Immune profiling of BRCA-mutated breast cancers.

585Background: Increased tumor infiltrating lymphocytes (TILs) are predictive and prognostic for improved outcomes in breast cancers. Increased tumor mutational burden can be immune activating. BRCA-mutated (BRCA+) breast cancers may have increased tumor mutational burden compared to BRCA wildtype (BRCA-). Immune system responses to BRCA+ breast cancers have not been well described. The primary aim of our study was to assess tumor infiltrating immune cells in early stage breast cancers with and without germline BRCA mutations. Methods: Here we report TILs and genomic profiling from our full study cohort. Assuming the %TILs in the BRCA- group was 20% we determined 124 early stage breast cancers with and without BRCA mutations was needed to detect a 20% difference in TILs between cohorts to attain 80% power with a one-side alpha of 0.05. We identified 124 early stage untreated breast cancers with BRCA mutations (n = 62) and without (n = 62). Our BRCA- control group were matched by hormone receptor (HR) stat...