It is a prospective, randomized study in patients with metastatic colorectal carcinoma progressing after two lines of prior therapy. Patients will be randomized (1:1) to receive chemotherapy as determined by its oncologist or treatment according to chemosensitivity profile obtained. For obtaining the profile a histological tumor sample and a sample of venous blood in a tube with heparin standard are necessary . This latter sample will be processed to isolate circulating tumor cells by cell adhesion with matrix coated glass spheres. The RNA from these circulating tumor cells as well as from tumor cells of tumor biopsies from the same patients will be extracted by a standard procedure for extracting RNA for genetic expression analysis. Based on the analysis performed on tumor biopsy is generated a ranked list of potentially more effective treatments in every case