Effect of treatment with interferon and cyclophosphamide on the growth of a spontaneous liposarcoma in rats.

A spontaneous non-immunogenic transplantable liposarcoma in BN rats was found to be sensitive to the antitumor effects of rat fibroblast interferon (RIF) when it was administered from the day of tumor implantation onwards. Treatment with RIF starting at 7 days after implantation was not effective. Tumor growth was markedly inhibited by cyclophosphamide (Cyclo). At the time and dose schedules used, Cyclo was more effective than RIF. When the growth of the tumor was inhibited by Cyclo, subsequent treatment with RIF did not lead to an additional retardation of tumor growth. Administration of RIF interfered with the beneficial effect of Cyclo when both agents were given concomitantly. RIF and Cyclo gave similar results to those obtained with RIF alone and these were inferior to those obtained with Cyclo alone.