Objective: Combined chemotherapy with S-1 and irinotecan (IRIS) for metastatic colorectal cancer has been reported to be effective and safe. However, there are only a few studies on the effects of adding bevacizumab to IRIS. We conducted a clinical study to evaluate the efficacy and safety of IRIS plus bevacizumab as first-line therapy for metastatic colorectal cancer. Methods: Forty metastatic colorectal cancer patients were enrolled in this phase II study. All patients received irinotecan (80 mg/m²) and bevacizumab (7 mg/kg) on days 1 and 15 and S-1 (40-60 mg twice daily) on days 1-21 of a 5-week repeated cycle. Results: The response rate was 47.4% [95% confidence interval (CI) 31.5-63.2], progression-free survival was 11.9 months (95% CI 9.4-16.8), and overall survival was 23.4 months (95% CI 19.0-inf). The only grade 3 hematological toxicity was neutropenia (16%) and the incidences of grade 3 nonhematological toxicity were low at <10%, other than diarrhea (10.9%). Conclusion: In this clinical study, we revealed IRIS plus bevacizumab to be a promising first-line regimen for metastatic colorectal cancer with a low incidence of serious toxicities, in which favorable response rates and extension of survival time can be expected.

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