Panitumumab Monotherapy Compared with Cetuximab and Irinotecan Combination Therapy in Patients with Previously Treated KRAS Wild-Type Metastatic Colorectal Cancer

Background: The survival benefit for single-agent anti–epidermal growth factor receptor (EGFR) therapy compared with combination therapy with irinotecan in KRAS wildtype (wt) metastatic colorectal cancer (mCRC) patients in the third-line treatment setting is not known. The objective of the present study was to describe the characteristics of, and to compare survival outcomes in, two cohorts of patients treated with either singleagent panitumumab or combination therapy with cetuximab and irinotecan. Methods: The study enrolled patients with KRAS wt mCRC previously treated with both irinotecan and oxaliplatin who had received either panitumumab or combination cetuximab–irinotecan before April 1, 2011, at the BC Cancer Agency (BCCA). Patients were excluded if they had received anti-EGFR agents in earlier lines of therapy. Data were prospectively collected, except for performance status (PS), which was determined by chart review. Information about systemic therapy was extracted from the BCCA Pharmacy Database. Results: Of 178 eligible patients, 141 received panitumumab, and 37 received cetuximab–irinotecan. Compared with patients treated with cetuximab–irinotecan, panitumumab-treated patients were significantly older and more likely to have an Eastern Cooperative Oncology Group (ECOG) PS of 2 or 3 (27.7% vs. 2.7%, p = 0.001). Other baseline prognostic variables and prior and subsequent therapies were similar. Median overall survival was 7.7 months for the panitumumab group and 8.3 months for the cetuximab–irinotecan group. Multivariate analysis demonstrated that survival outcomes were similar regardless of the therapy selected (hazard ratio: 1.28; p = 0.34). An ECOG PS of 2 or 3 compared with 0 or 1 was the only significant prognostic factor in this treatment setting (hazard ratio: 3.37; p < 0.01). Conclusions: Single-agent panitumumab and cetuximab–irinotecan are both reasonable third-line treatment options, with similar outcomes, for patients with chemoresistant mCRC.