Antiandrogen Therapy and SBRT in Treating Patients With Recurrent, Metastatic Prostate Cancer

PRIMARY OBJECTIVES: I. To assess the efficacy of combined systemic and tumor directed therapy for recurrent oligometastatic M1a,b prostate cancer patients with 1-5 metastases (exclusive of pelvic nodal N1 metastases) staged by prostate-specific membrane antigen (PSMA) positron emission tomography (PET)-computed tomography (CT). SECONDARY OBJECTIVES: I. Time to biochemical progression. II. Time to additional antineoplastic therapy. III. Prostate cancer specific survival. IV. Safety and tolerability. V. Assessment of health related quality of life using the Functional Assessment of Cancer Therapy - Prostate (FACT-P) scale. CORRELATIVE OBJECTIVES: I. To determine genomic and transcriptomic features present in metastatic tumors in patients that respond to this multimodal therapy. II. To evaluate biomarkers of response using circulating tumor cells (CTCs). III. To evaluate biomarkers of response using circulating tumor deoxyribonucleic acid (DNA) (ctDNA). IV. To evaluate immunophenotypes of circulating immune cells. OUTLINE: Patients receive a single dose of leuprolide subcutaneously (SC) on day 1 and apalutamide orally (PO) once daily (QD) and abiraterone acetate PO QD for up to 6 months in the absence of disease progression or unacceptable toxicity. Beginning 2 months of initiation of antiandrogen therapy (ADT), patients also receive SBRT over 1, 3, or 5 fractions in the absence of disease progression or unacceptable toxicity. After completion of study treatment, patients are followed up within 2 -4 weeks, every 30 days for 6 months, and then every 3 months thereafter.