Here, we simultaneously evaluated BRCA1 methylation status and BRCA1 protein expression and their clinicopathological significance in a population of 248 sporadic TNBCs from patients without familial BC history or known germline BRCA1 pathogenic variants, in order to evaluate the robustness of the IHC evaluation of protein expression as a surrogate endpoint of epigenetic inactivation, and to evaluate their association with prognosis and PD-L1 expression. This evidence concerns the gene BRCA1 and breast cancer.