RAD51C and MYST3 Mutations in a Case of Desmoid-Type Fibromatosis With No Mutation in CTNNB1 or APC.

Most cases of desmoid-type fibromatosis (DTF) exhibit a mutation in APC or CTNNB1. We report a case of mesenteric DTF in which no mutation in APC or CTNNB1 was found, but a germline variant of uncertain significance (VUS) in RAD51C and a subclonal mutation in MYST3 were identified. Whether these genetic changes are important in DTF in this case, or whether genetically conventional DTF cells were present at a density below detection is unknown; it will be of interest to see results in further studies of wild-type APC/CTNNB1 cases.