Germline protein-truncating variants (PTVs) in 5 genes (ATM, BRCA1, BRCA2, CHEK2, and PALB2) were strongly associated with a risk of BC.15 PTVs in these 5 genes (hereinafter referred to as the 5 major genes for BC) are used for providing future cancer risks in the multifactorial Breast and Ovarian Analysis of Disease Incidence and Carrier Estimation Algorithm (BOADICEA) model16,17 included in the CanRisk tool.18 However, to our knowledge, the specific association of these genes with IC or SDC has not been studied. Here, CHEK2 is linked to breast cancer.