Project Summary/Abstract Cancer is a highly heterogenous disease, composed of and characterized by a diverse set of genetic phenotypes driven by complex dynamic cellular interactions within spatially distinct organized microenvironments. The ability to accurately delineate this intra tumor heterogeneity and its contribution to metastasis, therapeutic resistance and ultimately the impact of clinical outcomes, remains a challenge. In addition, the molecular mechanisms underpinning the cross-talk between tumor and its microenvironment are largely lacking. This prostate cancer Program Project sets out to investigate the tumor cell intrinsic as well as stromal and immune microenvironmental factors in tumor progression using single cell sequencing technologies. Additionally, the Program will incorporate a multi-disciplinary and integratory approach that aims to integrate single-cell RNA-sequencing and systems analyses of genetically engineered mouse and organoid models, with complementary analyses of human tissue samples in naïve, castration-resistant and neuroendocrine tumors, both local and metastatic. The Pathobiology Core (Core A) will support the projects by providing expert histopathologic analysis of murine and human tumors, validating antibodies and probes for use in mouse and human tissue, comparing and contrasting multiple signals in epithelium and microenvironment in mouse models and patient samples. Innovative approaches including organotypic cultures and recombination experiments will be utilized as functional assays. Finally, refining strategies in computational methods to compare single cell analyses in human and mouse as well as developing novel approaches to improve and automate in situ expression modalities will represent the innovation arm of this core.