Neoadjuvant apalutamide (APA) plus leuprolide (LHRHa) with or without abiraterone (AA) in localized high-risk prostate cancer (LHRPC).

5504 Background: Novel androgen signaling inhibitors (ASI) with medical castration may improve outcomes in LHRPC. We previously reported relapse free survival association with pathologic measures of tumor regression. However a wide range of persistent cancers was recorded. To build on our findings and test candidate predictors of outcome, we conducted a study examining APA effect in LHRPC. Methods: This is a phase II neoadjuvant study of 6 months APA+LHRHa +/- AA (randomized 1:1) in LHRPC (≥ cT2 + Gleason Score ≥ 8 or ≥ cT2b + Gleason ≥ 7 + PSA > 10 ng/mL) followed by radical prostatectomy (RP). We studied treatment effect by pathology measures [path. stage, tumor volume (TV), tumor cellularity % (TC), tumor epithelial volume (TEV: TC x TV)]. Tumor expression of candidate markers of outcome was assessed in the diagnostic biopsy by IHC [AR signaling (AR-N, ARC19, ARV7, PSA), PTEN, glucocorticoid receptor (GR), Ki67, p53, RB] and DNA/RNA seq. A previously identified candidate predictive molecular signature (AR-N overexpression, nARV7 absence, no GR overexpression, Ki67 ≤10%) was tested. Univariate (Fisher’s exact, Wilcoxon) and multivariate (logistic, linear models) analyses employed. Results: Sixty three -of 65 pts enrolled- had RP. PS-ECOG 0, median age 65 (43-77). Treatment was well tolerated with Grade 3 hypertension in 7 (2 APA + LHRHa). Presurgical PSA was ≤0.1 in 62/63 (98%). Organ confined disease (≤ypT2N0) found in 13/32(41%) APA+LHRHa vs. 12/31 (39%) APA+AA+LHRHa treated. 2 (3%) had pathologic complete remission (APA+AA+LHRHa), 6 (10%) minimal residual disease (5 on APA +LHRHa). Despite uniformity in PSA response, we recorded heterogeneity in measures of tumor viability: TV (0-11.5cc), TC (1-80%), TEV (0-6.1cc). ≤ypT2N0 associates with diagnostic biopsy positivity for the prespecified molecular signature (p <0.0001), PTEN expression (p: 0.004), absence of cribriform/ intraductal spread (p 0.002) but not with Gleason Score. On multivariate analysis only the prespecified biopsy signature associates with outcome (p 0.003). Findings were replicated when analyzed by TV, TC and TEV measures. Conclusions: Neoadjuvant Apalutamide plus LHRHa is tolerable and results in tumor regression in a subset of LHRPC patients. Dual ASI treatment does not further improve outcomes. Biopsy positive for a prespecified molecular signature, associated with response. Study results emphasize the need to consider biologic heterogeneity and pursue validation of predictors of response in order to improve therapeutic outcomes in LHRPC. Clinical trial information: NCT03279250 .