It is known since many years that the pineal hormone melatonin (MLT) may play anticancer activity through several mechanisms, including antiproliferative and immunostimulating effects. Moreover, it exerts an important antioxidant action. Therefore, MLT could be useful in the treatment of human neoplasms, either alone or in association with chemotherapy. The present study was performed to evaluate the influence of a concomitant MLT administration on efficacy and toxicity of several chemotherapeutic combinations in metastatic solid tumor patients, suffering from non-small cell lung cancer (NSCLC) or gastrointestinal tumors. The study included 370 patients who were randomized to receive chemotherapy alone or chemotherapy plus MLT (20 mg/day orally in the evening every day). NSCLC patients received cisplatin (CDDP) plus etoposide or CDDP plus gemcitabine. Colorectal cancer patients were treated with oxaliplatin plus 5-fluorouracil (5-FU), or weekly CPT-11 or 5-FU and folates (FA). Finally, gastric cancer patients received CDDP, epirubicin, 5-FU and FA or weekly 5-FU plus FA. The overall tumor regression rate achieved in patients concomitantly treated with MLT was significantly higher than that found in those treated with chemotherapy alone. Moreover, the 2-year survival rate was significantly higher in patients concomitantly treated with MLT. These results confirm in human the anticancer therapeutic properties of the pineal hormone MLT, which may enhance the efficacy of the standard anticancer chemotherapies. (c) 2007 Elsevier Masson SAS. All rights reserved.