Non-small cell lung cancer (NSCLC) is associated with IL-2-dependent cell-mediated immunodeficiency. As IL-2 is the main lymphocyte growth factor, a phase III randomized multicenter trial was conducted to evaluate the impact of subcutaneous low-dose IL-2 added to standard chemotherapy (CT) on overall survival (OS) in advanced NSCLC patients. Patients (n=241) with histologically confirmed stage IIIb or IV non-operable NSCLC underwent stratified randomization on the basis of center, ECOG PS, stage of disease and percentage of weight loss. Patients received gemcitabine (1000 mg/m2) on days 1 and 8 + cisplatin (100 mg/m2) on day 2 every 21 days for a maximum of 6 cycles [chemotherapy (CT) arm]. In the CT+IL-2 arm, patients also received low-dose subcutaneous IL-2 3,000,000 IU/die on days 3-5, 9-11, 15-17. The study had 90% power to detect a 20% absolute increase in 1-year OS with 118 patients/arm. An overall response (OR) rate of 12.8% (14% in the CT+IL-2 arm and 11.4% in CT arm) was observed. Stable disease was 70 and 66.7%, and progressive disease 16 and 21.8% in the CT+IL-2 and CT arms, respectively. No differences in response were found in any subgroup analysis. At a median follow-up of 32 months, 1-year OS was 45% for the CT+IL-2 arm vs. 51% for the CT arm (p=0.456 log-rank). Median progression-free survival was 6.6 months in the CT+IL-2 arm vs. 6.9 months in the CT arm (p=0.573, log-rank). A higher number of grade 4 toxicities were reported with CT+IL-2. The most common grade ≥3 adverse events were gastrointestinal toxicity (mainly nausea and diarrhea) and myelosuppression. No relevant differences in clinical outcome were observed from the addition of IL-2 to CT. Future studies investigating the role of T-regulators in chemoimmunotherapeutic regimens could be performed.