Prospective cohort study of patients treated with systemic chemotherapy for unresectable metastatic colorectal cancer. The chemotherapy monitoring is currently based on radiological evaluation (RECIST criteria) and clinical evaluation. Circulating markers as CEA, free mutant DNA, CTC represent an alternative approach. A previous study on usefulness of the serum Carcinoembryonic antigen (CEA) kinetic for chemotherapy monitoring in patients with unresectable metastasis of colorectal cancer has been published (J Clin Oncol 2008;26:3681-6). The present study is designed to validate the previous data. The secondary purpose is to evaluate variations of free mutant DNA and CTC during the chemotherapy. Patients will be included prospectively in 4 centers in Normandy. All systemic chemotherapy and biotherapy validate in this clinical situation by the French National Cancer Institute (INCa) is accepted. Evaluation of response based on RECIST criteria will be performed every 3 months. Blood samples for CEA and CA 19-9 levels will be performed every courses of chemotherapy during first 3 months. Blood samples for detection of free mutant DNA and CTC will be performed at day 1 and 42 of chemotherapy.