Familial adenomatous polyposis associated with gastrointestinal stromal tumor: report of a case.

Familial adenomatous polyposis (FAP) is an autosomal dominant, hereditary syndrome that is characterized by the presence of hundreds to thousands of colorectal adenomas, which, if not surgically treated, develop into colorectal cancer in all cases. FAP is caused by germline mutations of the adenomatous polyposis coli (APC), which has been defined as a tumor suppressor gene and is basic for the Wnt signaling pathway (1,2). Therefore, up-regulation of Wnt pathways, due to APC gene mutations in all cells, is not only responsible for the development of colorectal adenomas and subsequent malignant transformation, but also determines the occurrence of benign and malignant tumors in other sites (2). Indeed, an association of FAP with extracolonic manifestations (ECMs) has been described extensively (2,3). FAP can be combined with soft tissue tumors. Among these, desmoid tumors (in particular, within the abdominal cavity and retroperitoneum) are one of the most common ECMs of the disease, and they contribute significantly to morbidity and mortality rates (4). However, sarcoma is seen rarely in patients with FAP (6-10).