Exploratory endpoints include to identify, in the context of translational research, tumour tissue and blood-based biomarkers with prognostic/predictive significance in patients with metastatic colorectal cancer treated with rechallenge panitumumab in combination with standard third-line irinotecan-based or oxaliplatin-based chemotherapy, who were initially treated with, and benefiting from, first line irinotecan-based or oxaliplatin-based chemotherapy combined with an anti-EGFR monoclonal antibody, followed by second line chemotherapy not containing anti-EGFR agent.