Re-challenge Therapy With Chemotherapy & Panitumumab in Metastatic Colorectal Cancer Patients Treated With an Anti-EGFR

This is a single arm pilot multicenter prospective study. We will recruit KRAS/RAS wild metastatic colorectal cancer patients who received at least 2 lines of chemotherapy and the 1st line must include cetuximab/panitumumab combined with chemotherapy. We will repeat RAS testing after progression on the last line of therapy. RAS testing will be taken via liquid biopsy using ctDNA or tissue biopsy from either a new tumour lesion or a previously present lesion which shows evidence of disease progression by radiological imaging. Only RAS-wild patients upon re-testing will be enrolled and will receive re-challenge therapy with panitumumab combined with chemotherapy similar to that given at 1st line (5-fluorouracil/leucoverin combined with oxaliplatin or irinotecan). Those converted to RAS mutant will not be enrolled. All patients will be treated until disease progression, unacceptable toxic effects or withdrawal of consent.