Approximately 25 to 50% of patients with high-risk localized prostate cancer experience biochemical recurrence within 2 years of radical prostatectomy. The Apa-RP study (NCT04523207) investigated whether adjuvant apalutamide plus androgen deprivation therapy in high-risk patients who have undergone radical prostatectomy improved biochemical recurrence-free survival. Apa-RP was a multicenter, open-label, single-arm, phase 2 study conducted in community urology practices in the United States. High-risk patients who had radical prostatectomy received 12 cycles of apalutamide (240 mg daily; 28-day cycles) plus androgen deprivation therapy. The primary endpoint was biochemical recurrence-free survival. Secondary endpoints included testosterone recovery (≥150 ng/dL) and safety. One hundred eight patients were enrolled; median age was 66.0 years (range 46.0-77.0). Median pre-operative prostate specific antigen and baseline testosterone were 7.6 ng/mL (range 2.2-62.7) and 340.0 ng/dL (range 43.0-939.0), respectively. The biochemical recurrence-free rate at 24 months (12 months after completion of planned therapy) was 100% (90% CI 93-100). Serum testosterone recovery rate (≥50 and ≥150 ng/dL) 12 months after treatment completion was 96% (95% CI 88-98) and 77% (95% CI 66-85), respectively. Overall, 107 (99%) patients experienced treatment-emergent adverse events, with 24 (22%) experiencing grade 3 to 4 events. In Apa-RP, BCR-free survival was 100% with 77% of patients having testosterone recovery (≥150 ng/dL) within 12 months of actual treatment completion and a manageable safety profile. These results provide proof of concept that treatment intensification with 12 cycles of apalutamide plus ADT could become an option for patients with high-risk localized prostate cancer who have undergone radical prostatectomy.