Abstract 7568: Molecular effects of neo-adjuvant hormone therapy for locally advanced prostate cancer: An ancillary study of the ARNEO phase 2 trial

Abstract Intensified hormone therapy in combination with radiotherapy improves outcome for very high-risk locally advanced prostate cancer. The impact of hormone therapy with surgery, however, is uncertain. In order to understand this better, we ran an ancillary translational study on ARNEO (NCT03080116), a Phase 2 clinical trial, which randomized 89 locally-advanced prostate cancer patients to 12 weeks LHRHa +/- apalutamide (APA) followed by prostatectomy. We performed clinical-grade transcriptome-wide expression array analysis (Veracyte, Inc. San Diego, CA) of FFPE diagnostic core biopsies (N=89) and tumors removed at prostatectomy (N=32 LHRHa, N=23 LHRHa + APA). We also performed RNASeq on fresh frozen biopsies of prostatectomy tumors (N=42 LHRHa, N=45 LHRHa + apalutamide) and LHRHa-naive control cases (N=61) matched for clinical and pathological risk factors. Pre-surgery serum PSA decreased by a median of 98% (IQR:90.2-99.3) after hormone treatment. This decrease was better associated with tumor AR signaling (r2=0.11) versus pre-treatment serum PSA (r2=0.0005), or between pre-treatment serum PSA with diagnostic biopsies (r2=0.008). We confirmed APA more potently suppressed AR signaling than LHRHa alone, with no detectable difference in direction of effect for differentially regulated genes/pathways. LHRHa + APA had less residual tumor (median Residual Cancer Burden, RCB=0.48cm3) than in LHRHa (median RCB=1.7cm3) but in cases with sufficient tumor, we observed residual active AR signaling pathways at prostatectomy in both treatment arms. To orthogonally confirm this, we selected 28 ERG positive cases (by IHC pre-treatment) and found retained ERG expression in 12/13 on LHRHa and 10/15 on LHRHa + APA. Using pathway analysis in the RNAseq data, we identified LHRHa +/- APA induced down-regulation of AR, metabolic pathways, as well as DNA repair, and up-regulation of hallmark NOTCH, Hedgehog, TGF-beta, WNT and immune signaling (adjusted p-value cutoff=0.001). Comparing differentially expressed genes on RNASeq between treatment-naïve versus LHRHa +/- APA treated tumors, we observed STING1 as significantly higher in LHRHa +/- APA vs control (Wilcoxon rank sum test p-value <0.001). We found that expression of STING1 was positively correlated with hallmark interferon alpha response (r=0.7, rs=0.6) that was correlated with apoptosis (r=0.5, rs=0.5). Whilst we show that adding APA to LHRHa increases suppression of AR activity and ERG expression, we find that 12 weeks is insufficient to abrogate AR signaling in most tumors, despite ~98% decrease in serum PSA. We identify novel processes modulated in humans by potent suppression of androgen activity, including upregulation of STING1-type 1 interferon response as a potential key modulator of treatment effect. Citation Format: Mazlina Ismail, Wout Devlies, Marina Parry, Gaetan Devos, Stefanie Friedrich, Charles Parker, Larissa Mendes, Elai Davicioni, Mark Linch, Frank Claessens, Steven Joniau, Gerhardt Attard. Molecular effects of neo-adjuvant hormone therapy for locally advanced prostate cancer: An ancillary study of the ARNEO phase 2 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7568.