CTNNB1 and Familial adenomatous polyposis: Although the cell of origin of desmoid tumors is not clearly defined, it is suggested that desmoid tumors arise from mesenchymal progenitor cells.4 they are usually thought to be locally invasive but non-metastasizing.5 Most cases occur sporadically, with most cases having mutation in the beta-catenin pathway, in the gene CTNNB1.6 They usually arise in the mesentery or retroperitoneum, when intraabdominal.3 Desmoid tumors have also been associated with familial adenomatous polyposis (FAP), usually caused by a mutation in the APC gene when abdominal.