A nation‐wide study comparing sporadic and familial adenomatous polyposis‐related desmoid‐type fibromatoses

Desmoid‐type fibromatoses are neoplasms of fibroblastic origin, occurring sporadically or associated with familial adenomatous polyposis (FAP) coli. By comparing sporadic and FAP‐associated desmoid‐type fibromatoses, we tried to identify clinical characteristics, which may indicate FAP. Histopathology data of all Dutch patients with desmoid‐type fibromatoses diagnosed between 1999 and 2009 were retrieved from PALGA, the nation‐wide network and registry of histopathology in the Netherlands. For calculation of incidence rates, person‐years from the general matched population were used. Based on polyp counts in pathological records, the cohort was divided into a FAP group and a non‐FAP group. Patient‐ and tumor characteristics were compared between the two groups. A total number of 519 patients older than 10 years with a confirmed diagnosis of desmoid‐type fibromatoses were included. Thirty‐nine (7.5%) desmoid patients were documented of having FAP. The incidences of sporadic and FAP‐related desmoid‐type fibromatoses were 3.42 and 2,784 per million person‐years, respectively. The majority of FAP patients developed desmoid‐type fibromatoses after the diagnosis of FAP. Having FAP was associated with male gender [odds ratio (OR) 2.0, p = 0.034], desmoid diagnosis at an earlier age (mean 36 vs. 42 years, p = 0.031), and desmoid localization intra‐abdominally (OR 18.9, p ≤ 0.001) or in the abdominal wall (OR 4.8, p ≤ 0.001), compared to extra‐abdominal desmoid localization. In conclusion, patients with desmoid‐type fibromatoses are at risk of underlying FAP. Especially cases with desmoid localization intra‐abdominal or in the abdominal wall, and all patients younger than 60 years, have a substantial increased risk and should be referred for colonoscopy.