Induction of colorectal cancer in rats by 20-methylcholanthrene

Colorectal carcinoma was induced in Sprague-Dawley rats by 20-methylcholanthrene. Macroscopical studies revealed that the tumors, either sessile type or semi-pedunculated polyp, were generally observed after 32 weeks of the carcinogen treatment. In the distal colon 46.9% tumors appeared, whereas 20.4% and 32.6% tumors were found in the rectum and proximal colon, respectively. Sequential histopathological studies indicated that hyperplasia of goblet cells was common in early stages, which was reduced thereafter. Carcinogenesis progressed with the appearance of the different grades of dysplasia in colorectal mucosa with first incidence of the severe dysplasia in rats at the 20th week and in situ carcinoma at the close of 28th week. Most of the carcinomas were multifocal in origin and were well differentiated adenocarcinoma with primary invasion at the submucosa. In immunohistological studies, this carcinoma was also reactive with monoclonal antibody 660, prepared against a colorectal carcinoma associated mucin antigen.