COMPARATIVE CLINICOPATHOLOGICAL AND IMMUNOHISTOCHEMICAL STUDY OF RAS AND P53 IN FLAT AND POLYPOID TYPE COLORECTAL TUMORS

Mutations in oncogenes and tumour suppressor genes may have an importa nt oncogenic role. Although flat type tumours have been frequently det ected in recent years, ras and p53 expressions have not been studied i n these tumours. Using a monoclonal and polyclonal antibody to the ras p21 and p53 product, paraffin wax embedded sections of 98 colorectal tumours (43 cases of the flat type colorectal tumour and 55 cases of p olypoid type tumour) were stained using the immunoperoxidase technique . Staining was evaluated by light microscopic examination. Positive st aining rate of ras p21 for the flat type was 0%; for the polypoid type , it was 60% in cancer with submucosal invasion, 82% in adenoma with h igh grade dysplasia, and 0% in adenoma with low grade dysplasia. The p ositive staining rate of p53 for the flat type was 50% in submucosal c ancer, 9% in adenoma with high grade dysplasia, and 0% in adenoma with low grade dysplasia. For the polypoid type, it was 40% in submucosal cancer, 12% in adenoma with high grade dysplasia, and 0% in adenoma wi th low grade dysplasia. The intermediate staining rate of p53 in the p olypoid type was 20% in submucosal cancer and 41% in adenoma with high grade dysplasia. It was seen that p53 was commonly expressed in both flat and polypoid lesions, p21 was not expressed in flat lesions, wher eas it was commonly expressed in polypoid neoplasms. In the flat type cancer, a genetic change different from that of the polypoid type canc er is suggested.