Combined effect of 5-fluorouracil and interferon on experimental liver metastases of rat colon carcinoma.

The combined effect of 5-Fluorouracil (5-Fu) and partially purified rat interferon (RIFN) was assessed on experimental liver metastases of a transplantable colon tumor in rats. Treatment was given for 8 weeks and started 1 week after inoculation into the portal vein of 5 X 10(5) tumor cells. Administration of 10(5) units RIFN/kg/day for 7 days, in alternate weeks, had no effect on the number or size of liver metastases as judged by laparotomy on days 30 and 50, whereas treatment with 5-Fu at a dose of 15 mg/kg once a week had a moderate but significant inhibitory influence. The combined administration of RIFN and 5-Fu led to earlier development of liver metastases than in the control group. There was no difference in survival time between the control group and the RIFN-treated group; all animals died within 20 weeks after tumor cell injection. However, three of eight animals in the 5-Fu group and, surprisingly, four of ten animals in the RIFN + 5-Fu group survived for more than 20 weeks and were found to be free of tumor when inspected after 175 days. The data indicate that 5-Fu, given either alone or combined with RIFN, is effective in about 40% of cases, and further suggest that RIFN has tumor-enhancing properties in those animals in which treatment with 5-Fu has no antitumor effect.