Aim of the present study is to investigate whether baseline or early post-treatment (one month after treatment commencement) frequency of peripheral T regulatory lymphocytes (Tregs OR CD4+/CD25high/FOXP3+ T cells), known to suppress antitumor immune response, may influence long-term clinical outcome (i.e. radiological response, progression-free survival or overall survival) in metastatic colorectal cancer patients treated with a standard first-line chemotherapy including fluorouracil, irinotecan and bevacizumab