Couch, Fergus J.

Abstract Background: Use of menopausal hormone therapy (MHT) is associated with increased risk for breast cancer. However, the relevant mechanisms and its interaction with genetic variants are not fully understood. Methods: We conducted a genome-wide interaction analysis between MHT use and genetic variants for breast cancer risk in 27,585 cases and 34,785 controls from 26 observational studies. All women were post-menopausal and of European ancestry. Multivariable logistic regression models were used to test for multiplicative interactions between genetic variants and current MHT use. We considered interaction p-values<5x10-8 as genome-wide significant, and p-values<1x10-5 as suggestive. Linkage disequilibrium (LD)-based clumping was performed to identify independent candidate variants.Results: None of the 9.7 million genetic variants tested for interactions with MHT use reached genome-wide significance. Only 213 variants, representing 18 independent loci, had p-values<1x105. The strongest evidence was found for rs4674019 (p-value=2.27x10-7), which showed genome-wide significant interaction (p-value=3.8x10-8) with current MHT use when analysis was restricted to population-based studies only. Limiting the analyses to combined estrogen-progesterone MHT use only or to estrogen receptor (ER) positive cases did not identify any genome-wide significant evidence of interactions. Conclusions: In this large genome-wide SNP-MHT interaction study of breast cancer, we found no strong support for common genetic variants modifying the effect of MHT on breast cancer risk. These results suggest that common genetic variation has limited impact on the observed MHT–breast cancer risk association.

In this study we aim to examine gene–environment interactions (GxEs) between genes involved with estrogen metabolism and environmental factors related to estrogen exposure. GxE analyses were conducted with 1970 Korean breast cancer cases and 2052 controls in the case-control study, the Seoul Breast Cancer Study (SEBCS). A total of 11,555 SNPs from the 137 candidate genes were included in the GxE analyses with eight established environmental factors. A replication test was conducted by using an independent population from the Breast Cancer Association Consortium (BCAC), with 62,485 Europeans and 9047 Asians. The GxE tests were performed by using two-step methods in GxEScan software. Two interactions were found in the SEBCS. The first interaction was shown between rs13035764 of NCOA1 and age at menarche in the GE|2df model (p-2df = 1.2 × 10−3). The age at menarche before 14 years old was associated with the high risk of breast cancer, and the risk was higher when subjects had homozygous minor allele G. The second GxE was shown between rs851998 near ESR1 and height in the GE|2df model (p-2df = 1.1 × 10−4). Height taller than 160 cm was associated with a high risk of breast cancer, and the risk increased when the minor allele was added. The findings were not replicated in the BCAC. These results would suggest specificity in Koreans for breast cancer risk.

PURPOSE Among patients with metastatic breast cancer (mBC), the frequency of germline mutations in cancer susceptibility genes and the clinical relevance of these mutations are unclear. In this study, a prospective cohort of patients with mBC was used to determine mutation rates for breast cancer (BC) predisposition genes, to evaluate the clinical characteristics of patients with mutations, and to assess the influence of mutations on patient outcome. PATIENTS AND METHODS Germline DNA from 2,595 patients with mBC enrolled in the prospective PRAEGNANT registry was evaluated for mutations in cancer predisposition genes. The frequencies of mutations in known BC predisposition genes were compared with results from a prospective registry of patients with nonmetastatic BC sequenced using the same QIAseq method and with public reference controls. Associations between mutation status and tumor characteristics, progression-free survival, and overall survival were assessed. RESULTS Germline mutations in 12 established BC predisposition genes (including BRCA1 and BRCA2) were detected in 271 (10.4%) patients. A mutation in BRCA1 or BRCA2 was seen in 129 patients (5.0%). BRCA1 mutation carriers had a higher proportion of brain metastasis (27.1%) compared with nonmutation carriers (12.8%). Mutations were significantly enriched in PRAEGNANT patients with mBC compared with patients with nonmetastatic BC (10.4% v 6.6%, P < .01). Mutations did not significantly modify progression-free survival or overall survival for patients with mBC. CONCLUSION Multigene panel testing may be considered in all patients with mBC because of the high frequency of germline mutations in BRCA1/2 and other BC predisposition genes. Although the prognosis of mutation carriers and nonmutation carriers with mBC was similar, differences observed in tumor characteristics have implications for treatment and for future studies of targeted therapies.

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and potentially permanent adverse effect of chemotherapeutic agents including taxanes such as paclitaxel and platinum-based compounds such as oxaliplatin and carboplatin. Previous studies have suggested that genetics may impact the risk of CIPN. We conducted genome-wide association studies (GWASs) for CIPN in two independent populations who had completed European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ)-CIPN20 assessments (a CIPN-specific 20-item questionnaire which includes three scales that evaluate sensory, autonomic, and motor symptoms). The study population N08Cx included 692 participants from three clinical trials (North Central Cancer Treatment Group (NCCTG) N08C1, N08CA, and N08CB) who had been treated with paclitaxel, paclitaxel plus carboplatin, or oxaliplatin. The primary endpoint for the GWAS was the change from pre-chemotherapy CIPN20 sensory score to the worse score over the following 18 weeks. Study population The Mayo Clinic Breast Disease Registry (MCBDR) consisted of 381 Mayo Clinic Breast Disease Registry enrollees who had been treated with taxane or platinum-based chemotherapy. The primary endpoint for the GWAS assessed was the earliest CIPN20 sensory score available after the completion of chemotherapy. In multivariate model analyses, chemotherapy regimen (p = 3.0 × 10−8) and genetic ancestry (p = 0.007) were significantly associated with CIPN in the N08Cx population. Only age (p = 0.0004) was significantly associated with CIPN in the MCBDR population. The SNP most associated with CIPN was rs56360211 near PDE6C (p =7.92 × 10−8) in N08Cx and rs113807868 near TMEM150C in the MCBDR (p = 1.27 × 10−8). Due to a lack of replication, we cannot conclude that we identified any genetic predictors of CIPN.

Abstract Background: Preventive endocrine therapy (ET) has been proven extensively to decrease breast cancer (BC) risk by 50-65%. Despite this significant reduction, a small proportion of high risk women take ET, due to attitudes toward medications, inaccurate risk perception and drug side-effects. The addition of a polygenic risk score (PRS), comprised of 77 BC genetic susceptibility loci (Single Nucleotide Polymorphisms (SNP)), to the standard risk calculator estimates, can be used to improve BC risk estimation. We previously reported on the influence of the PRS-adjusted BC risk estimates on the intent to use ET (Abstract, SABCS, 2019). Here we report on the influence of PRS-adjusted BC risk estimates on ET adherence at 1 and 2 year follow –up. We also report on ET side effects over this same time period. Methods: Women older than age 35 were eligible if they were deemed at high risk for BC by either a 5 year Gail Model risk of ≥3% or 10 year Tyrer-Cuzick risk (IBIS) of ≥5%. We excluded women with a personal history of BC or hereditary BC syndromes. At baseline, participants were counseled on their BC risk using standard risk calculators: Gail and IBIS risk scores (5 yr, 10 yr, & lifetime) and ET options were discussed, including benefits and risks. Blood samples were obtained and genotyped for 77 SNPs, and an updated BC -PRS risk report was shared with study participants that reflected the IBIS and Gail risk predictions for 5 yr, 10 yr, & lifetime BC risk with and without the PRS. A baseline self-reported questionnaire assessed understanding of BC risk and decision to take ET. Follow-up questionnaires at 1 and 2 years assessed self-reported ET adherence and ET side effects (vasomotor symptoms, vaginal symptoms, sexual dysfunction, weight gain, GI symptoms, headaches, breast sensitivity, mood changes, and joint pain). Adherence to ET at 1 and 2 year follow-up was stratified by three categories of lifetime PRS-BC risk: 0-20%; 20-40%; 40-100%. Results: 151 women at Mayo Clinic Rochester and CancerCare Manitoba were enrolled in the study from 2016 to 2017. Of the 149 participants with evaluable data at 1 and 2 year follow-up, 57 (38%) started on ET therapy, all within 1 year of the baseline visit; 43 (29%) were taking ET at 1 year and 33 (22%) were taking ET at 2 year follow-up, representing a discontinuation rate of 26% at 1 year and 42% at 2 year follow-up. Adherence to ET use at 1 year and 2 year follow-ups correlated significantly with the category of PRS-BC risk estimation: at 1 year follow up, 17% of those in the lowest PRS-IBIS risk category, 23% in the middle risk category and 50% of those in the highest risk category were taking ET (p=0.001). At 2 year follow up, 12% of those in the lowest PRS-IBIS risk category, 18% in the middle risk category and 38% of those in the highest risk category were taking ET (p=0.008). At 1 year follow up, participants taking ET reported significantly more bothersome symptoms of vaginal itching (p=0.010), weight gain (p=0.015) and joint pain (p=0.044), compared with those not on ET. There was a trend towards increased irritability and mood swings on those taking ET (p=0.059). At year 2 there was no significant difference in side effects between those taking and not taking ET. Conclusion: Adherence to ET in a population of women at high risk for BC decreased overtime and strongly correlated with the level of risk, with 38% of those at highest risk of breast cancer taking ET at 2 year follow up. Side effects of vaginal itching, weight gain and body aches were more common on those taking ET versus not taking ET at the 1 year follow-up, but did not differ at 2 year follow-up, possibly due to the fact that those with the most bothersome symptoms have discontinued ET by the 2 year follow up. Citation Format: Daniela Stan, Julian Kim, Daniel Schaid, Erin Carlson, Andrew Cooke, Christina A. Kim, Benjamin Goldenberg, Jason Sinnwell, Debjani Grenier, Amy Degnim, Fergus Couch, Celine Vachon, Sandhya Pruthi. Influence of a breast cancer polygenic risk score on adherence to preventive endocrine therapy in high risk women at 1 and 2 year follow-up: The genetic risk estimate (GENRE) trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS8-02.

Abstract Background: Growing data established the pivotal role of preexisting immune response in triple negative breast cancer (TNBC). Conventionally, preexisting immune response can be evaluated by quantifying tumor infiltrating lymphocytes mainly in the stroma or gene expression analysis from the whole tumor section. Due to technical challenges with these conventional methods, limited data regarding specific subtypes and spatial distribution of these immune infiltrates are currently available. Methods: NanoString IO360 gene expression analysis and Digital Spatial Profiling (DSP) were used. DSP was used to quantify 29 immune-related proteins in stromal and tumor-enriched segments from 44 TNBC samples from the FinXX trial (NCT00114816) and 335 samples from the Mayo Clinic (MC) cohort of centrally reviewed TNBC (Leon-Ferre BCRT 2018). In FinXX trial, 22 patients with recurrence and 22 patients without recurrence were included. In MC cohort, 217/335 patients received adjuvant chemotherapy while 118 patients had surgery only without adjuvant chemotherapy. Regions were segmented based on pancytokeratin staining. The general linear model was used for statistical analysis of differential expression with recurrence free survival (RFS) as a categorical variable (recur yes or no). Kaplan-Meier (KM) estimates and Cox regression models were also used for analysis. Results: In the FinXX trial, there were 12 out of 29 proteins in tumor epithelial segments (intraepithelial) which were significantly expressed at higher levels among patients who were free of recurrence. These proteins include Beta-2 microglobulin, CD11c, CD20, CD40, CD56, CD8, Granzyme B, HLA-DR, ICOS, PD-L1, PD-L2, and TGFB1. In contrast, merely 5 out of 29 proteins in stromal segments were significantly differentially expressed in these 2 groups of patients. Granzyme B, IDO1, PD-L1, and PD-L2 in stroma were significantly higher and SMA was significantly lower in patients without recurrence. Using Cox regression models, intraepithelial CD56, CD40, and HLA-DR were significantly associated with outcome. When comparing between highest and lowest intraepithelial protein expression by tertile, intraepithelial CD56 (HR 0.12, 95%CI 0.03-0.39, p &lt; 0.001), CD40 (HR 0.13, 95%CI 0.04-0.46, p = 0.002), and HLA-DR (HR 0.24, 95%CI 0.06-0.89, p = 0.032) were significantly associated with improved outcome. However, expression of these same proteins in stroma was not associated with outcome. Using KM estimates, intraepithelial CD56 (p &lt; 0.0001), CD40 (p = 0.0006), and HLA-DR (p = 0.013) were also significantly associated with improved outcome. Nonetheless, RNA expression of these proteins by IO360 from whole tumor sections were not significantly associated with outcome (CD56 p = 0.27, CD40 p = 0.21, HLA-DR p = 0.48). Similar findings with DSP were observed in MC TNBC cohort. Comparing between the highest and lowest quartiles, there were significantly fewer patients who developed recurrence with high protein expression of intraepithelial CD56 (p &lt; 0.001), CD40 (p = 0.002), and HLA-DR (p = 0.006). Conclusions: Using an in-depth analysis with spatially defined context, we identify that there were numerically more intraepithelial immune-related proteins associated with outcome compared to proteins in stroma. Specifically, intraepithelial CD56, CD40, and HLA-DR were significantly associated with improved outcome in both FinXX and MC TNBC cohorts. However, neither expression of these proteins in stroma nor RNA expression from whole tumor were associated with outcome. Our study highlights the impact of spatial biology and the importance of evaluating each potential biomarker in a spatially defined manner. Support: W81XWH-15-1-0292, BCRF 19-161, P50CA116201-9, P50CA015083 Citation Format: Saranya Chumsri, Jodi M. Carter, Yaohua Ma, Douglas Hinerfeld, Heather Ann Brauer, Sarah Warren, Torsten O. Nielsen, Karama Asleh, Heikki Joensuu, Edith A. Perez, Roberto A. Leon-Ferre, David W. Hillman, Judy C. Boughey, Minetta C. Liu, James N. Ingle, Krishna R. Kalari, Fergus J. Couch, Keith L. Knutson, Matthew P. Goetz, E. A. Thompson. Spatially defined immune-related proteins and outcome in triple negative breast cancer in the FinXX trial and Mayo Clinic cohort [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-02.

Abstract Introduction: Stromal tumor-infiltrating lymphocytes (sTILs) have established prognostic and predictive significance in triple-negative breast cancer (TNBC). However, the roles of other immune cells in TNBC are less well-established. We performed high-plex quantitative spatial profiling in a cohort of early-stage TNBC to 1) apply spatial context to tumoral immune landscapes and 2) identify immune proteins associated with clinical outcomes, independently of TILs and other established prognostic clinicopathologic variables, in patients (pts) treated with or without adjuvant chemotherapy (CTX). Methods: The Mayo TNBC cohort comprises pts with centrally-verified, CTX-naive tumors resected from 1985-2012. Using a cohort-based TMA, with Nanostring GeoMX DSP, we quantitated 58 proteins within spatially-distinct intra-epithelial, cytokeratin-positive tumor segments and adjacent cytokeratin-negative/nuclei-positive stromal segments. Differentially-expressed (DE) proteins were identified using a negative binomial generalized linear model (SNR&gt;2, p&lt; 0.05) and a target DE protein set was dichotomized (80th percentile). After adjusting for prognostic clinicopathologic variables, proteins associated with recurrence-free survival (RFS, defined as time from surgery to either local, regional, and distant recurrence, or death by any cause) were identified by performing variable selection using the Akaike Information Criterion (AIC) obtained from fitting all possible Cox proportional hazards regression models (performed separately for intra-epithelial/stromal segments, and in groups +/- adjuvant CTX. Results: From the TNBC TMA, DSP data (N=250 tumors) included 169 pts who received adjuvant CTX+ and 81 who did not (CTX-). Overall, 85/250 developed recurrent disease. In the CTX+ group, intra-epithelial tumor segments from pts without recurrent disease were enriched in 10 immune proteins, including CD8, markers involved in antigen presentation/dendritic cells (CD11c, CD40, HLA-DR) or NK cells (CD56) (FC: 1.4-2.1, p&lt;0.05); CD14 was increased in stroma (FC: 1.5, p&lt;0.05). In contrast, in the CTX- group, both the intra-epithelial tumor and stromal segments from pts without recurrences were enriched in immune proteins (N= 12 and 15 respectively; FC 1.6-5.5, p&lt; 0.05) most markedly CD40, IDO1 and HLA-DR (FC: 3.2-5.5, p&lt; 0.05). Overall, CD3, CD4, CD27, CD44, and ICOS among others were enriched only in the CTX- group; CD14 and CD56 were enriched only in the CTX+ group. Based on these spatial data, biologic function and DSP data from another set of TNBC (FinXX trial), CD11c, CD14, CD27, CD40, CD56, and IDO1 were selected for RFS analysis. After applying our model selection criterion and adjusting for pt age at surgery, tumor size, lymph node status, and sTILs, intra-epithelial CD56 was independently associated with improved RFS in the CTX+ group (HR: 0.31[0.12, 0.81]). In the CTX- group, intra-epithelial CD11c was independently associated with improved RFS (0.10 [0.01, 0.81]). Conclusion: In this early-stage TNBC cohort, spatially-distinct tumor immune landscapes were associated with RFS but differed according to receipt of CTX after surgical resection. In the patients who received CTX, the intra-epithelial compartment, rather than stromal compartment, was immune-enriched in pts without recurrences. Among a targeted protein set, intra-epithelial CD56 remained associated with improved outcomes, independent of sTILs and other clinicopathologic features. In the CTX- group, spatial landscapes were more balanced, and intra-epithelial CD11c was independently associated with improved outcomes. These data provide insight into the spatial context of intrinsic immune landscapes in TNBC, and identify candidate prognostic immune biomarkers which may inform therapeutic strategies. Citation Format: Jodi M Carter, Saranya Chumsri, David W Hillman, David M Zahrieh, Yaohua Ma, Xue Wang, Jennifer M Kachergus, Judy C Boughey, Minetta C Liu, Krishna R Kalari, JC Villasboas, Roberto A Leon Ferre, Fergus J Couch, Matthew P Goetz, E. Aubrey Thompson. Intra-epithelial tumor immune landscapes are associated with clinical outcomes in early-stage triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS16-01.

Abstract BACKGROUND: Brain metastatic disease occurs in 10-30% of metastatic breast cancer cases. The incidence of brain metastases is increasing, yet overall survival remains &lt; 2 years. Treatment of brain metastases is limited with current clinical practice centered on radiation, chemotherapy and surgery. Although these treatments may prolong survival in the short term, targeting oncogenic alterations in brain metastases may deliver a more sustained clinical benefit. In this multicenter study, we comprehensively characterized DNA and RNA alterations that aberrantly drive specific oncogenic pathway activity pertinent to breast cancer brain metastases (BCBM). METHODS: RNA sequencing was performed on a cohort of patient-matched primary and resected brain metastatic tumours (45 patients; N=90 samples). Whole exome DNA sequencing (WXS) was performed for 18/45 patients (54 trios consisting of primary tumor, brain metastasis and matched normal tissue). An independent brain metastatic WXS cohort (N=21 patients) (PMID: 26410082) was also analysed resulting in a total of 39 patient samples. Recurrent somatic copy number alterations (SCNA), somatic single nucleotide variants (SNVs) and mutational signatures were identified from WXS data. Expressed gene fusions were detected computationally from RNA-Seq (N=45 cases) RESULTS: Of the 45 BCBM patients, median age at diagnosis was 51 years [25, 67], median overall survival 57 months (range 18-255) with median brain metastases free survival 34 months (range 5-216).Clinical molecular subtype of the primary tumour included 13 ER+/HER2- (29%), 16 HER2+ (35.5%) and 16 TNBC (35.5%). Regions of significant recurrent amplifications and deletions in BCBM (N=39 patients) were identified in 4q12, 10q11.21, 8p11.23, 8q23.3 and 17q12 (FDR &lt; 0.10). Recurrent expressed gene fusions identified in known cancer driver genes were associated with chromatin modification, MAPK and HER signaling pathways. Mutational signature analysis of SNVs identified signatures associated with ageing, mismatch repair and homologous recombination deficiency (HRD) mutational processes. The relative contribution of the HRD signature was significantly increased in brain metastases compared to matched primary tumour (p &lt; 0.05). Concordantly increased HRD in the brain metastatic transcriptome was confirmed in these patients by gene set variation analysis (GSVA) of homologous recombination pathway genes from KEGG database in RNA-Seq data. Moreover, in the extended BCBM RNA-Seq (N=45 patients) GSVA pathway scores were elevated in brain metastases relative to primary tumours, validating the functional significance of altered DNA repair defects in brain metastases CONCLUSIONS: Here, we report recurrent genetic drivers, supported by altered functional transcriptome, unique to brain metastasis that may have clinical implications for prognosis and treatment choice. Specifically, targeting defects in the homologous recombination repair mechanism may represent new therapeutic strategies and management opportunities for breast cancer brain metastases patients. Citation Format: Nicola S Cosgrove, Damir Varešlija, Stephen Keelan, Simon Furney, Jodi M Carter, Steven N Hart, Siddhartha Yadav, Arnold DK Hill, Steffi Oesterreich, Adrian V Lee, Fergus J Couch, Leonie Young. Homologous recombination deficiency represents a new therapeutic strategy for breast cancer brain metastases [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD13-01.

Abstract Background: About 10-20% of breast cancers (BC) are hereditary. Patients (pts) with BC and pathogenic variants (PVs) in the BRCA1 or BRCA2 gene are at increased risk of contralateral breast cancer (CBC). However, risks of CBC and recurrent BC associated with PVs in other established BC predisposition genes (e.g. PALB2, CHEK2, ATM) are less well established. We performed research genetic testing of over 4000 pts with BC treated at Mayo Clinic. Because most pts were unaware of their mutation status prior to selection of therapy, this cohort provides a unique opportunity to evaluate the natural history of BC recurrence after treatment of the index BC in pts with a deleterious mutation in predisposition genes. Methods: Women diagnosed and treated for BC at Mayo Clinic between 2001-2016 were enrolled in an IRB-approved research cohort. Pts were not selected for age of diagnosis or family history. Coding regions and consensus splice sites of established BC predisposition genes were subjected to amplicon-based deep sequencing using the QIAseq method in germline DNA extracted from peripheral blood or buccal samples. PVs in the genes were identified using GATK haplotype caller and Vardict. Patient, tumor, oncologic management and follow up data were reviewed. Herein we report on the differences in the incidence of local recurrence and CBC, among carriers and non- carriers and by predisposition gene using the cumulative incidence estimator and Fine and Gray regression to account for competing risks. Results: Of 4272 women with BC (median age 57, range 21-94), a PV in a BC predisposition gene was identified in 287 (6.7%). The most common PVs were seen in CHEK2 (67, 1.6%), BRCA1 (62, 1.5%), BRCA2 (60, 1.4%), ATM (47, 1.1%); 8 (0.2%) patients had more than one PV. Pts with any PVs presented at younger age (median 51 vs 58 years, p&lt;0.001), were more likely to have stage IV disease (4.5% vs 2.3%, p=0.02), estrogen receptor (ER) negative BC (19.5% vs 13.5%, p=0.005), and bilateral cancer (8.8% vs 4.3%, p&lt;0.001). ER- BC proportion varied by gene - 38.9% in pts with PVs associated with ER- BC (BRCA1, BARD1, BRIP1, RAD51C, RAD51D) and 11.9% in those with PVs associated with ER+ BC (BRCA2, ATM, CDH1, CHEK2), p&lt;0.001. NCCN criteria for genetic testing were assessed for 3763, with 69.9% of those with PVs qualifying for testing compared to 46.3% of those without PVs (p&lt;0.001). Among 3973 pts (249 with PVs, 3724 without) with unilateral stage 0-III cancer, 168 pts developed local recurrence, 131 pts developed CBC and 248 pts developed distant disease with median 5 years of follow-up. Patients with any PV had higher rates of local recurrence after breast conserving surgery (HR 2.3, 95% CI: 1.2-4.2, p=0.01) but overall did not have significantly higher risk of CBC if contralateral prophylactic mastectomy was not performed (HR 1.7, 95% CI: 0.9-3.2, p=0.11). Specifically, pts with PVs in genes other than BRCA1 or BRCA2 did not have a higher risk of CBC compared to pts with no PV (HR 1.0, 95% CI: 0.4-2.7, p=0.96); the comparison of CBC risk in BRCA1 or BRCA2 versus those with no PV was HR 2.9 (95% CI: 1.3-6.5, p=0.01), while BRCA1 or BRCA2 compared to those with other PVs was HR 2.7 (95% CI: 0.8-9.3, p=0.13). In pts with CHEK2 PVs, the probability of CBC at 10-years follow-up was 5.4%, which was similar to pts without a mutation (5.3%), p=0.47. Conclusion: While PVs in known BC predisposition genes increase risk of BC development, risk of CBC in carriers of PVs in non-BRCA predisposition genes with BC are not as high as seen with BRCA1 or 2 PV carriers. This information regarding future BC will be helpful in personalizing decisions on the extent of surgery in carriers of PVs in BC predisposition genes. Citation Format: Judy C. Boughey, Tanya L. Hoskin, Siddhartha Yadav, Fergus J. Couch. The influence of pathogenic variants in breast cancer predisposition genes on secondary breast cancer events in a prospectively collected cohort of breast cancer patients [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD10-02.