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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.

162 Background: Clinical trial conduct in advanced prostate cancer has changed dramatically with the continued development of new imaging approaches, molecular phenotypes and genetic subtypes, prognosis assessments, and effective therapies across a range of disease states. This created a need to redefine terminology and best practices for clinical trials. Methods: We convened PCWG4, an international expert committee of multidisciplinary working groups, between 2016 and 2025 to update and expand PCWG2-3 recommendations based on emerging evidence and clinical trial data in an innovative biomarker and imaging context to provide guidance for clinical trial design, eligibility, and endpoint assessments. Results: PCWG4 redefines terminology around disease states and prior therapies in a patient-centric context, considering imaging modalities, with a particular focus on PET-defined disease. New recommendations are provided for disease state terminology, defining eligibility criteria, imaging and non-imaging-based responses. We define delay/prevent endpoints including responses by pathology, ctDNA, circulating tumor cells, and PSA declines, and specify intervals for re-assessments including imaging, biomarker assessments, and patient reported outcomes. We propose new imaging-specific rPFS criteria including guidance with serial PSMA PET/CT imaging (Table). We provide recommendations in a biomarker-based context for the indication, reflective of patient benefit for specific interventions. We emphasize the need for development of validated PET imaging and molecular and phenotypic criteria as well as trial designs to appropriately risk stratify patients, predict and assess benefit, and measure post-treatment outcomes reliably in a trial framework. Conclusions: PCWG4 expands guidance on patient and tumor profiling, as well as therapy development, to include both androgen deprivation therapy sensitive and resistant settings, reflecting today’s more heterogeneous and diverse patient population to optimize outcomes. PCWG4-defined radiographic progression by imaging modality for patients with metastatic disease. Pretreatment Scan On-treatment Scan #1(≥week 8) On-treatment Scan #2 All Subsequent Scans Bone scintigraphy Comparator Comparator for subsequent scansPOD never called here POD:PCWG3 criteria (2+2 additional new lesions) POD:≤5 new lesions: PCWG3 criteria 2 new lesions confirmed≥6 new lesions CT/MRI Any measurable disease Comparator PCWG3/RECIST PCWG3/RECIST PCWG3/RECIST PSMA PET Bones, and lymph nodes and lung metastases (non-RECIST qualifying by + on PET only) Comparator POD:≤5 new lesions: 2 new lesions confirmed on a subsequent scan≥6 new lesions Same as prior Same as prior Liver and non-pulmonary viscera Comparator POD:Any single new lesion that represents disease Same as prior Same as prior

PURPOSE The continuous development of new imaging approaches, molecular phenotyping, genetic subtypes, prognosis assessments, and effective therapies across a range of disease states has created a need to redefine terminology and best practices for clinical trial conduct in patients with advanced prostate cancer. Methods We convened an international expert committee of diverse working groups, the Prostate Cancer Working Group 4 (PCWG4), between 2016 and 2025. Our objective was to formulate updated criteria based on emerging evidence and clinical trial data in a biomarker context to provide guidance for clinical trial design, eligibility, and end point assessments for patients with advanced prostate cancer. RESULTS PCWG4 redefines terminology around the disease state and previous therapies in a patient-centric context and terminology focused on androgen pathway modulation. We consider imaging, with a particular focus on positron emission tomography (PET)–defined disease. New recommendations are provided for disease state terminology, defining eligibility criteria, response and delay/prevent end points, intervals for reassessments including imaging, and patient-reported outcome determination. We provide recommendations in a biomarker-based context of use for the intended indication, reflective of patient benefit for specific interventions. We emphasize the need for development of validated PET imaging and molecular and phenotypic criteria as well as trial designs to appropriately risk stratify patients, predict and assess benefit, and measure post-treatment outcomes reliably in a trial framework. CONCLUSION PCWG4 updates recommendations on patient and tumor characterization, therapy development, and imaging criteria and extends guidance into earlier androgen pathway modulator–naïve/sensitive disease states to reflect an evolving, heterogeneous, and diverse patient population to optimize treatment benefits for all patients.

e17064 Background: Analyses of clinical trials data suggest thatBlack men have equal or even improved overall survival (OS) with certain treatments for mCRPC compared with other races. Moreover, retrospective analysis of the PROCEED registry indicated that Black men who received Sip-T, an autologous cellular immunotherapy, had longer survival compared with other men with mCRPC. The Abi Race and PANTHER clinical trials prospectively assessed the effect of ARPIs on clinical outcomes among Black and White patient (pt) cohorts, and included pts who had received Sip-T either prior to or during study. We combined data from Abi Race and PANTHER to investigate associations between OS, Sip-T and race. Methods: Data from the Abi Race (N=100) and PANTHER (N=93) studies were retrospectively pooled for this analysis. Propensity scores for Sip-T treatment were calculated based on Karnofsky performance status, race, Gleason score, and study. Kaplan-Meier estimates for OS, with and without inverse propensity score weighting, were generated and stratified by Sip-T use. This analysis was stratified by race to examine whether the relationship between Sip-T use and OS differed by race. Results: Of the 93 Black pts and 100 White patients included from both studies, 123 patients did not receive Sip-T, while 70 patients did (60 before study, 10 on study). Pts who received Sip-T had a median OS (mOS) of 44 months (95% Confidence Interval (CI) 39, NR) compared to 36 months (95% CI 31, 48) for those who did not. Weighted by propensity scores, Black men who received Sip-T had a mOS of 72 months (95% CI 43, NR), while those who did not had a mOS of 38 months (95% CI 30, NR). Among White men, patients who received Sip-T had a mOS of 39 months (95% CI 30, NR), while those who did not had a mOS of 32 months (95% CI 29, 48) (see Table). Conclusions: Our findings from an investigator-led retrospective analysis independent of sponsors provide independent clinical trial support of prior retrospective findings that suggest Black men with mCRPC who receive Sip-T may have a greater OS than White men. While our analysis controlled for factors that may influence the use of Sip-T, it is limited by potential unmeasured confounders or timing of Sip-T. Further, adequately powered prospective trials specifically evaluating outcomes with Sip-T by race in earlier clinical settings are needed. Drug support and funding for Abi Race and PANTHER were provided by Janssen Scientific Affairs, LLC. Death counts and median overall survival (mOS) in months by race and Sipuleucel-T use. Black Men White Men Sipuleucel-T use Deaths / Total N No 36 / 64 38 / 59 Yes 12 / 29 24 / 41 Unweighted mOS (95% CI) No 36 (29, NR) 32 (29, 48) Yes 72 (43, NR) 39 (31, NR) Weighted mOS (95% CI) No 38 (30, NR) 32 (29, 48) Yes 72 (43, NR) 39 (30, NR) NR = not reached, mOS = median overall survival, CI = confidence interval.

309 Background: Standard of care (SOC) treatment options for HR-PCa include RT with long-term androgen deprivation (LT-ADT) or RP with selective use of post-operative RT +/- androgen deprivation therapy (ADT). The optimal treatment approach has been assessed in retrospective population-based and multi-center comparisons, which have yielded mixed results with substantial bias. Therefore, we conducted an emulated randomized comparison of RT vs RP in HR-PCa leveraging patients enrolled in RCTs. Methods: We searched Medline for RCTs in HR-PCa with a SOC arm of an RT- or RP-based regimen. Inclusion required similar experimental treatment and contemporaneous enrollment in the same country to reduce bias. This identified 2 trials, NRG/RTOG 0521 (RT+LT-ADT +/- 6 cycles docetaxel [doce]), and CALGB 90203 (RP +/- neoadjuvant 6 cycles doce and ADT). Due to inherent difference in the biochemical recurrence criteria after RT vs RP, we chose inverse probability of treatment weighted (IPTW) cumulative incidence of distant metastasis (DM) as the primary endpoint, considering deaths as competing events. Death after DM was measured to create a harmonized metric of deaths likely attributed to PCa. To assess potential residual selection bias, death without DM to capture non-cancer associated deaths was analyzed. Results: Overall, 1290 patients (RT n=557, RP n=733) were included, with similar median follow-up of 6.4 years. Prior to IPTW, RP patients were significantly younger with lower baseline PSA compared to RT patients. Adjuvant (18%) and salvage therapy (44%) was used in RP cohort. Cumulative incidence of DM was significantly lower in patients who underwent RT compared to RP (8-year DM: 16% vs 23%; p=0.01; subdistribution hazard ratio [sHR] 0.48 [95%CI 0.34-0.69], p<0.001). 8-year rates of death after DM were 10% vs 8% (p=0.72) in the RP and RT patients, respectively. RT patients had significantly greater risk of death without DM (HR 2.09 [1.01-4.34], p=0.048) with early differences measured. On a cross-arm comparison, 8-year cumulative incidence of DM when comparing SOC RT+LT-ADT group versus the doce+ADT+RP group was 18% vs 21%, respectively (sHR 0.75 [0.45-1.24], p=0.26). Conclusions: HR-PCa patients enrolled on RCTs had significantly lower incidence of DM with an RT-based strategy compared to an RP-based approach. Longer follow-up is needed to assess deaths attributed to PCa. Despite the strengths of the comparison (use of cooperative group RCT data, contemporaneous enrollment in the same country, patients fit enough for chemotherapy, and IPTW adjustments) there appears to be residual unmeasured bias, as expected, based on greater early deaths without DM in the RT arm. Utilization of post-operative radiotherapy and ADT+Doce may mitigate differences between RP and SOC RT+LT-ADT.

LBA531 Background: Muscle-invasive urothelial carcinoma (MIUC) is an aggressive disease with high relapse rates. Neoadjuvant platinum-based chemotherapy (NAC) is the standard of care in patients (pts) who are cisplatin (Cis)-eligible. However, many pts are Cis-ineligible or have persistent muscle-invasive disease after NAC and surgery. We evaluated pembrolizumab (Pembro) as adjuvant therapy in pts with high-risk MIUC following surgical resection. Methods: The AMBASSADOR study is an open-label, randomized, phase III trial that enrolled pts with histologically confirmed MIUC of the bladder, upper tract, or urethra who (1) had ≥ pT2 and/or pN+ or margins+ at surgery (radical cystectomy, nephrectomy, nephroureterectomy, or ureterectomy) following NAC or (2) ≥ pT3 and/or pN+ or margins+ at surgery without NAC and were either Cis-ineligible or declined adjuvant Cis-based therapy. Pts were registered ≥4 to 16 weeks after surgery and randomized 1:1 to receive Pembro 200 mg every 3 weeks for 1 year or observation (Obs). Randomization was stratified by pathologic stage, centrally tested PD-L1 status, and prior NAC. The dual primary endpoints were disease-free survival (DFS) and overall survival (OS) with a target sample size of 739 pts and required 387 DFS and 320 OS events for final analysis. Secondary objectives included evaluation of DFS and OS in PD-L1-positive and -negative pts and assessing safety. Here we present the interim DFS and OS results. Results: Between 09/2017 and 08/2021 a total of 702 pts were randomized prior to early closure due to US FDA approval of nivolumab for MIUC pts: 354 pts to Pembro and 348 pts to Obs; 13.0% vs 21.6% withdrew from study without event in the Pembro vs Obs arms, respectively. 74 pts (21%) in the Obs arm received an immune checkpoint inhibitor. Median follow-up was 22.3 months (mos) for DFS and 36.9 mos for OS. The DFS endpoint (based on 319 events needed for interim analysis) crossed the efficacy boundary. Median DFS was 29.0 months (95% confidence interval (CI) 21.8‒not evaluable (NE)) with Pembro and 14.0 months (95% CI 9.7‒20.20) with Obs (hazard ratio (HR) 0.69 [95% CI 0.55–0.87]; p=0.0013). At the interim analysis (n = 257 events), median OS was 50.9 months (95% CI 43.9‒NE) with Pembro and 55.8 months (95% CI 53.3‒NE) with Obs (HR 0.98 [95% CI 0.76–1.26]; p=0.88). Grade 3+ adverse events occurred in 48.4% and 31.8% of pts in the Pembro and Obs arms, respectively. Conclusions: Adjuvant Pembro demonstrated a statistically significant and clinically meaningful improvement in DFS vs Obs for high-risk MIUC pts after radical surgery. The OS endpoint may have been impacted by pts on the Obs arm receiving a checkpoint inhibitor. Pembro was tolerable with no new safety signals. These results support adjuvant Pembro as a new therapeutic option for pts with MIUC with high risk for recurrence. Additional follow-up is ongoing for the final DFS/OS, PD-L1 subgroups, and ctDNA analyses. Clinical trial information: NCT03244384 .

PURPOSE Patients with biochemically recurrent prostate cancer (BRPC) after radical prostatectomy and a short PSA doubling time are at risk for distant metastases. Apalutamide, an androgen receptor antagonist, and abiraterone acetate plus prednisone (AAP) prolong survival in the metastatic setting. We evaluated whether intensification of androgen-deprivation therapy (ADT) improves outcomes in BRPC. PATIENTS AND METHODS PRESTO is a randomized phase III, open-label trial in patients with BRPC and PSA doubling time ≤9 months (ClinicalTrials.gov identifier: NCT03009981 ). Patients were randomly assigned 1:1:1 to receive a finite 52-week treatment course with ADT control, ADT + apalutamide, or ADT + apalutamide + AAP. The primary end point was PSA progression-free survival (PSA-PFS), defined as serum PSA >0.2 ng/mL after treatment completion. RESULTS Five hundred three patients were enrolled. The median PSA was 1.8 ng/mL (IQR, 1.0-3.6). At the first planned interim analysis, both experimental arms significantly prolonged PSA-PFS compared with the control arm (median, 24.9 months for ADT + apalutamide v 20.3 months for ADT; hazard ratio [HR], 0.52 [95% CI, 0.35 to 0.77]; P = .00047; median, 26.0 months for ADT + apalutamide + AAP v 20.0 months for ADT; HR, 0.48 [95% CI, 0.32 to 0.71]; P = .00008). Median time to testosterone recovery did not differ across treatment arms. The most common grade ≥3 adverse event was hypertension (7.5%, 7.4%, and 18% in ADT, ADT + apalutamide, and ADT + apalutamide + AAP arms, respectively). CONCLUSION Intensified AR blockade for a finite duration prolongs PSA-PFS with a manageable safety profile, without adversely affecting time to testosterone recovery. The addition of apalutamide to ADT should be considered in patients with high-risk BRPC.

ImportanceSystematic data on the association between anticancer therapies and thromboembolic events (TEEs) in patients with COVID-19 are lacking.ObjectiveTo assess the association between anticancer therapy exposure within 3 months prior to COVID-19 and TEEs following COVID-19 diagnosis in patients with cancer.Design, Setting, and ParticipantsThis registry-based retrospective cohort study included patients who were hospitalized and had active cancer and laboratory-confirmed SARS-CoV-2 infection. Data were accrued from March 2020 to December 2021 and analyzed from December 2021 to October 2022.ExposureTreatments of interest (TOIs) (endocrine therapy, vascular endothelial growth factor inhibitors/tyrosine kinase inhibitors [VEGFis/TKIs], immunomodulators [IMiDs], immune checkpoint inhibitors [ICIs], chemotherapy) vs reference (no systemic therapy) in 3 months prior to COVID-19.Main Outcomes and MeasuresMain outcomes were (1) venous thromboembolism (VTE) and (2) arterial thromboembolism (ATE). Secondary outcome was severity of COVID-19 (rates of intensive care unit admission, mechanical ventilation, 30-day all-cause mortality following TEEs in TOI vs reference group) at 30-day follow-up.ResultsOf 4988 hospitalized patients with cancer (median [IQR] age, 69 [59-78] years; 2608 [52%] male), 1869 had received 1 or more TOIs. Incidence of VTE was higher in all TOI groups: endocrine therapy, 7%; VEGFis/TKIs, 10%; IMiDs, 8%; ICIs, 12%; and chemotherapy, 10%, compared with patients not receiving systemic therapies (6%). In multivariable log-binomial regression analyses, relative risk of VTE (adjusted risk ratio [aRR], 1.33; 95% CI, 1.04-1.69) but not ATE (aRR, 0.81; 95% CI, 0.56-1.16) was significantly higher in those exposed to all TOIs pooled together vs those with no exposure. Among individual drugs, ICIs were significantly associated with VTE (aRR, 1.45; 95% CI, 1.01-2.07). Also noted were significant associations between VTE and active and progressing cancer (aRR, 1.43; 95% CI, 1.01-2.03), history of VTE (aRR, 3.10; 95% CI, 2.38-4.04), and high-risk site of cancer (aRR, 1.42; 95% CI, 1.14-1.75). Black patients had a higher risk of TEEs (aRR, 1.24; 95% CI, 1.03-1.50) than White patients. Patients with TEEs had high intensive care unit admission (46%) and mechanical ventilation (31%) rates. Relative risk of death in patients with TEEs was higher in those exposed to TOIs vs not (aRR, 1.12; 95% CI, 0.91-1.38) and was significantly associated with poor performance status (aRR, 1.77; 95% CI, 1.30-2.40) and active/progressing cancer (aRR, 1.55; 95% CI, 1.13-2.13).Conclusions and RelevanceIn this cohort study, relative risk of developing VTE was high among patients receiving TOIs and varied by the type of therapy, underlying risk factors, and demographics, such as race and ethnicity. These findings highlight the need for close monitoring and perhaps personalized thromboprophylaxis to prevent morbidity and mortality associated with COVID-19–related thromboembolism in patients with cancer.

5077 Background: In the phase 3 PRESTO study, intensified androgen deprivation therapy (ADT) with apalutamide (Apa) with or without abiraterone acetate plus prednisone (AAP), administered for a finite treatment period of 52 weeks, prolonged prostate-specific antigen progression-free survival (PSA PFS) in pts with high-risk biochemically relapsed prostate cancer (BRPC). We evaluated the association between PSA nadir within 3 months of treatment initiation with subsequent PSA PFS in this study. Methods: PRESTO is a randomized phase 3, open-label trial in pts with BRPC following radical prostatectomy (RP) and PSA doubling time (PSADT) ≤ 9 months, without distant metastases on conventional imaging (NCT03009981). Pts were randomized 1:1:1 to receive a finite 52-week treatment course with ADT, ADT + Apa, or ADT + Apa + AAP, stratified by PSADT (< 3 vs 3–9 months), with post-treatment follow-up. The association between PSA nadir within the first three months on treatment with subsequent PSA PFS was analyzed in a post hoc fashion. Results: 504 pts were randomized to ADT alone (N = 167), ADT + Apa (N = 168) or ADT + Apa + AAP (N = 169). 463 pts were evaluable for PSA nadir at 3 months. Across the three treatment arms, a PSA nadir of less than 0.1, between 0.1 – 0.2, and ≥ 0.2 ng/mL within the first three months of treatment was observed in 86.3%, 4.4%, and 9.3% of patients, respectively. A PSA nadir of < 0.2 ng/mL was reached within 3 months of treatment initiation in 79.8%, 96.9%, and 95.0% of pts randomized to the ADT, ADT + Apa, and ADT + Apa + AAP arms, respectively. The association between time to PSA nadir and subsequent PSA PFS was -0.30 (standard error = 0.03, Kendall’s tau modified for bivariate censoring), and median time to PSA nadir was 2.0 months (interquartile range 1.12 – 4.76 months). Failure to reach a PSA nadir < 0.2 ng/mL within the first three months of treatment was associated with a significantly shorter PSA PFS compared to pts with a PSA nadir ≤ 0.1 ng/mL (median PSA PFS of 13.9 vs. 22.8 months from 3 months post-treatment initiation; hazard ratio = 5.60, 95% CI: 3.58 – 8.75, p < 0.0001). There was also a significant difference in PSA PFS in those with a three-month PSA nadir between 0.1 – 0.2 vs ≤ 0.1 ng/mL (median PSA PFS 17.4 vs 22.8 months, HR = 2.63, 95:CI: 1.49 – 4.63, p = 0.0008). Conclusions: Using a landmark analysis at 3 months, a failure to reach PSA nadir less than 0.1 ng/mL within three months following initiation of ADT in BRPC is associated with shorter time to subsequent progression following treatment discontinuation. Follow-up is ongoing to integrate genomic profiling of primary prostate cancer tissues and whole blood RNA in pts with suboptimal PSA nadir to identify potential markers of relative androgen pathway inhibitor resistance. Clinical trial information: NCT03009981 .