Abstract
This study deals with the treatment by chemotherapy of carcinogen-induced tumors in the colon of rats. These tumors mimic colonic adenomatosis and carcinomatosis in man. The rats were given an intrarectal (i.r.) instillation of methylnitrosourea for producing colonic tumors, and thereafter received a long-term chemotherapy which was started on nascent microscopic lesions of carcinoma. The colonic tumor incidence was significantly lower in rats treated for 10 weeks than in untreated rats. An inhibition rate of tumor development was 100% in rats with i.r. doses of 5-FU, or 57% in rats with intraperitoneal (i.p.) doses of Ftorafur. However, it was found that a few microscopic lesions of carcinoma were still present in the normal-appearing colonic mucosa, even after the completion of the effective treatment. The 10-week cessation of the treatment following the 5-week chemotherapy permitted the tumor development. The results indicate that the nascent microscopic lesions of carcinoma (premalignant lesions) in the colon can be inhibited or regulated from developing into grossly visible tumors by the effective chemotherapy, i.e., intermittent and/or long-term treatment with sensitive chemotherapeutic agents and effective way of administration.