The primary purpose of the study is to confirm the results of previous study about the usefulness of the serum Carcinoembryonic antigen (CEA) kinetic for chemotherapy monitoring in patients with unresectable metastasis of colorectal cancer (J Clin Oncol 2008;26:3681-6). The secondary purpose is to evaluate the value of circulating free mutant DNA and circulating tumor cells (CTC) and their variations during the treatment.