[Circulating tumor cells: a new efficacy marker in the treatment of metastatic colorectal cancer].

Colorectal cancer metastasis is the result of several interacting processes at the end of which cancer cells survive in distant organs. Penetration of primary tumor cells into blood is central to the whole phenomenon of metastasis and is a common step in all cancer types. The detection of circulating tumor cells (CTC) in peripheral blood of patients with colorectal cancer could have clinical usefulness in three aspects: 1) as evidence of early dissemination, and then as a risk factor of clinical recurrence, 2) as a relevant risk factor for metastatic progression and worse prognosis, and 3) as predictive marker of response to treatment.