Loss of Heterozygosity Affecting the p53, Rb, and mcc/apc Tumor Suppressor Gene Loci in Dysplastic and Cancerous Ulcerative Colitis

Allelic deletions of tumor suppressor genes have been observed fre-quently in a variety of human tumors. These losses are believed to contribute to the development of human cancer. Three of the most frequently deleted chromosomal loci contain the tumor suppressor genes pS3, retinoblastoma (Rb), and mcc/apc. In order to detect loss of heterozygosity (LOH) within these genes in dysplastic and cancerous ulcerative colitis, we used an application of the polymerase chain reaction. LOH affecting p53 was observed in 8 of 17 (47%) of heterozygous patients, while LOH of Rb and the mcc/apc locus was observed in 9 of 27 (33%) and 13 of 39 (33%) of heterozygotes, respectively. Among 35 patients heterozygous at 2 or more loci, LOH of p53, Rb, and/or mcc/ ape was observed in 18 (51%). LOH was more common in left-sided neoplasms. These data suggest that allelic deletion of p53, Rb, mcc, and/ or ape is involved in the pathogenesis and/or progression of at least a subset of colonic dysplasias and carcinomas occurring in the setting of ulcerative colitis.