Chromosome Changes in Desmoid Tumors Developed in Patients with Familial Adenomatous Polyposis

Chromosome analyses were performed on benign desmoid tumors obtained from two female patients with familial adenomatous polyposis (FAP), one of whom was diagnosed as having Gardner syndrome (GS). The modal chromosome number was 46 in both specimens, and detailed Q‐banding analysis in Case 1 (GS) revealed a clonal abnormality of an interstitial deletion of the long arm of chromosome 5, del(5)(q2lq31). The deleted region included an assigned locus for an FAP major gene (5q21‐q22). All of the metaphases analyzed in this case showed an extra segment of bright fluorescence on the short arm of chromosome 15, but this unusual chromosome (15p +) was observed in both peripheral lymphocyte and skin fibroblast cultures from the patient, indicating that the 15p+ was constitutional in nature. In Case 2, no clonal rearrangements were Identified and most cells had a normal karyotype. However, two cells showed rearrangements involving a 17q with non‐identical breakpoints, one of which was observed as a solitary chromosome change. Based on the present findings in Case 1 and those reported so far, the chromosomal defect on 5q might be one of the causal genetic events primarily associated with the development of both benign desmoid tumors and colorectal adenomas and carcinomas in FAP patients.