The proportion of probands (excluding the seven relatives in our cohort) reporting a personal or family history of breast cancer but no colorectal, endometrial, or ovarian cancer was lower among those with MLH1 or MSH2 PVs (MLH1: 0%, 0/65; MSH2: 2.2%, 2/92) than among those with PVs in MSH6 or PMS2 (MSH6: 8.0%, 11/137; PMS2: 24.6%, 30/122) (p < 0.001). Here, MSH6 is linked to breast cancer.