Androgen Ablation Therapy With or Without Niraparib After Radiation Therapy for the Treatment of High-Risk Localized or Locally Advanced Prostate Cancer

PRIMARY OBJECTIVE: I. Determine the efficacy of addition of adjuvant niraparib to maximal androgen signaling ablation (AAP + ADT) versus maximal androgen signaling ablation alone (Apa + ADT) following definitive radiation therapy (XRT) for biomarker-selected men with poor histopathologic response to neoadjuvant androgen signaling ablative therapy. SECONDARY OBJECTIVES: I. Determine the safety and tolerability of adjuvant niraparib with androgen ablation versus androgen ablation alone following definitive XRT in the study population. II. Determine the impact of the addition of adjuvant niraparib to maximal androgen signaling ablation (AAP + ADT) versus maximal androgen signaling ablation alone (Apa + ADT) following definitive XRT for biomarker-selected men with good and poor histopathologic response to neoadjuvant androgen signaling ablative therapy on overall survival III. Determine the impact of the niraparib + AAP + ADT and Apa+ADT treatment on eugonadal (non-castrate levels of testosterone) progression free survival. IV. Determine the impact of favorable versus unfavorable histologic response on progression-free survival (PFS) in men who received maximal androgen signaling ablation prior to definitive radiation. CORRELATIVE OBJECTIVE: I. Collect and archive solid and liquid tumor samples, as well as normal blood samples for germline deoxyribonucleic acid (DNA), immune, and metabolic profiles from all study patients for later hypothesis generating associations. Assess the relationship of histopathologic score with circulating markers and clinical outcomes of progression free survival for biomarker discovery. OUTLINE: PART 1 NEOADJUVANT PHASE (CYCLES 1-3): Patients receive apalutamide orally (PO) once daily (QD) on days 1-28, and physician's choice ADT. Treatment repeats every 28 days for up to 3 cycles in the absence of disease progression or unacceptable toxicity. PART 2 RADIATION PHASE (CYCLES 4-6): Within 30 days of completing Part 1, patients undergo radiation therapy. Patients also receive apalutamide PO QD on days 1-28 and physician's choice ADT. Treatment repeats every 28 days for up to 3 cycles in the absence of disease progression or unacceptable toxicity. PART 3 ADJUVANT PHASE (CYCLES 7 AND BEYOND): Patients with favorable response after Part 2 continue Apa + ADT. Patients with unfavorable response after Part 2 are randomized to 1 of 2 groups. GROUP A: Patients receive apalutamide PO QD on days 1-28 and physician's choice ADT. Treatment repeats every 28 days for up to 12 cycles in the absence of disease progression or unacceptable toxicity. GROUP B: Patients receive abiraterone acetate PO QD, prednisone PO twice daily (BID), physician's choice ADT, and niraparib PO QD. Treatment repeats every 28 days for up to 12 cycles in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up within 14 days, at 30-90 days, and then every 3 months for 3 years.