Intestinal tumors in mice treated with a single injection of N-nitroso-N-butylurea

N-Nitroso-N-butylurea was injected once at dosage levels of 150 or 75 mg/kg into 3- or 6-week-old male C57BL/L mice. Intestinal tumors occurred in 100% of the mice that survived more than 15 weeks after injection with a high dose of N-nitroso-N-butylurea at 6 weeks of age, and in 35 to 70% of the mice in other treatment groups. These intestinal tumors were seen primarily at the junction of the pylorus and duodenum and in the anterior portion of the small intestine, with a few in the cecum, colon, and rectum. The tumors at the junction were not very invasive tumors and frequently appeared as polypoid growths. Tumors not at this location were adenocarcinomas that invaded all the layers of the gut wall but which did not metastasize. Colorectal tumors were adenomas and adenocarcinomas. N-Nitroso-N-butylurea also induced tumors of the stomach, hematopoietic system, lung, and liver.