Background: PRL-02 is a long-acting IM depot injection of abiraterone decanoate, a novel prodrug of abiraterone delivered through the lymphatic system. PRL-02 potently blocks androgen production with minimal increases in mineralocorticoids or decreases in glucocorticoids through preferential inhibition of Cytochrome P450 (CYP)17 lyase versus CYP17 hydroxylase. Phase 1 is a standard 3+3 design intended to identify a recommended Phase 2 dose (RP2D). PRL-02 is administered every 84 days (1 cycle). As of 9/8/22, 17 pts (6 mCRPC, 11 mCSPC) were treated across 5 dose cohorts (180, 360, 720, 1260, 1800mg). At 720mg and above, 9 of 11 had a 90% reduction in testosterone (T), including 2 pts with T≤ Lower Limit of Quantitation (LLOQ) of 0.1ng/dL. A PSA decline of ≥50% from baseline (PSA50) was observed in 8 of 10pts. PRL-02 was very well tolerated. Only minimal and transient changes in ‘upstream’ steroids (e.g., progesterone) were observed at doses of 1260 mg (the RP2D) and lower. Methods: Phase 2a is an A'Hern single-stage design. Group 1 includes pts with mCSPC divided into 2 groups (1A: previously untreated high-volume disease and 1B: previously untreated, low-volume disease). Group 2 includes pts with mCRPC. Enrollment of 66 pts is planned across 30 sites in the U.S. (NCT04729114). Patient populations, interventions and study design are described below. Clinical trial information: Clinical Trial information: NCT04729114.