Background: Molecular imaging (i.e. PSMA directed agents) identifies metastatic prostate cancer at an earlier disease state than conventional imaging resulting in a new clinical entity within metastatic hormone-sensitive prostate cancer (mHSPC): molecular positive HSPC (mpHSPC). Historically, patients in this category with prior local therapy would have been classified as having a biochemical recurrence only, and observation was routine. Approaches to mpHSPC include observation or the use of focal and/or systemic therapies. Focal radiation for mpHSPC may delay the need for systemic therapy, yet many patients require further focal or systemic treatment. Androgen deprivation therapy (ADT) with abiraterone (abi) benefits men with high-risk localized disease and standard mHSPC. mpHSPC hypothetically resides somewhere between these two disease states. Finally, the inhibition of poly(ADP-ribose) polymerase (PARP) with olaparib plus abi shows promise in metastatic castration resistant prostate, suggesting this approach may be worthy of testing in earlier disease states. Methods: FAALCON is a single-site, phase 2 clinical trial testing olaparib with abi, ADT and radiation therapy in oligometastatic mpHSPC. Oligometastatic mpHSPC is defined as up to 5 radiation treatment sites (5 cm maximum size each) and must encompass all visible disease on the molecular scan. Patients must have had their prostate previously treated. The primary endpoint is the percentage of patients without treatment failure 24 months from study start. Treatment failure is defined as one of the following: new or progressive metastases on CT/MRI, new lesions on bone scan without alternate explanation, clinical progression, or a PSA doubling time under 6 months with an absolute final PSA over 1.5 ng/mL. Additional radiation therapy is deemed progression. Select secondary endpoints include time to any subsequent therapy, and percentage of patients with undetectable PSA with a recovered testosterone at multiple timepoints. Correlative work will analyze quality of life and prior prostatic tissue. ADT and abi (1000 mg daily) are given for 6 months, and radiation is completed by day 40. Olaparib (300 mg PO twice daily) is started 2 weeks after radiation completes and continues for the remaining ̃5 months. After therapy completion, patients are monitored by PSA q3 months with imaging based on predetermined PSA cutoffs. Molecular imaging (PSMA-PET) may be offered on study. Historical disease control at 24 months is estimated at 40% from prior molecular guided radiation studies and intermittent ADT. With 80% power and a one-sided 5% type-I error, we can detect a hazard ratio of 0.5 (80% control rate) at 24 months with 26 patients. To account for dropout, 29 patients will be accrued. Clinical trial information: NCT04748042.