An open, non-randomized phase II study was carried out including patients with advanced solid tumors who achieved an objective response or disease stabilization as a result of previous chemotherapy, to receive a maintenance treatment with recombinant interleukin-2 (rIL-2) plus medroxyprogesterone acetate (MPA) plus antioxidant agents alpha-lipoic acid (ALA) and N-acetyl cysteine (NAC). The first study endpoints were to define clinical outcome and toxicity as well as the evaluation of quality of life. As secondary endpoints we measured the changes of lymphocyte absolute count, the serum levels of proinflammatory cytokines, IL-2, C-reactive protein (CRP) and leptin after treatment. rIL-2 was administered at a dose of 1.8 MIU subcutaneously 3 times/week on alternate days for the first two weeks of every month and MPA was given orally at a dose of 500 mg/day at alternate days without interruption. ALA 300 mg/day orally and NAC 1800 mg/day orally were also administered continuously. Twenty-eight patients were enrolled in the study. The median duration of maintenance treatment was 10 months (6-30+). The response to maintenance treatment at September 15, 2001 was: CR 11 patients (39.3%); SD 2 patients (7.1%); PD 15 patients (53.6%). The median duration of response was 11 months (6-34+). The median follow-up duration was 11 months (6-34+). The median OS was not reached. The median PFS was 21.5 months (1-40+). The 1-year survival rate was 72.2%. At September 15, 2001, 16 patients were still surviving. No grade 3/4 toxicity and one grade 2 skin toxicity were observed. We found a significant increase of the absolute lymphocyte count and serum levels of IL-2 and a significant decrease of TNF alpha after treatment. The evaluation of patient subgroups showed the following: the patients alive at the end of study had a significant increase of lymphocyte count, IL-2 and leptin, and a significant decrease of IL-1 beta, IL-6 and TNF alpha, whereas the patients who had died had only a significant increase of lymphocyte count and IL-2. Among the patients alive, those in objective clinical response (CR + PR) + those in SD had a significant increase of lymphocyte count, IL-2 and leptin and a significant decrease of IL-1 beta, IL-6 and TNFalpha, whereas those with PD had no significant changes in any of the above values. We conclude that the combination of s.c. rIL-2 with oral MPA and anti-oxidant agents ALA and NAC in an intermittent schedule, repeated for a long-term period, is feasible, has a very low toxicity and results in the improvement of biological markers which are predictive for patient outcome.