BRCA1 and breast cancer: BC also exhibits strong familial clustering, with BRCA1 and BRCA2 being well-known high-penetrance genes associated with increased risk, and a polygenic origin suggested by medium-low penetrance genes, such as PALB2, PTEN, PIK3CA, ATM, PALB2, BARD1, CHEK2, RAD51C, RAD51D, and TP53 [7,8,9,10].