Studies on the effect of cyclophosphamide on Yoshida sarcoma ascites cells implanted into the colon wall of rats

Yoshida ascites cells in doses of 10(3)X300, 500, 1500, and 3000 cells per animal were injected into the wall of the descending colon of 10 male Sprague-Dawley rats each. Doses of 10(3)X1500 cells and more per animal yielded a 100% rate of take-up of the graft. Whereas untreated control animals died medianly after 17 days, a single i.p. application of 70 mg/kg cyclophosphamide on days 8 or 10, respectively, after the tumor cell inoculation considerably prolonged the survival times. In both cases the median survival time amounted to more than 60 days. The application of the cytostatic drug 12 days after tumor cell implantation yielded only a slight increase in the median survival time (23 days). The introduction of this tumor model for screening new chemotherapeutics or combinations of chemotherapeutics to be used against colon tumors is discussed.