The ORs calculated for women with biallelic PVs (8.69 for invasive breast cancer and 4.98 for DCIS) suggest that biallelic CHEK2 PV carriers could have breast cancer risks higher than those associated with PVs in BRCA1 and BRCA2. It may therefore be reasonable to consider biallelic findings in CHEK2 as high, rather than moderate, penetrance for the purposes of management. This evidence concerns the gene BRCA1 and ductal breast carcinoma in situ.