[Effect of mitomycin C on human gastric and colon carcinomas serially transplanted to nude mice--with special reference to the start of drug administration].

Three human gastric carcinomas and one colon carcinoma serially transplanted to nude mice were used for experimental chemotherapy of mitomycin C (MMC) with special reference to the start of drug administration. BALB/c nu/nu male originated from the Central Institute for Experimental Animals were used. All the experiments were carried out under the specific pathogen-free conditions using laminar air flow racks. Tumors used for experiments were St-4; poorly differentiated adenocarcinoma of stomach, St-15; mucinous adenocarcinoma of stomach, KS-1; poorly differentiated adenocarcinoma of colon. MMC at the doses of 2 or 3 mg/kg were administered intraperiatoneally once a week for 3 or 4 times starting from 24 hours (DAY-1 Adm.) or 2 weeks (DAY-14 Adm.) after tumor inoculation. Response to chemotherapy was evaluated on the basis of growth curves, tumor weights, and histopathological changes. Whereas St-15, a sensitive strain to MMC, was suppressed by DAY-1 and DAY-14 administration. Similarly, DAY-1 administration revealed more excellent effect on the other three tumors than DAY-14 administration. These results indicated that MMC was more effective when the tumor mass was smaller, and also suggested that the adjuvant chemotherapy of surgical operation should be started as soon as possible after tumor resection or reduction. In the case of DAY-1 treatment, the false positive result by anti-vascularization effect of MMC could not be excluded, it seems to be adequate that drug administration should be started after the initiation of logarithmic growth phase of the tumors.