CHEK2 and breast cancer: Consequently, wild-type CHEK2 allele loss in the tumor of a c.1100delC mutation carrier would not necessarily mean that the mutator phenotype was acquired through CHEK2 inactivation, as another BC predisposing gene could have been inactivated before.18 This model also predicts that the BC risk for a female c.1100delC mutation carrier is higher when she has first degree relatives with BC as compared with a female carrier with no or more distant relatives with BC.