Purpose: A number of clinical trials, including the FIRIS study, have shown that S-1 plus irinotecan (IRIS) is safe and effective in patients with colorectal cancer. Several different treatment protocols for IRIS are commonly used in Japan, besides the one used in the FIRIS study. This study was designed to evaluate the feasibility of a 5-week cycle of IRIS. Methods: Between January 2005 and February 2008, a total of 55 patients with metastatic colorectal cancer were enrolled at nine centers in Japan. All patients received irinotecan intravenously (80 mg/m2) on days 1 and 15 and S-1 orally (40-60 mg twice daily, according to body surface area) on days 1-21 of a 5-week repeated cycle. Results: The overall response rate was 29.1 %. The response rate was 43.8 % in patients who received IRIS as first-line therapy and 23.1 % in those who received IRIS as second-line or subsequent therapy. The median survival time was 678 days (22.6 months). Adverse events of Grade 3 or higher that occurred at an incidence of ≥10 % were neutropenia (12.7 %) and diarrhea (10.9 %). Conclusion: Our efficacy and safety data suggest that a 5-week cycle of IRIS is an effective alternative to used currently regimens.
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