BRCA1 and neoplasm: We found that ~21% (6/39) of BCBM cases had the presence of Breast K signature mutually exclusive to the other BCBM enriched mutational signatures, independently of somatic or germline BRCA1/2/PALPB2 mutations and tumor mutational burden (Fig. 6a and Supplementary Fig. 10; Supplementary Data 17).