Desmoid tumor patients carry an elevated risk of familial adenomatous polyposis

The prevalence of desmoid tumors among patients with familial adenomatous polyposis (FAP) is at least 10%, and the prevalence of FAP among desmoid patients varies between 7.5-16%.

Data included 106 desmoid patients identified from the database of the Department of Pathology, Helsinki University Hospital, years 2000-2012. We evaluated the risk of FAP among patients by using endoscopy and we identified individuals with attenuated FAP by APC gene mutation test. We compared sporadic desmoid patients' and FAP patients' clinical characteristics.

Ten of 106 patients already had FAP diagnosis before the desmoid. Eleven patients had had FAP screening already earlier due to desmoid and three of them were found to have FAP. Total of 52 patients participated into prospective screening of FAP. No new cases of FAP were found. The risk of FAP among desmoid tumor patients was 4.8%. In the FAP desmoid group, there were more males and patients were younger than in the sporadic group. Intra-abdominal desmoids were more common in the FAP group.

Patients with desmoid carry an elevated risk of FAP and therefore screening is indicated. Asymptomatic patients with desmoid situated in extra truncal region may not need to be screened.