4603 Background: Patients with metastatic renal cell carcinoma have a poor prognosis, including those with pulmonary metastases (PMRCC). The objective of this study was to obtain efficacy and safety data on inhaled rIL-2 used in clinical practice in PMRCC patients. Methods: Data provided from 107 PMRCC patients from 48 centres in Spain and 6 in Portugal, treated with inhaled rIL-2 between 2000 and 2005 were evaluated. Data were analyzed by ITT, considering a valuable patient when receiving the first dose of inhaled rIL-2. The treatment schedule was: 3 cycles of 36 MIU rIL-2 per day for 5 days/week for 12 weeks (with one week treatment free between cycles) in Spain and for 3 weeks (out of each 4 weeks) for 12 weeks in Portugal. Efficacy was assessed by best response following each treatment cycle and overall (WHO criteria). The Kaplan-Meier method was used to estimate progression free survival (PFS) and overall survival (OS) that were measured from the time of administration of the first dose of inhaled rIL-2 until progression or death. Safety data were analysed using descriptive statistics, with toxicities expressed as number of weeks in which each toxicity was reported by cycle and by grade. Results: After 1902 treatment weeks administered (median 17.8), the overall objective response rate (complete and partial response,) was 12.2% (95% CI: 6.0–18.4) and a stable disease rate of 22.45% (95% CI: 14.5–30.3). Median PFS and OS were 3.72 (95% CI: 2.86–4.57) and 18.5 (12.69– 23.61) months, respectively. Non-haematological toxicities were the most notable adverse events observed, especially in terms of cough (20.4% of weeks) and fatigue (4.4%) being grade 1 or 2 in severity and reversible by removing the treatment in all cases. Conclusions: This study provides data of efficacy and mild toxicity of inhaled rIL-2. On the basis of these findings inhaled rIL-2 might be considered as an alternative to its systemic administration to treat patients with PMRCC. No significant financial relationships to disclose.