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1110 Background: CDK4/6 inhibitors with endocrine therapy are widely used for HR+/HER2– metastatic breast cancer (BC). While studies have shown similar progression-free outcomes across agents, overall survival (OS) data are limited. Since OS is a definitive endpoint and BMI may influence outcomes, this study examines BMI-dependent OS differences among CDK4/6 inhibitors. Methods: A retrospective cohort study was conducted using the Mayo Clinic Platform full AMC1 dataset. Postmenopausal women with BC receiving palbociclib/ribociclib/abemaciclib plus aromatase inhibitor (AI) were included. Patients with prior use of fulvestrant, anthracyclines, radiation therapy, GnRH agonists, or history of MACE, heart failure, myocardial infarction, or stroke before BC diagnosis were excluded. Patients were stratified by BMI and CDK4/6 inhibitor. The primary outcome was 5-year OS. Results: Among 1,989 patients (palbociclib: 868; ribociclib: 465; abemaciclib: 656), palbociclib was associated with significantly worse OS compared to ribociclib in BMI <25 (HR 2.91; 95% CI: 1.76–4.79; P < 0.01) and BMI ≥30 (HR 1.91; 95% CI: 1.21–3.01; P < 0.01). Compared to abemaciclib, palbociclib showed worse OS: BMI <25 (HR 1.73; P < 0.01), BMI 25–30 (HR 1.56; P < 0.01), and BMI ≥30 (HR 1.82; P < 0.01). No significant OS differences were observed between ribociclib and abemaciclib. Palbociclib patients were older, particularly in BMI <25 (Cohen's D = 0.39 vs. ribociclib; 0.27 vs. abemaciclib) and BMI ≥30 (0.28 vs. ribociclib; 0.23 vs. abemaciclib). In the BMI 25–30 group, palbociclib group was also older than ribociclib group (Cohen's D = 0.26). Conclusions: In postmenopausal BC patients on AIs and CDK4/6 inhibitors, palbociclib was associated with worse OS in BMI < 25 and BMI ≥ 30 groups, while ribociclib and abemaciclib showed similar outcomes across BMI groups. Palbociclib patients were older than those on other drugs, which may partially confound results; however, in the BMI 25–30 group, despite similar age differences, no survival difference was observed between palbociclib and ribociclib, suggesting age alone may have limited impact. These findings indicate a potential interaction between BMI and drug choice, and highlight the need for prospective studies to confirm and adjust for these variables. Limitations include the observational design and inability to perform multivariable regression analyses to adjust for confounders. Overall survival comparisons by CDK4/6 inhibitor and BMI subgroup. Comparison BMI Group Hazard Ratio (95% CI) P-value Palbociclib vs Ribociclib <25 2.91 (1.76 – 4.79) < 0.01 25 – 30 1.34 (0.87 – 2.071) 0.17 ≥30 1.91 (1.21 – 3.01) < 0.01 Palbociclib vs Abemaciclib <25 1.73 (1.29 – 2.32) < 0.01 25 – 30 1.56 (1.09 – 2.23) < 0.01 ≥30 1.82 (1.15 – 2.88) < 0.01 Ribociclib vs Abemaciclib <25 1.27 (0.81 – 1.99) 0.29 25 – 30 0.87 (0.54 – 1.43) 0.59 ≥30 1.05 (0.63 – 1.75) 0.85

1108 Background: Metastatic breast cancer (MBC) remains limited by resistance and cumulative toxicity in heavily pretreated patients. Bria-IMT combines a whole-cell vaccine (SV-BR-1-GM) with anti-PD-1 (CPI) to enhance tumor antigen presentation and overcome immune exhaustion. SV-BR-1-GM is an irradiated breast cancer cell line engineered to secrete GM-CSF, promoting HLA class I and II antigen presentation and T-cell activation. We identified a subset with durable clinical benefit and biologic correlates. Methods: Phase I/II evaluating the Bria-IMT regimen (SV-BR-1-GM with CPI (pembrolizumab or retifanlimab). In the phase II portion, pts were randomized 1:1 to CPI initiation at cycle 1 (C1) or delayed start at cycle 2 (C2). Two SV-BR-1-GM formulations were administered: IFNγ-stimulated (IFγ) or unstimulated (≠IFγ). Baseline circulating tumor cells (CTCs) and delayed-type hypersensitivity (DTH) responses to SV-BR-1-GM were assessed as biomarkers. Progression free survival (PFS) and overall survival (OS) were analyzed using Kaplan Meier (KM). Subgroup comparisons (CPI sequencing, IP formulation, DTH status, and baseline CTC status) are exploratory. Results: 32 phase 2 pts were randomized: median age 61 (range 41-80); median prior lines 6 (range 2-13); PFS 3.5 mo (95% CI 3.0 - 4.2); OS 9.5 mo (95% CI 7.0 - 17.4). Among CPI C1 vs C2 starts: median OS 13.3 v 7.4mo (HR 0.8; 95% CI 0.4-1.9, p = 0.6); OS KM probability at 12 mo 47% v 58%. Median OS w ≠IFγ v IFNγ IP =16.6 v 9.1 mo (HR 0.58; 95% CI 0.2-1.4, p = 0.23); OS KM at 12 mo 52.4% v 27.3%. DTH+ v DTH- median OS 11.9 v 4.7 mo (HR 0.0009; p = <0.001), OS KM @12 mo 48% v 0%. CTCs <5 v > 5 at baseline had median OS 16.6 v 5.5 mo (HR 0.005; 95% CI 0.0003-0.09, p < 0.001), OS at 12 mo 49% vs 33%. Among long term survivors @12mo, OS probability 44.0% (95% CI 26.2-59.7%) and @24 mo 26% (95% CI 12.1-42.4%). Median follow up 25.8 with PFS 5.4 mo. 5 received ≠IFγ formulation v 1 w IFNγ. All 6 (3 with CPI @C1, 3@C2) experienced delayed type hypersensitivity reaction to inoculation. 67% of long responders matched HLA at >1 allele, 33% no match. Grade ≥3 AEs in 47% of pts, most common injection site rxn, nausea, fatigue; no tx related D/C; no unexpected safety signals. Conclusions: In heavily pretreated MBC, Bria-IMT demonstrated a tolerable safety profile and the emergence of a long-term survivor cohort. Durable survival was observed beyond 12 and 24 months. Differential survival favoring Ph3 formulation, DTH positivity, lower baseline CTC burden, and early CPI sequencing was observed. These findings support prospective validation of DTH and CTC as predictive biomarkers and the continued use of the Ph3 IP formulation in the ongoing phase 3 study Bria-ABC (NCT06072612). Clinical trial information: NCT06072612 .

11078 Background: Unmet essential needs, such as food, transportation, and housing insecurity, can create barriers to timely cancer treatment. Delayed or prolonged courses of definitive radiotherapy (RT) can compromise cancer outcomes like recurrence and survival. There are limited prospective data testing interventions to improve timely cancer treatment completion by meeting essential needs. Methods: We conducted a pragmatic single-arm pilot study testing an enhanced financial assistance intervention for unmet needs during RT. Eligibility criteria included adults with a cancer diagnosis and unmet social needs (via social risk screening and/or social worker evaluation) who were prescribed or undergoing a course of RT with > 10 fractions remaining. Participants received standard institutional assistance (e.g., limited support for travel/lodging with strict eligibility criteria) plus the enhanced assistance intervention, including needs assessments prior to and during RT and up to $2000/patient of tailored unconditional monetary transfer via gift cards for all essential needs identified. The primary outcome was delay-free completion of RT (DFC: completing all prescribed RT fractions and delaying < 5 fractions). The study was powered (power = 80%, 1-sided alpha = 0.2 for this pilot study) to detect a 10-percentage point increase in % DFC relative to a historic benchmark of 83% (based on similar patients from our institution), with required sample size of N = 33. Due to delays in gift card administration (on average ~2 weeks after consent), we also present per protocol analysis, limited to patients who had > 10 fractions remaining after first receiving financial assistance. Post-hoc analyses using generalized linear mixed models evaluated percentages of delayed fractions prior to and after an individual’s receipt of financial assistance. Results: 35 met inclusion criteria and were approached, 33/35 enrolled. Participants received median assistance of $1800 ($700-2000) and had a median of 27 RT fractions after consent (range: 12-35) and 17 (3-34) after receiving assistance. In the overall cohort, 1 patient did not complete RT and 2 patients had ≥5 delayed fractions, leading to 30/33 achieving DFC (90.9%, 80% CI = 83.9 – 100), significantly higher than the 83% benchmark. In the per protocol analysis, 27/28 achieved DFC (96.4%, 80% CI = 89.7–100, P = .037). Among the 27 patients who started RT prior to receiving assistance, mixed model analysis showed more delayed fractions prior to (7.1%) vs. after (3.0%) receiving assistance (OR 2.84, 95% CI = 1.43-5.80, P = .003). Conclusions: In this prospective pilot study, a tailored enhanced financial assistance intervention for unmet essential needs led to improved delay-free completion of RT over a historic benchmark. Further analysis on patient-reported quality of life and financial toxicity will be reported in the future. Clinical trial information: NCT06582849 .

11025 Background: Adjuvant endocrine therapy (AET) improves outcomes in HR+ breast cancer. Nonadherence to AET is common, but manual screening for nonadherence is fraught. High-specificity structured cancer electronic health record (EHR) data, particularly if it includes key variables like stage, could streamline these steps for both clinical care and research purposes. We conducted an analysis of approaches to identifying patients as eligible for a multi-site AET adherence study to understand how variation in structured data informatics-supported screening impacts coordinator time. Methods: Mayo Clinic implemented a two-step identification: (1) EHR structured data (diagnosis date, stage, ER/PR/HER2 positivity, medication script) to prescreen for eligibility; (2) SureScripts fills to flag nonadherence using proportion of days covered < 80% across early fills. Medical College of Wisconsin (MCW) implemented a more manual screening process for Step 1 using only medication scripts. Coordinators at both sites then conducted a medical record review to assess if the resulting list of patients had a plan to continue AET for at least two additional years. Opt-out clinician permission preceded patient contact; pharmacists delivered a patient reported outcome (PRO)-guided intervention and documented encounters. Results: At Mayo, 829 patients were prescreened for study eligibility through informatics workflow; 120 (14.5%) met eligibility criteria. At MCW, 1,763 patients were prescreened; 168 (9.5%) were eligible. EHR filters included non–breast cancer encounters (50% at MCW) and ineligible based on time since cancer (36% at Mayo; 26% at MCW). At Mayo, screening required 5.6 minutes/patient for experienced coordinators. At MCW, experienced coordinators averaged 6.67 minutes/patient and inexperienced coordinators averaged 9.33 minutes/patient. Conclusions: Structured EHR data, pharmacy-fill information, and standardized workflows allowed consistent prescreening, intervention and recruitment processes across sites. Higher-specificity informatics-supported screening reduced the percentage of patients requiring manual review and reduced coordinator screening time. It also supported timely provider-permission steps and patient outreach. These workflows were feasible to implement at both institutions, and study enrollment is ongoing. Clinical trial information: NCT06765707 .

10610 Background: The role for genetic testing (GT) for prostate cancer (PCa) patients (pts) has expanded to find pts with germline pathogenic variants (PV) for therapeutic opportunities given FDA-approvals for PARP inhibitors in metastatic PCa as well as understanding familial cancer risk and opportunities for tailored screening and risk reduction. The PROMISE Registry (NCT04995198) was set up as a genetic registry to partner with PCa pts for rapid access to a new standard of care given insurance coverage and clinical implementation were initially major barriers. A second goal is to characterize disease features and treatment outcomes to inform management and provide updates about novel therapeutic clinical trials, both of which remain important to rare genetic variant carriers. Methods: PROMISE is a US decentralized prospective PCa genetic registry initiated in 2021 with initial phase to enroll and provide clinical-grade germline genetic testing (30 gene cancer-specific panel) to 5,000 PCa pts to identify ~500 PCa pts with variants of interest (pathogenic variants, PV, and variants of uncertain significance, VUS) in DNA repair genes for long-term clinical follow-up of 15 years (LTFU). Here, we report the initial phase testing results and identification of the LTFU cohort. Study design and enrollment strategy have been reported separately. Results: Between 2021-2026, 7,275 pts with any stage PCa across 50 US states self-consented to PROMISE, of which 5,674 (78%) of pts completed genetic testing, indicating feasibility of patient-directed, decentralized enrollment. We have identified 495 (8.7%) pts for LTFU. Baseline data is reported for n=367 (Table 1, will be updated at time of presentation). The most frequently observed PV/LPV variants being in CHEK2 (25%) , BRCA2 (23%) , ATM (12%) , and BRCA1 (4.6%). At the time of PCa diagnosis, the majority of LTFU pts had non-metastatic disease, with 47% of pts with Gleason>7, median PSA of 5 ng/mL, and median time from diagnosis to PROMISE GT of 25 months. Conclusions: PROMISE is a nationwide decentralized PCa genetic registry that has completed initial goal to recruit 5,000 PCa pts to offer germline genetic testing and recruit a cohort of 500 for LTFU. Data about diagnosis characteristics are reported, and analysis of ongoing disease course, treatment response/outcomes and overall survival is being collected. Clinical trial information: NCT04995198 . Long-term follow-up participant demographics. Characteristic Overall, N = 367 Age at Diagnosis (yrs) 63 (57, 69) Race N = 361 (6, nr) Asian, American Indian or Alaska Native, Multiracial, Other 22 (6.0%) Black or African American 22 (6.0%) White 317 (86%) Disease State at Diagnosis N = 348 (19, nr) Metastatic 46 (13%) Non-metastatic 302 (87%) Time from Diagnosis to PROMISE GT (months) 25 (4, 82) Gleason Score N = 280 (87, nr) </= 7 148 (53%) >7 132 (47%) PSA At Diagnosis (ng/mL) 5 (0, 10) (88, nr) Subjects with baseline data entered. nr=not reported. Median (Q1, Q3); n (%).

10576 Background: Type 2 diabetes mellitus (T2DM) and excess adiposity are independent risk factors for pancreatic cancer. Pancreatic cancer risk within T2DM across body-mass index (BMI) strata is heterogeneous in real-world cohorts and lean T2DM individuals may represent a distinct high risk phenotype. We compared pancreatic cancer incidence and post-diagnosis survival across BMI strata. Methods: We performed a retrospective comparative outcomes analysis using the TriNetX network. Adults with T2DM (HbA1c ≥6.5%) were categorized as obese (BMI ≥30 kg/m²) or lean (BMI <25 kg/m²). The lean cohort additionally excluded any patient with prior BMI of >25 kg/m² to control for cancer associated weight loss. The index event was first T2DM diagnosis, and outcomes were evaluated after a 365-day window. Patients with pancreatic cancer prior to the outcome window were excluded. Propensity score matching was done using the following parameters: age, sex, smoking status, pancreatitis, pancreatic cysts, chronic kidney disease, gallstones, family history of pancreatic cancer, and HbA1c. Outcomes assessed were incident pancreatic cancer over 10 years and all-cause mortality among patients with pancreatic cancer and T2DM. Results: Total number of patients in the obese group was 1,759,075 with mean age of 57 ± 13.4 years and in the lean cohort were 205,193 with a mean age of 61.8 ± 16.6 years. After propensity score matching, there were 204,086 patients in each group. Mean HbA1c levels were 7.4 ± 1.8% in the obese group and 7.9 ± 2.2% in the lean BMI group. The incidence of pancreatic cancer was 0.16% (n = 335) in obese patients as compared to 0.23% in lean (n = 478) patients with a risk difference of 0.07% (p <0.001). Obesity was associated with lower pancreatic cancer risk (RR 0.692, 95% CI 0.603–0.797; p < 0.001). In the subgroup analysis of patients diagnosed with pancreatic cancer, obese patients had longer median survival (1,109 vs 651 days) with HR 0.853 (95% CI 0.793 - 0.918; p <0.001). Conclusions: Lean adults with T2DM had a higher incidence of pancreatic cancer and worse post-diagnosis survival than obese patients. These results identify lean T2DM as a distinct high-risk phenotype and demonstrate that pancreatic cancer risk within T2DM is heterogeneous and not solely attributable to excess adiposity. Further investigation is needed to elucidate the biological mechanisms underlying this association and its implications for clinical risk assessment. Pancreatic cancer incidence and associated risk estimates among obese and lean adults with type 2 diabetes mellitus. Cohort Pancreatic cancer incidence RD RR Obese T2DM(n = 204,086) 0.16% (n = 335) 0.07% (95% CI: 0.04 - 0.10), p < 0.001 1.44 (95% CI: 1.25 - 1.66) Lean T2DM(n = 204,086) 0.23% (n = 478) Abbreviations: CI, confidence interval; RD, risk difference; RR, relative risk; T2DM, type 2 diabetes mellitus.

10585 Background: Prior studies suggest that thyroid cancer (TC) survivors may have an elevated risk of secondary malignancies. However, whether this risk differs by TC histology, specifically with breast cancer (BC), remains unclear. We aimed to investigate the association between TC subtype—papillary thyroid carcinoma (PTC) versus medullary thyroid carcinoma (MTC)—and subsequent BC risk, adjusting for demographic factors. Methods: We conducted a retrospective cohort study using the SEER (2000–2022), including adults with a primary, microscopically confirmed PTC or MTC. Subsequent BC occurrence was defined as a binary outcome (yes/no). Multivariable logistic regression was used to estimate adjusted odds ratios (aORs) for MTC versus PTC, controlling for age (<50 vs ≥50 years), sex, and race. Stratified analyses by age and race were also performed. Stata 15 was used for statistical analyses. Results: 14,840 patients (14,563 PTC, 277 MTC) were included. MTC patients were older (mean 59.08±12.66 vs 56.16±12.98 years, p<0.001) and had a higher proportion of males (44.4% vs 29.4%, p<0.001). The overall incidence of secondary BC was lower in MTC patients (7.6% vs 22.5%, p<0.001). In unadjusted logistic regression, MTC was associated with significantly lower BC risk (OR=0.28, 95% CI: 0.18–0.44, p<0.001). After adjustment, MTC remained significantly protective (aOR=0.34, 95% CI: 0.22–0.55, p<0.001). Stratified analyses demonstrated consistent findings across age groups (<50: aOR=0.10, 95% CI: 0.03–0.42; ≥50: aOR=0.34, 95% CI: 0.21–0.54), , as well as white and Hispanic patients. Conclusions: Survivors of MTC have a substantially lower risk of developing secondary BC compared to PTC survivors. This association persists after adjustment for age, sex, and race, and is consistent across age and most racial subgroups. However, different BC types were not assessed due to limited number of BC patients among MTC survivors, and the small MTC sample size and potential survival differences between groups may affect the results. These findings highlight a possible effect of TC subtype on BC risk, suggesting the potential influence of underlying biological or genetic mechanisms. Baseline demographic characteristics of patients with papillary and medullary thyroid carcinoma. Characteristic Papillary Thyroid Carcinoma (PTC) (N=14,563) Medullary Thyroid Carcinoma (MTC) (N=277) P-value Age at Diagnosis 0.0002* Mean ± SD, years 56.16 ± 12.98 59.08 ± 12.66 Median, years 57 61 Sex, n (%) <0.001† Female 10,288 (70.6) 154 (55.6) Male 4,275 (29.4) 123 (44.4) Race, n (%) 0.015† White 10,263 (70.5) 197 (71.1) Black 921 (6.3) 15 (5.4) American Indian 77 (0.5) 1 (0.4) Asian 1,379 (9.5) 13 (4.7) Hispanic 1,903 (13.1) 50 (18.1) SD: Standard Deviation. *P-value from two-sample t-test (equal variances assumed). †P-value from chi-square test for the overall distribution across categories.

10578 Background: Multicancer detection (MCD) testing using cell-free DNA methylation patterns is a novel blood-based approach to cancer screening. In 2022, Mayo Clinic implemented offering MCD testing into routine clinical practice. Prior real-world reports have been limited to single-site experiences. We evaluated enterprise-wide implementation of MCD testing across all three Mayo Clinic sites using the Mayo Clinic Platform. Methods: We performed a retrospective analysis of de-identified clinical data from Mayo Clinic Platform Discover, including GRAIL Galleri tests performed at Mayo Clinic sites in Rochester, MN; Scottsdale, AZ; and Jacksonville, FL. This activity did not require IRB review per 45 CFR 46.102. Demographics, test results, cancer diagnoses, and prior cancer history were extracted using a privacy-preserving protocol, with data de-identified by expert determination. ICD-10 diagnostic codes were used to identify subsequent cancer diagnoses. Results: A total of 8,201 Galleri tests were performed in 7,300 patients; some patients underwent repeat testing. Fifty-seven tests (0.7%) were positive. Among MCD-positive patients, cancer diagnostic codes were identified in 32 patients, yielding a positive predictive value (PPV) of 58.7%. The most common cancers identified were oropharyngeal (34.4%), lymphoid and hematopoietic (34.4%), and gastrointestinal malignancies (18.8%).Among 8,144 MCD-negative tests (99.3% of all testing performed), 423 patients (5.2%) subsequently received a cancer diagnostic code, yielding a negative predictive value of 92.5%. The most commonly identified cancers in this group were male genital organs (36.6%), urinary tract (10.6%), and thyroid or other endocrine glands (7.3%). Overall, 10.1% of patients had a prior cancer history, which was more common in MCD-positive than MCD-negative patients (22.6% vs 10.0%). Patients with positive tests were older (mean age 68.4 vs 61.5 years) and more often male (67% vs 62%). Race distribution was similar. Conclusions: Enterprise-wide implementation of MCD testing across diverse clinical settings is feasible within routine workflows. Over half of positive tests were associated with cancer diagnostic codes, supporting the clinical promise of MCD testing. Limitations include incomplete capture of externally diagnosed cancers and lack of cancer signal-of-origin data. The Mayo Clinic Platform enables scalable, secure analytics to support future cancer interception strategies.

1056 Background: Resistance to HER2-directed therapies remains a major challenge in HER2-positiveMBC. In preclinical models, HER2+ tumors overexpress poly (ADP-ribose) polymerase (PARP), and PARP inhibition induces apoptosis through NF-κB suppression even in the absence of pathogenic mutations in BRCA 1/2 . We evaluated the safety, efficacy, and translational correlates of niraparib combined with trastuzumab in patients (pts) with refractory HER2+ MBC. Methods: This open-label Phase 1b/2 trial (NCT03368729) enrolled pts with HER2+ MBC (IHC 3+ and/or FISH amplified), measurable disease, LVEF ≥50%, and progression on ≥1 prior HER2-targeted therapy; stable CNS disease was allowed. Pts with germline BRCA1/2 mutations or prior PARP inhibitor exposure were excluded. Niraparib 300 mg orally was administered on Days 1–21 of a 21-day cycle with trastuzumab 6 mg/kg IV every 3 weeks (loading dose 8 mg/kg on cycle 1). The Phase 2 portion used a Gehan/Simon two-stage design with early stopping for futility (P0=24%); ≥1 response among the first 20 patients triggered expansion to 40 patients. ORR was assessed by RECIST v1.1, meeting the primary endpoint and allowing response rate estimation with <7% standard error and a two-sided 95% exact CI width of 0.28. Gene expression profiling of paired tumor tissue and peripheral blood mononuclear cells (PBMCs) was performed using the NanoString nCounter Tumor Signaling 360 panel at pretreatment compared to cycle 2. Results: Forty-six pts were enrolled (9/2019–2/2025); 41 were evaluable for response. Pts were heavily pretreated (median 3 prior regimens), including trastuzumab deruxtecan in 22 pts; 33% had brain metastases. Treatment-related adverse events were predominantly grade 1–2 and manageable. Clinical benefit rate (CBR) was 44% (18/41) including 1 complete response, 2 partial responses, and 15 stable disease. Eleven patients achieved disease control ≥ 6 months; 1 patient remained on treatment at data cutoff. Tumor profiling revealed enrichment of a B-cell–driven tertiary lymphoid structure signature with reduced hypoxia signaling in responders. Matched PBMC analyses demonstrated coordinated downregulation of interferon signaling, DNA damage response, metabolic activation, angiogenesis, and resistance pathways in clinical responders, whereas non-responders retained signatures of chronic stress and immune exhaustion. Conclusions: Niraparib plus trastuzumab demonstrated a favorable safety profile and durable clinical benefit in heavily pretreated HER2+ MBC. Integrated tumor and blood-based analyses identify immune-organized tumor microenvironments and systemic immune normalization as key correlates of prolonged response, supporting further investigation of PARP inhibition strategies. Clinical trial information: NCT03368729 .

10522 Background: Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality. While antiviral and metabolic therapies have reduced incidence, scalable pharmacologic strategies for primary prevention (PP) remain a critical unmet need. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have demonstrated preclinical antitumor activity and the potential to mitigate hepatic lipotoxicity while promoting metabolic reprogramming to stabilize cirrhosis. However, while chemoprevention signals are observed in metabolic dysfunction-associated steatotic liver disease (MASLD) and type 2 diabetes, the efficacy of GLP-1RAs for PP across diverse liver disease etiologies remains underexplored. To address this gap, we conducted a global, multicenter analysis on the efficacy and safety of GLP-1RAs for the PP of HCC in a pan-etiology high-risk cohort. Methods: A retrospective cohort study was conducted using the TriNetX database (150M patients across 108 health organizations). Adults 18–90 years at elevated HCC risk with ≥ 1 risk factor (chronic viral hepatitis, cirrhosis, MASLD, alcohol use disorder, or hereditary liver disorders) were identified. Cohort A (≥3 months of GLP-1RA) was propensity score-matched 1:1 with Cohort B (non-users) on demographics, HbA1c, BMI, and MELD-Na scores. The primary endpoint was incident HCC, and secondary endpoints were incidence of gastrointestinal (GI) side effects. We employed a 3-month lag period to mitigate immortal time bias. Time-to-event outcomes were assessed via Kaplan-Meier analysis and Cox proportional hazards models. Sensitivity & subgroup analyses were performed to confirm robustness across non-metabolic etiologies. Results: After matching, 592,718 patients were analyzed (296,359 per cohort). Median follow-up was 2,450 days for GLP-1RA users vs 2,114 days for non-users. GLP-1RA use was associated with a 73% reduction in incident HCC (140/296,345 events vs 432/296,198) [HR 0.271 (0.224-0.328)], (NNT=1,015). Notably, the protective effect was most pronounced in non-diabetics [HR 0.179 (0.140-0.229)] and lean patients (BMI < 29) [HR 0.161 (0.103-0.252)]. Risk reductions were sustained across all etiologies, including alcohol liver disease (HR 0.379), cirrhosis (HR 0.456), chronic viral hepatitis (HR 0.477), and MASLD (HR 0.605). GLP-1RA use was associated with a significant increase in GI adverse events. Conclusions: GLP-1RA use was associated with a 73% reduction in incident HCC, consistent across subgroups. The enhanced benefit in non-diabetic and lean cohorts suggests a direct anti-neoplastic mechanism independent of weight loss or glycemic control. The NNT of 1,015 highlights the substantial public health impact of GLP-1RA therapy in preventing a high-mortality malignancy. These findings warrant prospective validation.