Alshalalfa, Mohammed

392 Background: Cancer-associated fibroblasts (CAFs) are a major component of the tumor microenvironment, exerting both tumor-promoting and tumor-restrictive effects, and in some cases, dual roles. CAFs are heterogeneous and have been implicated in tumor progression, metastasis, and therapeutic resistance. Recent translational evidence suggests the existence of at least two CAF subtypes: CAV1+ CAFs and FAP+FN1+ CAFs. The clinical utility of subclassifying CAFs in prostate cancer remains undefined. In this study, we aimed to examine the correlation of CAF subtypes in localized prostate cancer with Decipher genomic classifier (GC) scores, Grade Group (GG), and the presence of adverse pathological features (APF). Methods: We retrieved de-identified transcriptomic and pathological data from 55,329 radical prostatectomy (RP) samples tested with the Decipher prostate genomic classifier (Veracyte, San Diego, CA) between 2016 and 2024, available through the GRID registry (NCT02609269). A subset of 855 patients (META855 cohort) treated with RP was utilized for outcomes analyses. CAF subtypes were defined based on the expression of key biomarkers (FN1, FAP, and CAV1), normalized to total CAF estimates. Correlation analyses and multivariable Cox regression models were performed to evaluate the association of CAF subtypes with GC scores, GG, APF. Metastasis-free survival (MFS) estimates were generated using Kaplan–Meier methodology. Results: FAP and FN1 normalized expressions were highly correlated (r=0.61) and weakly correlated with CAV1 suggesting that they represent two distinct subtypes of CAF. Samples with high expression (top 25%) of FN1 (FN1+) and FAP (FAP+) were enriched with very high Decipher (> 0.85, VHD) and GG4-5. As such, 37% and 32% of FAP+ were VHD and GG4-5 respectively compared to ~18% for low FAP(low 25%). While for FN+ 33.9% were VHD, and 31.5% GG4-5. Patients with FAP+FN1+, 42.5% and 37.1% were VHD, and had GG4-5. Samples with high CAV1 (CAV1+) were associated with lower rate of VHD (15.5%) or GG4-5 (20.8%) compared to low CAV1 (35.4% for VHD and 24.5% for GG4-5). When evaluating VHD in FAP+FN1+CAV1- subgroup, 58% were VHD compared to 6.4% in FAP-FN1-CAV1+. The 5-year MFS was 78% in FAP+FN1+CAV- compared to 96% in FAP-FN1-CAV1+ (p<0.01). When evaluating the biological implications of FAP+FN1+, we found that FAP and FN1 expression is highly correlated to angiogenesis and EMT pathways, radiation sensitivity signature (PORTOS). Conclusions: FAP+FN1+CAV- is a unique subset of CAFs that is associated with aggressive prostate cancer behavior. Our findings may lay the foundation for future efforts to modulate CAFs in localized prostate cancer with existing therapeutics targeting FAP or FN1.

382 Background: Androgen receptor signaling drives prostate cancer (PC) progression, and genes involved in androgen production, uptake, and conversion (APUC) are key therapeutic targets. We previously defined a 6-APUC gene set ( HSD3B1, HSD3B2, CYP3A43, CYP11A1, CYP11B1, and CYP17A1 ), that identified metastatic PC with favorable prognosis and predict docetaxel benefit. However, the expression landscape and clinical relevance of APUC genes have not been interrogated in localized PC. Methods: We analyzed the expression of 21 APUC genes in 55,329 radical prostatectomy tumor samples that underwent Decipher prostate genomic classifier (GC) testing (Veracyte Inc) between 2016-2024. Baseline clinical/pathologic factors were retrieved from Decipher GRID database (NCT02609269). Associations between gene expression quartiles with PathoGenomic Risk Factors (PGRF) including Very High Decipher score >0.85 (VHD), Grade Group (GG) 4-5, LNI and SVI were examined. Associations with distant metastatic (DM) outcomes and metastasis free survival (MFS) were evaluated using logistic regression in Mayo545 and Cox regression in Meta855 RP cohorts, respectively. Results: High expression of SRD5A2 was associated with favorable PGRF (lower odds ratio (OR), p<0.0001), lower rate of development of DM (OR 0.36, p<0.05), and longer MFS (Hazard ratio (HR) 0.51, p<0.05). HSD17B6 showed similar results for PGRF (lower OR, p<0.0001), DM (OR 0.58, p<0.05) and longer MFS (HR 0.39, p<0.05) despite being associated with GG4-5 and SVI+ in samples with VHD. In contrast, high expression of SRD5A3 and HSD17B10 had high OR for PGRFs (p<0.0001). High expression of SLCO2B1 , an androgen uptake gene, had the strongest association with GG4-5 and SVI/LNI (p<0.001 for both). We noted that SRD5A2 lacked correlation with SRD5A1 and SRD5A3 , which instead correlated with each other. Compared to all APUC genes, SRD5A2 had limited correlations with almost all APUC genes, including ones that exhibited robust cross correlation with each other . Similar to our prior finding, most APUC genes demonstrated negative correlation with AR expression and AR activity signatures. Key outcomes were validated based on transcriptomic data from 492 samples from TCGA database. Conclusions: Comprehensive analysis of 21 APUC genes in over 55,000 PC identified distinct, context-dependent associations with metastatic outcomes and clinical and molecular risk factors. Notably, high SRD5A2 expression was associated with lower odds of high-risk features and metastatic outcomes, whereas SRD5A1 and SRD5A3 linked to adverse outcomes, suggesting critical yet divergent roles among 5-alpha-reductase family members. These findings underscoring androgen-metabolic heterogeneity and highlighting SRD5A2 as a potential biomarker of indolent biology in localized prostate cancer.

Abstract Background Prostate cancer is a heterogeneous disease comprising diverse cell types within the tumor microenvironment that support cancer cell survival. Using single cell and spatial transcriptomics, we previously identified subpopulations of treatment-persistent cancer cells exhibiting regenerative properties and a distinct molecular signature. Herein, we aimed to characterize the locked ‘Persist’ signature (PS) and its association with outcomes in a large cohort of non-metastatic prostate cancer tumors. Methods Patients with non-metastatic prostate cancer that underwent Decipher prostate genomic classifier and whole-transcriptome profiling on biopsy (BX, n=146,941) and radical prostatectomy (RP, n=55,329) specimens between October 2016 and February 2024 were included (Veracyte Inc., San Diego, CA, USA). Baseline clinical and pathological data from deidentified patients as well as signature scores were retrieved from the Decipher Genomic Resource for Intelligent Discovery (GRID) registry (Clinical Trials identifier: NCT02609269). The PS score based on the expression of 17 genes was calculated for all samples. Results PS was significantly associated with adverse clinical and pathological variables. In biopsy sample, PS was higher in cases with worse T3/4 clinical stage, Grade group (GG4-5), and high/very high NCCN risk (p&lt;0.001 for all). In RP sample, PS was significantly higher in patients with GG4-5, extraprostatic extension, seminal vesicle invasion and lymph node involvement (p&lt;0.001 for all). PS was also higher in patients with very high Decipher (&gt;0.85) in both BX and RP (p&lt;0.001 for both). When evaluating the prognosis of PS in multiple retrospective cohorts, PS in biopsy was prognostic of adverse pathology features at RP. PS was also prognostic of distance metastasis (DM) in multiple RP cohorts with long-term follow up (META855). In the ARNEO trial testing apalutamide in addition to ADT as neo-adjuvant treatment prior RP, PS was prognostic of early recurrence. In the Stampede trial, PS was prognostic of progression free survival, PCSM and OS in both non-metastatic and metastatic disease. When associating PS with other GRID signatures, PS was higher in samples with homologous recombination deficiency, TP53 mutations, Luminal B and luminal proliferating subtypes. On the other hand, PS was lower in samples with low androgen receptor-activity, RB-loss and neuroendocrine-like tumors. Finally, PS was positively correlated with radiation sensitivity signatures. Conclusions Persist is a novel molecular signature associated with more aggressive tumor characteristics. Future studies aim to further examine beyond this signature potential to identify patients at risk of aggressive prostate cancer, and understand what the optimal treatments for those with treatment-persistent prostate cancer cells are. Citation Format: Francesco Ballesio, Sinja Taavitsainen, Mohammed Alshalalfa, Antti Kiviaho, Mazlina Ismail, Reetta Nätkin, Alexander Giesen, Thomas Munro, James A. Proudfoot, Hyunnam Ryu, Elai Davicioni, Matthew C. Cooperberg, R. Jeffrey. Karnes, Ruochen Jiang, Steven Joniau, Gerhardt Attard, Frank Claessens, Matti Nykter, Alfonso Urbanucci. Persist: a molecular signature for prostate cancer patients with preexisting treatment-persistent cells associated with aggressive disease [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Prostate Cancer Research and Treatment; 2026 Jan 20-22; Philadelphia PA. Philadelphia (PA): AACR; Cancer Res 2026;86(2_Suppl):Abstract nr B079.