7525 Background: CTLA-4 is a negative regulator of cytotoxic T cell responses and may contribute to tumor escape from immune surveillance. MDX-010 is an IgG1κ fully human monoclonal antibody that blocks CTLA-4 function and is being studied in patients with metastatic melanoma and other malignancies. The current Phase II study was conducted to determine the safety and efficacy of MDX-010 when given alone or in combination with dacarbazine in chemotherapy and vaccine naive patients with unresectable metastatic melanoma. Dacarbazine is an FDA approved agent for metastatic melanoma with an approximate 10% objective response rate (ORR) but no demonstrable survival benefit. Long-term follow-up data on response duration and median progression-free survival for this Phase II study is now reported. Methods: Patients were randomized to receive MDX-010 at 3 mg/kg monthly x 4 (arm A; n=37) or MDX-010 in combination with dacarbazine 250 mg/m2 for 5 days monthly x 4 (arm B; n=35). Clinical response was measured by RECI...