR=0.48 [95% CI 0.26-0.88]). Treatment completion of randomized therapy was lower in the everolimus arm compared to placebo (47.9% v 72.7%). Grade 3 and 4 toxicities were noted in 6.5% and 0.5% of patients in the placebo arm and in 31.2% and 3.7% in the everolimus arm respectively. CONCLUSIONS: Addition of one year of adjuvant everolimus to standard adjuvant ET did not improve IDFS or OS and was associated with low completion rate and increased AEs. Among premenopausal patients there was a benefit in IDFS and OS that is hypothesis generating. Future translational studies will evaluate potential predictors of everolimus benefit and drug toxicity.

Citation Format: Marianna Chavez, Jieling Miao, Lajos Pusztai, Matthew P. Goetz, Priya Rastogi, Patricia A. Ganz, Eleftherios (Terry) Mamounas, Soonmyung Paik, Hanna Bandos, Wajeeha Razaq, Anne O’Dea, Virginia Kaklamani, Andrea L.M. Silber, Lisa E. Flaum, Eleni Andreopolu, Joseph Baar, Albert G. Wendt, Jennifer F. Carney, Priyanka Sharma, Julie R. Gralow, Danika L. Lew, William E. Barlow, Gabriel N. Hortobagyi. Results from a phase III randomized, placebo-controlled clinical trial evaluating adjuvant endocrine therapy +/- 1 year of everolimus in patients with high-risk hormone receptor-positive, HER2-negative breast cancer: SWOG S1207 [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 GS1-07.

Abstract P4-07-56: Mayo Clinic Enterprise patterns of growth-factor utilization for sacituzumab govitecan (SG)-induced neutropenia among patients with metastatic triple negative breast cancer

Background: SG was approved in 2020 for the treatment of metastatic triple negative breast cancer (TNBC). The most common grade 3/4 adverse event in the ASCENT trial was neutropenia (51.2%) with a 6% incidence of febrile neutropenia. 1 Package insert recommendations do not endorse primary prophylactic growth factor support, rather only initiating if severe neutropenia occurs on treatment.2

Objective: This study retrospectively reviewed the utilization of growth factor support in patients (pts) with metastatic TNBC initiated on SG at each Mayo Clinic Enterprise site.

Methods: We performed a multi-center, retrospective review of all pts with TNBC who received SG from January 2021 to December 2021 at Mayo Clinic sites in Minnesota, Florida, Arizona, and its community-based health system network. Data collected included history of neutropenia with previous cycles of SG resulting in a treatment delay, number of cycles, grade of neutropenia and cycle/day of treatment plan when growth factor added. Pts who received only one dose of SG were excluded. The Fisher’s exact test was utilized to compare the difference in the use of primary prophylaxis between sites.

Results: 67 pts received at least two doses of SG. Within this cohort, 42 pts (63%) received growth factor support during treatment with SG. Growth factor support was most often added during the first two cycles (59.5%). A total of 12 patients initiated growth factor with no history of delays related to neutropenia and without neutropenia at the time of administration. Eleven of these pts had growth factor support added on Cycle 1 as primary prophylaxis. Primary prophylaxis was most common at Mayo Clinic – Rochester compared to the other sites (Table 1), however there was not a statistically significant difference (p=0.27). There were 26 pts (39%) with a treatment delay due to neutropenia while receiving SG, of which 21 (81%) were managed with the addition of growth factor (13 pegfilgrastim, 8 filgrastim). The median number of cycles for all pts was 5 (range: 1-25). Pts who received growth factor were treated with a median of 5 cycles (range: 1-25) and pts who did not receive growth factor were treated with a median of 4 cycles (range: 1-19) (p=0.10).

Conclusions: We observed wide variability in the use of prophylactic growth factor between Mayo Clinic sites with SG. The optimal practice of growth factor use with SG warrants further exploration.

References:

1. Bardia A, Hurvitz SA, Tolaney SM, et al. Sacituzumab govitecan in metastatic triple-negative breast cancer. N Engl J Med. 2021;384(16):1529-1541

2. Immunomedics, Inc. Trodelvy (sacituzumab govitecan-hziy) [package insert]. Foster City, CA: Gilead Sciences; 2020.

Table 1: Grade of neutropenia for patients receiving SG when growth factor initiated

Citation Format: Kaylee Clark, Jamie L. Carroll, Alvaro Moreno-Aspitia, Brenda Ernst, Farah Raheem, Ashley Heil, Beth Boyer, Kristin Mara, Matthew P. Goetz, Roberto A. Leon-Ferre, Karthik V. Giridhar, Jodi Taraba. Mayo Clinic Enterprise patterns of growth-factor utilization for sacituzumab govitecan (SG)-induced neutropenia among patients with metastatic 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 P4-07-56.

Abstract OT1-01-02: EMBER-4: A phase 3 adjuvant trial of imlunestrant vs standard endocrine therapy (ET) in patients with ER+, HER2- early breast cancer (EBC) with an increased risk of recurrence who have previously received 2 to 5 years of adjuvant ET

Background: Adjuvant ET has been the standard of care for patients with estrogen receptor-positive (ER+), human epidermal growth factor receptor 2-negative (HER2-) EBC. A significant proportion of patients with increased risk still experience disease relapse despite available ET and more optimum ET is needed to prevent patients developing incurable metastatic cancer. Distant recurrence risk ranges from 20% to 40% after 5 years of adjuvant ET, depending on clinicopathological (clin-path) features at diagnosis. Consequently, there is a need to further optimize adjuvant treatment, particularly in those patients who are at increased risk of recurrence. Imlunestrant is an orally bioavailable selective estrogen receptor degrader (SERD) with pure antagonistic properties and the potential to overcome ET resistance. In early phase trials, imlunestrant monotherapy showed favorable safety with pharmacokinetic (PK) exposures exceeding fulvestrant and preliminary efficacy in ER+, HER2- advanced breast cancer patients (EMBER, Jhaveri 2022) along with robust biological/pharmacodynamic activity and tolerability in EBC (EMBER-2, Neven). Trial Design: EMBER-4 is a randomized, open-label, global phase 3 study comparing imlunestrant versus physicians’ choice of ET, in patients who are at an increased risk of recurrence based on clin-path features and who have received 2 to 5 years of standard adjuvant ET. Approximately 6,000 patients will be randomized 1:1 to receive imlunestrant (400 mg daily) for 5 years or physicians’ choice of adjuvant ET (tamoxifen or an aromatase inhibitor, AI, dosed per label). Study treatment duration is 5 years. Males and pre-/peri-menopausal women will receive concomitant treatment with a GnRH agonist if receiving imlunestrant or an AI. Stratification factors include time from initial adjuvant ET, use of prior adjuvant cyclin dependent kinase 4/6 inhibitors, nodal status, menopausal status, and geographic region. Eligibility criteria: Eligible patients are adult males and females (pre-, peri- or postmenopausal) with ER+, HER2- EBC who have completed definitive locoregional therapy and have received 2 to 5 years of prior adjuvant ET without disease recurrence, but who are at increased risk of recurrence based on clin-path features at diagnosis. Prior (neo) adjuvant chemotherapy and/or targeted therapy with a CDK4/6- or PARP- inhibitor is permitted. Study endpoints: The primary endpoint is invasive disease-free survival (IDFS), excluding second non-breast primary invasive cancers. Key secondary endpoints include distant relapse-free survival, overall survival, IDFS including second non-breast primary invasive cancers, safety, PK and patient reported outcomes. Recruitment for EMBER-4 begins globally in Q4 2022.

Citation Format: Komal Jhaveri, Joyce O’Shaughnessy, Fabrice Andre, Matthew P. Goetz, Nadia Harbeck, Miguel Martín, Francois-Clement Bidard, Zachary M. Thomas, Suzanne Young, Roohi Ismail-Khan, Lillian M. Smyth, Michael Gnant. EMBER-4: A phase 3 adjuvant trial of imlunestrant vs standard endocrine therapy (ET) in patients with ER+, HER2- early breast cancer (EBC) with an increased risk of recurrence who have previously received 2 to 5 years of adjuvant ET [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT1-01-02.

Abstract P5-05-04: Estrogen receptor 1 (ESR1) mutations in circulating tumor DNA (ctDNA) from patients with ER+/HER2- metastatic breast cancer (mBC) treated with lasofoxifene or fulvestrant in the ELAINE 1 study

Introduction: Acquired ESR1 mutations (mutESR1) after long-term endocrine therapy drive treatment resistance, metastasis, and poor prognosis for patients (pts) with ER+/HER2- metastatic breast cancer (mBC). Lasofoxifene (LAS), a selective estrogen receptor modulator, alone or with a CDK4/6 inhibitor (CDK4/6i) reduced tumor growth better than fulvestrant (Fulv) in mutESR1 BC xenograft models. ELAINE 1 is a randomized trial of LAS vs Fulv in pts with mutESR1 and prior progression on aromatase inhibitor and CDK4/6i. Preliminary results (ESMO 2022) showed that LAS prolonged median progression-free survival (mPFS) compared with Fulv with a favorable safety profile. Here, we report changes in ESR1 ctDNA mutant allele frequency (MAF) from baseline to 8 wks and their associations with clinical benefit (CB) and mPFS.

Methods: ELAINE 1 pts were randomized to oral LAS 5 mg daily or IM Fulv 500 mg on days 1, 15, and 29, then every 4 wks, until disease progression or severe toxicity. ctDNA mutESR1 mutations (baseline and 8 wks) were assessed using the Sysmex Inostics OncoBeam or SafeSeq assays—which detect mutESR1 at low allele fractions. MAF changes from baseline to wk 8 were characterized as decreased (decrease in ESR1 MAF or fully cleared), increased (increase in MAF), or equivocal (polyclonal patients [&gt;1 mutESR1] with some increasing and decreasing MAF trends); correlations with PFS and CB were explored. Efficacy measures included objective response rate (ORR), PFS, and CB at 24 wks (CB defined as response or stable disease ≥24 wks).

Results: 103 pts received LAS (n=52) or Fulv (n=51). Most common baseline ESR1 variants detected were D538G (56%), Y537S (39%), Y537N (29%), E380Q (22%); 56 (54%) pts were polyclonal. Of the 61 pts with evaluable baseline and wk 8 ctDNA, LAS decreased mutESR1 MAF in 29/35 pts (83% [11 complete clearance]) while Fulv decreased mutESR1 MAF in 16/26 pts (61.5% [6 complete clearance]) (Table).

mPFS with LAS was 8 and 4 mos for pts with decreased/cleared MAF and increased MAF, respectively, and with Fulv was 4.5 and 2.8 mos, respectively (Table). LAS decreased the common mutESR1 variants more frequently than Fulv (median relative change -87.1% vs -14.7%). In pts with decreased MAF, CB was observed in 16/29 LAS pts (55%) and 4/16 Fulv pts (25%). The predictiveness of ESR1 MAF clearance for CB was also explored. Of 11 pts with ESR1 MAF clearance taking LAS, 10 achieved CB, yielding a positive predictive value (PPV) of 90.9%. In contrast, 2/6 pts with ESR1 MAF clearance taking Fulv had CB for a PPV of 33.3%. Sensitivity for predicting CB based on direction of ESR1 MAF change was 94% with LAS and 80% with Fulv. In pts with Y537S MAF (n=33), LAS decreased Y537S in 13/15 (87%), with a median relative MAF decrease of 89%. In marked contrast, Fulv increased Y537S MAF in 11/18 pts (61%), corresponding to an MAF relative increase of 82%. LAS and Fulv resulted in complete clearance of Y537S MAF in 33% and 6% of pts, respectively.

Conclusion: Our data demonstrate that LAS more effectively decreased or cleared mutESR1 than Fulv. Further, mutESR1 clearance was associated with prolonged PFS and more CB in LAS but not Fulv pts, suggesting that LAS results in robust mutESR1 target engagement. Taken together, our data suggest mutESR1 as a potential liquid biomarker for predicting response to LAS in mutESR1, endocrine-resistant mBC pts.

Table. Change from baseline to week 8 in ESR1 MAF and clinical benefit at 24 weeks. CI, confidence interval; MAF, mutant allele fraction; ND, none detected; PFS, progression-free survival.

Citation Format: Matthew P. Goetz, Einav Gal-Yam, Daniel Stover, Sarah L. Sammons, Stephanie L. Graff, Grace Wang, Massimo Cristofanilli, Gary Riordan, Hillary S. Sloane, Dominic Carroll, Paul V. Plourde, David J Portman. Estrogen receptor 1 (ESR1) mutations in circulating tumor DNA (ctDNA) from patients with ER+/HER2- metastatic breast cancer (mBC) treated with lasofoxifene or fulvestrant in the ELAINE 1 study [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-05-04.

Abstract P6-01-22: Age, Ki-67, Nodal pCR and overall survival following Neoadjuvant Chemotherapy for Node Positive ER+/Her2- Breast Cancer

Background: The role of chemotherapy in node positive (N+) luminal breast cancer (BC) is often debated, given low total pathologic complete response (pCR) rates following neoadjuvant chemotherapy (NAC) and discrepancy in adjuvant chemotherapy benefit. A prior single institution study of cN+ luminal BC showed that pts age &lt; 50 and tumor Ki-67 ≥ 20% had high nodal pCR (&gt; 35%). This study’s goals were 1) to validate Ki-67 and age in relation to nodal pCR and 2) evaluate the prognostic impact of nodal pCR on overall survival (OS).

Methods: We queried the National Cancer Database 2010-2019 for pts with cN+ ER+/HER2- BC treated with NAC and surgery. Breast pCR was defined as ypT0/ypTis and nodal pCR as ypN0/ypN0i+. Ki-67 was available in 2018 & 2019 only and was used to evaluate Ki-67 and nodal pCR. 2010-2018 data were used to evaluate nodal pCR and OS. OS was analyzed using multivariable Cox proportional hazards regression.

Results: In 2018-2019, 4,801 pts were identified and 2,473 (51.5%) had Ki-67 available. Nodal pCR was 23.7% and was higher in pts &lt; 50 years old (28.1% vs 21.1%) and in those with Ki67 ≥ 20% (28.4% vs 12.7%), both p &lt; 0.001. Pts &lt; 50 with Ki67 ≥ 20% had the highest nodal pCR at 31.7%, followed by age ≥ 50 with Ki67 ≥ 20% at 26.3%. With Ki67 &lt; 20%, nodal pCR was 15.4% (in age &lt; 50) and 11.3% (in age ≥ 50).

From 2010-2018, we identified 20,084 cN+ ER+/HER2- BC pts treated with NAC. Total pCR was 7.4%, 14.3% had nodal pCR only, 3.8% had breast pCR only, and 74.5% had residual disease in breast and nodes. OS at 5 years was 79.1% and varied by NAC response: 90.8% with total pCR, 83.8% with nodal pCR only, 80.7% with breast pCR only, and 76.9% with residual disease in breast and nodes. Specifically nodal pCR (with or without breast pCR) was seen in 22.0% and was associated with 5-year OS rate of 86.4% compared to 77.1% without nodal pCR, p &lt; 0.001. On multivariable analysis adjusted for other clinical and treatment factors, nodal pCR was associated with better OS (adjusted HR 0.56, 95% CI: 0.50-0.61, p &lt; 0.001) in all ages combined and within both the age &lt; 50 and age ≥ 50 subgroups (see Table).

In a subgroup of pts approximating RxPonder entry criteria (defined as cT1-3, N1, Grade I or II, ER+/PR+), results were consistent with the overall cohort: nodal pCR varied by both age (17.5% in age &lt; 50 and 13.6% in age ≥ 50, p &lt; 0.001) and by Ki67 ≥ 20% vs &lt; 20% (16.8% vs 7.9%, p &lt; 0.001) and nodal pCR remained prognostic for OS with adjusted HR 0.63 (95% CI: 0.50-0.81, p &lt; 0.001).

Conclusion: In cN+ ER+/HER2- BC treated with NAC, nodal pCR is more common in pts&lt; 50 and those with high Ki-67 and is highly prognostic for OS. These data strongly suggest that NAC chemotherapy benefit should not be evaluated using total pCR rates in isolation, but for N+ pts to also consider nodal response. Given that nodal pCR is highly prognostic for OS, future neoadjuvant strategies should consider nodal pCR as a potential intermediate biomarker for long term survival.

Multivariable analysis of factors associated with overall survival, including the adjusted effect of nodal pCR

Citation Format: Dan Moldoveanu, Matthew P. Goetz, Tanya L. Hoskin, Courtney N. Day, Judy C. Boughey. Age, Ki-67, Nodal pCR and overall survival following Neoadjuvant Chemotherapy for Node Positive ER+/Her2- 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 P6-01-22.

Abstract GS1-09: Abemaciclib plus endocrine therapy for HR+, HER2-, node-positive, high-risk early breast cancer: results from a pre-planned monarchE overall survival interim analysis, including 4-year efficacy outcomes

Background Adjuvant abemaciclib (a CDK4 and 6 inhibitor) combined with ET resulted in significant and clinically meaningful improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) in patients (pts) with HR+, HER2-, node-positive, high risk EBC in the monarchE trial, and is an approved adjuvant therapy for these patients. Here we present efficacy results from a pre-specified overall survival interim analysis (OS IA2) which was planned to occur 2 years (yrs) after the primary outcome analysis. Methods Pts were randomized (1:1) to receive ET for up to 10 yrs +/- abemaciclib for 2 yrs (study treatment period). High-risk EBC was defined as either ≥4 positive axillary lymph nodes (ALN), or 1-3 ALN with either Grade 3 disease and/or tumor ≥5 cm (Cohort 1). While the proliferation biomarker Ki-67 was centrally assessed in all pts with available tissue sample, an additional smaller group of pts with 1-3+ ALN and central Ki-67 ≥20% as the only high-risk feature were included (Cohort 2). The intent-to-treat (ITT) population consisted of both Cohort 1 (5120 pts) and Cohort 2 (517 pts). Hazard ratios (HR) were estimated using Cox proportional hazard model. Results At a median follow-up of 42 months, all pts were off abemaciclib. IDFS and DRFS data illustrate a sustained benefit beyond the treatment period. In the ITT population, the HR for IDFS was 0.664 (95% CI: 0.578, 0.762) and DRFS was 0.659 (95% CI: 0.567, 0.767). At 4 yrs, this reflected an improvement in IDFS rates from 79.4% to 85.8% (absolute difference 6.4%), and in DRFS rates from 82.5% to 88.4% (absolute difference 5.9%). The continued separation of the curves was associated with an increase in absolute benefit in IDFS 4-year rates compared to 2-and 3-year IDFS rates (absolute difference 2.8% and 4.8% respectively). While OS remained immature, there was a lower number of deaths observed in the abemaciclib plus ET arm compared to the ET alone arm (157 [5.6%] vs 173 [6.1%], HR 0.929 [95% CI: 0.748, 1.153], p = 0.503), suggesting that the robust benefit in IDFS and DRFS began to translate into a numerically favorable OS HR. As previously described, within Cohort 1, a Ki-67 index of ≥20% was associated with a worse prognosis, but similar abemaciclib treatment effects were observed regardless of Ki-67 index. No new safety signals were observed. Conclusion The clinically meaningful benefit of adjuvant abemaciclib added to ET in HR+, HER2-, node-positive, high-risk EBC persists beyond completion of abemaciclib therapy, yielding an increase in absolute IDFS and DRFS benefit at 4 yrs. While OS remains immature at this time, the lower number of deaths in the abemaciclib arm compared to the ET arm suggest that a survival signal favoring abemaciclib is emerging.

Citation Format: Stephen Johnston, Masakazu Toi, Joyce O’Shaughnessy, Priya Rastogi, Mario Campone, Patrick Neven, Chiun Sheng Huang, Jens Huober, Georgina Garnica Jaliffe, Irfan Cicin, Sara Tolaney, Matthew P. Goetz, Hope Rugo, Elżbieta Senkus, Laura Testa, Lucia Del Mastro, Chikako Shimizu, Ran Wei, Ashwin Shahir, Maria Munoz, Belen San Antonio, Valerie Andre, Nadia Harbeck, Miguel Martín. Abemaciclib plus endocrine therapy for HR+, HER2-, node-positive, high-risk early breast cancer: results from a pre-planned monarchE overall survival interim analysis, including 4-year efficacy outcomes [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 GS1-09.

Adjuvant Exemestane With Ovarian Suppression in Premenopausal Breast Cancer: Long-Term Follow-Up of the Combined TEXT and SOFT Trials

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical Trial Updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported.The combined analysis of SOFT-TEXT compared outcomes in 4,690 premenopausal women with estrogen/progesterone receptor-positive (ER/PgR+) early breast cancer randomly assigned to 5 years of exemestane + ovarian function suppression (OFS) versus tamoxifen + OFS. After a median follow-up of 9 years, exemestane + OFS significantly improved disease-free survival (DFS) and distant recurrence-free interval (DRFI), but not overall survival, compared with tamoxifen + OFS. We now report DFS, DRFI, and overall survival after a median follow-up of 13 years. In the intention-to-treat (ITT) population, the 12-year DFS (4.6% absolute improvement, hazard ratio [HR], 0.79; 95% CI, 0.70 to 0.90; P < .001) and DRFI (1.8% absolute improvement, HR, 0.83; 95% CI, 0.70 to 0.98; P = .03), but not overall survival (90.1% v 89.1%, HR, 0.93; 95% CI, 0.78 to 1.11), continued to be significantly improved for patients assigned exemestane + OFS over tamoxifen + OFS. Among patients with human epidermal growth factor receptor 2-negative tumors (86.0% of the ITT population), the absolute improvement in 12-year overall survival with exemestane + OFS was 2.0% (HR, 0.85; 95% CI, 0.70 to 1.04) and 3.3% in those who received chemotherapy (45.9% of the ITT population). Overall survival benefit was clinically significant in high-risk patients, eg, women age < 35 years (4.0%) and those with > 2 cm (4.5%) or grade 3 tumors (5.5%). These sustained reductions of the risk of recurrence with adjuvant exemestane + OFS, compared with tamoxifen + OFS, provide guidance for selecting patients for whom exemestane should be preferred over tamoxifen in the setting of OFS.[Media: see text].

Abstract P2-24-03: Z-Endoxifen Allosterically Inhibits PKCβI and its Paradoxical Membrane Translocation

Z-Endoxifen Allosterically Inhibits PKCβI and its Paradoxical Membrane Translocation Sayantani Sarkar Bhattacharya1, Taylor L. Witter1, Anh Q. T. Cong1, Elizabeth Bruinsma2, Swaathi Jayaraman2, Matthew P. Goetz2, John R. Hawse1, and Matthew J. Schellenberg1 1Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN USA 55905 2Department of Oncology, Mayo Clinic, Rochester, MN USA 55905 Background: Z-Endoxifen (ENDX), the active metabolite of tamoxifen (TAM) and a selective estrogen receptor modulator (SERM), exhibited high antitumor activity in endocrine-resistant hormone receptor-positive breast and other gynecologic cancer. ENDX has also been shown to be a protein kinase C (PKC) inhibitor. PKCs participate in diverse cellular functions and their activity is often elevated in breast tumors. Guided by mechanistic insights from our recently determined crystal structure of PKCβI, we sought to determine the effects of ENDX on PKCβI in a breast cancer cell line model. Methods: To determine how ENDX regulates PKC activity, we used a Z’LYTE kinase activity assay. This Fluorescence Resonance Energy Transfer (FRET) based biochemical method can detect differential sensitivity of phosphorylated and non-phosphorylated peptides to proteolytic cleavage. We probed changes in activity for conventional and novel PKCs, as well as the purified catalytic domain of conventional PKCs in vitro. Alongside, as kinase activity of PKC relies on its spatial assembly, therefore we studied its intracellular localization using live cell confocal imaging. MCF7 cells expressing YFP-tagged PKCβI were grown in a glass bottom chamber and treated with ENDX and other modulators for relevant time and doses for this study. Images were taken using Zeiss LSM 780 confocal laser scanning microscope and analyzed in Zeiss-ZEN microscope software and GraphPad Prism 9. Results: Our data from an in vitro kinase assay indicates that ENDX inhibits the kinase activity of conventional (PKCβI) and novel (PKC𝛿) PKC isoforms with a similar IC50, however PKCβI catalytic domain is less sensitive to ENDX. We also identified a multi-domain mechanism of PKC inhibition through an allosteric inhibitory mechanism. Our live cell imaging study demonstrated that ENDX promotes the recruitment of PKCβI to the cell membrane in both a dose and time-dependent manner. Moreover, this translocation can also be mitigated by co-treatment with inhibitors of the PKC-regulator PHLPP phosphatases. Conclusion: Taken together, these results suggest the allosteric effects of ENDX trigger PKCβI recruitment to the cell membrane, yet since ENDX also inhibits kinase activity it suggests that ENDX triggers a non-productive interaction with the enzyme and "breaks" the well-known mechanism of PKC activation upon binding the cell membrane. Furthermore, ENDX is likely to trigger dephosphorylation and ultimately degradation, suggesting that ENDX represents a new mechanistic basis for targeting and downregulating PKC in cancer cells. Hence, the current study provides an integrated pattern of highly specific treatments regimen that can exploit PKCβI as a repurposing clinical target in breast cancer.

Citation Format: Sayantani Sarkar Bhattacharya, Taylor L. Witter, Anh T. Cong, Elizabeth S. Bruinsma, Swaathi Jayaraman, Matthew P. Goetz, John Hawse, Matthew Schellenberg. Z-Endoxifen Allosterically Inhibits PKCβI and its Paradoxical Membrane Translocation [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 P2-24-03.

Abstract P4-01-22: Clinical outcomes of metastatic breast cancer patients treated with poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPi): the Mayo Clinic experience

Background: Two poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPi) are currently FDA-approved for the treatment of HER2-negative metastatic breast cancer (MBC) in carriers of germline pathogenic variants (PVs) in BRCA1 or BRCA2 (BRCA1/2). This study explores the clinical outcomes of MBC patients treated with a PARPi. Methods: In this retrospective study, we included MBC patients treated with a PARPi between January 2017 and February 2022 at Mayo Clinic (Minnesota, Arizona, Florida, and Mayo Clinic Health Systems). We used the Kaplan Meier method to estimate the time-to-treatment-failure (TTF) and the log-rank test to compare different subsets. In addition, predictors of TTF were identified in a multivariate cox-proportional hazard regression model, including age at PARPi initiation, race, ethnicity, histology, estrogen receptor (ER), progesterone receptor (PR), and HER2 expression of the tumor, the number of prior therapies, type of PARPi, and PV carrier status (germline BRCA1/2 or PALB2 vs. somatic BRCA1/2 vs. other). Results: Sixty-five patients treated with PARPi (olaparib: 51; talazoparib: 14) were included in the final analysis. Fifty-five patients were carriers of germline PVs in BRCA1 (n=24, 37%), BRCA2 (n=27, 42%) or PALB2 (n=4, 6%), whereas ten patients (15%) had no germline PVs but the tumor had a somatic mutation in the homologous recombination-related (HRR) genes (7 in BRCA1/2, 2 in ATM, and 1 in CDKN2A and CDH1). At the data cutoff, 48 (74%) patients had discontinued PARPi due to progression or death. Fifteen (23%) patients required a dose reduction due to side effects. Occurrence of grade ≥ 3 side effects: anemia in 8, fatigue in 4, neutropenia in 2, and thrombocytopenia in 2 patients. Eight (15.7%) patients in the olaparib group and seven (50%) patients in the talazoparib group required a dose reduction for side effects. No patient on olaparib required drug discontinuation due to side effects, whereas two patients on talazoparib were switched to olaparib due to cytopenias and could tolerate olaparib. Median TTF in the overall population was 8 months (95% confidence interval [CI]: 6.4 – 9.6), and there was no difference (p=0.64) in TTF between the olaparib and talazoparib groups. Median TTF in the germline BRCA1, BRCA2, and PALB2 PV carriers were 7, 8, and 11 months, respectively (p=0.57). Among patients with somatic BRCA1/2 mutations, the median TTF was 4 months. Numerically, patients with HER2-positive tumors (n=8) had a shorter TTF compared to HER2-negative tumors (Median TTF: 4 vs. 8 months, p=0.098). No significant difference in TTF was observed by ER or PR status of the tumor, age at initiation of PARPi, the number of prior therapies, and prior use of platinum-based chemotherapy or CDK4/6 inhibitors. In multivariate analysis, HER2 positivity (hazard ratio [HR]: 8.0, 95% CI: 2.2 – 29.4, p=0.002), somatic BRCA1/2 mutations (HR: 7.6, 95% CI: 1.2 – 50.0, p=0.03) and somatic mutations in other HRR genes (HR: 19.1, 95% CI: 3.1 – 118.6, p=0.002) were associated with worse TTF. Conclusions: In the real world, PARPi were well-tolerated with promising time-to-treatment-failure (TTF) benefits comparable to data from clinical trials. Notably, relatively shorter TTF was observed in patients with somatic BRCA1/2 and other HRR gene mutations and HER2-positive MBC. These findings improve our understanding of the role of PARPi in MBC and will help to guide treatment decisions with PARPi in the clinical setting.

Citation Format: Nusrat Jahan, Jodi Taraba, Karthik V. Giridhar, Roberto A. Leon-Ferre, Amye J. Tevaarwerk, Elizabeth Cathcart-Rake, Ciara C. O’Sullivan, Prema Peethambaram, Timothy J. Hobday, Kathryn Ruddy, Lida A. Mina, Pooja Advani, Felipe Batalini, Matthew P. Goetz, Tufia C. Haddad, Fergus J. Couch, Siddhartha Yadav. Clinical outcomes of metastatic breast cancer patients treated with poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPi): the Mayo Clinic experience [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 P4-01-22.

Abstract OT1-04-02: Anastrozole dose escalation for optimal estrogen suppression in postmenopausal early stage breast cancer: A prospective trial

Introduction: We performed matched case-control studies utilizing cohorts of postmenopausal women with ER+ breast cancer receiving adjuvant aromatase inhibitors (AI) on MA.27 [anastrozole, exemestane] or PreFace [letrozole] to assess the association between estrogen suppression after 6 months of treatment and an early breast cancer (EBC) event within 5 years of AI initiation (Clin Cancer Res 2020;26:2986-98). We found a significant 3.0-fold increase in risk of an EBC event for those taking anastrozole with levels of estrone (E1) ≥1.3 pg/mL and estradiol (E2) ≥0.5 pg/mL, but not for exemestane or letrozole. Given these findings we designed a prospective pharmacodynamic (PD) study to evaluate the impact of anastrozole (1 mg/day: ANA1) on E1 and E2 levels, and among those with inadequate estrogen suppression (IES: E1 ≥1.3 pg/mL and E2 ≥0.5 pg/mL), to evaluate the safety and PD efficacy of high-dose anastrozole (10 mg/day: ANA10), which has been found to be safe in prior clinical trials (Cancer 1998;83:1142-52). Methods: Post-menopausal women with stage I-III, ER ≥1% positive/HER2-negative breast cancer who were candidates for anastrozole were eligible after completion of locoregional therapy and chemotherapy, as clinically indicated. Women who were pre-menopausal at diagnosis were not eligible. All patients received 8-10 weeks of ANA1, after which those with adequate estrogen suppression (AES: E1&lt; 1.3 pg/mL or E2&lt; 0.5 pg/mL) came off study. Those with IES went on to receive ANA10 for 8-10 weeks, followed by letrozole (2.5 mg/day: LET) for 8-10 weeks. All patients were managed at their treating oncologist’s discretion following study discontinuation. E1 and E2 blood levels were measured pre-treatment and after completion of each treatment cycle by a CLIA-approved liquid chromatography with tandem mass spectrometry in the Immunochemical Core Laboratory at Mayo Clinic. With a sample size of 29 patients with IES after ANA1, a one-sided binomial test of proportions with a significance level of 0.05 will have an 87% chance of rejecting the proportion with AES after ANA10 is at most 25% (Ho) when the true proportion is at least 50%. Specifically, the null hypothesis is rejected if the number of women with AES after ANA10 is 12 or more. Data lock was July 6, 2022. Results: Of the 161 women enrolled from April 2020 through May 2022, 3 withdrew consent prior to start of ANA1 and 2 were ineligible; thus, 156 women comprised the study cohort. Median patient age was 64 years (range 44-86), 10% of patients were of Hispanic ethnicity and/or non-white race, and 15% received chemotherapy. Six patients remain on ANA1, and 10 discontinued ANA1 due to refusal (7), adverse event (AE) (2), or COVID-19 (1). Forty-one of the remaining 140 patients (29.3%; 95%CI: 21.9-37.6%) had IES with ANA1. Nine of these 41 patients did not go on to ANA10 due to refusal (6) or AE (3). Of the 32 patients who started ANA10, 8 remain on treatment, 5 discontinued due to refusal (3) or AE (1-grade 2 urinary tract infection; 1-grade 1 palpitations), and 19 had a blood draw 45 days or more after starting ANA10. No grade 3-5 AEs or grade 2 hot flashes or arthralgias were reported. Of these 19 patients, 14 achieved AES with ANA10 (73.7%; 95%CI: 48.8-90.9%). All 19 patients switched to LET of which 3 remain on treatment, 1 is missing E1/E2 data, and 15 had a blood draw 45 days or more after starting LET. Of these 15 patients, 10 maintained AES, 2 acquired AES with LET, and 3 no longer had AES. Anastrozole and letrozole drug levels will be reported at the meeting. Conclusions: Approximately 29% of postmenopausal women with ER+/HER2- BC receiving adjuvant anastrozole 1 mg/daily had IES. A majority of these patients achieved AES with dose escalation to ANA10 without tolerability issues. E1 and E2 levels are logical biomarkers given the mechanism of action of anastrozole, and further study utilizing them to determine the optimal dose of anastrozole for a given patient should be performed.

Citation Format: Tufia C. Haddad, Vera Suman, Karthik V. Giridhar, Alvaro Moreno-Aspitia, Donald Northfelt, Brenda Ernst, Kostandinos Sideras, Ciara C. O’Sullivan, Ravinder Singh, Zeruesenay Desta, Jodi Taraba, Barbara Goodnature, Matthew P. Goetz, Liewei Wang, James N. Ingle. Anastrozole dose escalation for optimal estrogen suppression in postmenopausal early stage breast cancer: A prospective trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT1-04-02.

Disruption of estrogen receptor beta's DNA binding domain impairs its tumor suppressive effects in triple negative breast cancer

Triple negative breast cancer (TNBC) is an aggressive sub-type of the disease which accounts for a disproportionately high percentage of breast cancer morbidities and mortalities. For these reasons, a better understanding of TNBC biology is required and the development of novel therapeutic approaches are critically needed. Estrogen receptor beta (ERβ) is a reported tumor suppressor that is expressed in approximately 20% of primary TNBC tumors, where it is associated with favorable prognostic features and patient outcomes. Previous studies have shown that ERβ mediates the assembly of co-repressor complexes on DNA to inhibit the expression of multiple growth promoting genes and to suppress the ability of oncogenic transcription factors to drive cancer progression. To further elucidate the molecular mechanisms by which ERβ elicits its anti-cancer effects, we developed MDA-MB-231 cells that inducibly express a mutant form of ERβ incapable of directly binding DNA. We demonstrate that disruption of ERβ's direct interaction with DNA abolishes its ability to regulate the expression of well characterized immediate response genes and renders it unable to suppress TNBC cell proliferation. Loss of DNA binding also diminishes the ability of ERβ to suppress oncogenic NFκB signaling even though it still physically associates with NFκB and other critical co-factors. These findings enhance our understanding of how ERβ functions in this disease and provide a model system that can be utilized to further investigate the mechanistic processes by which ERβ elicits its anti-cancer effects.

Efficacy and safety results by menopausal status in monarchE: adjuvant abemaciclib combined with endocrine therapy in patients with HR+, HER2-, node-positive, high-risk early breast cancer

Background

Abemaciclib is the first and only cyclin-dependent kinases 4 and 6 inhibitor approved for adjuvant treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-), node-positive, and high-risk early breast cancer (EBC), with indications varying by geography. Premenopausal patients with HR+, HER2- tumors may have different tumor biology and treatment response compared to postmenopausal patients.

Objectives

We describe the efficacy and safety of abemaciclib plus endocrine therapy (ET) for the large subgroup of premenopausal patients with HR+, HER2- EBC in monarchE.

Design

Randomized patients (1:1) received adjuvant ET with or without abemaciclib for 2 years plus at least 3 additional years of ET as clinically indicated.

Methods

Patients were stratified by menopausal status (premenopausal versus postmenopausal) at diagnosis. Standard ET (tamoxifen or aromatase inhibitor) with or without gonadotropin-releasing hormone agonist was determined by physician's choice. Invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) by menopausal status were assessed at data cutoff on 1 April 2021 (median follow-up of 27 months).

Results

Among randomized patients, 2451 (43.5%) were premenopausal and 3181 (56.4%) were postmenopausal. The choice of ET for premenopausal patients varied considerably between countries. Treatment benefit was consistent across menopausal status, with a numerically greater effect size in premenopausal patients. For premenopausal patients, abemaciclib with ET resulted in a 42.2% and 40.3% reduction in the risk of developing IDFS and DRFS events, respectively. Absolute improvement at 3 years was 5.7% for IDFS and 4.4% for DRFS rates. Safety profile for premenopausal patients was consistent with the overall safety population.

Conclusion

Abemaciclib with ET demonstrated clinically meaningful treatment benefit for IDFS and DRFS versus ET alone regardless of menopausal status and first ET, with a numerically greater benefit in the premenopausal compared to the postmenopausal population. Safety data in premenopausal patients are consistent with the overall safety profile of abemaciclib.