OVERALL SUMMARY Conventional views of cancer as a predominantly genetic disease that proceeds in a step-wise, linear manner, have ceded to an understanding that tumor progression involves a multifaceted set of tumor cell-intrinsic and micro-environmental adaptations that co-evolve dynamically and non-linearly. However, much remains to be discovered about how different cell populations in the local environment drive metastatic behavior at different stages of tumor progression. Primary melanomas that are only millimeters thick can disseminate to lymph nodes and distant organs. This clinical feature suggests that egress of tumor cells from a primary site occurs early in melanoma development making melanoma an exceptional model to study these dynamic adaptations during the earliest stages of tumor progression. Our central hypothesis is that melanoma metastasis is driven by a combination of tumor cell–intrinsic features and interactions with micro-environmental compartments that govern early dissemination and immune evasion in the regional draining lymph nodes. To test this hypothesis, we propose three inter-related projects, supported by three cores that will collectively build an in- depth transcriptional and cellular map of critical compartments in the tumor microenvironment during early melanoma dissemination, in both mouse models and patient biospecimens. Successful completion of these projects will identify genes and transcriptional programs within those compartments that drive and maintain tumorigenic adaptations and ultimately metastatic dissemination. Our aims are to: 1. Map the cellular and molecular evolution of primary melanomas and their local and regional microenvironments to identify critical ‘switches’ that drive non-linear tumor progression; 2. Mechanistically dissect the emergence and functional relevance of transcriptionally defined cell state heterogeneity of malignant and non-malignant cell populations; 3. Identify novel therapeutic vulnerabilities to intercept early dissemination, mobilize systemic immune surveillance, and improve patient outcomes; and 4. Leverage the information gained to define new biomarkers of melanoma metastasis. We expect that knowledge generated through our approach may define new biomarkers of melanoma metastasis and therapeutic strategies to manage early disease. Our approach can serve as a roadmap to study early tumor progression at an unprecedented level of cellular, spatial and temporal resolution. It will provide a comprehensive picture of interactions both within the tumor microenvironment and tumor draining lymph nodes that influence tumor cell behavior and condition the host to be receptive to metastatic spread. We will leverage the complementary and synergistic expertise of our research team with an established record of productive collaboration, our novel genetically engineered mouse model that recapitulates early progression of human melanoma, and our access to high quality, clinically annotated patient samples from over 4,700 patients enrolled in a prospective clinicopathological database. The scope and scalability of the knowledge gained will serve other sites of the Metastasis Research Network.

OVERALL NARRATIVE The NYULH MetNet Center will leverage the complementary expertise of the NYU Melanoma program investigators to build an in-depth transcriptional and cellular characterization of tumor-microenvironment interactions that dictate early dissemination, using novel clinically relevant mouse models and well-annotated patient biospecimens.