Combination chemoimmunotherapy for metastatic colorectal cancer using 5-fluorouracil, leucovorin and interleukin-2

25 patients with metastatic colorectal cancer were entered into a phase II trial of combination chemoimmunotherapy using a sequential regimen of 5-fluorouracil (5-FU) and leucovorin and high-dose recombinant human interleukin-2 (rIL-2). Patients initially received three cycles of chemotherapy consisting of 500 mg/m2 of intravenous leucovorin followed by 375 mg/m2 of bolus 5-FU both given daily on days 1-5 of a 21 day cycle. Ten days after the last dose of chemotherapy in cycle 3, patients began high-dose rIL-2 at 720,000 IU/kg intravenously every 8 h to the maximum tolerated number of doses. After 7-10 days of recovery, this rIL-2 treatment was repeated to complete one full course of chemoimmunotherapy. There was no grade IV toxicity associated with 183 cycles of chemotherapy. Other than slight increases in the frequency of diarrhoea, stomatitis and hyperbilirubinaemia, rIL-2 toxicity was similar to that seen in patients given rIL-2 without chemotherapy. Of 23 evaluable patients, the overall response rate (partial + complete response) was 46% with 2 complete responses. Only 3 patients showed major tumour regression during the rIL-2 phase of therapy, but these 3 patients included both complete responders and the 3 most durable responses (15, 16 and 24 months). We conclude that sequential 5-FU/leucovorin and rIL-2 can be given safely without major increases in toxicity over either therapy alone, and although nearly all responses seen are largely attributable to chemotherapy, a contribution of immunotherapy to the minority of patients achieving complete or durable responses cannot be ruled out.