Family history of breast cancer in non-BRCA male breast cancer: A case-control study.

e13032 Background: Approximately 85% of male breast cancer (MBC) patients test negative for a BRCA mutation, and the role of genetic predisposition is unclear. Cancer risk counseling for unaffected relatives of BRCA-negative MBC patients relies on accurate cancer risk estimates, but there is limited data on the risk of breast cancer (BC) for relatives of these men. We characterized the association between MBC and family history of BC in patients who test negative for BRCA mutations in order to facilitate cancer risk counseling and to explore the possibility of unidentified MBC susceptibility alleles. Methods: We performed a case-control study of patients who had full length sequencing and large-rearrangement analysis for germline mutations in BRCA1/2 or the mismatch repair (MMR) genes at a commercial laboratory from 2006-2012. Cases were MBC patients who tested negative for a BRCA1/2 mutation (n = 3,647); controls were male colon cancer patients who tested negative for mutations in MMR genes (n = 4,269). Information on family history of BC was ascertained from test request forms completed by the ordering healthcare provider at the time of testing. Unconditional multivariable logistic regression models estimated odds ratios (OR) and 95% confidence intervals (CI) for associations between family history of BC in first- (FDR) and second-degree relatives (SDR) and MBC with adjustment for potential confounders (age, ethnicity, year of testing). Results: Compared to controls, MBC cases had higher odds of BC in a FDR or SDR (OR = 4.7; 95% CI 4.1, 5.3). Associations were strongest for family history of BC in 1 female FDR (OR = 3.9; 95% CI: 3.3, 4.6), ≥2 female FDR (OR = 7.5; 95% CI 5.0, 11.4), BC in a FDR < 45 years old (for cases diagnosed < 45, OR = 6.9; 95% CI 3.9, 12.4), a male FDR or SDR with BC (OR = 17.9; 95% CI 7.6, 42.1), and both a male and female FDR or SDR with BC (OR = 15.7; 95%CI 4.4, 55.3). Conclusions: MBC patients who test negative for a BRCA mutation have significantly higher odds of reporting family members affected by breast cancer, particularly with affected FDR < 45 years old, multiple affected relatives, and male relatives with BC. This data can guide risk counseling in MBC families, and suggests the existence of unidentified MBC susceptibility alleles.