Niraparib Before Surgery in Treating Patients With High Risk Localized Prostate Cancer and DNA Damage Response Defects

Inclusion Criteria: * Ability to understand and willingness to sign an informed consent form * Ability to adhere to the study visit schedule and other protocol requirements * Patients must have histologically or cytologically confirmed prostate cancer that is clinically localized as defined by negative cross-section imaging and/or bone scan, and classified as high or very high risk per National Comprehensive Cancer Network (NCCN) guideline * Eastern Cooperative Oncology Group (ECOG) performance status (PS) score of 0 or 1 * Life expectancy \>= 10 years * Men who have selected radical prostatectomy as the primary treatment for their prostate cancer * Prostate cancer tumors with alterations in key DNA repair genes. This will include at least one alteration in a gene involved in DNA repair primarily through the homologous recombination pathway including BRCA1/2, ATM, CHEK1/2 FANCA, FANCD2, FANCL, GEN1, NBN, PALB2, RAD51, RAD51c, and BRIP1. Mutations will be selected that are known or likely pathogenic. Mean allele frequencies will be assessed to estimate mono versus biallelic loss of function. Patients with biallelic deletions or mutations will be prioritized for inclusion to make up at least 30% of the enrollment (i.e., 10 patients) to gauge response in this group over monoallelic loss. Final inclusion will be determined by the principal investigator * Must be able to swallow whole capsules * To avoid risk of drug exposure through the ejaculate, male subjects (even if they hav…