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Abstract Rationale Pulmonary arterial hypertension (PAH) is associated with significant morbidity and mortality. The extent of medication nonadherence in PAH is uncertain and may be linked to adverse outcomes. There has been a lack of multicenter, registry-based studies assessing medication nonadherence and patient-centered outcomes in PAH. Objectives To determine the prevalence of self-reported nonadherence in Pulmonary Hypertension Association Registry (PHAR) participants with PAH or chronic thromboembolic pulmonary hypertension and the relationship of nonadherence with several patient-centered outcomes (mortality, hospitalization rates, emergency department visits, and health-related quality of life). Methods Self-reported PAH medication nonadherence was captured at PHAR enrollment and during follow-up visits. Predictors of nonadherence were modeled using generalized estimating equations assuming a binary distribution. Outcomes associated with nonadherence were modeled using generalized estimating equations with a Poisson distribution. Results A total of 1,543 patients were included, of whom 1,092 (70.8%) were female and 1,340 (86.8%) had PAH. The overall rate of any self-reported nonadherence was 6.1% (95% confidence interval [CI], 5.3–6.9). Predictors of nonadherence included self-reported male sex at birth (odds ratio [OR], 1.4; 95% CI, 1.0–1.9; P = 0.02), poverty (OR, 1.6; 95% CI, 1.2–2.3; P = 0.01), not being married or partnered (OR, 1.5; 95% CI, 1.1–1.9; P = 0.01), having Medicaid or no health insurance (OR, 2.1; 95% CI, 1.5–2.9; P < 0.001), and having completed high school but not having a college degree (OR, 1.7; 95% CI, 1.1–2.9; P < 0.001). PHAR participants who reported any nonadherence had 50.0% more emergency department visits (P < 0.001), 13.3% more hospital admissions (P = 0.03), and 61.9% more days hospitalized (P = 0.01). No relationship was observed between nonadherence and the type or number of PAH therapies or all-cause mortality. Participants reporting nonadherence had worse mean Short Form-12 scores (P < 0.001) and worse emPHasis-10 scores (P = 0.02). Conclusions The rate of self-reported nonadherence in PHAR registrants was low but was associated with male sex and several social determinants of health. Although the complexity or type of PAH regimen did not appear to influence nonadherence, nonadherence was associated with numerous adverse patient-centered outcomes, including greater healthcare use and worse health-related quality of life. Because of limitations in the structure of the gathered data, relationships between exposure and outcomes were not temporally definitive; these observations warrant additional prospective studies.

261 Background: Clinicians use next-generation sequencing (NGS) to tailor targeted treatments for PCa patients. However, the results are often available in unstructured formats and are saturated with technical jargon, making them inaccessible for patients. Therefore, we aimed to assess the efficacy of LLMs to accurately extract genomic characteristics from unstructured reports and generate patient-friendly summaries for ease of variant interpretation in PCa patients. Methods: This retrospective study included patients with PCa who underwent NGS from 2023-2024. The GPT4 model was utilized using structured zero-shot prompts to extract genomic characteristics from unstructured reports in a non-decomposed manner. Prompt development was conducted iteratively using a 2% random sample of the dataset. Genomic characteristics ascertained by LLM were assessed against held out vendor-curated test dataset for evaluation. Performance was assessed using weighted evaluation metrics (precision, recall, and F1-score). Additionally, the extracted variables were organized using rule-based criterion and presented as a separate prompt to GPT4 to generate summaries for interpretation at the level of each biologically relevant variant. Mean Flesch-Kincaid scores and Vocd-D statistic with standard deviations were computed to assess readability and lexical diversity of LLM-generated variant interpretation summaries. Results: A total of 331 patients (370 NGS reports) were included in the study. Evaluation on the held-out test dataset (Table) showed that the weighted average precision ranged from 80% for extracting tumor mutational burden to 100% for extracting the CtDNA fraction from unstructured reports. The weighted average recall ranged from 85% for extracting CtDNA tumor fraction to 99% for ascertaining variant/alteration. The weighted average F1-scores varied from 0.83 for extracting tumor mutational burden to 1.0 for extracting specimen site from NGS reports. The mean Flesch-Kincaid score was 8.29 ± 1 indicating average/standard readability ease. The mean Vocd-D statistic was 7.55 ± 1 indicating focused summaries, however, with limited lexical diversity. Conclusions: This study suggests that large language models can effectively extract genomic characteristics from unstructured reports and can potentially improve genomic literacy among prostate cancer patients by providing easy-to-interpret variant summaries. However, targeted prompting may be required to increase lexical diversity for improved engagement. Performance across different genomic characteristics. Category Precision Recall F1-Score Altered gene 0.86 0.97 0.89 Variant/alteration type 0.98 0.99 0.98 Variant allele fraction 0.96 0.96 0.96 Test name/type 1 0.99 1 Specimen site 1 0.99 1 Tumor mutational burden 0.8 0.93 0.83 CtDNA tumor fraction 1 0.85 0.92 MSI status 0.99 0.97 0.98

247 Background: Approximately 10% to 15% of men with metastatic castration-resistant prostate cancer (mCRPC) harbor germline mutations. Circulating tumor-derived DNA (ctDNA) as non-invasive approach to characterizing somatic alterations. In this study, we report longitudinal ctDNA assessments in mCRPC patients who have undergone germline testing. Methods: A total of 238 patients, who had undergone both germline testing and ctDNA assessment from Tulane Cancer Center were included in this study. Germline testing was conducted using a multi-gene cancer panel from Invitae, covering 50-86 genes, while somatic alterations in ctDNA were tested through Guardant 360, including 70-83 genes. Somatic alterations with <0.1%, synonymous, and variants of unknown significance were excluded from analyses. Statistical analyses were performed using Pearson Chi-Square Test or Fisher Exact Test. Results: From 2015-2024, 17.2% (41/238) had pathogenic or likely-pathogenic (P/LP) germline mutations. The most common pathogenic germline mutations were in BRCA2 (17.1%; 7/41), BRCA1 (9.8%; 4/41), and CHEK2 (9.8%; 4/41). In ctDNA, germline positive patients were more likely to have frameshift mutations (OR= 1.75, 95% C.I. [1.09, 2.81], p=0.02) and less likely to have copy number amplifications (OR= 0.58, 95% C.I. [0.36, 0.93], p= 0.03) compared to germline negative patients. Among mCRPC patients with germline HRR P/LP mutations, frameshift alterations were significantly more frequent (OR=5.03, 95% CI [2.03, 13.23], p-value=0.0008). mCRPC patients with germline P/LP mutations were more likely to have somatic mutations in BRCA2 (OR=2.85; 95% CI: [1.62, 4.93]; p=0.0002) and GATA3 (OR=3.37, 95% CI: [1.26, 8.51]; p=0.016) detected ctDNA and less likely to have EGFR alterations (mutations and/or amplifications) (OR=0.46; 95%CI: [0.25, 0.80]; p=0.0094). BRCA2 somatic mutations are also more likely to be detected in patients with germline P/LP mutations in HRR genes (OR=0.11, 95% CI [0.03, 0.33], p=0.00004). Conclusions: mCRPC patients with pathogenic germline mutations are more likely to have frameshift and less likely to have copy number amplifications compared to germline negative mCRPC patients. Frameshift mutations are more likely to be detected in patients with germline P/LP in HRR genes. Patients with germline P/LP mutations are more likely to have somatic mutations BRCA2 and GATA3 and less likely to have mutations and/or amplifications in EGFR.

245 Background: Circulating tumor DNA (ctDNA) can be used as a prognostic biomarker in mCRPC patients, with changes in ctDNA providing insight into patient survival. In this study, we evaluate the ctDNA landscape of patients with mCRPC prior to their death. Methods: A retrospective clinical data review, 2015-2024, was conducted at Tulane Cancer Center to identify mCRPC patients who underwent ctDNA testing prior to death. All ctDNA data were obtained through a multi-gene cancer panel via the Guardant 360 assay (70-83 genes). Lethal mCRPC was defined as patients who underwent ctDNA testing ≤3 months prior to death. A matched control group (CTRL) was defined as mCRPC patients with ctDNA collection ≥2 years prior to death or most recent follow-up. Statistical analyses were performed using Pearson Chi-Square Test or Fisher Exact Test whenever appropriate. Furthermore, survival analysis was conducted using the Kaplan-Meier method. Results: There were 70 patients in lethal mCRPC group and 157 patients in CTRL group. Compared to the CTRL group, in lethal mCRPC, somatic mutations and/or amplifications in BRAF(OR=2.1549, 95% C.I. [1.1136,4.1523], p=0.0298), CCND2 (OR=3.7925, 95% C.I.[1.1937,13.3380], p=0.03326), MYC (OR=2.6332, 95%C.I. [1.4158, 4.9120], p=0.0029), PDGFRA (OR=2.5235, 95% C.I. [1.1438, 5.5793], p=0.0291), and PIK3CA (OR=2.0328, 95% C.I. [1.1098, 3.7166], p=0.02846) were significantly more frequent. Additionally, lethal mCRPC patients were more likely to have missense (OR=4.3194, 95% C.I. [1.443456,19.3338], p=0.01687) and nonsense (OR=1.9364, 95% C.I. [1.06091,3.5250], p=0.04112) mutations at the end-of-life. Patients with a higher allelic fraction (≥0.6%) of TP53 alterations had a shorter median survival (p-value= 0.034). Conclusions: ctDNA mutations and/or amplifications in BRAF, CCND2, MYC, PDGFRA, and PIK3CA were more frequently detected in lethal mCRPC compared to matched CTRLs. Additionally, mCRPC patients with a lethal phenotype were more likely to have missense and nonsense mutations compared to the CTRL group. CtDNA assessment of copy number alterations was limited to amplifications only; additionally, with this assay, distinguishing between gene level and large scale chromosomal amplification is not assessable. Though this study is limited to a single-institution with retrospective analyses of clinical testing, understanding the somatic landscape of lethal mCRPC is critical for development of new biomarkers, strategies and ultimately druggable targets.

TPS303 Background: The treatment of advanced prostate cancer (PC) is challenging, with undesirable side effects that impact patient quality of life. Radioimmunotherapy (RIT) can localize therapy to specific tumor cells in multiple organs to reduce or eliminate damage to normal tissue. The cell surface glycoprotein prostate-specific membrane antigen (PSMA) is an ideal therapeutic target as it is highly expressed by malignant prostate cells. There is a strong rationale for further investigation of the 177 Lu-labeled, chelator-conjugated antibody, 1 77 Lu-rosopatamab, as a potential first-line RIT candidate for the treatment of PC. Methods: This multinational, multicenter, prospective, randomized, open label phase 3 study will have 2 parts: a dosimetry and safety lead-in (n=30) and a randomized treatment expansion (n=490). In Part 1, patients will be divided into 3 groups (n=10 each) to receive 2 single intravenous (IV) injections of 76 millicuries (mCi) each, 14 days apart, of 177 Lu-rosopatamab with best standard of care (SoC) combinations with abiraterone, enzalutamide, or docetaxel to fully characterize biodistribution and safety profiles of 177 Lu-DOTA-rosopatamab + SoC combinations. SoC received will be determined prior to treatment with 177 Lu-rosopatamab. In Part 2, patients will be enrolled in a 2:1 ratio to receive either the best SoC or 2 single IV injections of 76 mCi each (equivalent to a 45 mCi/m 2 dose in a standard 1.7m 2 individual) of 177 Lu-rosopatamab, given 14 days apart, plus best SoC. SoC will be determined prior to randomization, and a change in planned SoC will not be permitted. Eligible patients must have PSMA-expressing metastatic castration-resistant PC (mCRPC) that have progressed despite prior therapy with either enzalutamide or abiraterone plus prednisone, and 1 line of prior taxane therapy or have refused or are ineligible for taxanes. Patients must have adequate organ function including at least 150x10 9 /L platelets, hemoglobin 10 g/dL, and have PSMA-positive disease on 68 Ga-PSMA-11 PET/CT imaging as confirmed by a central reader. Key exclusion criteria include small cell histology, increased risk of hemorrhage or bleeding, known brain or hepatic metastases, or history of stroke, seizure, or treatment with radioisotopes within 6 months prior to randomization. The primary endpoint is radiographic progression-free survival. Key secondary endpoint is OS. Additional secondary endpoints include 5-year overall survival, tumor objective response rate, time to symptomatic skeletal event, and health-related quality of life. Clinical trial information: NCT04876651 .

TPS272 Background: Prostate-specific membrane antigen (PSMA)-targeting positron emission tomography (PET) radiopharmaceuticals enable early detection of metastatic and recurrent prostate cancer (PCa). High urinary radioactivity of some PSMA-PET agents can affect interpretation of scans in the pelvic region (prostate/prostate bed [PB]; pelvic lymph nodes [PLN]). 18 F-Piflufolastat and 18 F-flotufolastat are FDA-approved, mainly renally cleared, diagnostic PSMA-PET agents; data suggest 18 F-flotufolastat has lower urinary radioactivity than 18 F-piflufolastat, but no clinical differences have been confirmed by head-to-head intra-patient studies. The present study will directly compare the urinary radioactivity of 18 F-piflufolastat with 18 F-flotufolastat in men with low prostate-specific antigen (PSA) biochemical recurrence (BCR) of PCa after radical prostatectomy (RP). Methods: This multicenter, prospective, intra-patient comparator study will include men (≥ 18 years old) with low PSA (≤ 0.5 ng/mL) BCR of PCa who have had RP ≥ 6 months before enrollment (with undetectable PSA post surgery) and are due to have routine 18 F-piflufolastat PET. Men who have had prior 18 F-piflufolastat PET or salvage therapy, or with conditions affecting urinary output, will be excluded. Eligible patients will undergo 18 F-piflufolastat PET followed by 18 F-flotufolastat PET ≥ 24 hours but ≤ 10 days later. No diuretic will be administered for scanning purposes. Each radiopharmaceutical will be administered as a single intravenous bolus per approved US prescribing information (USPI). Scanning (with the same scanner for both scans) will start 50–90 minutes post injection of 18 F-piflufolastat and 50–70 minutes post injection of 18 F-flotufolastat. Each patient will be their own control. The primary endpoint will be difference in mean standardized uptake value (SUV mean ) between 18 F-piflufolastat and 18 F-flotufolastat as assessed in volumes of interest drawn on the urinary bladder. Secondary endpoints for both agents will include detection rates: at the patient level (overall; by baseline PSA); for local recurrences in PB subregions; and for PLN lesions. For secondary endpoints, PET scans will be interpreted per product-specific USPI by 2 specially trained, blinded, central readers (a third reader will adjudicate disagreements). Safety will be monitored until 24 hours after the second scan. Around 60 men will be screened and ≥ 52 with evaluable PET scans for both agents will be included in the primary analysis. The primary endpoint will be assessed for normality and a difference in SUV mean will be tested using 2-sided paired tests (Wilcoxon signed-rank test [non-normal]; t-test [normal]). All further endpoints, including safety, will be summarized descriptively. The trial has been open for enrollment since 10/24. Clinical trial information: NCT06604442 .

686 Background: Blue-light cystoscopy (BLC) is an established procedure for use in the diagnosis and surveillance of patients with non-muscle-invasive bladder cancer (NMIBC). It is associated with improved detection rates compared to white light cystoscopy (WLC); however, limited data is available regarding its role in upstaging and/or upgrading when used alongside WLC. The aim of this study is to assess the incidence and features of patients undergoing upstaging and/or risk-group migration with the implementation of BLC. Methods: Using data from the prospective multi-institutional Cysview Registry (2014-2024), patients with NMIBC who underwent transurethral resection or biopsy of bladder tumors were identified. The patients in whom malignant lesions were exclusively detected by BLC, as well as those experiencing an upward change in risk category (as defined by the American Urological Association [AUA] classification) based on BLC findings, were documented. The clinical features of these patients were subsequently reviewed. Results: In this study, 2,854 patients were enrolled, who collectively underwent 4,158 resections and provided 6,432 separate pathology samples. A total of 201 (7%) patients had at least one malignant lesion detected exclusively by BLC while having negative WLC. These lesions (total 335) included carcinoma in-situ (CIS) in 145 (43%), low-grade Ta in 53 (16%), high-grade Ta in 95 (28%), high-grade T1 in 37 (11%), and high-grade T2 in 5 (1%). In patients with multifocal disease, BLC resulted in AUA risk-group upward migration in 66 (2.3%) patients.Theclinical features of these two groups are presented in the table. Taken together, the total rate of upgrading or upstaging using BLC was 9.3%, including migration to low-risk in 1.2%, intermediate-risk in 2.1%, and high-risk in 6%. Conclusions: Using BLC during transurethral resection or biopsy of bladder tumors results in risk group migration in over 9% of patients with NMIBC. This impacts patient management, including the administration of intravesical therapy when it was not initially planned, an extension in the duration of therapy, or the decision to proceed with radical cystectomy. Clinical features of patients with malignant lesions detected by BLC only (A) and those with risk group migration (B). Clinical features A B Age, median (IQR), year 71 (63-76) 71 (61-77) Gender, n (%) Male Female 140 (74)49 (26) 54 (82)12 (18) History of smoking, n (%) 117 (62) 40 (61) Primary occurrence, n (%) 65 (34) 14 (21) History on intravesical therapy, n (%) 92 (49) 40 (61) Urine cytology * , n (%) Positive Suspicious Atypical Negative/NA 33 (17)21 (10)41 (20)106 (53) 13 (20)7 (11)10 (15)36 (54) IQR: interquartile range; NA: not available. *Detected by either voided urine or bladder wash.

458 Background: Renal angiomyolipoma (AML) is a common benign solid tumor of the kidney, typically found incidentally through imaging. These tumors can also present with symptoms like flank pain, hematuria, or retroperitoneal bleeding. AMLs are usually monitored and treated when they reach sizes between 4 and 6 cm based on clinical judgment, although the timing for intervention remains debated. This study aimed to investigate growth rates, assess radiographic features, and evaluate trends in clinical presentation. Methods: This multicenter, single-institution retrospective study reviewed patients diagnosed with renal AML at three Mayo Clinic locations (Rochester, Arizona, Jacksonville) from 1997 to 2021. Eligible patients had at least three abdominal scans over a minimum of two years and 36 months of follow-up. We reviewed radiologic reports, images, and charts to record demographics, tumor characteristics, imaging modalities, intervention rates, tumor sizes, and growth rates. The Mann-Whitney and Fisher exact tests were used for comparisons. Results: Among 839 patients, most were female (81.6%), with a median age of 58.55 years. Bleeding patients had significantly larger initial tumors (median 6.50 cm) compared to non-bleeding patients (median 1.20 cm), p < 0.001. Treatment with everolimus was more common in bleeding patients (12.2% vs. 2.1%), and the prevalence of tuberous sclerosis was higher in the bleeding group (19.5% vs. 6.3%). All bleeding patients underwent intervention, while 22.3% of the overall cohort received treatment. Follow-up duration and total scans did not differ significantly between groups. Over 12 months, non-bleeding patients had a median growth change of 0.00 cm [IQR: 0.00, 0.30], whereas bleeding patients showed a median growth change of 0.40 cm [IQR: 0.15, 1.00], p = 0.002. Conclusions: This study reveals significant differences in characteristics and growth patterns of renal angiomyolipomas between bleeding and non-bleeding patients. Bleeding patients had larger initial tumors and greater growth changes over time. Further studies on radiographic features may help identify lesions needing earlier intervention. Demographic and clinical characteristics of patients with renal AML: Comparison bleeding vs non-bleeding groups. Overall Non-bleeding Bleeding P-Value N 839 798 41 Gender (%) Female 685 (81.6) 650 (81.5) 35 (85.4) 0.793 Male 152 (18.1) 146 (18.3) 6 (14.6) Unknown 2 (0.2) 2 (0.3) 0 (0.0) Age (median [IQR]) 58.55 [47.04, 66.95] 58.72 [47.32, 67.19] 53.84 [42.88, 60.82] 0.015 Follow up (months) (median [IQR]) 45.30 [37.12, 89.15] 46.45 [36.32, 89.52] 39.70 [36.30, 61.63] 0.233 Total scans (median [IQR]) 3.00 [3.00, 5.00] 4.00 [3.00, 5.00] 3.00 [3.00, 4.00] 0.282 Initial size (cm) (median [IQR]) 1.30 [0.80, 2.70] 1.20 [0.70, 2.50] 6.50 [3.00, 9.30] <0.001 Everolimus (%) Yes 22 (2.6) 17 (2.1) 5 (12.2) 0.001 Tuberous sclerosis (%) Yes 58 (6.9) 50 (6.3) 8 (19.5) 0.003 Intervention (%) Yes 187 (22.3) 147 (18.4) 41 (100) <0.001

454 Background: Limited data exist on outcomes in mRCC patients with major venous involvement (MVI). Assessment of impact of a given variable on prognosis in cancer patients is challenging given competing causes of death (PMID: 25417239). This analysis aims to estimate cancer prognosis in mRCC patients with MVI, considering death from competing causes. Methods: Data from the Surveillance Epidemiology and End Results (SEER) database (2010-2020) were analyzed for survival and mortality in mRCC patients with MVI. 5-year (y) overall survival (OS) and 5-y probability of cancer death were calculated using the actuarial method in SEER*Stat 8.4.4, reported as percentages with 95% confidence intervals (CI). Results were based on the site of MVI (renal vein, inferior vena cava [IVC]) and stratified by age (<65, >65 years), gender (male, female), and race/ethnicity (Non-Hispanic [NH] White, NH Black, NH Asian/Pacific Islander [API], Hispanic). Results: A total of 89047 mRCC patients were included in our analysis of whom 10785 (12%) had major venous involvement (MVI). Overall, patients who experienced MVI had worse prognosis as compared to those who did not have MVI (5-y OS: 53.2% vs 84.4% and 5-y cancer death: 38.6% vs 8.2% respectively). Among cohort with MVI, prognosis was poor with IVC involvement as compared to involvement of renal vein (5-y OS: 36% vs 57%; 5-y cancer death: 56% vs 35% respectively). Patients who had the worst prognosis with MVI included older adults (>65 y) (5-y OS: 47.8%; 5-y cancer death: 40.8%) and NH Black (5-y OS: 41.5%; 5-y cancer death: 49.8%) (Table). Conclusions: Prognosis in mRCC with MVI, especially with IVC involvement, was poor, particularly for older adults (>65 y) and NH Black patients. Further research is needed for better prognostication and risk stratification to improve outcomes for high-risk patients. Subgroup No MVI MVI N 5-year OS (%), 95% CI 5-year Cancer death (%), 95% CI N 5-year OS (%), 95% CI 5-year Cancer death (%), 95% CI Overall population 78,262 84.4 (84.1-84.7) 8.2 (8.0-8.4) 10,785 53.2 (52.0-54.3) 38.6 (37.5-39.7) Age <65 y 49,217 89.0 (88.6-89.2) 6.5 (6.3-6.8) 5,897 57.5 (56.0-59.0) 36.8 (35.4-38.3) >65 y 29,045 77.0 (76.1-77.2) 10.9 (10.5-11.4) 4,888 47.8 (46.0-49.5) 40.8 (39.2-42.4) Gender Male 49,221 83.0 (82.7-83.5) 8.9 (8.6-9.2) 7,503 53.2 (51.8-54.6) 38.3 (37.0-39.6) Female 29,041 86.5 (86.0-86.9) 7.0 (6.7-7.4) 3,282 53.0 (51.0-55.0) 39.4 (37.4-41.3) Race/ethnicity NH White 49,520 84.0 (83.7-84.4) 8.3 (8.0-8.5) 7,182 53.5 (52.1-54.8) 38.0 (36.7-39.3) NH Black 8,878 82.0 (81.0-82.9) 8.1 (7.5-8.8) 685 41.5 (37.1-45.9) 49.8 (45.4-54.1) NH API 4,747 86.0 (85.1-87.4) 8.5 (7.6-9.4) 713 52.9 (48.2-57.3) 39.9 (35.5-44.1) Hispanic (All Races) 13,826 86.5 (85.8-87.2) 7.9 (7.4-8.4) 2,014 56.2 (53.4-58.8) 36.7 (34.1-39.2) N: number of cases; OS: overall survival; CI: confidence interval; NH: Non-Hispanic; API: Asian/Pacific Islander; MVI: major venous involvement.

270 Background: Inconsistent reporting of subgroup data across clinical trials makes interpretation and application of the evidence from trials challenging. We conducted a living systematic review to summarize evidence for American Society of Clinical Oncology (ASCO) guidelines for management of metastatic castration resistant prostate cancer (mCRPC). Here, we provide an overview of reporting patterns of subgroup data across mCRPC trials. Methods: MEDLINE and EMBASE were systematically searched from each database's inception through September 20 th , 2024, to identify phase II/III/IV randomized clinical trials assessing the efficacy and safety of treatment options in mCRPC. For outcomes of overall survival (OS) and progression free survival (PFS), data from the subgroup analyses was collected and compared across trials to assess heterogeneity in the reporting of subgroups. Results: This analysis included 141 trials (phase II: 83; phase III: 56; phase IV: 2). OS was reported by 113 (80%) trials; 32 (28%) reported OS by any subgroups with 95 unique subgroup categories. PFS was reported by 110 (78%) trials; 23 (21%) reported PFS by any subgroups with 63 unique subgroup categories. Even among consistently reported subgroups, such as age, ECOG performance status, race, geographical area, and Gleason score, considerable heterogeneity in different subgroup levels/thresholds was observed across trials. Top ten most commonly reported subgroups are summarized (Table). Conclusions: Lack of consistent reporting for subgroup analysis in mCRPC trials preclude meaningful conclusions about clinically relevant subgroup and synthesizing evidence for clinical guidelines. A standardized framework for consistent reporting of subgroup data across trials can help inform clinical practice and clinical practice guidelines. OS PFS Number of trials 113 110 Reporting subgroup analysis – N (%) 32 (28) 23 (21) Commonly reported subgroups – (N) Age (26)ECOG-PS (26)LDH (21)PSA (18)Geographic area (15)Alkaline phosphatase (14)Visceral disease (14)Gleason score (9)Race (9)Brief pain inventory level (8) Age (21) ECOG-PS (19)PSA (18)LDH (14)Geographic area (13)Visceral disease (11)Gleason score (10)Alkaline phosphatase (9)Bone metastasis (9)Disease location (9) Age – (N) <65 (14); ≥65 (9); ≤68 (1); ≥69 (1); <70 (5); ≥70 (5); ≤74 (4); 65-75 (5); ≤ 71 (1); >71 (1); ≥75 (11); >Median (1); <Median (1) <65 (12); 65-74 (6); ≥65 (6); <70 (5); ≥70 (5); <75 (4); ≥75 (10); 76-80 (1); >80 (1) ECOG-PS – (N) 0 (15); 0-1 (11), 1 (11); 1-2 (5); 2 (12) 0 (15); 0-1 (5), 1 (12); 1-2 (2); 2 (6) Race – (N) White (9)Non-white (6)African American/black (2)Asian (2) White (8)Non-white (5)African American/black (2)Asian (4) Geographic Area – (N) Europe (8)North America (14)United States (1)Australia (1)Asia (2) Europe (11)North America (13)United States (1)Australia (1)Asia (2)North and South America (2) Gleason Score – (N) 2-6 (1); 7 (1); 8 (1); <8 (8); ≥ 8 (8); 9-10 (1) <8 (10); ≥ 8 (10)