3040 Background: Tremelimumab is an investigational anti-CTLA4 monoclonal antibody that prolongs T-cell activation and expansion. It has been shown to induce durable tumor responses in patients with melanoma and is undergoing evaluation as a cancer therapy. Methods: An analysis of safety data across 6 single-agent clinical studies at the intended dose (15 mg/kg Q3mo) was performed. Adverse events (AEs) were graded according to NCI-CTC criteria. Results: As of November 2007, 786 pts (91% with melanoma) had received ≥1 cycles of tremelimumab constituting 1,249 doses (range 1–7 doses/pt). 60% of pts were male, 93% were white, and 29% were >65 years of age. Seventy-nine percent of pts reported one or more treatment-related AEs; 70% of which were mild to moderate (CTC grade 1 or 2). 15.4% of pts had grade 3 and 2.8% had grade 4 treatment-related events. Treatment discontinuation due to AEs was 6%. Event frequency and severity was lower in cycle ≥2. The most common and clinically significant AE was diarrhea (36...