The observation that multiple pilomatricomas with CTNNB1 mutations have been observed in patients with constitutive mismatch repair deficiency (CMMR-D) associated with PMS2 germline mutations [22] and that CTNNB1 mutations are frequent in colon cancers of HNPCC patients with MLH1 or MSH2 germline mutations suggested that the DNA mismatch repair mechanisms might play a role in CTNNB1 mutation susceptibility. Here, CTNNB1 is linked to hereditary nonpolyposis colon cancer.