The role of the Organoid Core (Core E) is to generate a bank of state-of-the-art next-generation 3D in vitro organoid models of prostate cancer and provide them to the SPORE research projects for investigation. The study of castration-resistant prostate cancer (CRPC) has been limited by lack of in vitro models that represent the molecular and phenotypic diversity of the disease. We have developed optimized growth conditions for 3D prostate organoids from benign human and mouse prostate epithelial cells that can be engineered with defined genetic lesions using patient-derived CRPC biopsy specimens. The organoids maintain the histology and 3D architecture of the cancer tissue. We have generated 17 CRPC organoid lines over the past 2 years that harbor a number of genetic alterations not present in publicly available cell line models. Leveraging our program’s commitment to collect, annotate, and sequence biopsy specimens from >2000 patients with CRPC, we plan to establish 20 clinically and molecularly annotated CRPC organoid lines annually. We will collaborate with each research project to engineer and study CRPC organoids that harbor specific genetic alterations or molecular phenotypes, including those with mutations in the DNA repair pathway (RP-1), mutations in the PI3K pathway (RP-2), mutations in TP35, silencing of RB1, and/or altered lineage specification (RP-3), and overexpression of different glucocorticoid receptor isoforms (RP-4). Working with the Animal Models Core (Core D), we will generate murine prostate organoids from genetically engineered mouse models harboring the specific genetic alterations of interest for the research projects. We will work with each project to develop protocols for in vitro drug treatment, in vivo xenograft studies, and genetic engineering of the organoid lines such as RNAi-mediated knockdown and CRISPR (clustered regularly interspaced palindromic repeats)-mediated somatic knockout. We will also conduct independent research aimed at improving services, including further optimization of organoid acquisition and growth protocols, identification of clinical and molecular determinants of successful organoid growth, and development of protocols to engineer genetic lesions into benign human prostate organoids.