An open-label, single-arm study assessing safety and efficacy of panitumumab in patients with metastatic colorectal cancer refractory to standard chemotherapy

Background: A phase 3 study demonstrated that panitumumab, a human monoclonal anti-epidermal growth factor receptor antibody, significantly prolonged progression-free survival versus best supportive care (BSC) in patients with chemorefractory metastatic colorectal cancer. Patients and methods: This open-label extension study evaluated panitumumab monotherapy in BSC patients with radiographically documented disease progression in the phase 3 study. Patients received panitumumab 6 mg/kg every 2 weeks. The primary end point was safety; efficacy was also evaluated. Results: One hundred and seventy-six patients were randomly assigned to the BSC arm of the phase 3 study received ≥1 panitumumab dose in this extension study. Panitumumab was well tolerated. The most frequent treatment-related adverse events were skin toxic effects. Three (2%) patients had a grade 4 treatment-related adverse event. There were no infusion reactions. One (0.6%) patient had a complete response; 19 (11%) patients had a partial response; and 58 (33%) patients had stable disease. Median progression-free survival time was 9.4 [95% confidence interval (CI): 8.0-13.4) weeks. Median overall survival time was 6.3 (95% CI: 5.1-6.8) months. Anti-panitumumab antibodies were detected in 3 (4.2%) of 71 patients with a post-baseline sample. Conclusions: These findings are comparable to those from the phase 3 study and support panitumumab monotherapy for chemorefractory colorectal cancer.