CTNNB1 and Familial adenomatous polyposis: Meanwhile, a small number of cases of ovarian MCST had been reported in patients with familial adenomatous polyposis (FAP), an autosomal-dominant cancer predisposition syndrome caused by a germline mutation in the adenomatous polyposis coli (APC) gene on chromosome 5q21, illustrating that MCST might be an extracolonic manifestation of FAP.[5,14,15] McCluggage et al[13] found APC mutations occurred in a minority of MCST and were mutually exclusive with CTNNB1 mutation.