Colonic tumorigenesis in rats with 1,2-dimethylhydrazine.

Subcutaneous injections of the carcinogen dimethylhydrazine in inbred Fischer 344 male rats induced squamous-cell carcinomas in the ear canal, adenocarcinomas in the small bowel and duodenum, and adenomas and adenocarcinomas in the large bowel. The incidences of the tumors induced in the large bowel and ear canal were dose-related. As for tumors of the large bowel, the average size of adenomas was less than that of adenocarcinomas with massive infiltration beyond the muscularis mucosa. The average size of early adenocarcinomas was greater than that of adenomas but less than that of adenocarcinomas with massive infiltration beyond the muscularis mucosa.