Purpose: To determine the effectiveness of fluorouracil plus levamisole administered postoperatively to patients with resected stage II (Dukes' B2) colon cancer.

Patients and methods: This randomized controlled clinical trial (INT-0035) was performed by National Cancer Institute-sponsored cancer clinical trials cooperative groups. Patients were assigned to observation only or to fluorouracil (450 mg/m2 intravenously [IV] daily for 5 days and, beginning at 28 days, weekly for 48 weeks) plus levamisole (50 mg orally three times daily for 3 days repeated every 2 weeks for 1 year). Cancer recurrence, survival, and treatment side effects were assessed.

Results: Three hundred eighteen eligible patients were analyzed with a median follow-up time of 7 years. Fluorouracil plus levamisole reduced the recurrence rate by 31%, although this trend was not statistically significant (P = .10). A total of 87 patients died: 43 on observation and 44 on fluorouracil plus levamisole. Disparity between effects on recurrence rate and overall survival is partially explained by a higher rate of non-colon cancer-related deaths on fluorouracil plus levamisole (15 v seven) and by the effects of salvage surgery with curative intent. Of seven patients with recurrence who were rendered disease-free by salvage surgery, six were on the observation arm. As was observed in patients treated with fluorouracil plus levamisole for stage III disease, toxicity was acceptable and compliance was excellent.

Conclusion: Fluorouracil plus levamisole is tolerable and accepted as standard surgical adjuvant therapy for patients with stage III colon cancer, but the data from this study in stage II patients suggest a decreased relapse rate without a significant improvement in survival.