Although some mesenteric fibromatosis lesions appear to be circumscribed grossly, they usually infiltrate microscopically into the surrounding tissues. Complete surgical removal is extremely difficult and accounts for frequent recurrences. Genetics: Tumors arising in the setting of FAP/Gardner syndrome carry inactivating mutations of the APC gene on chromosome 5q. Majority of the sporadic cases have mutations in CTNNB1 that codes for beta-catenin. These mutations result in nuclear accumulation of beta-catenin which can be detected immunohistochemically. Other genetic alterations that have been seen in fibromatoses include trisomy of chromosome 8 and 20 and loss of Y chromosome.