BRCA gene mutations do not shape the extent and organization of tumor infiltrating lymphocytes in triple negative breast cancer.

This study investigated the prevalence of TIL subpopulations, TLS, PD-1 and PD-L1 in tumors from TNBC patients harboring wild-type or mutated BRCA1 or BRCA2 germline genes. This TNBC cohort included 85% TIL-positive (≥10%) tumors with 21% classified as TIL (≥50%). Interestingly, the BRCA group had a significantly higher incidence of TIL tumors compared to the BRCA group (P = 0.037). T cells were dominant in the infiltrate but no statistically significant differences were detected between BRCA and BRCA for CD3, CD4 and CD8 T cells or CD20 B cells. TLS were detected in 74% of tumors but again no significant differences between the BRCA groups. PD-1 expression was observed in 33% and PD-L1 in 53% (any cell, cut-off ≥1%) tumors for the entire TNBC cohort. PD-1 expression correlated with PD-L1 and both with TIL and TLS but was not associated with BRCA mutational status. Our analyses reveal that BRCA and BRCA TNBC are similar except for a significant increase of TIL tumors in the BRCA group. While BRCA gene mutations may not directly drive immune infiltration, the greater number of TIL tumors could signal greater immunogenicity in this group.