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

Inclusion Criteria: * Histologically confirmed metastatic adenocarcinoma of the colon or rectum with initially KRAS/RAS wild tumours. * Patients received at least 2 lines of chemotherapy including a fluoropyrimidine, irinotecan and oxaliplatin± bevacizumab. * First line chemotherapy regimen with a fluoropyrimidine and irinotecan or fluoropyrimidine and oxaliplatin in addition to an anti-EGFR agent (cetuximab/panitumumab). * No evidence of disease progression for at least 4 months from the start of 1st line therapy. * At least one measurable lesion ≥ 10 mm as assessed by CT-scan or MRI must be available and accessible for re-biopsy and RAS testing. * Repeated RAS testing before re-challenge therapy must be done. * Age ≥18 years. * ECOG Performance status (PS) 0-2. * The patient has adequate organ function, defined as : Absolute neutrophil count (ANC) ≥ 1.5 x 109/L, hemoglobin ≥ 9 g/dl, and platelets ≥ 100 x 109/L. Total bilirubin ≤ 1.5 times upper limit of normal value (ULN), serum alkaline phosphatase level \< 5 times ULN, Serum creatinine level \<1.5 mg/dl. * For female patients of childbearing potential, negative pregnancy test within 7 days before starting the study treatment. * Subject must provide informed consent prior to initiation of any study specific activities/procedures Exclusion Criteria: * Significant cardiovascular disease including unstable angina or myocardial infarction within 12 months before initiation of study treatment or a history of ventricular arrhythmia (treated or not). * History or evidence of central nervous system metastasis (CT-scan or MRI are not mandatory if no clinical symptoms). * Known allergy or hypersensitivity to panitumumab. * Patients with right-sided colon cancer originating from the ascending colon or hepatic flexure. * Patients with known MSI-high status. * Patients with known HER2-positive status. * Previous or concurrent malignancy except for basal or squamous cell skin cancer, in situ carcinoma of the cervix, low-risk prostate cancer according to d'Amico classification or other solid tumors treated curatively and without evidence of recurrence for at least 5 years prior to the study. * Active or uncontrolled clinically serious infection. * Known human immunodeficiency virus (HIV) infection or acquired immunodeficiency syndrome (AIDS)-related illness. * Other serious and uncontrolled non-malignant disease. * Pregnancy. * Breast feeding. * Treatment with any other investigational medicinal product within 28 days prior to study entry. * Concomitant administration of live, attenuated virus vaccine such as yellow fever vaccine.