Desmoid tumors in familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is a cancer syndrome caused by a germline mutation in the adenomatous polyposis coli (APC) gene. It is characterized by the presence of hundreds of colonic polyps, which have a high tendency to undergo malignant transformation. Among associated lesions in FAP, desmoid tumors represent a common possible life-threatening condition that requires special attention. They are rare tumors occurring with a particularly high incidence in FAP, especially after surgery. In agreement with Knudson's 'two-hit' theory, the inactivation of the residual APC gene in FAP is a critical step in the development of both colorectal cancer and desmoids. Several lines of evidence show that germline mutations affect the functional domains of the APC gene that are responsible for interactions of the transcript with beta-catenin, whereas somatic second mutations involve the downstream region of the gene. Hence, an understanding of the molecular pathways underlying desmoid progression in FAP could be important for research and a valid resource for the early prevention and tailored treatment of this disease. In this review, we provide an updated insight into desmoids in FAP syndrome, from molecular pathogenesis to the main issues in management, with special attention given to genetic and molecular features of these tumors.