The clinical benefit of resection of the primary tumour in patients with synchronous unresectable metastases is not known. In the literature studies usually describe retrospective selected patients with synchronous metastases treated with or without resection of the primary tumour. All these studies are biased in patient selection and there are no prospective randomized studies on this topic. In patients with few or absent symptoms of the primary tumour, arguments both in favour and against initial resection have been presented, and therefore a randomized trial is warranted. Although recent publications suggest that resection of the primary tumour in synchronous metastasized colon cancer patients might not be necessary, this appears to be based on feasibility and not on clinical outcome. Several studies comparing large groups of patients with or without resection of the primary tumour suggest an improved survival when the primary tumour is resected. A potential benefit of resection of the primary tumour is to prevent complications of the primary tumour during chemotherapy treatment or during later stages of the disease. A recent analysis of the CAIRO and CAIRO2 data showed that metastatic colon cancer patients who had a resection of the primary tumour prior to study entry, had an improved survival compared to patients without a resection of the primary tumour. However, these patients were selected after the primary tumour was resected and therefore these results are not corrected for surgical morbidity and mortality. The investigators here propose a randomized trial in order to demonstrate that resection of the primary tumour does improve overall survival.

Inclusion Criteria:

• Histological proof of colorectal cancer
• Resectable primary tumour in situ with unresectable distant metastases
• No indication for neo-adjuvant (chemo)radiation
• No severe signs or symptoms related to the primary tumour (i.e. severe bleeding, obstruction, severe abdominal pain) that require immediate surgery or other symptomatic treatment (e.g. stenting)
• No prior systemic treatment for advanced disease
• Age ≥ 18 years
• WHO performance status 0-2
• Laboratory values obtained ≤ 4 weeks prior to randomization: Adequate bone marrow function (Hb ≥ 6.0 mmol/L, absolute neutrophil count ≥ 1.5 x 109/L, platelets ≥ 100 x 109/L), renal function (serum creatinine ≤ 1.5x ULN and creatinine clearance, Cockroft formula, ≥ 30 ml/min), liver function (serum bilirubin ≤ 2 x ULN, serum transaminases ≤ 3 x ULN without presence of liver metastases or ≤ 5x ULN with presence of liver metastases)
• Expected adequacy of follow-up
• Written informed consent
• CT scan abdomen and CT thorax/X-thorax performed ≤ 4 weeks prior to randomization

Exclusion Criteria:

• Pregnancy, lactation
• Unresectable primary tumour (i.e. neurovascular encasement, substantial ingrowth in pancreatic head), or any condition preventing the safety or feasibility of resection of the primary tumour, i.e. massive ascites or extensive peritoneal disease
• Requirement of neoadjuvant (chmo)radiation therapy
• Second primary malignancy within the past 5 years with the exception of adequately treated in situ carcinoma of any organ or basal cell carcinoma of the skin
• Any medical condition that prevents the safe administration of systemic treatment
• Previous intolerance of fluoropyrimidines, known dihydropyrimidine dehydrogenase (DPD) deficiency
• Planned radical resection of all metastatic disease
• Uncontrolled hypertension, i.e. values consistently > 150/100 mmHg
• Use of ≥ 3 antihypertensive drugs
• Significant cardiovascular disease < 1 yr before randomization (symptomatic congestive heart failure, myocardial infarction, unstable angina pectoris, serious uncontrolled cardiac arrhythmia, cerebro vascular event)
• Chronic active infection
• Concurrent treatment with any other anti-cancer therapy as described per protocol