Primary endpoint will be to evaluate the efficacy, in terms of overall response rate, of the addition of panitumumab rechallenge to standard third-line irinotecan-based or oxaliplatin-based chemotherapy in patients with metastatic colorectal cancer 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 agents.