[Experimental combination chemo-radiotherapy on human breast carcinoma (MX-1) transplanted into nude mice]

Experimental combination chemo-radiotherapy of mitomycin C (MMC) and Linac irradiation was performed on human breast carcinoma transplanted into nude mice. The treatment was started on 2 wks. after tumor inoculations and the effects were evaluated by T/C ratio of the tumor weight. Cell kinetic analysis was studied by flow cytometry, 3H-thymidine uptake labeling index (L.I.) and mitotic index (M.I.) on 24 hrs. after treatments. Effect of MMC (0.5, 1 and 2 mg/kg) and irradiation (500, 1000 and 2000 rads/mouse) revealed exponential linear dose response curves against T/C ratio which was significantly correlated with L.I. In combination therapy, the synergistic action was observed when 500 rads/mouse and 1 mg/kg were combined, and the effect was found to be more excellent when the radiation was performed 24 hrs. before MMC administration than the reversed sequence. By MMC and radiation, 2n and 3n cells increased with decrease of 4n cells. Whereas no change of M.I. was observed, L.I. was depressed. Increased 3n cells with depressed L.I. was supposed to be caused by S phase prolongation. As this change was more remarkable by radiation, the combination therapy was thought to be more effective when the radiation was performed before MMC administration. This nude mice-human tumor system was thought to be useful to analyze the combination chemoradiotherapy.