Sister chromatid exchanges in lymphocytes of cancer patients receiving mitomycin C treatment

Peripheral lymphocytes from cancer patients receiving mitomycin C treatment were examined for cytogenetic effects. The treatment consisted of i.v. injections of mitomycin C at a dose of 4 mg given twice a week for 2 weeks. The lymphocytes were cultured in vitro for 72 hr with phytohemagglutinin and 5-bromodeoxyuridine, and then sister chromatid exchanges were scored. Before treatment with mitomycin C, the frequencies of sister chromatid exchanges in lymphocytes of cancer patients were similar to those of healthy controls. After the first and second treatments in vivo with mitomycin C, the frequencies of sister chromatid exchnages increased with time, reached a peak in about 24 hr, and then returned to the pretreatment level in about 48 hr, in contrast to the case of in vitro exposure to mitomycin C. After the third and fourth injections, however, the frequency increased further and did not return to the original level. The significance of the specific kinetics of change in the sister chromatid exchnage frequency after in vivo treatments is discussed in relation to cancer chemotherapy.