CHEK2 and breast carcinoma: Moreover, 914 breast cancer patients (8.3%) carried a CHEK2 mutation (659 missense mutations and 255 protein-truncating mutations (47 1100delC; 91 IVS2 + 1G/A and 117 del5395 mutations) and 502 breast cancer patients (4.6%) carried a BRCA1 mutation.