Results of a phase II trial of intense androgen deprivation therapy prior to radical prostatectomy (RP) in men with high-risk localized prostate cancer (PC).

5503 Background: Patients with high-risk localized PC have an increased risk of recurrence and death despite treatment. Abiraterone acetate (AA), a potent CYP17 inhibitor, and apalutamide, a next generation anti-androgen, have each demonstrated improved overall survival in metastatic PC. In this multicenter randomized phase II trial we investigate the impact of intense androgen deprivation on RP pathologic response (NCT02903368). Methods: Eligible patients had a Gleason score ≥4+3=7, PSA >20 ng/mL or T3 disease (by prostate MRI) and lymph node <20 mm. During Part 1 of the study, patients were randomized 1:1 to AA + prednisone + apalutamide + leuprolide (APAL) or AA + prednisone + leuprolide (APL) for 6 cycles (1 cycle=28 days) followed by RP. All RPs underwent central pathology review. The primary endpoint was the rate of a pathologic complete response (pCR) or minimum residual disease (MRD, tumor ≤5 mm). Secondary endpoints include PSA response, surgical staging at RP, positive margin rate, and safety. Results: 118 patients were enrolled at four sites. Median age was 61 (range 46-72) years. The majority of patients had NCCN high-risk disease [n=111, 94%; T3 n=73 (62%), Gleason 8-10 n=84 (71%), PSA >20 ng/mL n=28 (24%)]. 114 (97%) patients completed 6 therapy cycles followed by RP. Median PSA nadir was <0.01 versus 0.02 ng/mL and time to nadir was 4.2 versus 4.6 months in the APAL and APL arms, respectively. RP outcomes are displayed in Table. The combined pCR or MRD rate was 21.8% in the APAL arm and 20.3% in the APL arm (p=0.85). 13 (11%) patients (8 in APAL; 5 in APL) experienced grade 3 treatment-related adverse events (TrAEs). The most common grade 3 TrAEs were hypertension (5%), elevated ALT (3%) and elevated AST (3%). No grade 4 or 5 TrAE was reported. Conclusions: Intense neoadjuvant hormone therapy followed by RP in men with high-risk PC resulted in favorable pathologic responses (<5 mm residual tumor) in 21% of patients. Pathologic responses were similar between the treatment arms. Follow-up is necessary to evaluate the significance of a pathologic response on recurrence rates. Part 2 of this trial will investigate the impact of an additional 12 months of APAL post-RP on biochemical recurrence. A phase 3 trial investigating neoadjuvant apalutamide + leuprolide prior to RP is ongoing. Clinical trial information: NCT02903368 . [Table: see text]