Single-arm, multi-centre phase II study The primary objective is to evaluate the time to failure of the strategy.

The purpose of the OPTIPRIME phase II non-randomised study is to evaluate the efficacy and tolerability of the combination of FOLFOX plus panitumumab according to a "stop and go" strategy. If disease control is achieved while on induction treatment, oxaliplatin and panitumumab will be stopped after the sixth cycle; a maintenance treatment of fluoropyrimidine alone will be continued. In case of progression during maintenance treatment, oxaliplatin and panitumumab reintroduction loops will take place according to the same regimen (maintenance treatment after six cycles of the reintroduced therapy if disease control is achieved).

Inclusion Criteria:

• - Histologically proven colorectal adenocarcinoma without RAS mutation
• Confirmed, non-resectable metastatic disease (Stage IV)
• No prior chemotherapy except perioperative or adjuvant chemotherapy discontinued for more than 12 months
• At least one measurable metastasis according to the RECIST v1.1 criteria
• Age ≥ 18 years
• WHO ≤ 2
• Neutrophils > 1500 /mm3, platelets> 100 000/mm3, Hb > 9 g/dL
• Creatinine clearance > 50 mL/min according to the MDRD formula
• Serum bilirubin < 25 µmol/L, AST, ALT, Alk Phos < 2.5 x ULN or < 5 x ULN in case of liver metastases
• PT > 60%, albumin ≥ 25g/L
• Estimated life expectancy ≥ 3 months
• Patient affiliated to a social security scheme
• Patient informed and informed consent form signed

Exclusion Criteria:

• - Presence of uncontrolled symptomatic brain metastases
• RAS mutation (KRAS or NRAS mutation)
• Patient taking warfarin. If treated with anticoagulant at the indicated effective dose, this must be replaced with low molecular weight heparin before inclusion
• Known DPD deficiency
• Peripheral neuropathy > 1 (NCI CTCAE v4.0)
• Patient with interstitial pneumonitis or pulmonary fibrosis
• History of chronic diarrhoea or inflammatory disease of the colon or rectum, or obstruction or sub-obstruction during symptomatic treatment
• Poorly controlled chronic skin disease
• Any known specific contraindication or allergy to the medicinal products used in the study
• Patient simultaneously included in another clinical trial involving an investigational drug (example: chemotherapy, targeted therapy, immunotherapy)
• Arterial hypertension not controlled by medical treatment (Systolic BP ≥ 160 mmHg end/or diastolic BP ≥ 90 mmHg)
• Any progressive pathology not stabilised over the past 6 months: hepatic failure, renal failure, respiratory failure
• The following conditions in the 6 months prior to inclusion: myocardial infarction, severe/unstable angina, coronary artery bypass surgery, congestive heart failure NYHA class II, III or IV, stroke or transient ischaemic attack
• Patient who has received a transplant, is seropositive for HIV, hepatitis B or hepatitis C or has other immunodeficiency syndromes
• History of malignant pathologies during the past 5 years except basal cell carcinoma of the skin or cervical carcinoma in situ, properly treated
• QT/QTc interval > 450 msec for men and > 470 msec for women
• K+ < LNL, Mg2+ < LNL, Ca2+ < LNL
• Lack of effective contraception in patients (men and/or women) of childbearing age, pregnant or breastfeeding women, women of childbearing age who have not had a pregnancy test
• Persons in custody or under wardship
• Impossibility of undergoing medical monitoring during the trial for geographical, social or psychological reasons