Metastatic Colorectal Cancer (RAS-wildtype) After Response to First-line Treatment With FOLFIR Plus Cetuximab

Inclusion Criteria: * Histologically confirmed, UICC stage IV adenocarcinoma of the colon or rectum (metastatic colorectal cancer), primarily nonresectable or with surgery refused by the patient * RAS wild-type tumour status (KRAS and NRAS exon 2-4) (proven in the primary tumour or metastasis) at any timepoint of randomisation * Age ≥18 * ECOG performance status 0-1 * Patients suitable for chemotherapy administration * Patient's written declaration of consent obtained * Estimated life expectancy \> 3 months * Presence of at least one measurable reference lesion according to the RECIST 1.1 criteria (chest and abdominal CT 4 weeks or less before randomisation) * Primary tumour tissue available and patient consents to storage and molecular and genetic profiling of blood, plasma and tumour material (patients included directly at Part 2 of the study in whom primary tumour material is no longer available may be included in the study, provided that tumour material from the compulsory biopsy on progression following second-line treatment is available). * Effective contraceptive measures in men and in women of childbearing age (Pearl index \<1) * Adequate haematopoietic function: * Leukocytes ≥ 3.0 x 109/L with neutrophils ≥ 1.5 x 109/L * Thrombocytes ≥ 100 x 109/L, * Haemoglobin ≥ 5.6 mmol/L (equivalent to 9 g/dL) * Adequate hepatic function: * Serum bilirubin ≤ 1.5 x upper normal limit, * ALAT and ASAT ≤ 2.5 x upper normal limit (in the presence of hepatic metastases, ALAT and ASAT ≤ 5 x upper normal limit) * INR \< 1.5 and aPTT \< 1.5 x upper normal limit (patients without anticoagulation). Therapeutic anticoagulation is allowed if INR and aPTT have remained stable within the therapeutic range for at least 2 weeks. * Adequate renal function: * Serum creatinine ≤ 1.5 x upper normal limit or creatinine clearance (calculated according to Cockcroft and Gault) ≥ 50ml/min. * adequate cardiac function: ECG and echocardiogram with a LVEF of ≥55% * Any significant toxicities of previous treatments must have resolved or stabilised * Last administration of an anti-EGFR substance ≥ 4 months before randomisation 2 Inclusion criterion solely for Part 1: * No previous chemotherapy for metastatic disease * Time since last administration of a previous adjuvant chemotherapy \>6 months Additional inclusion criteria solely for Part 2: * Former first-line treatment of the metastatic colorectal cancer with FOLFIRI and cetuximab; data available for the duration of treatment and the response within the context of first-line treatment * Former second-line treatment of the colorectal cancer without FOLFIRI, irinotecan or an anti-EGFR substance with data available for the substances administered, duration of treatment and response within the context of the second-line treatment * Proof of a RAS wild-type tumour (KRAS and NRAS exons 2-4) in a tumour biopsy (metastasis) within 4 weeks before randomisation * CT examinations with evidence of a partial response (PR) or complete response (CR) or stable disease (SD) ≥6 months according to RECIST Version 1.1 criteria as best response within the context of the first-line treatment with FOLFIRI and cetuximab Exclusion Criteria: * Proof of a RAS mutation (KRAS or NRAS, exons 2-4 in the tumour (proven in the primary tumour or metastasis) or absence of testing for RAS mutation * Primarily resectable metastases and the patient wishes for resection * Grade III or IV heart failure (NYHA classification) * Myocardial infarction, unstable angina pectoris, balloon angioplasty (PTCA) with or without stenting within the past 12 months before inclusion in the study * Pregnancy (exclusion to be ascertained by a beta hCG test) or breast feeding * Medical or psychological impairments associated with restricted ability to give consent or not allowing conduct of the study * Additional cancer treatment (chemotherapy, radiation, immune therapy or hormone treatment) during the study treatment in first-line and third-line treatment (treatments that are conducted as part of an anthroposophic or homeopathic treatment approach, e.g. mistletoe therapy do not represent an exclusion criterion) * Previous chemotherapy for the colorectal cancer with the exception of adjuvant treatment, completed at least 6 months before entering the study (exclusion criterion solely for part 1) * Participation in a clinical study or experimental drug treatment within 30 days prior to inclusion or during participation in the study * Known hypersensitivity or allergic reaction to any of the following substances: 5-fluorouracil, cetuximab, oxaliplatin, irinotecan, bevacizumab and chemically related substances * Known or clinically suspected brain metastases * History of acute or subacute intestinal occlusion or chronic inflammatory bowel disease or chronic diarrhoea * Symptomatic peritoneal carcinosis * Severe, non-healing wounds, ulcers or bone fractures * Uncontrolled hypertension * Marked proteinuria (nephrotic syndrome) * Arterial thromboemboli or severe haemorrhage within 6 months prior to inclusion in the study (with the exception of tumour bleeding before tumour resection surgery) * Haemorrhagic diathesis or tendency towards thrombosis * Known DPD deficiency (specific screening not required) * Known glucuronidation deficiency (Gilbert's syndrome) (specific screening not required) * History of a second malignancy during the past 5 years before inclusion in the study or during participation in the study, with the exception of a dermal basal cell or squamous cell carcinoma or cervical carcinoma in situ, if these were treated curatively. * Known history of alcohol or drug abuse * A significant concomitant disease which, in the investigating physician's opinion, rules out the patient's participation in the study * Absent or restricted legal capacity