<p><b>OBJECTIVE</b>To evaluate the efficacy and safety of subcutaneous injection of recombinant human interleukin-2 (Proleukin) in the treatment of metastatic renal cell carcinoma (RCC).</p><p><b>METHODS</b>Forty-one patients with pathologically confirmed metastatic RCC after radical nephrectomy were enrolled into this study. Two or four consecutive cycles of subcutaneous injection of rhLL-2 were given, with each cycle duration of five weeks consisting of 4 weeks of treatment and one week of rest. The rhLL-2 was injected twice daily subcutaneously at a dose of 9 MIU on D1-D5 during week one, then 9 MIU twice daily on D1-D2 and followed by 9 MIU daily on D3-D5 during week 2-4. Patients were evaluated after the second cycle of treatment. If an objective response or stable disease was observed, the patient would receive another two cycles of treeatment.</p><p><b>RESULTS</b>Of the 41 patients, the overall objective response rate was 17.1% (95% confidence interval, 5.6% to 28.6%) with a complete response (CR) rate of 0.0% and partial response rate (PR) of 17.1%. However, nineteen patients (46.3%) still had a stable disease (SD), and 15 (36.6%) had progressed disease (PD). The disease control rate was 63.4% and the median time to progression (mTTP) was 6 months. The 1-year survival rate was 71.2% with a median overall survival (mOS) rate of 22.5 months. Among 36 PP population, the overall objective response rate was 19.4% (95% confidence interval, 6.5% to 32.3%) with CR rate of 0.0% and PR rate of 19.4%. Sixteen patients(44.4%) had stable disease, and 13 (36.1%) progressed disease. The disease control rate was 63.9%. The 1-year survival rate was 66.7% with a median time to progression of 6 months. The median overall survival (mOS) had not reached yet. The follow-up data showed that the long term survival of the patient who responsed to the IL-2 therapy can be prolonged. Severe toxicity (> or = grade III) was rarely observed. Grade I or II toxicities such as fatigue (100.0%) and fever (82.9%) were frequently observed but reversible.</p><p><b>CONCLUSION</b>Subcutaneous injection of recombinant human interleukin-2 may prolong the survival of patients with a metastatic renal cell carcinoma. This regimen is tolerable with rare severe toxicities.</p>