Citations

5069 Background: Inhibition of androgen receptor (AR)-signaling results in increases in double-strand DNA breaks and genomic instability. PARP inhibitors (PARPi) are a standard treatment option for patients (pts) with homologous recombination repair mutations (HRRm). Combinations of PARPi and AR pathway inhibitors (ARPI) are associated with synthetic lethality in multiple pre-clinical studies. Clinical trials have suggested potential benefits with co-targeting PARPi and ARPI in pts with and without HRRm. Methods: Alliance A031902 compared radiographic progression-free survival (rPFS) and overall survival (OS) as co-primary endpoints with enzalutamide and rucaparib (Enz/Ruca) versus enzalutamide plus placebo (Enz/Plac) for pts with metastatic castration resistant prostate cancer (mCRPC) regardless of BRCA/HRRm status. This trial was conducted by the Alliance for Clinical Trials in Oncology in 36 centers in the US. Target sample size was 1,002 patients. Eligibility required mCRPC with or without measurable metastatic disease and was agnostic regarding HRRm status. The trial was discontinued in 10/2023 due to changes in the treatment landscape for this pt population. Results: Between 10/21 and 4/23, 61 pts were randomized to Enz/Ruca (n=30) or Enz/Plac (n=31). Known BRCA1/2 or PALB2 mutations were present in 1 pt (3.3%) in the Enz/Ruca arm and 1 pt (3.2%) in the Enz/Plac arm; wildtype in 14 (46.7%) vs 15 (48.4%), and unknown in 15 (50%) vs 15 (48.4%), respectively. Three patients (11.5%) in the Enz/Ruca arm discontinued due to an adverse event (AE) vs 0 in the Enz/Plac arm. Among response-evaluable pts, 7/26 (27%) in the Enz/Ruca arm discontinued due to disease progression vs 10/31 (33%) in the Enz/Plac arm. Most common grade 3+ AEs were anemia (33% vs 3%) and hypertension (17% vs 10%) in the Enz/Ruca arm and Enz/Plac arm, respectively. All 61 pts were evaluable for response assessment. PSA declines ≥50% and ≥90% were observed in 79% vs 45% and 60% vs 43% of pts receiving Enz/Ruca versus Enz/Plac, respectively. Median PFS in the Enz/Ruca vs Enz/Plac arms was 17.1 vs 14.2 mos, respectively (HR 1.13 [95% CI: 0.42-3.01], p=0.81), median rPFS (inclusive of unequivocal clinical progression) was 17.1 vs 11.7 mos ( HR 0.72; 95% CI: 0.31-1.67, p = 0.44), and median OS was not reached vs 27.0 mos (HR 0.65; 95% CI: 0.29-1.45, p=0.29). Conclusions: In this prematurely terminated phase III study, Enz/Ruca was generally well tolerated, with the safety profile consistent with prior PARPi/ARPI combinations. Efficacy outcomes for rPFS and OS are inconclusive due to limited sample size. Definitive conclusions regarding the clinical benefit of this combination cannot be determined from this study. Clinical trial information: NCT04455750 .

5004 Background: Patients (pts) with metastatic hormone-sensitive prostate cancer (mHSPC) treated continuously with testosterone suppression (TS) plus an androgen receptor pathway inhibitor (ARPI) can experience cumulative toxicity. We conducted this single-arm phase 2 trial (NCT05241860) to test the hypothesis that pts who achieve favorable response to TS + ARPI can have prolonged treatment-free interval with testosterone recovery after treatment interruption (TI). Here we report on the primary endpoint. Methods: Eligible pts had mHSPC by conventional imaging with prostate-specific antigen (PSA) ≥ 5 ng/ml and testosterone ≥ 150 ng/dl prior to starting TS+ARPI, with PSA < 0.2 ng/ml and testosterone < 50 ng/dl at the time of enrollment after having received TS for 540-750 days and ARPI for ≥ 360 days. Prior local therapy, radiation to metastases and docetaxel were permitted. After enrollment, pts discontinued TS and ARPI and were followed with PSA and testosterone levels every 3 months (mo), CT/MRI and bone scan at least every 6 mo, and FACT-P questionnaire for patient-reported outcomes (PROs) every 6 mo. Treatment was resumed for PSA ≥ 5 ng/ml, radiographic change (progressive disease [PD] per RECIST 1.1 on CT/MRI or unconfirmed PD per PCWG3 on bone scan), or prostate cancer-related symptoms. The primary endpoint was proportion of men remaining treatment-free 18 mo after TI with eugonadal testosterone ( > 150 ng/dl). Target enrollment was 75 pts to differentiate 18-mo treatment-free rates of 0.30 (H 0 ) and 0.45 (H a ). Results: Of 79 pts enrolled between 07/2022 and 03/2024, 78 were eligible and underwent TI. Among these 78, median PSA prior to starting TS+ARPI was 19 (range 5-6759), 27 (35%) had high volume disease, 31 (40%) never received local therapy, and 55 (71%) did not receive radiation to metastases. By 18 mo after TI, 67% (52/78) recovered testosterone and 58% (45/78) remained treatment-free; 41% (32/78) remained treatment-free with testosterone recovery (80% CI 33.5-48.9%, one-sided p 0.0249). At median follow-up of 21.2 mo, 35% (27/78) resumed initial TS+ARPI after meeting re-initiation criteria (of whom 1 required treatment switch for PD 9 mo later); 5% (4/78) resumed prior to meeting criteria; 9% (7/78) pursued alternative therapy instead of resuming TS+ARPI per protocol; 5% (4/78) withdrew; 1 died of myocardial infarction prior to resuming treatment. 4 pts died, 1 of prostate cancer. Conclusions: The primary objective was achieved with 41% of favorable responders to TS+ARPI remaining treatment-free with testosterone recovery at 18 mo after TI. Analyses of biomarkers and PROs are in progress, and pts will be followed for long-term outcomes. Support: U10CA180821, U10CA180882, UG1CA189823, https://acknowledgments.alliancefound.org, Veracyte Inc. Clinical trial information: NCT05241860 .

5005 Background: Androgen receptor pathway inhibitors (ARPIs) may have distinct central nervous system (CNS) penetration and differential effects on cognition or quality of life (QOL). AFT-47, “ARACOG” is a prospective, randomized open-label phase 2 trial comparing objective and patient-reported cognitive and QOL outcomes between patients with metastatic hormone sensitive prostate cancer (mHSPC), metastatic castration-resistant prostate cancer (mCRPC) or non-metastatic castration-resistant prostate cancer (nmCRPC) treated with darolutamide (DAR) or enzalutamide (ENZ). Methods: Between 8/17/2021 and 3/11/2025, 111 pts were enrolled and randomized 1:1 to treatment with ENZ or DAR. CANTAB, a validated computer-based platform evaluating 5 cognitive domains (PALFAM-memory recall, SWM- spatial working memory, SSP-short-term visual memory, working memory, RVP-rapid visual processing, and OTSMCC- executive function), was performed at baseline, 12, 24, and 48 weeks. Crossover (Xover) was allowed at 12 or 24 weeks for significant pre-specified decline in cognitive testing or patient reported outcome measures (PROMs), or for CNS-associated adverse events, including falls. The primary endpoint was the percent change in the maximally changed cognitive domain (MCCD) from baseline to 24 weeks and was compared between groups with the Wilcoxon rank sum statistic. Patients crossing over prior to 24 weeks were evaluated at the time of Xover and analyzed with their randomized arm. Secondary endpoints included comparison of Xover rates. Results: Among 111 pts, 55 received DAR and 56 received ENZ; median age was 71, 83% White. 95 pts (48 DAR, 47 ENZ) were evaluable for the primary endpoint. Baseline CANTAB was similar between groups. Median cognitive change in MCCD between baseline and 24 weeks was -15.8% and -36.1% for the DAR and ENZ pts, respectively (p = 0.009) (Table). Individual cognitive domains suggest possible learning effect (increased scores) for DAR and are stable or show mild decline for ENZ treated patients at 24 weeks. 32 DAR (58%) and 33 ENZ (59%) participants were eligible for Xover by 24 weeks, and 23 pts crossed over by 24 weeks. All Xover was pts randomized to ENZ (crossed to DAR), with the most common causes being decline in objective (N = 14) or subjective (N = 11) cognitive testing. Conclusions: In this US randomized trial comparing DAR to ENZ, the primary endpoint of differential cognitive effects was met. ENZ showed significantly greater cognitive score decline than DAR at 24 weeks in the MCCD after treatment initiation. Learning effect was seen with DAR but not ENZ. Longer term follow-up of cognitive change and PROM analyses are ongoing. Clinical trial information: NCT04335682 . Percent change in maximally changed cognitive domain by treatment. DAR (N=48) ENZ (N=47) Wilcoxon Rank Sum Test Result CANTAB domain PALFAM SWM Degree of change -15.8 (-38.8, -2.6) -36.1 (-59.3, -16.7) P=0.009

4500 Background: BM occur in ~30% of RCC pts and are associated with poor survival and symptomatic skeletal events (SSEs). Radium-223, an alpha-emitting bone-seeking radioisotope, prolongs survival in advanced prostate cancer. A pilot study of radium-223 with VEGF tyrosine kinase inhibitors (TKI) in RCC with BM showed safety and early efficacy (McKay, CCR, 2018). Cabozantinib is a TKI that showed efficacy in BM. RADICAL (NCT04071223) was designed to investigate cabozantinib ± radium-223 in RCC with BM. Methods: This open label multicenter study enrolled RCC pts with ≥1 symptomatic BM not previously irradiated and Karnofsky performance status ≥60%. Prior therapies were allowed; non-clear cell population was limited to 20%. Randomization was 1:1 to cabozantinib with (Arm A) or without (Arm B) radium-223, stratified by osteoclast-targeted therapy (OTT), prior therapy, baseline opioid use, and IMDC risk. In Arm A, cabozantinib was 40 mg daily cycle 1, 60 mg thereafter if tolerated; radium-223 was 1.49 microcurie/kg IV every 28 days for 6 doses. In Arm B, cabozantinib was 60 mg daily. The primary endpoint was SSE-free survival (SSE-FS). Secondary endpoints were safety, objective response rate (ORR), progression-free survival (PFS) and overall survival (OS). The study was designed with 85% power to detect improvement in 6-month SSE-FS from 65% to 78% (one-sided α=0.05), with planned interim futility analysis at 50% of expected events. Results: From 12/2019 to 9/2025, 90 pts were enrolled and evaluable for the interim analysis. Median age was 63 years; 74.4% male, 90.0% White, 83.3% clear cell histology. 11.1% were treatment naïve, 80.0% received OTT, 51.1% had baseline opioid use. IMDC risk was 16.7% favorable, 68.9% intermediate, 14.4% poor. Median cabozantinib dose was 31.4 mg (Arm A) and 40.0 mg (Arm B); median radium-223 cycles was 6. Median follow-up was 13.1 (range 0.1-49.4) months with 50 events, 17 SSEs (Arm A: 10; Arm B: 7) and 33 deaths (Arm A: 13; Arm B: 20). Outcomes are in Table. 71 pts were evaluable for response. ORR was 22.2% (Arm A), 22.9% (Arm B). Any grade treatment-related adverse events were 97.7% (Arm A), 93.2% (Arm B); grade ≥3 were 65.9% (Arm A), 56.8% (Arm B). The trial closed after interim analysis as SSE-FS did not meet the prespecified futility boundary (HR≤1). Conclusions: Radium-223 did not improve the primary endpoint of SSE-FS when added to cabozantinib but a numerical prolongation in OS was observed. Combination treatment was safe. Alternative radiotherapeutics warrant investigation in RCC. Clinical trial information: NCT04071223 . Interim efficacy analysis. Arm Median(95% CI) HR (95% CI) Stratified SSE-FS A 17.9 (15.0-NE) 1.24 (0.62-2.48) B 17.6 (10.9-NE) Unstratified SSE-FS A 17.9 (15.0-NE) 0.90 (0.51-1.59) B 17.6 (10.9-NE) OS A 32.2 (17.9-NE) 0.77 (0.42-1.41) B 21.3 (12.3-NE) Stratified PFS A 11.0 (5.8-17.4) 1.39 (0.72-2.66) B 11.2 (9.0-18.5)

4514 Background: Maintenance avelumab is a standard of care in patients (pts) with la/mUC who do not progress after first-line PBC. Cabozantinib (CABO) is an oral inhibitor of MET, VEGFR and TAM, active in multiple solid tumors. We hypothesized that an avelumab (Av)-CABO combination would improve outcomes in pts with mUC with an acceptable safety profile compared to avelumab maintenance alone. Methods: MAIN-CAV (NCT05092958) is a phase III randomized, multicenter, international trial for la/mUC pts who did not progress after 4-6 cycles of any PBC (gemcitabine-cisplatin, gemcitabine-carboplatin, MVAC, ddMVAC). Pts were randomized 1:1 to Av 800 mg IV every 2 weeks alone or with CABO 40 mg daily for ≤2 years. Stratification factors were response to first-line PBC (complete response [CR] vs partial response [PR] vs stable disease [SD]) and visceral metastases. The primary endpoint was overall survival (OS); secondary endpoints included progression-free survival (PFS), safety and quality of life. The target accrual was 654 pts; the trial closed early after enrollment of 68 pts following adoption of enfortumab vedotin plus pembrolizumab as the new preferred first-line standard in the US. Results: From 3/2022 to 3/2024, 68 pts were randomized (Av n = 33; CABO-Av n = 35). Median OS was 24.8 months (mo) with Av and 23.0 mo with Avb-CABO (Hazard ratio 1.41; 95% CI 0.66–3.01; p = 0.186). Median PFS was 4.6 mo with Av vs 6.0 mo with Av-CABO (p = 0.343). Objective response rate among pts with PR or SD after first-line PBC was 20.8% with Av vs 11.5% with Av-CABO (p = 0.424). Grade ≥3 treatment-related adverse events occurred in 24.2% pts on the Av arm vs 39.4% of pts on the Av-CABO arm and CABO dose reductions occurred in 63% of pts. Conclusions: Addition of CABO to Av did not improve OS or PFS compared with Av alone in this underpowered, prematurely closed phase III trial; safety was consistent with known profiles. U10CA180821,U10CA180882; U24CA196171, U10CA180863. (CCTG);U10CA180888 (SWOG); https://acknowledgments.alliancefound.org. Clinical trial information: NCT05092958 .

Abstract Stromal tumor infiltrating lymphocytes (sTILs), quantified via hematoxylin and eosin (H&E) tumor slides, are associated with improved response to chemotherapy and better overall survival (OS) in triple-negative breast cancer (TNBC). Digitization of H&E slides offers the opportunity for image-based computational approaches to enumerate sTILs. We describe QuTILs, a research-based TIL enumeration approach using a multilayer perceptron-based framework trained on open-source H&E images using the QuPath software and executed on a standard computer. QuTILs was applied to H&E images from two phase III TNBC clinical trials, CALGB 40502 and 40603 (total n = 462 patients). In Cox proportional hazards models, QuTILs showed significant univariate association in CALGB 40502, with higher TIL% associated with reduced hazard (HR: 0.75, 95% CI: 0.63–0.91), which remained significant in multivariable models and validation CALGB 40603 TNBC clinical trial. In summary, QuTILs provides a computationally efficient, open-source workflow for sTIL identification from digital H&E images for research application.

Abstract Purpose: B7-H3 (CD276) represents a promising therapeutic target tested in high-risk localized and treatment-refractory metastatic prostate cancer. To guide therapeutic development and treatment strategies, we examined prostate tumors and evaluated expression, molecular features, and overall survival (OS), accounting for tissue site, hormone sensitivity status, and race. Experimental Design: A total of 8,157 prostate cancer samples with paired DNA/RNA were analyzed based on annotations by tissue site, self-reported race, and disease state: hormone-sensitive prostate cancer (HSPC), castration-resistant prostate cancer (CRPC), or neuroendocrine prostate cancer (NEPC). Expression quartiles were B7-H3–high (&gt;75th percentile) or B7-H3–low (&lt;25th percentile). The OS was evaluated using Kaplan–Meier and Cox proportional hazards models. Results: B7-H3 expression was broadly maintained but varied by tumor site, hormone sensitivity status, and race. High expression aligned with AR-associated transcription factors (HOXB13 and FOXA1), AR-associated pathogenic dysregulations (AR-V7, SPOP, FOXA1, and TMPRSS2:ERG fusions), and actionable surface antigens (TROP2 and NECTIN-4). Weak correlations were found for lineage-plastic program regulators (EZH2, SOX2, and ASCL1) and NEPC-associated surface antigens (DLL3 and CEACAM5). High B7-H3 expression in primary tumors and HSPCs portended adverse OS [hazard ratio (HR), 1.342 and 1.30; confidence interval (CI), 1.19–1.512 and 1.15–1.46; q &lt; 0.0001] although it was favorable in metastatic tumors (HR, 0.823; CI, 0.719–0.942; q = 0.0048). No significant differences in OS were observed among CRPCs and NEPCs, although OS varied by race, with the poorest survival in Asian/Pacific Islander patients with metastatic prostate cancer (HR, 3.72; CI, 1.49–9.29; q = 0.012). Conclusions: Maintained B7-H3 expression in various prostate cancer settings supports its viability as a target. The associations with AR-related molecular factors, surface antigens, and investigative targets for cell therapy or antibody–drug conjugates suggest potential dual-targeting strategies. See related article by Sharma et al., p. 3365

Abstract Introduction: The National Cancer Institute estimated almost 317,000 new breast cancer and over 13,000 new cervical cancer cases in 2025. While the National Breast and Cervical Cancer Early Detection Program has served millions of women over the past two decades, inequities in cancer screening, subsequently delayed diagnosis, and timely and appropriate treatment remain a public health challenge in the United States. Despite the substantial impact of social determinants of health (SDOH) on cancer screening, few studies have accounted for SDOH at the individual level when assessing breast and cervical cancer screening adherence. The primary objective of this study is to examine whether the individual-level SDOH, measured using HOUsing-based SocioEconomic Status (HOUSES) index, is associated with breast and cervical cancer screening non-adherence (not current on respective USPSTF recommendations for age and frequency). Methods: In this retrospective study, patients were identified as those receiving primary care in the Mayo Clinic Health System and Mayo Clinic (Rochester, MN). The Midwest Quality Metrics panel was then used to assess patients due for screening for breast or cervical cancer in July 2023. The HOUSES, using home address and publicly available data on the residence which measures and categorizes housing status into quartiles, was obtained using the electronic health records (EHRs)-linkable patient-level information. Logistic regression analyses were conducted, controlling for Census block group-level adverse social exposome from the Area Deprivation Index, age, and comorbidities. Results are presented as odds ratios (OR) with corresponding 95% confidence intervals (CI). Results: For breast cancer, among 128,462 eligible patients, 20.1% (n= 25,857) were non-adherent. Compared to the highest HOUSES quartile (Q4), lower HOUSES groups showed significantly higher odds of non-adherence: Q3 OR=1.20 (95% CI=1.15, 1.25), Q2 OR=1.45; (95% CI=1.40, 1.53), and Q1 OR=1.90 (95% CI=1.81, 1.99). For cervical cancer, among 175,712 eligible patients, 29.9% (n=52,533) were non-adherent. Compared to the highest HOUSES quartile (Q4), lower HOUSES groups showed significantly higher odds of non-adherence: Q3 OR=1.07 (95% CI=1.03, 1.10), Q2 OR=1.16; (95% CI=1.12, 1.20), and Q1 OR=1.36 (95% CI=1.31, 1.41). Conclusions: A clinically meaningful association between the HOUSES index and cancer screening adherence was observed. A lower HOUSES index was associated with higher odds of non-adherence for both breast and cervical cancer screening, even after accounting for neighborhood-level risk, age, and comorbidities. Incorporating HOUSES into EHRs can be a practical “screening-for-screening” tool that enables close monitoring of higher-risk patients without additional burden of surveys. Citation Format: Eunice Y. Park, Madison Beenken, Dave Watson, Chung Il Wi, Tufia Haddad, Gladys Asiedu, Karla BALLMAN, James R. Cerhan, Carolyn Flock, Brian Lynch, Folakemi T. Odedina, Scott H. Okuno, Young J Juhn, . HOUSES as a screening tool for cancer screening: Patient-level housing-based socioeconomic status and breast and cervical cancer screening adherence [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7599.