131 Background: Immune-related adverse events (IRAE) occur commonly with immune checkpoint inhibitor therapy for the treatment of cancer, although the specific event and severity can vary widely. Little is known regarding factors that may predict which patients will develop an IRAE. The goal of this study is to identify blood biomarkers predictive of IRAE associated with immune checkpoint inhibitor therapy. Methods: Blood samples collected from patients with melanoma prior to receiving therapy with immune checkpoint inhibitors were obtained from the University of Colorado Skin Cancer Biorepository. Testing for a panel of autoantibodies and cytokines (ANA, CCP 3.1, IL-1 beta, IL-2, IL-6, IL-10, IL-12, IP-10, MCP-1, TNF alpha, IFN alpha 2, IFN gamma) in serum samples from patients who had at least one documented IRAE was performed by Exsera BioLabs. Descriptive statistics were used to evaluate biomarker levels in relation to type, grade, and number of adverse events. Results: Pre-treatment samples from 45 patients were evaluated. Median age was 55; 26 were male and 19 were female. The most common IRAEs were colitis (n = 22), thyroid dysfunction (n = 21), and dermatitis (n = 20). Most IRAEs were grade 2 in severity, and the majority of patients (n = 36) experienced more than 1 IRAE. TNF alpha was elevated in 60% of patient samples, while IFN alpha 2 was elevated in 44%. Borderline ANA was detected in 27% of samples and ANA was positive in 11%. No samples had elevation of IL-2. Between 9% and 18% of samples had elevation of the other immune markers tested (IFN gamma, IL-1 beta, IL-6, IL-10, IL-12, and CCP 3.1). Elevation of TNF alpha and IFN alpha 2 were associated with higher grades of IRAEs. No associations between immune markers and the number or type of adverse events in an individual patient were noted. Results from 15 patients who did not have a documented IRAE on immune checkpoint inhibitor therapy are currently pending to confirm these findings are unique to patients developing IRAE. Conclusions: This preliminary data suggests that baseline elevations of TNF alpha and IFN alpha 2 may predict development of IRAEs with immune checkpoint inhibitor therapy. Results from samples from patients who did not develop an IRAE on therapy will be reported at the meeting.