Continuous 5-fluorouracil infusion and alpha interferon in advanced cancers: a report of initial treatment results. Twenty-four patients with advanced metastatic cancer were treated with continuous intravenous 5-fluorouracil infusion 200-300 mg/m2/day and alpha interferon 3 million units subcutaneously 3 times per week. The average duration of treatment was 87 days (range 22-204 days). 5-fluorouracil could be infused 66% of the planned time on treatment, and patients received an average of 60% of the planned interferon injections. Objective tumor responses were seen in 6 of 17 previously untreated patients (35%). Twenty-two of the 24 patients (92%) experienced toxicity (greater than or equal to ECOG grade II) that required treatment interruption and subsequent dose reduction predominantly for the following reasons: mucositis (67%), hand-foot syndrome (21%), and leukopenia (25%). The incidence of treatment limiting toxicity is higher than previously observed with 5-fluorouracil infusion alone. This suggests true augmentation of 5-fluorouracil effect by interferon. 5-Fluorouracil infusion and alpha interferon is a potentially useful combination that needs further evaluation in future phase II and phase III trials. 