- To compare efficacy and tolerability of weekly irinotecan combined with 5-fluorouracil (5-FU) bolus and folinic acid (FA) regimen (IFL) versus biweekly irinotecan with infusional 5-FU and FA (FOLFIRI) in patients (pts) with advanced stage colorectal cancer. Treatments outcome of 86 pts (IFL - 38 pts, FOLFIRI - 48 pts) was evaluated. Chemotherapy regimens were as follows: IFL - intravenous (i.v.) infusion irinotecan 125 mg/m(2) over 90 min and 5-FU 500 mg/m(2) preceded by FA 20 mg/m(2) both given by i.v. bolus injection, all repeated on days 1, 8, 15 and 22 every 6 weeks; FOLFIRI - i.v. irinotecan 180 mg/ m(2) on days 1 and 15 with subsequent FA 200 mg/m(2) administered as a 2-hour infusion and i.v. bolus injection of 400 mg/m(2) 5-FU immediately followed by 22-hour i.v. infusion of 600 mg/m(2) 5-FU on days 1, 2, 15 and 16 every 4 weeks. Treatment continued until disease progression or unacceptable toxicity. A total of 152 (mean - 4) IFL cycles and 328 (mean - 6) FOLFIRI cycles were administered. Average dose intensity was 0.8 and 0.78 respectively. Toxicities were mild and manageable for both regimens evaluated. Overall response rate was 36.8% in IFL arm and 44.7% in FOLFIRI arm. At the median follow-up of 16 months in IFL arm and 14 months in FOPFIRI arm the two year survival was 38% and 45%, the median survival was 18 months and 21.5 months, and the median progression free survival was 6 months and 9.4 months respectively. In our experience, both IFL and FOLFIRI regimens have acceptable toxicity at a similar level of dose intensity. Compared to IFL, FOLFIRI seems to improve progression-free survival.