Background: Levamisole combined with 5-fluorouracil (5-FU) was previously shown to significantly reduce tumor relapses and improve patient survival when given postoperatively in patients with resected stage III colon cancer. Laboratory investigations subsequently documented a direct dose-dependent enhancement of 5-FU cytotoxicity with increasing concentrations of levamisole against human cancer cell lines. A clinical trial was designed to test the value of levamisole given at its maximum tolerated dose in combination with 5-FU-based chemotherapy.
Patients and methods: Eight hundred seventy-eight patients who had undergone complete surgical resection of high-risk stage II/III colon cancer were stratified by known prognostic factors and randomized to receive 1 of 2 treatment regimens: standard-dose levamisole combined with 5-FU and leucovorin; or high-dose levamisole combined with the same chemotherapy. Serum neopterin was monitored in a cohort of patients to evaluate immune function.
Results: Severe vomiting and neurologic side effects required reduction in the dose of levamisole that could be safely administered on the high-dose levamisole regimen. There were no significant differences in disease-free survival, overall survival, or levels of serum neopterin between the treatment regimens.
Conclusion: It was not possible to improve the efficacy of surgical adjuvant chemotherapy for patients with high-risk colon cancer by giving levamisole at its maximum tolerated dose in combination with 5-FU and leucovorin. High rates of severe gastrointestinal and neurologic side effects were observed with the high-dose levamisole regimen.