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e14524 Background: Immune checkpoint inhibition has demonstrated meaningful clinical benefit in microsatellite instability–high (MSI-H) colorectal cancer (CRC); however, outcomes remain heterogeneous. The interaction between tumor immune microenvironment features, tumor mutational burden (TMB), and survival outcomes has not been fully characterized. We conducted an integrative analysis of publicly available genomic data to evaluate the prognostic impact of immune infiltration stratified by MSI status and TMB in CRC. Methods: Transcriptomic, somatic mutation, and clinical data for primary colorectal adenocarcinoma were obtained from TCGA-COAD and TCGA-READ. About 600 patients with overall survival data were analyzed. MSI status was taken from TCGA molecular subtype annotations. TMB was defined as the number of nonsynonymous somatic mutations per tumor and dichotomized at the median.Immune infiltration (CD8⁺ and CD4⁺ T cells, macrophages, neutrophils, dendritic cells) was estimated using TIMER. Patients were classified as high or low infiltration by the median. Overall survival was assessed using Kaplan–Meier analysis and Cox models adjusted for age, sex, and tumor stage., and tumor stage. Results: The cohort included approximately 15% MSI-H tumors, which demonstrated significantly higher TMB compared with microsatellite-stable (MSS) tumors. MSI-H tumors exhibited an inflamed immune phenotype, with approximately twofold higher CD8⁺ T-cell infiltration relative to MSS tumors. Across the overall cohort, high CD8⁺ T-cell infiltration was associated with improved OS compared with low infiltration (median OS not reached vs approximately 60–70 months). In contrast, increased macrophage infiltration was associated with inferior survival outcomes. When stratified by genomic features, the favorable prognostic association of CD8⁺ T-cell infiltration was most pronounced in MSI-H and TMB-high tumors, corresponding to an estimated 30–40% relative reduction in mortality risk compared with MSI-H/TMB-high tumors with low immune infiltration. Immune infiltration demonstrated weaker and less consistent associations with OS in MSS/TMB-low tumors. In multivariable analyses, CD8⁺ T-cell infiltration remained independently associated with improved OS after adjustment for clinical covariates, whereas macrophage infiltration remained independently associated with worse outcomes. Findings were consistent across colon and rectal cancer subgroups. Conclusions: In this integrative analysis of TCGA colorectal cancer datasets, features of the tumor immune microenvironment, together with MSI status and TMB, were associated with survival. These results support immune-genomic stratification and suggest that combining immune and molecular biomarkers may improve prognostic assessment and immunotherapy trial design in colorectal cancer.

8519 Background: Non-classical mutations (NCM) of epidermal growth factor receptor (EGFR) represent a broad group of oncogenic mutations in non-small cell lung cancer (NSCLC), often associated with resistance to osimertinib (e.g., P-loop and αC-helix compressing [PACC] mutations). Patients (pts) with NCM have inferior clinical outcomes with a high incidence of CNS metastases (CNSm). Silevertinib (BDTX-1535) is a fourth-generation, covalent EGFR TKI with high CNS penetrance targeting both EGFR classical mutations and NCM. The antitumor activity and safety of silevertinib in pts with advanced NSCLC were evaluated in a Phase 2 trial (NCT05256290). Methods: Pts with advanced EGFR NCM NSCLC who received no prior systemic therapy were enrolled (Cohort 3) based on a local molecular test. Silevertinib 200 mg was administered orally once daily. The primary endpoint of objective response rate (ORR) was assessed using RECIST v1.1. CNS ORR was assessed using Response Assessment in Neuro-Oncology for Brain Metastases (RANO-BM) in pts with no prior CNS therapy. Secondary endpoints include progression-free survival (PFS), duration of response (DOR), disease control rate (DCR), and safety. Results: From February 2024 to July 2025, 43 pts with 35 unique NCMs (including 25 pts with PACC mutations) were enrolled in Cohort 3: median age 70.0 years, 72% female, 74% white, and 42% never smoked cigarettes. As of November 3, 2025, median follow-up was 7.2 months. ORR by RECIST v1.1 is shown in the table. Sixteen pts (37%) had CNSm, including 7 pts (16%) with measurable CNS disease. RANO-BM CNS response was 86% (n=6/7). Complete clearance of EGFR VAF ctDNA was observed in 21/26 (81%) evaluable pts. Serious treatment-related adverse events (TRAEs) were reported in 5 pts (12%), and 4 pts (9%) discontinued treatment due to TRAEs. The most common TRAEs included rash (19%, grade 3), diarrhea (19%, grade 3), stomatitis (9%, grade 3), and paronychia (5%, grade 3). While 77% of pts had a dose reduction, 19/22 (86%) patients with a radiographic response maintained or deepened their response after dose reduction, including all patients with CNS response. Conclusions: Silevertinib demonstrated robust antitumor activity in treatment-naïve pts with a broad spectrum of NCM EGFR driver mutations with high intracranial activity in pts with brain metastases. The safety profile was consistent with the known AEs of the EGFR TKI class. Clinical trial information: NCT05256290 . Data as of November 3, 2025 N ORR n (%) 95% CI DCR n (%) 95% CI ITT Population * 43 26 (60) (44.4, 75.0) 39 (91) (77.9, 97.4) PACC mutations 25 14 (56) (34.9, 75.6) 22 (88) (68.8, 97.5) Compound mutations † 16 11 (69) (41.3, 89.0) 15 (94) (69.8, 99.8) *No pts with classical (E746_A750del or L858R) mutations were enrolled. † Presence of ≥ 2 NCMs. As of December 27, 2025, the 6-month PFS rate was 86% overall and 80% in pts with CNSm; available PFS and DOR data will be presented.

7548 Background: Glucagon-like peptide-1 (GLP-1) receptor agonists are widely used for the treatment of type 2 diabetes and obesity, and emerging evidence suggests their benefits beyond glycemic control, including cardiovascular effects and potential anti-inflammatory and anti-proliferative properties. Therapeutic advances in multiple myeloma (MM) have improved the overall life-expectancy in our patients. However, metabolic comorbidities remain common, likely driven by disease burden, functional decline, ongoing inflammation, and treatment related effects. Our study evaluates the impact of GLP-1 receptor agonists on outcomes in patients with MM, exploring potential interactions between metabolic modulation and disease outcomes. Methods: We conducted a real-world retrospective cohort study using the TriNetX Global Collaborative Network, covering January 2000 to December 2025, encompassing data from 168 global healthcare organizations. Patients aged 18 and above with multiple myeloma were identified and then stratified into two groups based on treatment with GLP-1 agonists or not. The two groups were then propensity-matched based on age, sex, race, and various comorbidities. We assessed outcomes including overall mortality, myocardial infarction (MI), ischemic stroke, sepsis, anemia, pancreatitis, venous thromboembolism (VTE), and ED visits. Time-to-event analyses were performed using Kaplan-Meier methods and Cox proportional hazards models. Results: We identified 1716 patients with MM and obesity who received GLP-1 receptor agonists, and 13,491 patients with MM and obesity who did not receive GLP-1 therapy. After propensity matching, each cohort consisted of 1712 patients with well-balanced baseline characteristics. We followed these patients for 5 years from treatment initiation. Patients with MM who received GLP-1 had a significantly lower risk of overall mortality (Hazard Ratio [HR]: 0.423, 95% CI: 0.351-0.509, p-value <0.001), MI (Risk Difference [RD]: -3.6 %, 95% CI: -5.4 % to -1.7 %, p-value <0.001), ischemic stroke (RD: -1.7 %, 95% CI: -3.3 % to -0.1 %, p-value = 0.04), sepsis with and without shock (RD: -3.0 %, 95% CI: -4.9 % to -1.1 %, p-value = 0.002), and anemia (RD: -9.6 %, 95% CI: -12.9 % to -6.4 %, p-value <0.001). There was no statistically significant difference in the rates of VTE, ED visits, and pancreatitis between the two cohorts. Conclusions: Our study revealed that patients with MM with obesity who received GLP-1 therapy had significantly lower rates of overall mortality, MI, ischemic stroke, sepsis with and without shock, and anemia. Additional longitudinal cohort studies are required to explore the associations between these agents and inform clinical practice guidelines in these patients.

603 Background: Accurate prediction of pathologic complete response (pCR) after preoperative therapy for HER2-positive (HER2+) breast cancer can help triage patients to immediate surgery vs additional preoperative therapy. Pre-surgery (i.e., after neoadjuvant therapy) imaging studies may help estimate the likelihood of pCR. In EA1181, patients (pts) with stage II-IIIA HER2+ breast cancer received four cycles of preoperative taxane, trastuzumab, and pertuzumab (THP×4). Pre-surgery imaging was required, though the specific imaging modality was not mandated. Here, we report the accuracy of pre-surgery breast MRI to predict pCR (ypT0/Tis, ypN0). Methods: Among 2,141 pts treated with THPx4, 1,378 had pre-surgery breast MRI and were representative of the overall cohort, although T3 tumors were more common (16% vs 9%). MRI reports were available for 1,351 pts; all reports were centrally reviewed and classified as radiologic complete response (rCR; no residual tumor enhancement and normalization of lymph nodes, if applicable) or radiologic residual disease (rRD). Reports with indeterminate radiologic response were independently reviewed by two study radiologists blinded to pathology outcomes. Among pts with rCR who had pathologic residual disease (pRD), we also assessed the extent of residual disease by residual cancer burden (RCB) score. Among pts with rRD who had a pCR, we determined the proportion who only had residual ductal carcinoma in situ (DCIS). Results: See Table. Conclusions: After neoadjuvant therapy, preoperative MRI accurately predicted pCR in 86% of patients with HER2+/ER− disease and may help identify patients who can proceed directly to surgery. MRI is insufficient to predict pCR for pts with HER2+/ER+ disease, as only 55% with complete response on MRI had a pCR at surgery. A pre-surgery MRI that indicated residual disease was accurate in 80% of pts with HER2+/ER+ disease, but in only 45% of pts with HER2+/ER- cancer. Accurately predicting residual disease after THPx4 allows for consideration of additional therapy that may increase the chance of pCR. Combining imaging like MRI with other biomarkers, such as tissue-based markers or circulating tumor DNA, may improve prediction of pCR and facilitate personalization of treatment decisions in HER2+ breast cancer. All pts with pre-surgery MRI (n=1351)pCR rate overall in this cohort = 47% MRI result Pathology pCR pRD rCR 70.6% (341/483) 29.4%(142/483) 78% had RCB1 rRD 34%(295/868) 21% of 295 had DCIS only 66.01% (573/868) ER- (n=589)*Overall pCR rate in ER- subset = 68% MRI result Pathology pCR pRD rCR 86.1% (205/238) 13.9% (33/238) 85% had RCB1 rRD 55.3% (194/351) 19% of 194 had only DCIS 44.7% (157/351) ER+ (n= 762)*Overall pCR rate in ER+ subset = 31% MRI result Pathology pCR pRD rCR 55.5% (136/245) 44.5% (109/245) 76% had RCB1 rRD 19.5% (101/517) 26% of 101 had only DCIS 80.5% (416/517)

5543 Background: Glucagon-like peptide-1 (GLP-1) receptor agonists are widely used for the treatment of type 2 diabetes and obesity. Emerging evidence suggests that these agents may have potential anti-tumor activity as GLP-1 signaling may influence pathways involved in cell proliferation and inflammation. Endometrial cancer is the most common gynecologic malignancy, and obesity represents a well-established, modifiable risk factor that may adversely affect oncologic outcomes through chronic inflammation and metabolic dysregulation. Our study aims to evaluate the impact of GLP-1 receptor agonists on outcomes among patients with endometrial cancer and comorbid obesity. Methods: A retrospective cohort study was conducted using the TriNetX Global Collaborative Network, covering January 2000 to December 2025, encompassing data from 168 global healthcare organizations. Patients aged 18 and above with endometrial cancer and comorbid obesity were identified and then stratified into two groups based on treatment with GLP1 agonists or not. The two groups were then propensity-matched based on age, ethnicity, medical comorbidities, and stage of cancer. Outcomes were assessed for five years from treatment initiation and included overall mortality, myocardial infarction (MI), ischemic stroke; development of peritoneal, lymph node, and visceral metastases; sepsis, pancreatitis, and ED visits. Time-to-event analyses were performed using Kaplan-Meier methods and Cox proportional hazards models. Results: After propensity matching, 6352 patients were included in each cohort with balanced baseline characteristics. Our analysis found that patients with endometrial cancer and comorbid obesity who received GLP-1 agonists had a significantly lower risk of overall mortality (Hazard Ratio [HR]: 0.45, 95% CI: 0.39-0.51, p-value <0.001), development of peritoneal metastases (Risk Difference [RD]: -2.16%, 95% CI: -2.74% to -1.58%, p-value <0.001), nodal metastases (RD: -0.41%, 95% CI: -0.72% to -0.09%, p-value =0.01), visceral metastases (RD: -3.76%, 95% CI: -4.60% to -2.93%, p-value =0.01), and sepsis with and without shock (RD: -1.42%, 95% CI: -2.14% to -0.70%, p-value <0.001) compared to patients who did not receive GLP-1 agonists. There was no statistically significant difference in the rates of MI, ischemic stroke, ED visits, and pancreatitis between the two cohorts. Conclusions: In this large real-world analysis, patients with endometrial cancer and comorbid obesity who received GLP-1 agonists had lower rates of overall mortality; peritoneal, lymph node, and visceral metastases, and sepsis with or without shock. Additional longitudinal cohort studies are imperative to explore the associations between these agents and inform clinical practice guidelines in this patient population.

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 .

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.

10520 Background: Therapeutic options for breast cancer (BC) prevention for high-risk women remain limited, and not all eligible patients opt for endocrine therapy due to concerns related to adverse events (AEs). GLP1RAs are widely used for obesity and type 2 diabetes mellitus; their role in BC primary prevention (PP) in high-risk women with obesity has not been evaluated. Methods: Using the TriNetX Global Network (150 million patients, 108 organizations), we analyzed de-identified records of high-risk women aged 18–90 years with a BMI ≥ 30 who had health care encounters between January 1, 2000, and January 1, 2025, identified via ICD-10 codes. High risk was defined as at least one of the following: genetic predisposition to BC, family history of BC, atypical ductal hyperplasia, atypical lobular hyperplasia, lobular carcinoma in situ, or dense breasts. Patients were grouped as having GLP1-RA use or no GLP-1RA use. Patients with a prior history of BC or use of endocrine therapy were excluded. GLP-1RA users were propensity score-matched 1:1 with non-users based on demographics, comorbidities, social determinants of health, lifestyle factors, BMI, HbA1c, and prior breast imaging. Incident BC served as the primary endpoint, with key AEs as secondary measures. Kaplan–Meier analysis and Cox proportional hazards models were utilized to assess outcomes, which were further validated through subgroup and sensitivity analyses. Results: Among 80,480 high-risk women with a BMI ≥ 30, 46,581 were assigned to each cohort. Baseline demographics were balanced between cohorts (mean age: 46 years, 70% White, 21% Black). Median follow-up was 2,790 vs 2,630 days for GLP-1RA users and non-users, respectively. BC incidence was 2.95% in GLP-1RA users (1,164/39,495 cases) vs 3.01% in non-users (1,200/39,057 cases) (3.27 vs. 3.57 cases per 1,000 person-years; HR 0.844; 95% CI, 0.779–0.915). GLP-1RA users exhibited an increased risk of endometrial cancer (HR 1.273; 95% CI, 1.088–1.491) and osteoporosis (HR 1.124; 95% CI, 1.054–1.199). No significant association was observed for venous thromboembolism. Gastrointestinal AEs were significantly higher in the GLP-1RA cohort. Conclusions: GLP-1RA use was associated with a modest reduction in BC incidence among high-risk women with obesity in this real-world study. Prospective randomized trials are needed to validate these associations.

10507 Background: Despite advances in understanding leukemogenesis, no validated primary prevention strategies exist. Obesity is a dose-dependent risk factor for leukemia. Emerging data implicate epigenetic regulators, specifically the histone methyltransferase GLP (EHMT1), as a driver of leukemic survival; its inhibition induces cell death in CLL and promotes differentiation in AML. We present the first real-world analysis evaluating GLP-1 receptor agonists (GLP-1RA) for the primary prevention of leukemia in high-risk populations. Methods: Using the TriNetX global research network (150 million patients across 108 healthcare organizations), we identified adults at elevated leukemia risk based on ≥1 factor (prior chemo/radiation, MDS, MPN, family history, genetic syndromes, tobacco use, or BMI ≥30). Patients with ≥2 months of GLP-1RA use were propensity-matched 1:1 to non-users by demographics, comorbidities, and prior chemotherapy. The primary endpoint was the incidence of ALL, AML, CLL, or CML; secondary endpoints were adverse events related to GLP-1RA. Individuals with pre-existing leukemia were excluded. Cox proportional hazards models and sensitivity analyses were used to assess associations. Sensitivity and subgroup analysis confirmed robustness. Results: Of 426,670 high-risk individuals, 213,335 were matched to each cohort; standardized mean differences were <0.1 for all covariates. Across >1.2 million person-years of follow-up, GLP-1RA use was associated with a 63% risk reduction in incident AML (47/213,300 vs 75/213,261; HR 0.37, 95% CI 0.26–0.53; p < 0.001) and a 50% reduction in ALL (42/213,304 vs 53/213,277; HR 0.50, 95% CI 0.33–0.75; p = 0.001). The protective effect for AML remained significant when restricted to patients with prior chemotherapy exposure and was independent of baseline BMI. No significant reductions were observed for CML or CLL. While GI adverse events were higher in the GLP-1RA cohort, the protective signal was consistent across age and ethnic subgroups. Conclusions: This is the first large-scale study to demonstrate a significant reduction in incident AML and ALL using GLP-1 receptor agonists in high-risk patients. By linking clinical metabolic intervention to the EHMT1 epigenetic pathway, these findings provide a novel, scalable pharmacologic strategy for the primary prevention of acute leukemias, potentially transforming the management of high-risk and obese populations.