Effect of 5-fluorouracil on gastrointestinal carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in rats.

This study was undertaken to determine the effect of 5-fluorouracil on gastrointestinal carcinogenesis. Sixty rats were divided into three groups of 20 rats each. All rats were exposed to N-methyl-N'-nitro-N-nitrosoguanidine for the first 20 weeks. Group 1 rats received intraperitoneal injections of 5-fluorouracil for the first 20 weeks and were then observed for the second 20 weeks. Group 2 rats also received 5-fluorouracil injections, but for the second 20 weeks. Group 3 rats received no 5-fluorouracil treatment. Four of 20 rats in group 1 developed an invasive adenocarcinoma. In group 3, invasive squamous cell carcinoma and adenocarcinoma developed in one rat each. None of the group 2 rats had malignant lesions. These results suggested that 5-fluorouracil is not effective in suppressing the initial stage of gastrointestinal carcinogenesis with a coexisting carcinogen. Rather, the therapeutic effect is exerted in later stages of tumor progression.