Overall: Project Summary/Abstract Melanoma is the deadliest form of skin cancer, with an increasing incidence and mortality, and a 5-year survival rate less than 20% for patients with metastatic disease. Several recent landmark genomic and immunologic studies have generated important new insights into the pathogenesis, drivers, and regulators of this disease, translating into the approval of both targeted and immune therapies for patients with metastatic disease. While targeted therapies have achieved high response rates, they are generally transient; likewise, immunotherapies bring about dramatic, long-term, complete responses but only in a subset of patients and often with serious toxicities. Despite the progress that has been made, several key challenges remain to maximizing the clinical benefit of immunotherapy: 1) poorly understood markers and mechanisms of resistance to immunotherapy, and a lack of effective strategies to overcome them; 2) limited experience or efficacy in patients with central nervous system involvement, a common metastatic site and cause of death for melanoma and other cancers; and 3) lack of any benefit from single-agent immunotherapies in patients with non-cutaneous melanomas, particularly the uveal melanoma subtype. The central hypothesis of this SPORE proposal is that an integrated analysis of immune and molecular features in patients with advanced melanoma will improve our understanding of response and resistance to immunotherapy, and lead to more effective treatments. To test this hypothesis, we will focus on the most critical unmet needs of melanoma patients, building on current immunotherapeutic strategies and developing our own novel concepts to identify more effective treatment options by pursuing the following specific aims: • Address resistance to the PD-1 immune checkpoint inhibitor through inhibition of the PI3K pathway in PTEN- null metastatic melanoma patients (Project 1). • Determine the clinical utility of PD-1 blockade using nivolumab administered intrathecally in metastatic melanoma patients with leptomeningeal disease (Project 2). • Evaluate a new therapeutic strategy for uveal melanoma that uses adoptive cell therapy to target an immunogenic epitope of melanosomal transport protein SLC45A2 (Project 3). Three cores (Administrative Core, Clinical Database, Tissue Resource, and Translational Pathology Core [Core 2] and Biostatistics and Bioinformatics Core [Core 3]) provide specialized services to support our SPORE investigators and their proposed research studies. Together, these three projects and cores and our Developmental Research and Career Enhancement Programs will provide a comprehensive attack on critical unmet needs for patients battling these deadly manifestations of melanoma, and pave the way for other cancers with limited therapeutic options.