Phase I/II study of a 3-week cycle of irinotecan and S-1 in patients with advanced colorectal cancer

The combination of an oral fluoropyrimidine derivative, S-1, and irinotecan is expected to be a promising regimen for advanced colorectal cancer. This study was performed to determine the maximum tolerated dose (MTD) and recommended dose (RD) of irinotecan combined with S-1 in a 3-week cycle regimen and to observe the safety and efficacy for patients with previously untreated advanced colorectal cancer. Eighty milligrams per m² of S-1 was given orally for 14 consecutive days and escalated doses of irinotecan were administered on days 1 and 8 every 3 weeks in the phase I trial. Forty patients were treated at the RD during the phase II trial. Forty-three patients were enrolled between February 2005 and March 2007. The dose-limiting toxicity was diarrhea and abdominal pain. The MTD of irinotecan was 100 mg/m² and the RD was determined to be 80 mg/m² of irinotecan combined with 80 mg/m² of S-1. The phase II trial showed that 22 of 40 patients achieved a complete or partial response and eight had stable disease. The overall response rate was 55.0%. The median progression-free survival time and median survival time were 6.7 and 21 months, respectively. There were no treatment-related deaths. The main toxicities were leukopenia, neutropenia, anorexia and diarrhea. This study suggests the combination of irinotecan and S-1 repeated every 3 weeks is tolerable and effective for patients with previously untreated advanced colorectal cancer. (Cancer Sci 2010; 101: 2591-2595)