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Chemical carcinogenesis in transposed intestinal segments.

A research model has been devised to assist in an assessment of the relative susceptibility of small bowel and colonic mucosa to potential intestinal carcinogens, and an application of this model to azoxymethane is reported. Intestinal transpositions were performed on Sprague-Dawley rats. In one group, segments of small intestine were transposed to the ascending and descending colon and, in another group, colon segments were transposed to the level of the mide small bowel. Weekly i.m. injections of azoxymethane were started several weeks after operation. Usually, after 14 injections (although sometimes earlier) some of the rats died or presented clinical evidence of intestinal tumors. This preliminary report is based on findings obtained from specimens in these animals and in a few animals from the control groups.

Eighteen rats that had a colon transposition and that received azoxymethane developed adenocarcinoma in the transposed segment. None of the 17 rats that had a small bowel transposition and that received the carcinogen developed cancer in the transposed small intestine; however, each had one or more colon cancers. Control animals that received the carcinogen, but which had no operation, developed colon cancer. The animals in both control and operated groups that received the carcinogen developed small intestinal tumors that were localized in the duodenojejunal region. Control animals that had intestinal transpositions but no carcinogen did not develop cancer.

These early findings suggest that colon mucosa, regardless of its location in the intestinal tract, is susceptible to the carcinogen azoxymethane but that mucosa of the small intestine is not. The experiment does not parallel the clinical state but may prove helpful in understanding the biology of cancer.