Phase II Study of S-1 and Irinotecan Plus Bevacizumab as Second-line Treatment for Patients With Metastatic Colorectal Cancer Resistant to the Fluoropyrimidine-oxaliplatin-cetuximab Regimen

Background/Aim: The usefulness of angiogenesis inhibitors as second-line treatment after the progression of anti-epidermal growth factor receptor antibody drug-containing regimens for RAS wild-type metastatic colorectal cancer (mCRC) has not been fully investigated. Therefore, we conducted a phase II study to verify the efficacy and safety of the combination of S-1 and irinotecan plus bevacizumab (SIRB regimen) as second-line treatment for patients with oxaliplatin and cetuximab-refractory KRAS wild-type mCRC. Patients and Methods: Patients with mCRC who had previously received oxaliplatin and cetuximab-containing regimen were eligible for this study. Patients were infused with bevacizumab 7.5 mg/kg and irinotecan 150 mg/m² intravenously on day 1, whereas S-1 80 mg/m² was administered orally twice daily until day 15, followed by a 7-day drug holiday period. The primary end point was 6-month progression-free survival (PFS) rate. Results: In total, 17 patients were enrolled in this study. The 6-month PFS rate was 64.7% [95% confidence interval (CI)=41.99-87.43], median PFS was 10.1 months (95%CI=4.11-17.28), and median overall survival was 21.8 months (95%CI=9.79-37.91). The response rate was 23.5% (95%CI=6.81-49.90%). Grade ≥3 adverse events were observed in 10% of patients, and included leukopenia [3 (17.6%)], neutropenia [5 (29.4%)], anorexia [2 (11.8%)], diarrhea [2 (11.8%)], and hypertension [3 (17.6%)]. No treatment-related deaths or febrile neutropenia were observed. Conclusion: The SIRB regimen might be a promising second-line treatment option for patients with oxaliplatin and cetuximab-refractory KRAS wild-type mCRC in terms of efficacy and safety.