Determination of the optimal dose of 5-fluorouracil when combined with low dose D,L-leucovorin and irradiation in rectal cancer: results of three consecutive phase II studies. EORTC Radiotherapy Group.

In three consecutive phase II trials, 5-fluorouracil (5FU)-low dose leucovorin (20 mg/m2/day) was delivered in two 5-day courses during the first (d1 to d5) and the last (d29 to d33) week of a limited pelvic irradiation (45 Gy, 5 weeks, 25 fractions) in patients with locally extended rectal cancer. The three trials differed only by the 5FU dose in the chemotherapy (CT) schemes. In trial 1 (first CT course 5FU dose 425 mg/m2/day, second CT course 370 mg/m2/day), 16 patients were included. 5 patients suffered a grade 3+ toxicity and the compliance was 63%. In trial 2 (first and second CT course 5FU dose 370 mg/m2/day), 53 patients were included. 5 patients suffered a grade 3+ toxicity. The compliance was 94%. In the trial 3 (first and second CT course 5FU dose 350 mg/m2/day), 16 patients were included. 1 patient suffered a grade 3 toxicity and the compliance was 100%. The overall response rate (complete and partial responses) of local disease and distant metastasis were 87 and 7%, respectively. 43 patients were operated on after a mean delay of 8 weeks. Among the 41 macroscopic complete resections, 6 (14.6%) were sterilised and 12 (29.3%) were classified Asler-Coller A/B1. Regression curve analysis using either grade 3+ toxicity or incomplete treatment as an end point against the 5FU dose indicates that a 350 mg/m2/day 5FU dose is advisable for a phase III adjuvant multicentre trial.