Correspondingly, of 139 cases with ER-negative CBC, 52 women (37%) carried at least 1 deleterious BRCA1 or BRCA2 variant, or CHEK2 1100delC, with the majority carrying a deleterious variant in either BRCA1 or BRCA2. Of 276 matched controls, only 20 women (7%) carried at least 1 deleterious ATM, BRCA1, or BRCA2 variant or CHEK2 1100delC. Here, CHEK2 is linked to complete blood cell count.