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TPS1143 Background: Poly(ADP-ribose) polymerase (PARP) inhibitors (PARPi) have revolutionized the treatment of patients (pts) with germline BRCA1/2 (gBRCA)-associated HER2-negative BC. However, resistance eventually occurs in almost all pts. Tumor-associated macrophages (TAMs), a key component of the BC tumor microenvironment, are highly immunosuppressive and associated with poor clinical outcomes. In preclinical immunocompetent models of BRCA-associated BC, PARP inhibition induces suppressive CSF-1R+ TAMs, contributing to resistance, so that combining anti-CSF-1R therapy with PARPi significantly enhances progression free survival (PFS) compared to PARPi monotherapy (190d vs 92d). Axatilimab (SNDX-6352; Ab969.g2), a humanized IgG4 monoclonal antibody targeting CSF-1R, reduces TAMs, potentially slowing tumor growth and enhancing anti-tumor immunity. In the Phase I SNDX-6352-0502 study for advanced solid tumors, axatilimab showed tolerability at the highest dose (6 mg/kg), with biomarker modulation observed at doses as low as 1 mg/kg. Axatilimab is FDA-approved for chronic graft-versus-host disease (cGVHD). Methods: AXALAP (NCT06488378) is a non-randomized open-label, proof-of-concept phase 1 study designed to evaluate axatilimab 1mg/kg or 3mg/kg every 2 weeks in combination with olaparib 300 mg twice daily in pts with somatic or germline BRCA1/2 - and PALB2 -associated HER2-negative metastatic BC. Patients must be PARPi naïve, or have not progressed on prior PARPi, and have received up to 2 prior lines of chemotherapy for metastatic disease. Pts will receive a two-week lead-in of olaparib monotherapy, followed by combined olaparib and axatilimab. Pts will undergo mandatory tumor biopsies pre-treatment, after the 2-week olaparib lead-in, and after 2 cycles of olaparib/axatilimab, with an optional biopsy at time-of-progression. Primary objectives are to establish the maximum tolerated dose (MTD) and recommended phase 2 dose and to assess the safety and tolerability of axatilimab and olaparib. Secondary objectives include assessment of changes in CSF-1R+ CD163+ macrophage levels after olaparib monotherapy and after 2 cycles of combination treatment at the MTD; to determine the objective response rate and the median PFS of the combination per RECIST 1.1 criteria. The MTD will be determined by Bayesian Optimal Interval (BOIN) design. Pts will be treated in cohorts of 3 with a maximum of 10 at each dose. If the MTD is identified as 3mg/kg, we will complete enrollment of 10 pts at 1 mg/kg to assess biological effectiveness and clinical efficacy of the lower dose. We expect to treat up to 20 pts, who will receive study treatment until development of unacceptable toxicity or disease progression. Enrollment began on 5/2024 at Dana-Farber Cancer Institute and the trial will also open at Beth Israel Deaconess Medical Center and Mayo Clinic-Rochester. Clinical trial information: NCT03604692 .

e21600 Background: Uveal melanoma (UM), the most common intraocular malignancy in the U.S., metastasizes in 50% of patients, frequently to the liver (~90%) with poor prognosis (median overall survival [mOS] 1 year). Metastatic UM (mUM) literature is limited (due to its rarity/complexity) and management remains challenging, as standard therapies—liver-directed approaches (e.g. transarterial chemoembolization [TACE]) and systemic therapy with tebentafusp (limited to HLA-A*02:01-positivity)—offer limited efficacy, with no durable responses or significant survival benefits. Interestingly, Delcath’s recent FOCUS Phase 3 trial demonstrated the efficacy of the melphalan/Hepatic Delivery System for unresectable mUM, with an objective response rate (ORR) of 36.3%, 1-year OS of 80%, and median progression-free survival (PFS) of 9 months. Here, we present a large retrospective study of liver-predominant mUM treated with immunoembolization (IE) at a tertiary academic center. This study provides valuable data to the underreported mUM literature. We also compare our findings with Delcath’s trial to contextualize results and identify clinical factors influencing treatment response and prognosis. Methods: We retrospectively reviewed charts of mUM patients treated with IE (age ≥18 years, 2010–2023). Data collected included demographics, clinical/pathology/molecular details, and management/outcomes. Subgroup analysis on prior systemic therapy use was performed (similar to Delcath). The primary outcome was OS at 12 and 24 months. Results: 43 patients were included (100% White, 62.8% female, median age 62). Most had choroidal type (95.3%), hepatic-only metastases (90.7%), and were treatment-naïve before IE (72.1%). Across 249 IE procedures (5.8 per patient, mean duration 9.1 months), we observed median PFS and OS of 9.2 and 23 months, respectively - comparable to Delcath’s trial (9 and 20.5 months). Despite higher disease progression in our study (62.8% vs. 25.3%) and lower best clinical response (27.9% vs. 73.7%), 1-year (67% vs. 80%) and 2-year OS rates (49% vs. 43%) were similar. Subgroup analysis revealed better outcomes in previously treated patients (n = 12) compared to treatment-naïve patients (n = 31), with improved median PFS (29.9 vs. 7.2 months) and 1- and 2-year OS (75% vs. 65% and 58.3% vs. 41.9%, respectively). This contrasts with Delcath’s findings, where prior therapy did not significantly affect PFS or OS. Median PFS was comparable in treatment-naïve groups (7.2 vs. 9 months) but markedly improved in our previously treated group (29.9 vs. 9.2 months). Conclusions: We highlight IE’s comparable efficacy to Delcath’s melphalan/Hepatic Delivery System regarding mUM PFS and OS, with added benefits for previously treated patients. While our findings advance understanding of mUM management, more prospective studies are needed to improve therapeutic strategies/patient outcomes.

6008 Background: ATC patients present with advanced, often surgically unresectable disease with historically dismal prognosis. Median PFS and OS of DT without pembrolizumab were 6.7 and 13.5 months, respectively, in the ROAR trial. Neoadjuvant DTP achieved locoregional control without radical surgery in a retrospective series of BRAF m-ATC patients, providing rationale to evaluate efficacy and safety in a phase 2 prospective trial. Methods: In this single-arm multicenter phase 2 trial, patients with BRAF m-ATC stage IVB/IVC were enrolled in 5 US centers. Following a 3-6 week run-in with D (150 mg BID) and T (2 mg daily), P (200 mg Q3W) was added, with restaging every three (21-day) cycles. Post-operatively, patients continued P (or DTP) with radiotherapy or transitioned directly to adjuvant DTP (up to 26 cycles). Primary endpoints included R0/R1 resection rate (historically 5%) and overall survival (OS). Secondary endpoints included RECIST 1.1 response after DTP and progression-free survival (PFS). Results: Between 9/2021-1/2025, 42 patients were enrolled; 36 are included in the current analysis (3 not evaluable, 3 pending surgery) (Table). Patients received median 4 (range: 2-7) neoadjuvant DTP cycles, with 26 (72%) achieving radiographic PR/CR. 30 patients (83%) had surgery after neoadjuvant DTP, achieving R0/R1 resection in 29/30 (97%). Mean surgical morbidity score (0-4 scale, 4=unresectable) improved from 3.3 to 1.6 after DTP (p<0.01). Complete ATC pathologic response occurred in 20/30 patients (67%), while 10/30 (33%) had residual ATC in the surgical specimen. Postoperatively, 11/30 (37%) received adjuvant neck radiation, and 28/36 (78%) completed a median of 11 (range: 1-26) adjuvant DTP cycles. With median follow up 18 months, 15/36 (42%) patients died. Median OS was 20 months (95% CI: 12.6-NR); 1- and 2-year OS were 71% and 48%. Complete pathologic responders had better 2-year OS than those with residual ATC (69% vs. 22%, p=0.02). Median PFS was 13.9 months (95% CI, 7.5-NR); 1- and 2-year PFS were 57% and 36%. Grade 5 adverse events occurred in 8 patients (22%), including one possible (duodenal perforation), one probable (kidney injury with sepsis), and 6 unlikely/unrelated treatment-related deaths. Conclusions: Neoadjuvant DTP enables surgical resection in BRAF m-ATC compared with historical controls, and leads to improved PFS and OS. This approach should now be considered a standard of care for BRAF m-ATC. Clinical trial information: NCT04675710 . Total N=36 Age (y), median (range) 67 (46-86) Stage IVB/IVC, n (%) 15 (42%)/21 (58%) Best RECIST response neoadjuvant phase, n (%) CR 2 (6%) PR 24 (67%) SD 6 (17%) PD 4 (11%) Percent change target lesion diameter, mean (95% CI) -44% (-54%, -34%) Surgical morbidity score change, mean (95% CI) -1.7 (-2.1, -1.3)

e23020 Background: Precision medicine studies must overcome the challenges of identifying patients with uncommon molecular targets and small cohort sizes for correlative studies. BASECAMP-1 (NCT04981119) is a prescreening study that uses a single assay to address both problems by: 1) efficiently screening potentially eligible patients for subsequent clinical trials of Tmod logic-gated chimeric antigen receptor T-cell (CAR T) therapies; and 2) providing a large dataset available for translational studies. Methods: Initially, patients were identified for BASECAMP-1 by consenting and genotyping all potentially eligible patients for human leukocyte antigen (HLA)-A*02 heterozygosity. To improve screening efficiency, we co-developed a patient-matching program with Tempus AI, Inc (Tempus), in which Tempus informs the principal investigators of next-generation sequenced (NGS) patients with HLA-A*02 heterozygosity within their health system who may be eligible for BASECAMP-1. Patients are screened using the Tempus xT platform, which uses genomic and RNA sequencing (RNAseq) analyses to determine gene mutations and expression. Enrolled patients with colorectal (CRC), non-small cell lung, ovarian (OVCA), and pancreatic cancers (PANC) were analyzed for tumor purity, mutation distribution, HLA-A*02 loss of heterozygosity (LOH) status, and RNAseq to validate the data available for future clinical analyses. Results: As of January 3, 2025, 80 participants have been enrolled in BASECAMP-1. Through individual screening methods, 1684 patients were screened at 13 study sites, of which 30 patients had tumor-specific HLA-A*02 LOH and were enrolled (~1 eligible patient identified per 56 screened). The patient-matching program identified 282 patients with HLA-A*02 LOH at 12 sites; of these, 50 consented to the BASECAMP-1 study (~1 patient enrolled per 6 identified), demonstrating higher efficiency than the individual patient screening method. Correlative data from xT were available for 360 patients with germline HLA-A*02 and provided insights into mutational distribution and target expression. LOH status was not associated with tumor-specific differences in missense mutational distribution. RNAseq data demonstrated higher CEACAM5 expression in CRC and higher MSLN in PANC and OVCA vs other tumor types, while EGFR was consistently expressed with reduced variance across tumor types, confirming these as potential target antigens for Tmod CAR T interventional trials EVEREST-1, EVEREST-2, and DENALI-1. Conclusions: Identification and enrollment of HLA-A*02 LOH patients into BASECAMP-1 for logic-gated CAR T therapeutic studies were accelerated by the patient matching program. Concurrent xT analysis provides opportunities to augment analyses from robust propensity-matched comparisons, response correlation studies, and other translational discovery. Clinical trial information: NCT04981119 .

1649 Background: Findings from our prior large-scale comparative effectiveness trial showed the equivalent effect of delivering early palliative care via video versus in-person on quality of life among patients with advanced non-small cell lung cancer (NSCLC). We now report on whether the two care delivery modalities were equivalent with respect to patient-reported communication with clinicians about their end-of-life (EOL) care preferences and hospice utilization. Methods: Between 6/14/2018 and 5/4/2023, we enrolled 1250 patients with newly diagnosed advanced NSCLC in a randomized trial of early palliative care across 22 US cancer centers. Patients were randomly assigned to meet with a palliative care clinician every 4 weeks from enrollment through the course of the disease, either via video or in the outpatient clinic. Participants completed self-report surveys at baseline and weeks 12, 24, 36, and 48, including an item asking if they had discussed with their clinicians the care they would want to receive if dying (yes/no); patients’ final assessments prior to death or last follow up were analyzed. We reviewed patients’ health records to collect data on hospice referral and length of stay. To test the equivalence in these outcomes, we used a binomial generalized linear model with the identity link function (pre-specified equivalence margin of ±8% for patient-reported communication about EOL care) and linear regression (pre-specified equivalence margin of ±6 days for mean length of stay in hospice). P-values were adjusted for multiplicity using a Bonferroni correction. Results: Of the 1250 enrolled participants, 888 (71.0%) completed at least one survey post baseline regarding whether they communicated with clinicians about EOL care preferences. Among those, 29.1% of the video group and 26.0% of the in-person group reported “yes,” indicating that they recalled such EOL care discussions (difference = 3.1%, 95% CI: -1.8%, 8.1%; p = 0.26 for equivalence). During the course of the trial, 733/1250 (58.6%) patients died, of whom 537/733 (73.3%) were referred to hospice. Mean lengths of hospice stay were 25.3 days for the video group versus 25.1 days for the in-person group (difference = 0.2, 95% CI: -7.0, 7.4; p = 0.46 for equivalence). When excluding outlying patients receiving hospice services > 180 days (n = 13), the mean lengths of hospice stay were 19.1 (video group) versus 19.7 (in-person group) days (difference = -0.6, 95% CI: -4.6, 3.3; p = 0.06 for equivalence). Conclusions: Although thresholds were not met to confirm equivalence statistically, the two modalities for delivering early palliative care demonstrate very similar outcomes with respect to patient-clinician communication about EOL care and hospice utilization. These findings provide further evidence of the utility of video visits for providing high quality palliative and EOL care. Clinical trial information: ClinicalTrials.gov Identifier ( NCT03375489 ) .

Abstract Infection is increasingly recognized as a significant cause of morbidity and mortality in patients with relapsed/refractory (R/R) large B-cell lymphoma (LBCL) receiving CD19 chimeric antigen receptor (CAR) T-cell therapy. The current study analyzed the natural history, risk factors, and outcomes of infection in 3350 patients with R/R LBCL receiving commercial CD19 CAR T-cell therapy (n = 2804 axicabtagene ciloleucel [axi-cel], n = 546 tisagenlecleucel) from December 2017 to June 2022. Infection developed in 834 patients (24.9%) within 100 days after infusion, resulting in an infection density of 0.43 per 100 patient days and a 100-day cumulative incidence of 22%. Bacterial, viral, and fungal infections were recorded in 527 (15.7%), 374 (11.2%), and 108 patients (3.2%), respectively, with corresponding infection densities of 0.23, 0.15, and 0.04 per 100 patient days. After a 24-month median follow-up, 1482 patients (44%) had died, with infection as the primary cause in 173 cases (12%). The 100-day infection-related mortality (IRM) was 1.6% (95% confidence interval, 1.2-2.0). Patients with a Karnofsky performance score of ≤80, infection history before CAR T-cell therapy, axi-cel therapy, severe cytokine release syndrome (grade ≥3), and severe immune effector cell–associated neurotoxicity syndrome (grade ≥3) had increased infection risk. Infections within 100 days were an independent risk factor for inferior overall survival beyond day 100 after CD19 CAR T-cell therapy. In conclusion, study results show a significant incidence of infection and IRM in patients with R/R LBCL treated with CD19 CAR T-cell therapy. Furthermore, results identify patients at a heightened risk of infection, offering insights to guide potential interventions aimed at mitigating infection and improving patient outcomes after CAR T-cell therapy.

1586 Background: Black and Hispanic breast cancer (BC) survivors have a higher prevalence of obesity and experience less success with weight loss interventions (WLI) than White BC survivors. The BWEL trial (Alliance A011401; NCT02750826) is a phase III randomized trial evaluating the impact of a 2-year telephone-based WLI on invasive disease-free survival in participants (pts) with stage II-III HER2-negative BC and a BMI ≥ 27 kg/m 2 . At 12-months, the WLI induced significant weight loss across demographic factors, including race and ethnicity. However, Black and Hispanic pts lost less weight and completed fewer calls than White pts. Here, we evaluate intervention adherence, engagement and tool utilization in BWEL pts by race and ethnicity. Methods: BWEL randomized pts to a WLI plus health education (HE) or HE alone. WLI pts received semi-structured telephone-based health coaching, delivered in English or Spanish, and received an activity monitor and wireless scale. Pts self-reported race and ethnicity. Mean values for call duration, call density (time to complete the initial 12-week intensive intervention phase), intervention attrition, and frequency of Fitbit use and weight tracking over 12-months were compared by race and ethnicity, comparing least squares means with Tukey-Kramer adjustment for multiple comparisons with adjusted p-values. Results: Of 3181 pts randomized to the study between 08/2016 and 02/2021, 1591 pts were allocated to the WLI arm. 80.5% of pts were White, 12.8% Black, and 7.1% Hispanic. Average BMI was 34.5 (±5.7) kg/m2. Compared to White pts, Black pts had fewer days of Fitbit usage (113.6 vs. 159.8, p<0.0001) and weight tracking (77.9 vs. 135.6 days, p< 0.0001). Hispanic pts had fewer days of Fitbit usage (108.8 vs. 154.9, p= 0.001) and weight tracking (87 vs. 129.5 days, p=0.0002) compared to non-Hispanic pts. There were no differences in attrition rate, average call duration, or call density by race or ethnicity. Conclusions: In a phase III WLI trial, engagement with tools designed to support weight loss was significantly lower in Black and Hispanic pts. Future work is needed to explore ways to enhance engagement and improve weight loss outcomes for racial and ethnic minority pts. Support: U10CA180821, U10CA180882, UG1CA189823; https://acknowledgments.alliancefound.org . Clinical trial information: NCT02750826 . Measure of engagement Race Ethnicity WhiteN=1281 BlackN=204 p-value Non-HispanicN=1459 HispanicN=113 p-value Withdrew from intervention n (%) 58 (4.5%) 13 (6.4%) 0.56 70 (4.8%) 6 (5.3%) 0.51 Call Duration (min)Mean (SD) 34.5 (7.6) 34.6 (9.1) 0.99 34.6 (7.8) 33.3 (7.9) 0.25 Call density(weeks)Mean (SD) 14.2 (7.2) 14.2 (8.8) 0.99 14.2 (7.3) 14.2 (9.7) 0.99 Days of Fitbit UseMean (SD) 159.8 (132.2) 113.6 (124.7) < 0.0001 154.9 (131.8) 108.8 (125.7) 0.001 Days of weight trackingMean (SD) 135.6 (109.5) 77.9 (87.5) < 0.0001 129.5 (108.8) 87 (96.5) 0.0002

526 Background: The PALLAS trial (NCT02513394) investigated the efficacy of the addition of palbociclib (palbo) to standard adjuvant endocrine therapy (ET) to reduce breast cancer recurrence. Previous analyses of this trial have not shown significant benefit of combination palbo+ET over ET alone. Given prior data showing that extent of neutropenia is associated with response to palbo and other cell cycle-specific therapies, we evaluated whether extent of neutropenia could identify responders to palbo in the adjuvant setting. Methods: PALLAS is a global, open-label, phase III trial that randomized patients (pts) with stage II-III hormone-receptor positive, HER2-negative breast cancer to receive ET for ≥5 years with or without standard-dose palbo for 2 years in 28-day cycles. The primary endpoint is invasive disease-free survival (iDFS). For this exploratory analysis, the palbo population was classified into pts with treatment-emergent high-grade neutropenia (HGN) with maximum grade ≥3 (absolute neutrophil count <1000), or low-grade/no neutropenia (LGN) with maximum grade <2; these groups were compared to each other and to the ET alone group for 5-year iDFS outcomes. Logistic regression examined individual baseline characteristics associated with HGN during the first 3 cycles within the palbo group. Impact of HGN during the first 3, 6, and 12 cycles on iDFS was tested using univariate and multivariable landmark Cox regression. Results: The safety population included 5736 pts, 2840 allocated to palbo+ET, 2896 to ET alone. Prior publications reported no new safety signals, low rates of serious infection, and no grade 5 treatment-related events. The palbo+ET group consisted of 1006 (35.4%) LGN and 1834 (64.6%) HGN. 5-year iDFS results are shown in the table. Pts who received palbo+ET and developed HGN by the end of cycle 6 had significantly improved 5-year iDFS compared to those who received ET alone (p=0.04), which remained statistically significant when adjusting for body mass index (BMI), prior chemotherapy, and race. Multivariable logistic regression showed lower BMI, prior chemotherapy, Asian race, and prior mastectomy were significantly associated with HGN (all p<0.05). Conclusions: In this exploratory analysis of the phase III PALLAS adjuvant trial, addition of palbo to ET appeared to be superior to ET alone in pts who developed HGN in the first 6 cycles of treatment but not in those who had LGN. These findings are consistent with observations in the metastatic setting suggesting that neutropenia could be a useful biomarker for palbo concentration and efficacy. Clinical trial information: NCT02513394 . Maximum grade neutropenia measured at end of cycle: 5-year iDFS Palbo+ET HGN (%) Palbo+ET LGN (%) ET alone (%) Hazard Ratio p-value 3 84.9 84.4 1.06 0.54 84.9 82.9 1.17 0.06 6 85.6 84.9 1.08 0.44 85.6 83.4 1.19 0.04 12 86.3 85.9 1.06 0.57 86.3 85.0 1.12 0.20

561 Background: Obesity and other lifestyle factors are associated with breast cancer (BC) risk and outcomes. These relationships appear to vary in pre- vs postmenopausal women. Here we explore associations between pathological features, diet quality and physical activity (PA) in patients (pts) with BC enrolled in the BWEL (Alliance for Clinical Trials in Oncology A011401) trial, stratifying for menopausal status. Methods: BWEL is a phase III trial evaluating the impact of a weight loss intervention on disease outcomes in 3180 pts with stage II-III HER2– BC and body mass index ≥27 kg/m 2 . The first 542 BWEL pts underwent assessment of PA (7-Day PA Recall) and diet (24-hour Diet Recall) at enrollment. Healthy Eating Index 2020 (HEI) score (0-100, higher value = healthier diet) and minutes/week (min/wk) of moderate/vigorous PA (MVPA) were calculated. Estrogen receptor (ER) and progesterone receptor (PR) expression level (%) were abstracted from pathology reports. Analyses of links between HEI score, MVPA min/wk, % ER/PR, stratified by menopausal status, were conducted using t-tests; differential associations by menopausal status used linear regression models with interaction term. Results: In 523 pts with available pathology data, 76.5% had ER/PR+ BC, 56.2% were postmenopausal. Median HEI score was 50.1 (range 18.1-96.4), median MVPA min/wk was 0 (range 0-630), median time from diagnosis to enrollment was 10.0 months (range 2.4-13.1). In postmenopausal pts, higher diet quality was linked to increased % ER and PR (HEI above vs below median, mean % ER 78.0 vs 66.1, p=0.012; mean % PR 57.7 vs 43.1, p=0.004). The relationship between HEI score and % ER/PR differed significantly by menopausal status (interaction term of menopausal status and % ER: p=0.006; and % PR: p=0.012); there were no significant associations between HEI scores and % ER/PR in premenopausal pts. There were no significant associations between PA and % ER/PR. Conclusions: Healthier diet was associated with higher % ER and PR in postmenopausal pts with BC, but no relationship was seen in premenopausal pts. These data suggest that lifestyle factors may influence BC pathologic features related to outcomes in older women. Support: U10CA180821, U10CA180882, UG1CA189823, U24CA196171, https://acknowledgments.alliancefound.org . Clinical trial information: NCT02750826 . % ER mean (SD) p value % PR mean (SD) p value Post-Menopausal HEI* score≤50.1 [n=134]>50.1 [n=156] 66.1 (43.3)78.0 (36.8) 0.012 43.1 (41.8)57.7 (41.0) 0.004 MVPA † min/wk0 [n=147]≥1 [n=147] 74.5 (39.3)70.3 (41.2) 0.37 50.0 (41.8)53.0 (42.0) 0.41 Pre-Menopausal HEI* score≤50.1 [n=124]>50.1 [n=103] 70.5 (38.5)65.5 (43.0) 0.15 53.5 (41.1)49.1 (43.0) 0.43 MVPA † min/wk0 [n=112]≥1 [n=113] 66.3 (41.0)66.3 (41.2) 0.99 49.5 (41.4)52.6 (42.7) 0.59 *Healthy Eating Index. † Moderate/Vigorous Physical Activity.

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.