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.