CTNNB1 and desmoid tumor: The etiology of desmoid tumors is unknown; however, they are known to be associated with FAP, mechanical stimuli such as open surgery or trauma, estrogenic tumors, and increased estrogen levels related to pregnancy.4) In patients with FAP, germline mutations in the APC gene are involved in the development of desmoid tumors, while sporadic intra-abdominal desmoid tumors are attributed to somatic mutations in CTNNB1.