Including pre-existing cohorts, we exhaustively compared CHEK2 pBC genomes to those from BRCA1/2 mutation carriers, those that displayed homologous recombination deficiency (HRD) and ER− and ER+ pBCs, totaling to 574 pBC genomes. Here, CHEK2 is linked to hypoparathyroidism-retardation-dysmorphism syndrome.