Histology of polypoid lesions found in specimens resected for adenocarcinoma of the colon.

In a revision of 298 colectomy specimens resected for adenocarcinoma of the large bowell, 35 cases (13%) were found to have associated polypoid lesions. Twenty-nine of the polypoid lesions were adenomatous polyps, one a villous adenoma and other a retention polyp. Eight of the adenomatous polyps had a variable degree of benign atypical changes and malignant transformation occurred in four adenomatous polyps with the development of an adenocarcinoma. Four other lesions were small polypoid adenocarcinomas arising in normal colonic mucosa. Four double primary carcinomas were found among the 35 colectomy specimens with polyps. In this paper a significative incidence of malignant polypoid lesions associated with adenocarcinomas of the large bowell were found. The importance of well defined histological criteria in the diagnosis of malignancy and atypical changesin adenomatous polyps in stressed out.