Purpose: The clinical benefit of combination treatment with panitumumab and bevacizumab (PB) based on bevacizumab beyond progression (BBP) after the failure of second-line chemotherapy remains unclear. We assessed the tolerability and efficacy of PB as BBP in Japanese patients with metastatic colorectal cancer (mCRC).
Methods: This phase I study comprised two parts: (1) PB part to estimate the recommended PB dose, (2) CPB part to investigate the safety of PB with irinotecan (CPB). Three panitumumab doses (4, 5, and 6 mg/kg at Levels -1, 0 and 1, respectively) were set for the PB part, starting with Level 0. Bevacizumab was administered at a fixed dose of 5 mg/kg, regardless of panitumumab dose levels. All drugs were administered on day 1 and repeated every 2 weeks.
Results: No dose-limiting toxicities were observed at Levels 0 (n = 3) and 1 (n = 3) for the PB part, determining the recommended dose as Level 1. During the whole treatment course at Level 1, grade 3 acneiform rash was observed in two patients with a partial response. For six patients (irinotecan biweekly, 150 mg/m(2) n = 3, 120 mg/m(2) n = 3) enrolled in the CPB part, grade 3 toxicities were leukopenia/neutropenia (n = 1), mucositis (n = 1), diarrhea (n = 1), rash acneiform (n = 1) and thromboembolic event (n = 1), and two of six patients achieved partial responses.
Conclusion: Recommended doses for the PB regimen in mCRC were panitumumab 6 mg/kg and bevacizumab 5 mg/kg. PB and CPB showed manageable toxicities in KRAS wild-type patients previously managed with standard treatment, including bevacizumab.
Keywords: Bevacizumab; Bevacizumab beyond progression; Colorectal cancer; KRAS; Panitumumab.