Desmoid tumors -- a characterization of patients seen at Mayo Clinic 1976-1999.

Desmoid tumors occur with high frequency in individuals with Familial Adenomatous Polyposis (FAP). Because of this, individuals developing desmoid tumors may be referred for genetic risk assessment. Determining whether a person has a FAP-related desmoid tumor or a sporadic desmoid can be challenging. We sought to characterize the patients who were seen at our institution to determine if there were clinical differences in presentation between FAP-associated and sporadic desmoid tumors. We searched the Mayo Clinic-modified H-ICDA (Hospital adaptation of the International Classification of Diseases) diagnostic codes for all diagnoses of desmoid tumors in patients seen between 1976 and 1999. Charts were reviewed to determine accuracy of diagnosis, age when seen, gender, site of tumor, and presence of polyposis. A total of 454 patients (174 males and 280 females) met the search criterion. Of the 447 patients on whom all data was obtained, 70 had FAP and 377 had no evidence of FAP. The female/male ratio for FAP cases was 1.12 compared to female/male ratio of 1.71 for non-FAP cases. (P=0.17). Location of development of desmoid tumors was correlated with but not specific for distinguishing FAP from non-FAP desmoids. Abdominal desmoids comprised the majority of FAP desmoids and extra-abdominal desmoids comprised the majority of non-FAP desmoids (P<0.001) but age was not a discriminating factor. Using Bayesian analysis, we demonstrate how these findings can assist genetic professionals in their evaluation of patients with desmoid tumors by providing prior probabilities of FAP based upon clinical presentation.