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Abstract Background: Breast cancer (BC) in males represents a rare clinical entity, accounting about 1% of all breast malignancies diagnosed every year. Emerging evidence suggest that a gender medicine approach is critical in the research and treatment of cancer, based on the possibility that sex hormones, molecular differences, immune system, and other factors might play a crucial role in disease management. Here, we characterized molecular and immune differences between male BC (MaBC) and female BC (FeBC) across BC subtypes. Methods: 10,728 BC samples (male, n=137; female, n=10591) were analysed by next-generation sequencing (592, NextSeq; WES, NovaSeq), Whole Transcriptome Sequencing (WTS; NovaSeq) (Caris Life Sciences, Phoenix, AZ). Tumor mutational burden (TMB) totaled somatic mutations per tumor (high ≥10 mt/MB). Microsatellite-instability (MSI) was tested by IHC and NGS. Immune cell fractions were calculated by deconvolution of WTS: Quantiseq. Real world treatment-associated survival was extracted from insurance claims and calculated from sample collection to last contact using Kaplan-Meier estimates. Statistical significance was determined using chi-square and Mann-Whitney U test with p-values adjusted for multiple comparisons (q < 0.05). Results: MaBC represented higher HR+/HER2+ (6.61% vs 4.76%), HR+/HER2- (80.17% vs 60.66%) and lower HR-/HER2+ (1.65% vs 3.5%), TNBC (11.57% vs 31.08%) molecular subtypes compared to FeBC. Compared to HR+/HER2+ FeBC, MaBC had higher frequency of CHEK2, RAD51B, TSC1 mutation (Table 1) and RARα (100% vs 13.61%), DAXX (10% vs 0.16%) copy number alteration (all p < 0.05). HR+/HER2- MaBC had higher frequency of BRCA2, FOXA1, CREBBP, FLCN mutation (Table 1), and FGF3 (21.62% vs 14.31%), MRE11 (1.75% vs 0.23%), MEN1 (1.75% vs 0.13%) copy number alteration, but lower frequency of TP53, CHD1, ESR1 and AKT1 mutation (Table 1) (all p < 0.05). HR-/HER2+ MaBC had higher frequency of BRCA1 (p < 0.05) mutation (Table 1). Male TNBC had higher frequency of CDKN2A, KMT2D, STK11, ASXL1, MYC, NF2, PPM1D, WT1, EPHA2, AMER1, ARHGAP35 mutation (Table 1) and BCL6 (4.35% vs 0.05%) copy number alteration, but lower frequency of TP53 mutation (all p < 0.05) (Table 1). MaBC had higher AR protein expression (82.5% vs 60%) but lower frequency of fusion variant-AR (0.7% vs 3.9%) (all p < 0.05) compared to FeBC. There was no difference in TMB high (7.1% vs 8.4%, p = 0.5) and dMMR/MSI-H (1.8% vs 0.8%, p = 0.1). Analysis of inferred immune cell infiltrates showed that MaBC had increased immune cell infiltration of B cells (5.8% vs 5.3%) and M2 Mφ (4.9% vs 4.3%), but decreased infiltration of DC (2% vs 2.6%) (all p < 0.05). MaBC had increased expression of MHC class II gene HLA-DQB2 (FC: 1.3), but decreased expression of immune-related genes CD274 (FC: 1.2), IDO (FC: 1.4), IL1A (FC: 1.3) and IL12A (FC: 1.5) (all p < 0.05). Correlative analyses with survival will be presented at the meeting. Conclusions: These data indicate that MaBC has a differential mutational frequency, copy number alteration, immune gene expression and immune cell infiltration and overall survival compared to their FeBC counterparts. A better understanding of these sex-based differences with additional research may help inform disease outcomes, provide a rationale for tailored therapeutic approaches and design future treatments. Table 1. Mutation frequency in male and female breast cancer Citation Format: Dario Trapani, Sachin Deshmukh, Sharon Wu, Joanne Xiu, Phil Walker, Pooja Advani, Nancy Lin, Giuseppe Curigliano, Stephanie Graff, Chadi Nabhan, George Sledge Jr, Sara Tolaney, Jose Leone. Molecular and immunological landscape of sex-based differences in breast cancer: a distinct disease in men [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS13-09.

Abstract Background Two years of adjuvant abemaciclib + endocrine therapy (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 early breast cancer (EBC) in the monarchE trial (NCT03155997). The benefit of abemaciclib was sustained beyond completion of treatment and deepened in magnitude at 4 years for IDFS and DRFS. This pilot study investigated the technical feasibility of ctDNA detection beginning prior to study treatment, as well as rates of persistence and clearance in a subset of EBC pts from monarchE using the clinically validated SignateraTM ctDNA assay. Methods Samples were analyzed from a selected subset of pts (n=178; 84 from abemaciclib+ET arm; 94 ET alone) who had blood collected both before initiating protocol directed therapy, Visit 1 (V1; randomization + ≤ 3 days) and near completion of the 2-year treatment period, Visit 27 (V27; 24 months +/- 5 days from V1). This cohort of pts was enriched for overall IDFS events compared to the total monarchE study population, however pts with relapses occurring prior to V27 were excluded. Primary tumors from selected pts were subjected to whole exome sequencing (WES). Selected samples included those from pts with a range of tumor mutation burden. Cell-free DNA was extracted from 356 plasma samples. A Signatera ctDNA assay was developed for each pt based on up to 16 variants detected by WES from each baseline tumor sample. Results The IDFS event rate for the selected subset (n=178) was 39.3% (abemaciclib+ET 34.5% [29/84] and ET alone 43.6% [41/94]). Ten pts (5.6%) were initially ctDNA+ and 42 pts (23.6%) were persistently (7 pts, 3.9%) or became (35 pts, 19.7%) ctDNA+ at V27. Notably, 70% of pts who were initially ctDNA+ and 100% of pts who were either persistently ctDNA+ or became ctDNA+ experienced recurrence (see Table 1). In contrast, none of the 3 pts that cleared ctDNA+ developed recurrence. In pts persistently ctDNA negative (neg), 28 (21.1%) experienced recurrence. Overall, 10% (7/70) of pts with IDFS events were initially ctDNA+ and 50% (35/70) had detectable ctDNA at V27. Conclusions Detection of ctDNA soon after completing neoadjuvant chemotherapy was infrequent, but also associated with a high-risk of recurrence. ctDNA positivity was common at the end of the 2-year treatment period and was highly prognostic with all pts subsequently developing disease recurrence. Importantly, ~30% of pts with early ctDNA detection ultimately dropped below detection limits during the 2-year treatment period and none developed recurrence. Although some pts remained persistently ctDNA neg during this study and experienced recurrence, the delay in recurrence may indicate longitudinal benefit from remaining ctDNA neg. Future planned analysis of an expanded cohort reflective of the intent to treat population including additional timepoints within the 2-year treatment period will further define how ctDNA dynamics may identify pts at high-risk of recurrence. Table 1. Summary of Subset Positivity Rates. + positive; - negative; NA, not applicable. Citation Format: Sherene Loi, Stephen Johnston, Carlos Arteaga, Stephanie Graff, Sarat Chandarlapaty, Matthew Goetz, Christine Desmedt, Jorge Reis-Filho, Hironobu Sasano, Vanessa Rodrik-Outmezguine, Anthony Sireci, Cynthia Sandoval Rubenstein, Helen Won, Deli Liu, Lacey M. Litchfield, Nicholas Turner. Results from a pilot study exploring ctDNA detection using a tumor-informed assay in the monarchE trial of adjuvant abemaciclib with endocrine therapy in HR+, HER2-, node-positive, high-risk early breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS06-01.

Abstract Background: Triple-negative breast cancer (TNBC) is a heterogeneous disease and characterized by poor outcomes with a lack of targeted therapies. A comprehensive analysis of the molecular and immune landscape of invasive ductal TNBC can help improve our understanding of TNBC biology and identify novel targets and/or pathways for better management of this disease. Here, we characterized the molecular and immune signature of invasive ductal (ID) TNBC. Methods: 13,036 BC samples (ID TNBC, n=392; ID non-TNBC, n=927) were analyzed by NGS (592, NextSeq; WES, NovaSeq), WTS (NovaSeq) (Caris Life Sciences, Phoenix, AZ). A total of 10 pro-apoptotic (BAX, BAK1, BID, BAD, BIK, BCL2L11, BMF, HRK, PMAIP1, BBC3) and 6 anti-apoptotic (BCL2, BCL2L1, BCL2L2, MCL1, BCL2A1, BCL2L10) BCL2 family genes were analyzed. Immune cell fractions were calculated by deconvolution of WTS: Quantiseq. Real world overall survival (OS) and treatment-associated survival was extracted from insurance claims and calculated from tissue collection or treatment start to last contact using Kaplan-Meier estimates. Statistical significance was determined using chi-square and Mann-Whitney U test with p-values adjusted for multiple comparisons (q < 0.05). Results: ID TNBC had a higher frequency of TP53, RB1, NF1, PIK3R1, NOTCH1, CREBBP, BRCA1, FANCI, and HRAS mutations (Table 1), NOTCH2 (4.3% vs 0.47%), EGFR (3.4% vs 0%), NFIB (4% vs 0.6%), MYB (3.5% vs 0.5%), CCNE1 (4.4% vs 1.1%) and AKT2 (2.4% vs 0.3%) copy number alterations, and NOTCH2 (1.6% VS 0.2%) fusion (all p < 0.05) compared to invasive ductal non-TNBC. Analysis of inferred immune cell infiltrates showed that ID TNBC had increased infiltration of Tregs (2% vs 1.7%), DC (3.2% vs 2.4%), CD8 T cells (0.5% vs 0.1%), and M1 macrophages (M) (3.4% vs 2.9%), but decreased infiltration of B cells (4.5% vs 6%) and M2M (2.9% vs 4.5%) (all p < 0.05). ID TNBC had increased T cell inflamed score (23 vs -9, p < 0.05), IFNy score (-0.24 vs -0.34, p < 0.05), MHC class I genes (HLA-A, HLA-B, TAP1, TAP2, FC: 1.1-1.5, all p < 0.05), immune checkpoint genes (CD274, PDCD1, CTLA4, PD-L2, FOXP3, IDO, FC: 1.1-2, all p < 0.05) and PD-L1 protein expression (SP142: 49.8% vs. 28.4%; 22c3: 41.7% vs. 16.8%, all p < 0.05). ID TNBC had differential expression of BCL2 family genes (upregulation: BAK1, BID, MCL1, BCL2A1, BCL2L10, FC: 1.1-2.0; downregulation: BAD, BIK, BBC3, BCL2, BCL2L1, BCL2L2, FC: 1.2-2.8, all p < 0.05) compared to invasive ductal non-TNBC. ID TNBC was associated with worse OS compared to ID non-TNBC (mOS: 24.5 vs 54.6 months; HR: 0.5, 95% CI 0.47-0.57; p < 0.00001) but trend towards better survival with pembrolizumab (mOS: 29.4 vs 8.8 month; HR: 0.67, 95% CI 0.28-1.5; p=0.3) treatment. No significant OS difference was noted for by high vs. low pro and anti-apoptotic BCL2 genes except for anti-apoptotic BCL2A1 (higher expression associated with better OS (mOS: 5.7 months, HR: 0.78, 95% CI 0.6-0.99; p=0.047). Conclusion: These data indicate that ID TNBC is associated with distinct mutational profile compared to non-TNBC, has increased T cell inflamed score, IFNy score, MHC class I and immune checkpoint gene expression, and differential immune cell infiltration. Interestingly, TNBC was associated with increased M1 and decreased M2M. There is evidence to suggest that transcriptomically defined M1 high tumors are clinically aggressive and have worse OS in TNBC. BCL2 family genes are not prognostic for TNBC outcomes except BCL2A1, which needs further prospective validation. Table 1: Mutation frequency in invasive ductal TNBC and invasive ductal non-TNBC Citation Format: Pooja Advani, Sachin Deshmukh, Sharon Wu, Jacob Andring, Joanne Xiu, Alex Farrell, Jose Leone, Priya Jayachandran, Stephanie Graff, Matthew Oberley, George Sledge Jr, Asher Chanan-Khan. Comprehensive Molecular and Immunological Characterization of Invasive Ductal Triple-Negative Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-24-01.

Abstract Background: Metaplastic Breast Cancer (MBC) is rare (0.2-5%), aggressive form of BC characterized by chemotherapy resistance and has worse outcomes in comparison to other BC subtypes. Resistance to chemotherapeutic agents is related to defects in intact intrinsic apoptosis pathway and the BCL2 family of proteins are the central regulators of this pathway. Majority of MBC have triple-negative receptor status and have no standard therapeutic approach and validated prognostic markers. Here, we examine the association of BCL2 family pro-apoptotic and anti-apoptotic genes expression with metaplastic TNBC (MTNBC) patient survival. Methods: 13,036 BC samples (MTNBC, n=102; metaplastic non-TNBC, n=20) were analyzed by next-generation sequencing (592, NextSeq; WES, NovaSeq), Whole Transcriptome Sequencing (WTS; NovaSeq) (Caris Life Sciences, Phoenix, AZ). A total of 10 pro-apoptotic (BAX, BAK1, BID, BAD, BIK, BCL2L11, BMF, HRK, PMAIP1, BBC3) and 6 anti-apoptotic (BCL2, BCL2L1, BCL2L2, MCL1, BCL2A1, BCL2L10) BCL2 family genes were analyzed. MTNBC with PMAIP1-high(H) and -low(L) expression was classified by top and bottom quartile, respectively. Pathway enrichment was determined by GSEA (Broad Inst). Real world overall survival (OS) was extracted from insurance claims and calculated from tissue collection to last contact using Kaplan-Meier estimates. Statistical significance was determined using chi-square and Mann-Whitney U test with p-values adjusted for multiple comparisons (q < 0.05). Results: MTNBC had enrichment of apoptosis (NES: 1.4, FDR: 0.05), glycolysis (NES: 1.48, FDR: 0.03), PI3K/AKT/mTOR signaling (NES: 1.43, FDR: 0.05), P53 (NES: 1.51, FDR: 0.06), NOTCH signaling (NES: 1.39, FDR: 0.05), TGFβ signaling (NES: 1.41, FDR: 0.05), WNTβ catenin signaling (NES: 1.41, FDR: 0.05) and IL2/STAT5 signaling (NES: 1.33, FDR: 0.09) pathways compared to metaplastic non-TNBC. MTNBC had higher expression of BCL2 pro-apoptotic genes BAX (Fold Change (FC): 1.6), BAK1 (FC: 1.3), BID (FC: 2), BAD (FC: 1.6), BCL2L11 (FC: 2.5) and BBC3 (FC: 1.5), and anti-apoptotic genes BCL2L1 (FC: 1.6) and BCL2L2 (FC: 1.3) (all p < 0.05) compared to metaplastic non-TNBC. Higher PMAIP1 gene expression was associated with worse MTNBC patient survival (mOS: 14.3 month; HR: 0.37; 95% CI 0.19-1.41; p=0.002) (Table 1), but not in metaplastic non-TNBC (mOS: Inf; HR: 1.96; 95% CI 0.64-6.02; p=0.23). PMAIP1-H MTNBC had higher expression of immune checkpoint genes CD274 (FC: 2.8), PDCD1 (FC: 2.2), TIM3 (FC: 1.8), LAG3 (FC: 2.1) and IDO1 (FC: 5.7) (all p < 0.05), compared to PMAIP1-L MTNBC. PMAIP1-H MTNBC had higher frequency of IHC-PD-L1 positivity (68.4% vs 14.3%, p < 0.05). PMAIP1-H MTNBC had higher expression of stem cell related genes CD44 (FC: 1.7), ALDH1A2 (FC: 2.2), ALDH1A3 (FC: 2.6), SOX2 (FC: 5.21) and NANOG (FC: 2.13) (all p < 0.05) compared to PMAIP1-L MTNBC. Conclusion: This is the first comprehensive analysis of expression and prognostic role of BCL2 family proteins in MBC. Our data suggest a strong association of higher expression of PMAIP1 with worse MTNBC patient survival, potentially attributed to higher immune checkpoint, stem cell-related genes expression, and higher frequency of PD-L1 positivity in PMAIP1-H tumors. These findings indicate PMAIP1 as a potential prognostic biomarker candidate in MTNBC but needs further validation in large prospective studies Table 1. Overall survival of metaplastic TNBC patient based on BCL2 family gene expression. Citation Format: Pooja Advani, Sachin Deshmukh, Sharon Wu, Jacob Andring, Joanne Xiu, Alex Farrell, Milan Radovich, George Sledge Jr, Dario Trapani, Evanthia Roussos Torres, Stephanie Graff, Asher Chanan-Khan. Comprehensive Characterization of BCL2 Family Genes in Metaplastic Triple Negative Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-24-02.

Abstract Background Current American Joint Committee on Cancer (AJCC) breast cancer staging considers contralateral axillary metastasis (CAM) stage IV disease (M1). Retrospective studies suggest that women with CAM have improved overall survival (OS) compared to those with distant metastasis (M1) and/or comparable OS to locally advanced breast cancer (LABC). These studies support consideration of curative intent treatment; however, they contain heterogeneous cohorts with highly variable treatment strategies. We sought to evaluate treatment and outcomes in a well-defined CAM cohort treated with contemporary systemic and locoregional therapy. Methods We performed a retrospective multi-institution cohort study to compare OS of patients with CAM matched 1:3 on age +/- 5 years to LABC (defined as cN2-3 and/or pN2-3), and to non-CAM M1. CAM patients classified as type 1) de novo CAM, synchronous with the contralateral primary, 2) metachronous isolated CAM in the setting of prior surgical and/or radiation treatment to primary index cancer, 3) synchronous with, or 4) metachronous after an in-breast or axillary nodal recurrence of the primary index cancer. The M1 cohort included de novo and recurrent metastasis with varied sites and number of metastasis. OS was defined as time from CAM diagnosis to death or last follow-up for CAM patients; time from primary diagnosis to death or last follow-up for LABC; and time from metastatic diagnosis to death or last follow-up for M1. Unadjusted OS was estimated with the Kaplan-Meier method, and Cox proportional hazards models were used to estimate the association of group with OS after adjustment for covariates Results We identified 57 CAM and 155 LABC from 8 institutions (2016-2022), and 632 M1 from a single institution. The median age was similar between groups (CAM=59 years, LABC=58, M1=57, p=0.44), and there were no statistically significant differences in hormone receptor status (p=0.25). There were more Non-Hispanic Black patients in the M1 cohort compared to CAM or LABC (p< 0.001). The majority of CAM cases were delayed metachronous from the index cancer (type 2, 35.1%), or synchronous with a recurrence (type 3, 33.3%). Type 1 (de novo, 14%) and type 4 (delayed metachronous after breast cancer recurrence, 17.5%) were less frequent. Among CAM patients, 49.1% were hormone receptor positive (HR+)/HER2-negative (HER2-), 22.8% HR-/HER2-, 10.5% HR+/HER2+, and 5.3% HR-/HER2+. Comparing CAM versus LABC, invasive ductal carcinoma (IDC) was more commonly seen in CAM (82.5% vs 66.5%), as was grade 3 (45.6% vs 35.5%), and triple negative (22.8% vs 13.5%). Conversely, in LABC, treatment of the primary index cancer more frequently included chemotherapy (CAM=71.9%, LABC=92.3%), mastectomy (CAM=54.4%, LABC 74.2%), and adjuvant radiation (CAM=73.7%, LABC=90.3%). On multivariable analysis adjusting for age, race/ethnicity, and hormone receptor status, both CAM and M1 had inferior survival to LABC (Table 1), but with a 2.4-fold difference for CAM (95% CI 1.42-4.07, p=0.001) versus a 6.3-fold difference for M1 (95% CI 4.29-9.23, p=< 0.001). Discussion In this contemporary, multi-institution study, we demonstrated that CAM patients selected for presumed curative intent treatment experienced improved OS when compared to stage IV (M1) patients. Our data adds additional support for re-evaluating the current stage IV designation, in favor of N3, and consideration of curative intent treatment in this disease. Table. Adjusted* Overall Survival Comparing Patients with Breast Cancer Contralateral Axillary Metastasis (CAM) to those with Locally Advanced Breast Cancer (LABC) and Metastatic Disease (M1) *Adjusted for age, race/ethnicity, hormone receptors. Citation Format: Meghan R. Flanagan, Stephanie Downs-Canner, Samantha Thomas, Astrid Botty van de bruele, Margaret Lillie, Kristalyn Gallagher, Tammeza Gibson, James Jakub, Alexandra Verosky, Sarah Tevis, Malia Brennan, Francys Verdial, Jennifer Q. Zhang, Leisha Elmore, Jennifer Plichta, Laura Rosenberger. A Multi-Institutional Review of Contralateral Axillary Metastases: Time for Reclassification as Local-Regional Event? [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-05-13.

Abstract Rapid developments in cancer genetics and hereditary cancer risk assessments have enabled the identification of individuals at elevated risk for hereditary malignancies to guide enhanced cancer screening and prevention efforts. Multigene panel testing has emerged as the standard approach as emphasized in the National Comprehensive Cancer Network (NCCN) guidelines. The purpose of this study was to investigate the frequency of other pathogenic mutations identified through multigene panel testing in individuals who previously tested negative for germline BRCA1/2 and assess the clinical impact of panel testing. Patients either previously diagnosed with breast cancer or with a family history of breast or ovarian cancer that had also been seen by Oncology Genetics at a single institution and tested negative for BRCA1/2 genes but had not undergone prior multigene panel testing were invited via a letter to return for an additional genetic counseling visit to discuss multigene panel testing. Patients were also able to opt-in to a survey component of the study and received an email to fill out the Multidimensional Impact of Cancer Risk Assessment (MICRA) and Cancer Worry Scale (CWS). Surveys were completed prior to the initial genetic counseling appointment and repeated after discussion of the multigene panel test results. A total 24 women met with a genetic counselor of which 22 (92%) had a personal history of breast cancer, 1 (4%) had a family history of breast cancer, and 1 (4%) had a family history of ovarian cancer. The mean age was 52.6 years (range, 42-68) and 100% of women were Caucasian. Of the 24 women, 17 (71%) completed multigene panel testing. Of the women that underwent testing, 7 (41%) had negative results, 6 (35%) had variants of unknown significance (VUS), and 4 (24%) had a pathogenic mutation identified in another gene (CDKN2A, CHEK2, and CFTR). There was no significant change in MICRA or CWS scores after multigene panel results were reviewed in the 9 patients that completed both pre- and post-genetic testing surveys. The mean/median summary MICRA scores pre- and post-counselling were 30 (SD 12.4), median 26 (min 18, max 56), and 21.2 (SD 15.4), median 21 (min 3, max 43), respectively (p=0.19, Wilcoxon signed ranks test). The mean/median summary CWS scores pre- and post-counselling were 14.3 (SD 5), median 15 (min 7, max 24), and 13.6 (SD 2.59), median 14 (min 10, max 17), respectively (p=0.53, Wilcoxon signed ranks test). Of the 4 patients with newly identified pathogenic mutations, 2 started new screening protocols and 1 underwent a prophylactic mastectomy. In conclusion, multigene panel testing identified pathogenic mutations in a subset of individuals who previously tested negative for BRCA1/2 genes leading to changes in clinical management. The completion of multigene panel testing did not lead to a significant increase in MICRA or CWS scores. Key limitations of this study include a small sample size and an all Caucasian population. Citation Format: Devon Miller, Stephanie Pritzl, Angela Tess, Jessica Gooding, Lisa Barroilhet, Lori Dubenske, Kari Wisinski. Clinical Impact of Multigene Panel Testing in Patients with a Personal or Family History of Breast or Ovarian Cancer Previously Negative for BRCA1/2 Genes [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-09-03.

Abstract Background: In patients with micro- and macrometastases in the sentinel lymph node (SLN) after neoadjuvant chemotherapy (NAC), additional positive nodes are found in >60% of cases and axillary lymph node dissection (ALND) is currently considered standard of care. The likelihood of finding additional positive lymph nodes in patients with residual isolated tumor cells (ITCs) is unknown, and the benefit of ALND is unclear. As a consequence, surgical management of the axilla in these patients is not standardized. We sought to evaluate how often additional positive lymph nodes are found, to determine factors associated with ALND, and to compare oncological outcomes in patients treated with and without ALND after identification of residual ITCs in the SLN. Methods: Data were collected from 42 centers: 20 in the Oncoplastic Breast Consortium (OPBC) and EUBREAST networks, and 22 in North and South America. We included patients with cT1-4 N0-3 breast cancer at diagnosis who underwent NAC followed by axillary staging with either SLN biopsy (SLNB) or targeted axillary dissection (TAD) and were found to have residual ITCs [ypN0(i+)]. Single-tracer mapping was allowed for cN0 patients, while dual mapping or TAD was required for cN+ cases. Axillary treatment included completion ALND and/or nodal radiotherapy (RT). Competing risk analysis was performed to assess the cumulative incidence rates of any axillary recurrence (AR), locoregional recurrence (LRR), and any invasive (locoregional or distant) recurrence. Five-year cumulative incidence rates were compared between patients who underwent ALND and those who did not using the Gray’s test. Type I error rate was set to 0.05 (α). Results: We included 412 patients treated with NAC followed by surgery from 01/2009-05/2022. 146 (35.4%) had completion ALND and 266 (64.6%%) did not. Median patient age was 48 years. The majority (57%) of patients had clinical T2 tumors, and 68% had biopsy-proven N1 disease. Most were HR+/HER2- (41%) or HER2+ (39%). Most patients (80%) received anthracycline and taxane-based chemotherapy regimens. Nodal RT was administered to 83% of patients. The median number of SLNs with ITCs was 1. Patients treated with ALND were more likely to have ITCs detected on frozen section (61% v 6.7%, p< 0.001), to have N2/3 disease at presentation (15.1% v 5.6%, p=0.001) and to have LVI (40% v 26%, p=0.004) (Table 1). There was no significant trend over time in the proportion of patients undergoing completion ALND during the study period (p=0.5). In the ALND group, additional positive nodes were found in 43/146 (29.5%) of cases, and consisted of macrometastases in 11/146 (7.5%), micrometastases in 9/146 (6.2%), and ITCs in 23/146 (15.8%). 5-year rates of any AR, LRR, and any invasive recurrence in the entire cohort were 2.7% (95% CI 1.2-5.4), 2.8% (95% CI 1.2-5.4) and 16% (95% CI 11-21), respectively. There was no statistical difference between patients who underwent ALND and those who did not in any of the 3 endpoints (2.2% v 3.1%, p=0.6), (2.6% v 3.0%, p=0.4) and (14% v 18%, p=0.12), respectively. Conclusion: The likelihood of finding additional positive lymph nodes in patients with ITCs after NAC is lower than in patients with residual micro- and macrometastases, and in the majority of cases, they contain ITCs. Nodal recurrence after omission of ALND is rare in this population. Overall, these results do not support routine ALND in patients with residual ITCs. Table 1. Clinicopathological Features of the Study Cohort, Stratified by Type of Axillary Surgery Frequency (row percent) reported for categorical variables, and median (IQR) reported for continuous variables. SLNB sentinel lymph node biopsy; TAD targeted axillary dissection; SLNs sentinel lymph nodes; LNs lymph nodes; pCR pathologic complete response; ACT anthracycline and taxane; AC anthracycline; H Herceptin, HP, Herceptin and Perjeta; TC taxol (or Taxotere) and carboplatinum; LVI lymphovascular invasion; BCS breast-conserving surgery. ^ Applied to HER2- tumors only (n=252). ^^ Applies to HER2+ tumors only (n=160). # LVI was present on core biopsy or final pathology. * Applies to BCS patients only (n=175). ** Applies to mastectomy patients only (n=237). Citation Format: Giacomo Montagna, Alison Laws, Massimo Ferrucci, Mary Mrdutt, Natália Polidorio, Varadan Sevilimedu, Tracy-Ann Moo, Andrea Barrio, Marissa K. Boyle, Flavia Vidal Cabero, Daniela Cocco, Fabio Corsi, Angelena Crown, Meghan R. Flanagan, Mehmet Ali Gulcelik, Callie Hlavin, Justyna Jelinska, Hasan Karanlik, Susan Kesmodel, Henry Kuerer, Sherko Küemmel, Cornelia Leo, Tehillah Menes, Melissa Pilewskie, Nina Pislar, Nicola Rocco, Jai Min Ryu, Leonardo Soares, Christoph Tausch, M. Umit Ugurlu, CICERO URBAN, Astrid Botty van de Bruele, Denise Vorburger, Fredrik Wärnberg, Anna Weiss, Austin Williams, Stephanie Wong, Steven G. Woodward, Susie X. Sun, Jennifer Q. Zhang, M. Firdos Ziauddin, Guldeniz Karadeniz Cakmak, Nuran Bese, Thorsten Kühn, Judy Boughey, Tari King, Nina Ditsch, Maggie Banys-Paluchowski, Monica Morrow, Walter Weber. Are nodal ITCs after neoadjuvant chemotherapy an indication for axillary dissection? The OPBC05/EUBREAST-14R/ICARO study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS02-02.

Abstract Background: Oncofertility counseling in BRCA carriers has unique challenges due to a possible negative impact of germline pathogenic/likely pathogenic variants (PVs) on reproductive potential and the indication to undergo risk-reducing bilateral salpingo-oophorectomy. While previous studies demonstrated the safety of pregnancy in women with prior breast cancer (BC) history, limited evidence exists in BRCA carriers specifically. We report the results of the largest study to date investigating likelihood of pregnancy after BC, reproductive and disease outcomes specifically in BRCA carriers. Methods: This was an international, multicenter, hospital-based, retrospective cohort study including young BRCA carriers with history of BC (NCT03673306). Eligible patients were women harboring germline PVs in BRCA1 and/or BRCA2 and diagnosed with stage I-III invasive BC at the age of ≤ 40 years between January 2000 and December 2020. BRCA healthy carriers or patients with BRCA variants of unknown significance, non-invasive BC, lack of follow-up, prior ovarian cancer or other malignancies without history of BC were excluded. Primary endpoints were pregnancy rate and disease-free survival (DFS). Overall survival (OS), BC specific survival (BCSS), pregnancy, fetal and obstetric outcomes were secondary endpoints. To mitigate the impact of guaranteed time bias, two survival analyses were performed: 1) Extended Cox model with occurrence of pregnancy as a time-varying covariate; 2) Case-control analysis by matching 1:3 patients with and without a pregnancy for type of BRCA PV, hormone receptor status, nodal status and year at diagnosis; moreover, each control had to have a disease-free interval longer than the time occurring between BC diagnosis and conception of the matched case. Results: From 78 centers worldwide, 4,732 patients were included, of whom 659 had at least one pregnancy after BC (pregnancy cohort) and 4,073 did not (non-pregnancy cohort). Patients in the pregnancy cohort were significantly more likely to carry BRCA1 PVs, to be younger at BC diagnosis, to have node-negative and hormone receptor-negative (HR-) BC (all p< 0.01). Pregnancy rate at 10 years was 22% (95% CI 21%-24%) overall, 18% (95% CI 16%-21%) and 26% (95% CI 24%-26%) in patients with HR+ and HR- BC, respectively (p< 0.01). Median time from BC diagnosis to conception was 3.5 years (IQR 2.2-5.3 years), significantly longer in patients with HR+ than HR- BC (4.3 vs 3.2 years, p< 0.01). Among 659 patients with a pregnancy after BC, 45 (6.8%) and 63 (9.6%) experienced an induced abortion or a miscarriage, respectively. Of the 517 (78.5%) patients with completed pregnancy, 54 (10.4%) had twins and 406 (78.5%) delivered at term (delivery ≥37 weeks). Among the 571 babies born, 5 (0.9%) had congenital anomalies. Median follow-up was 7.8 years (IQR, 4.5-12.6 years). No significant difference in DFS was observed between the pregnancy and non-pregnancy cohorts (unadjusted HR 0.97, 95% CI 0.82-1.15, p=0.74; adjusted HR [aHR] 0.99, 95% CI 0.81-1.20, p=0.90). Patients in the pregnancy cohort showed significantly better BCSS (HR 0.53, 95% CI 0.38-0.74, p< 0.01; aHR 0.59, 95% CI 0.41-0.86, p< 0.01) and OS (HR 0.52, 95% CI 0.38-0.72, p< 0.01; aHR 0.58, 95% CI 0.40-0.85, p< 0.01). Similar results were obtained in the case-control analysis. Subgroup analyses of survival endpoints according to patient, tumor and treatment characteristics will be presented at the conference. Conclusions: In this global study, 1 out of 5 young BRCA carriers conceived within 10 years after a BC diagnosis, higher than rates previously reported in unselected young BC populations. Pregnancy following BC in BRCA carriers did not appear to adversely impact maternal prognosis or fetal outcomes. These findings should be incorporated into oncofertility counseling of young BRCA carriers with BC. Citation Format: Matteo Lambertini, Eva Blondeaux, Elisa Agostinetto, Anne-Sophie Hamy-Petit, Hee Jeong Kim, Camila Chiodi, Rinat Bernstein-Molho, Florentine Hilbers, Katarzyna Pogoda, Estela Carrasco Lopez, Kevin Punie, Jyoti Bajpai, Michail Ignatiadis, Halle Moore, Kelly-Anne Phillips, Angela Toss, Christine Rousset-Jablonski, Fedro Alessandro Peccatori, Tiphaine Renaud, Alberta Ferrari, Shani Paluch-Shimon, Robert Fruscio, Wanda Cui, Stephanie Wong, Claudio Vernieri, Kathryn Ruddy, Maria Vittoria Dieci, Alexios Matikas, Mariya Rozenblit, Cynthia Villareal Garza, Laura De Marchis, Lucia Del Mastro, Fabio Puglisi, Maria Del Pilar Estevez-Diz, Kenny A. Rodriguez-Wallberg, Bela Mrinakova, Sarah Meister, Luca Livraghi, Florian Clatot, Rinat Yerushalmi, Carmine De Angelis, Rodrigo Sánchez-Bayona, Icro Meattini, Natalia Cichowska-Cwalińska, Martine Berlière, Mahmoud Salama, Ugo De Giorgi, Amir Sonnenblick, Hatem Azim, Ann Partridge. Pregnancy after breast cancer in young women with germline BRCA pathogenic variants: results from an international cohort study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS02-13.

Abstract Background Two years of adjuvant abemaciclib combined with endocrine therapy (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 early breast cancer in the monarchE trial (NCT03155997). Abemaciclib benefit was sustained beyond the completion of treatment (tx) with deepening magnitude of absolute benefit in IDFS and DRFS at 5 years. Here, we evaluate comprehensive molecular profiling of archived primary tumor tissue and association with clinical outcomes. Methods For biomarker analysis, a proportionally stratified random sampling case-cohort design was utilized to include all patients who experienced an IDFS event at a pre-specified interim analysis with a median follow up of 54 months. A cohort of 895 pts (189 with IDFS event) in the abemaciclib + ET arm was matched 1:1 with 903 pts (270 with IDFS event) in the ET arm. Baseline primary tumor samples underwent exome-capture RNA sequencing (RNAseq; n=1324, 23% intent-to-treat (ITT) population) and paired tumor-normal (germline blood samples) whole-exome sequencing (WES; n=1234, 22% ITT population). Expression-based intrinsic subtypes (i.e., luminal A (LumA), luminal B (LumB), HER2-enriched (HER2E), basal- and normal-like) were characterized using the Absolute Intrinsic Molecular Subtyping model. The 21-gene expression signature score (Oncotype DX test) was inferred from RNAseq; samples were categorized into lower (0-25) and high (26-100) risk groups. To investigate associations of biomarkers with abemaciclib benefit, WES genomic events including oncogenic and hotspot mutations by OncoKB, and copy number events, of incidence >9% were pre-selected. Results The biomarker subset of monarchE was reflective of the ITT population. A total of 1190 tumors (abemaciclib+ET n= 605; ET alone n=585) yielded adequate RNAseq results. Intrinsic subtype distribution was consistent across tx arms (Table A). Low tumor purity limited assessment of the normal-like subtype. The 4-year IDFS benefit of abemaciclib was consistent across all subtypes. LumA cancers had the lowest risk of recurrence while HER2E and basal-like subtypes had the highest. Inferred 21-gene expression signature score showed similar benefits from abemaciclib in both lower and high-risk groups (Table B). A total of 1173 tumors yielded adequate WES results (abemaciclib+ET n=580; ET alone n=593). Consistent abemaciclib benefit was observed across the most frequently altered genes (Table C). In exploratory analysis, lower benefit from abemaciclib was seen in the subset of focal-high level MYC amplified tumors (n=176, HR 1.30, 95% CI, 0.77, 2.20) compared to MYC non-amplified tumors (n=997, HR 0.62, 95% CI, 0.47, 0.80, nominal interaction p=0.014). The treatment benefit of abemaciclib was observed across all subpopulations of altered genes based on gene expression data. Conclusions Adjuvant abemaciclib+ET maintained IDFS benefit compared to ET alone across all molecular subtypes as measured by RNAseq. Benefit was consistent across most altered genes assessed by WES, except for the subset of tumors with MYC amplification. Additional research is necessary to confirm these findings. Table. Citation Format: Nicholas Turner, Jorge Reis-Filho, Matthew Goetz, Christine Desmedt, Sarat Chandarlapaty, Hironobu Sasano, Carlos Arteaga, Sherene Loi, Stephanie Graff, Deli Liu, Vanessa Rodrik-Outmezguine, Anthony Sireci, Cynthia Sandoval Rubenstein, Helen Won, Lacey M. Litchfield, Maria Munoz, Stephen Johnston. Genomic and transcriptomic profiling of primary tumors from patients with HR+, HER2-, node-positive, high-risk early breast cancer in the monarchE trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr GS03-06.