CTNNB1 and Familial adenomatous polyposis: Around 85–90% of desmoid tumors are sporadic, associated with mutations in the CTNNB1 gene, which encodes β-catenin, and 5–10% develop in the context of familial adenomatous polyposis (FAP), in which a germline mutation of the adenomatous polyposis coli (APC) gene is detected [2,101].