GENETIC ALTERATIONS OF MIXED HYPERPLASTIC ADENOMATOUS POLYPS IN THE COLON AND RECTUM

Some mixed hyperplastic adenomatous polyps (MHAPs) contain dysplastic lesions or even carcinomas, These polyps are considered to be differen t from ordinary hyperplastic polyps and may have a preneoplastic poten tial, We investigated APC and K-ras mutations in MHAPs of the colon an d rectum, and also in colorectal adenomas and hyperplastic polyps to i dentify molecular differences between MHAPs, adenomas and hyperplastic polyps, using direct sequencing of mutation cluster regions (MCR) in APC and K-ras, No APC mutations were identified in 12 MHAPs and 8 hype rplastic polyps, whereas 10 of 27 (37.0%) adenomas showed somatic muta tions, K-ras mutations were identified in one of 12 (8.3%) MHAPs, one of 8 (12.5%) hyperplastic polyps, and 10 of 27 (37.0%) adenomas, p53 m utation was found in a carcinoma arising in an MHAP, Mutations other t han APC mutations may play a role in the development of MHAPs.