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e20139 Background: Extensive-stage small cell lung cancer (ES-SCLC) frequently presents with brain metastases, affecting approximately 20% of the patients at diagnosis. The prognostic impact of baseline brain metastases on survival outcomes in patients treated with contemporary chemo-immunotherapy remains unclear, creating uncertainty in first-line treatment selection for this high-risk population. We conducted a systematic review and meta-analysis to evaluate the impact of baseline brain metastases on treatment outcomes in ES-SCLC. Methods: This PRISMA-compliant systematic review and meta-analysis was prospectively registered in PROSPERO. PubMed, Embase, Cochrane CENTRAL, and ClinicalTrials.gov were systematically searched from database inception through January 2026 to identify randomized controlled trials evaluating PD-1/PD-L1-based chemo-immunotherapy versus platinum-etoposide chemotherapy in adults with ES-SCLC. Two reviewers independently screened studies and extracted data, with discrepancies resolved by consensus. Hazard ratios (HRs) for overall survival (OS) and progression-free survival (PFS) were pooled separately for patients with baseline brain metastases (BM+) and without brain metastases (BM−) using random-effects models with Hartung–Knapp adjustment. Analyses were performed using R. Prespecified subgroup analyses were conducted based on follow-up duration and immunotherapy regimen. Results: Twelve randomized controlled trials were included. Among patients with baseline brain metastases (BM+), pooled OS from seven studies did not show a significant survival benefit (HR 0.84, 95% CI 0.66–1.08, I² = 0.0%, P = 0.145), nor did pooled PFS from five studies (HR 1.03, 95% CI 0.60–1.79, I² = 0.0%). Subgroup analyses revealed no significant heterogeneity. In contrast, among patients without baseline brain metastases (BM−), pooled OS from nine studies demonstrated a significant survival benefit (HR 0.72, 95% CI 0.69–0.76, I² = 0.0%, P < 0.001), with corresponding improvement in PFS (HR 0.70, 95% CI 0.60–0.82, I² = 0.0%). These findings indicate a differential treatment effect according to baseline brain metastasis status. Conclusions: First-line chemo-immunotherapy does not apprear to confer a significant survival benefit in ES-SCLC patients with baseline brain metastases, reflecting a differential treatment effect by brain metastasis status. These findings suggest that baseline brain metastases should be considered in treatment selection and future clinical trial design and highlight the need for optimized systemic strategies for this high-risk population.

e15713 Background: Fruquintinib demonstrated overall survival benefit in heavily pretreated metastatic colorectal cancer (mCRC) in FRESCO and FRESCO-2. The FDA approved fruquintinib on Nov 8, 2023 for adult patients with mCRC after standard chemotherapy plus anti-VEGF therapy, with anti-EGFR therapy when appropriate (e.g., RAS wild-type). Observed geographic variation in post-approval uptake suggests potential disparities in the delivery of evidence-based medicine across U.S. regions. Methods: We conducted a retrospective cohort study using Epic Cosmos, a database of over 300 million patient records from over 1,500 hospitals nationwide. We identified adults with metastatic colorectal cancer (mCRC) with prior standard systemic therapy exposure and recorded fruquintinib exposure following FDA approval beginning Nov 8, 2023. Fruquintinib uptake was analyzed by U.S. Census region and state, expressed as the proportion of eligible mCRC patients receiving fruquintinib within each geography. Results: Among 116,116 pre-treated mCRC patients, 6,722 (5.79%) had recorded fruquintinib exposure during the post-approval period. Uptake varied nearly five-fold across states (2.27%–11.33%) (Table). High-uptake states were disproportionately concentrated in the central U.S./Midwest, whereas multiple low-uptake states were observed in the West and Northeast, suggesting broader regional variation beyond state-to-state differences. Conclusions: In a large national EHR-derived cohort of pre-treated mCRC patients after U.S. approval, fruquintinib uptake demonstrated substantial geographic variation. These findings raise concern for inequities in delivery of evidence-based later-line therapy and highlight the need to identify modifiable system- and site-level drivers (e.g., access, referral patterns, treatment infrastructure) to promote equitable adoption. Fruquintinib uptake among eligible metastatic colorectal cancer patients by U.S. state. Rank Geography Eligible mCRC (N) Fruquintinib uptake (%) Overall Overall 116,116 5.79 Top 1 Oklahoma 1,236 11.33 2 Kansas 1,312 10.75 3 Indiana 2,448 10.70 4 Missouri 1,521 9.47 5 Connecticut 2,208 9.24 Bottom 1 Washington 1,232 2.27 2 Nevada 441 2.72 3 Rhode Island 476 2.73 4 Tennessee 1490 2.82 5 Maine 614 2.93 Fruquintinib uptake is reported as the proportion of eligible pre-treated metastatic colorectal cancer (mCRC) patients with recorded fruquintinib exposure following U.S. FDA approval. States are ranked by uptake percentage.

e15647 Background: Colorectal cancer (CRC) screening offers an opportunity to prevent invasive disease by detecting and removing precancerous lesions. Colonoscopy-based detection of adenomas and serrated polyps is strongly associated with reduced risk of interval CRC. While the performance of noninvasive CRC screening tests is well described, comparative evidence on adenoma detection across screening colonoscopy and stool-based strategies with follow-up colonoscopy remains limited. We conducted a systematic review to compare adenoma detection across CRC screening modalities. Methods: MEDLINE (PubMed) and Embase were searched from January 1, 2000, through July 10, 2025, for peer-reviewed, U.S.-based studies reporting colonoscopy among average-risk adults aged ≥45 years, who underwent screening colonoscopy or follow-up colonoscopy after a positive stool-based screening test [fecal immunochemical test (FIT) or multi-target stool DNA (mt-sDNA) test]. The primary outcome was the detection of one or more adenomas at colonoscopy. High-risk or surveillance cohorts, AI-assisted colonoscopy, diagnostic accuracy trials, and non-U.S. studies were excluded. Results: Among 7,710 de-duplicated records, 147 studies underwent full-text review, and 47 studies were included in quantitative synthesis, with reported adenoma detection for screening colonoscopy alone (n = 31), follow-up colonoscopy after a positive FIT alone (n = 4), follow-up colonoscopy after a positive mt-sDNA test alone (n = 4), and for more than one of the screening strategies of interest (n = 8). Across included studies, overall adenoma detection differed by screening pathway. Follow-up colonoscopy after a positive mt-sDNA test demonstrated the highest adenoma detection (66.3%; 95% CI, 61.2-71.1), with lower adenoma detection observed for colonoscopy after a positive FIT (50.6%; 95% CI, 43.4-57.8) and screening colonoscopy alone (33.8%; 95% CI, 30.9-36.8) (Table 1). Conclusions: Detection of adenomas was highest following colonoscopy performed after a positive mt-sDNA test compared with FIT-positive follow-up or screening colonoscopy alone. These findings highlight differences in downstream detection across CRC screening tests and suggest that, in settings where colonoscopy resources are constrained, initial mt-sDNA screening with timely follow-up colonoscopy may help prioritize patients most likely to benefit. CRC screening modality No. of Studies Adenoma detected Study population Proportion, % (95% CI) Heterogeneity, I² (%) Between-study variance (τ 2 ) P-value* mt-sDNA 8 17,436 29,098 66.3 (61.2-71.1) 94.6 0.0924 <0.0001 FIT 11 17,588 32,630 50.6 (43.4-57.8) 94.0 0.2187 <0.0001 Screening colonoscopy 38 2,351,801 6,378,891 33.8 (30.9-36.8) 99.8 0.1710 NA *P-value represents adenoma detection vs. screening colonoscopy adenoma detection.

9568 Background: Stage IIB/C cutaneous melanoma is associated with high recurrence risk, however stratification of risk in relation to time after surgery has not been comprehensively evaluated. We evaluated recurrence-free survival (RFS) at key time points, stratified by clinicopathologic factors, to identify patients (pts) at higher recurrence risk and personalize postoperative surveillance strategies. Methods: In this multi-institutional, international retrospective cohort study from the Sentinel Lymph Node Working Group database, we included pts with pathologic T3b/T4a/T4b and N0 disease who underwent surgical resection and sentinel node biopsy from 1994-2025. The type of first recurrence (local, regional, distant) was characterized based on time category (0-12, 12-24, 24-60, and 60+ months after surgery). Restricted mean survival time (RMST) analysis was used to measure the average survival time up to a specified time point (6-, 12-, 24-, and 60-months after surgery), and associations of clinicopathologic variables (age, sex, Breslow thickness, ulceration and lymphovascular invasion [LVI]) with RFS. Results: We included 2514 stage IIB/C pts from 19 sites in 4 countries, with a median follow-up of 53 (stage IIB) and 49 (stage IIC) months. 675 (27%) pts experienced a recurrence (92 [14%] local, 238 [35%] regional and 345 [51%] distant), and 400 (59%) recurrences occurred within 24 months. The proportion of distant recurrences as the first recurrence increased significantly with time, comprising 39%, 50%, 62%, and 59% of recurrences in the 0-12, 12-24, 24-60, and 60+ month time categories respectively (χ 2 p<0.001). No significant differences were observed for the included clinicopathologic variables for 6-month RMST estimates. At 12 months, RMST estimates for thickness ≥4 mm (11.2 vs 11.6 months for thickness 2-3.99 mm, p<0.001) and presence of LVI (10.7 vs 11.4 months, p=0.009) were significantly different. 24-month RMST estimates differed for male sex (20.7 vs 21.5 months vs females, p=0.002), thickness ≥4 mm (20.5 vs 21.9 months, p<0.001), and presence of LVI (19.0 vs 21.1 months, p<0.001). Lastly, 60-month RMST estimates differed for male sex (42.0 vs 45.2 months, p=0.001), thickness ≥4 mm (41.5 vs 46.2 months, p<0.001), LVI (36.0 vs 43.7 months, p<0.001), and age >65 years (41.5 vs 46.4 for age <42, p=0.022). Conclusions: In this real-world, multi-center analysis of pathologic stage IIB/C melanoma pts, recurrence patterns varied based on time after surgery. Breslow thickness, LVI, male sex, and age were significantly associated with earlier recurrence at different time intervals on RMST analysis. Additionally, given that >50% of first recurrences 12+ months after surgery were distant, active surveillance for distant relapses may be warranted.

9524 Background: Unresectable melanoma in-transit metastases (ITM) can pose a significant clinical challenge. Our recently published data comparing first-line treatments for ITM, isolated limb infusion or perfusion (ILI/ILP), immune checkpoint inhibitors (ICI) and intralesional talimogene laherparepvec (TVEC), found superior outcomes with TVEC. However, TVEC was used more often in patients with lower disease burden and earlier stage (IIIB vs. IIIC/D). Therefore, we sought to better investigate these differences with a propensity score-matched (PSM) analysis. Methods: A multi-institutional, international IRB- approved retrospective analysis was conducted for unresectable melanoma ITM from 2016-2022. PSM analysis comparing first-line ILI/ILP, ICI, and TVEC for was performed. Patients were matched for stage, number of ITM, anatomical site, CLND status, gender and age. Kaplan-Meier curves (OS, PFS, DMFS) and Cumulative incidence function (MSS) were used to visualize time-to-event outcomes in the PSM cohort, though both methods do not account for the matched structure. Results: 274 patients were identified, 120 female/154 male; 96 treated with ILI/ILP, 111 with ICI, and 67 with TVEC. Median follow-up was 40 months (range, 1-80). PSM was performed and identified 36 TVEC–ICI pairs and 27 TVEC–ILI pairs. These were combined resulting in a final cohort of 108 observations (45 TVEC, 36 ICI and 27 ILI). The groups were well balanced. No statistical difference was found for metastasis-free survival (DMFS), progression-free survival (PFS), melanoma-specific survival (MSS), and overall survival (OS) between treatment modalities. TVEC was associated with significant improvement in local PFS (median was 2.2 years (y) for ILI/ILP, 1.5y for ICI and not reached for TVEC, p=0.048). While not statistically significant, a clinical benefit was seen in PFS being longer for TVEC (2.1y for TVEC vs. 1.2y for ILI/ILP and 1.1y for ICI; p=0.2) and OS (not reached vs 2.9y for ILI/ILP and 5.2y for ICI; p=0.2). On mixed effect Cox regression proportional hazard model using the matched data set, there were no significant differences in any of the survival and recurrence outcomes. Conclusions: When patients are propensity-matched, there were no significant differences in first-line treatment modalities for unresectable melanoma ITM. Treatment with TVEC did result in clinically meaningful improved overall and local PFS and OS. This supports that selection of ITM therapy should incorporate an individualized approach, incorporating disease distribution, stage, burden, treatment side effects and patient priorities.

8000 Background: The NCI’s ALCHEMIST program has screened thousands of patients with resected lung adenocarcinoma for mutations in EGFR and ALK. EA5142 studied the efficacy of adjuvant nivolumab after standard of care adjuvant therapy in patients with resected lung adenocarcinoma without sensitizing EGFR and ALK alterations and squamous cell carcinoma. Methods: Patients enrolled in the ALCHEMIST screening trial (A151216) with resected NSCLC tumors at least 4 cm and/or lymph node positive (N1/2) (for lung adenocarcinoma, without sensitizing EGFR and ALK alterations), were centrally tested for tumor cell PD-L1 expression using the DAKO 28-8 clone. After completion of all planned adjuvant therapy (chemotherapy and/or post-operative radiation) patients were randomized 1:1 to adjuvant nivolumab 480 mg IV every 4 weeks for up to 1 year or best supportive care. Patients were stratified by tumor histology, stage (AJCC 7 th edition IB/IIA vs IIB/IIIA), prior adjuvant treatment, and PD-L1 status (<1% vs ≥1%). The primary study endpoints were disease free survival (DFS) in all patients and in patients with high tumor PD-L1 expression (≥50%). Overall survival was powered to be tested hierarchically, if DFS was positive. Results: Between July 2016 and October 2019, 935 patients were randomized across 378 sites. The treatment arms were balanced for age (median 66 years), sex (52% male), smoking status (10% never smoked), histology (29% squamous), stage and PD-L1 expression (29% PD-L1 high). With a median follow-up of 72.6 months, nivolumab did not improve DFS in the intention to treat population (median DFS 71.3 months vs. 68.8 months in observation arm), hazard ratio (HR) 0.97 (95% CI 0.81-1.17, p=0.78) or the PD-L1 ≥50% subset (median DFS 89.8 months vs. 78.5 months in observation arm), HR 0.86 (95% CI 0.59-1.25, p=0.43). In multivariate analysis, adjusting for age, gender, and smoking history, the DFS HR was 0.99 (95% CI 0.82-1.19, p=0.89) in all randomized patients and 0.82 (95% CI 0.56-1.2, p=0.31) in the PD-L1 ≥50% subset. As the primary recurrence endpoint included any lung cancer, including new primaries, a sensitivity analysis was performed excluding new primary lung cancers, DFS HR 0.97 (95% CI 0.80-1.18, p=0.76) in all patients and HR 0.88 (95% CI 0.60-1.30, p=0.52 in the ≥50% subset. The median duration of treatment with adjuvant nivolumab was 9.4 months (range 0-12.7 months). The most common reasons for nivolumab discontinuation were adverse event (29%), patient withdrawal (11%), and disease progression while on treatment (10%). Treatment related grade 3-5 toxicities were reported in 25% of patients: Grade 3: 23%, Grade 4: 2%, Grade 5: <1%. Conclusions: In patients with resected NSCLC (≥4cm or LN+, EGFR/ALK -) adjuvant nivolumab did not improve DFS, irrespective of tumor PD-L1 expression. Clinical trial information: NCT02595944 .

7530 Background: B-cell maturation antigen (BCMA)-directed CAR-T therapy is a highly effective treatment with potential for long-term remission of RRMM with improved outcomes vs daratumumab-based regimens. CAR-T suitability may be limited by delays/manufacturing failure and changes in pt condition, financial situation, or access to specialized treatment centers. We characterized pts with RRMM who underwent leukapheresis to prepare for CAR-T and pt treatment waiting time, to understand the delays incurred prior to CAR-T infusion. Methods: A real-world study in the US using the PharMetrics Plus claims database (July 2020–September 2024) was performed. Eligible pts were aged ≥18 years with RRMM, had their first leukapheresis claim (index date) during the index period (March 2021–August 2024), were continuously enrolled in medical/pharmacy benefits for ≥180 days prior to and ≥30 days after index date, and were not clinical trial participants. Pt characteristics, rate of CAR-T receipt, and time to CAR-T receipt were assessed during the variable follow-up. Results: Overall, 337 pts who received leukapheresis were identified. Median (interquartile range) age was 62 (55–67) years, and 59.1% of pts were male. Mean National Cancer Institute (NCI) comorbidity index was 0.52. Most pts received care in the Midwest (31.8%) or Northeast (24.6%) regions. Most pts (95.9%) received leukapheresis in an outpatient setting. Median available follow-up time was 255 days (mean 337 days). During follow-up, 183 pts (54.3%) did not receive CAR-T after leukapheresis. Among pts who had ≥12 months of follow-up (n=143), the proportion of pts who did not receive CAR-T was similar at 53.1% (n=76). Among pts who received CAR-T during the follow-up (n=154; 45.7%), the median waiting time was 54.0 days (mean 56.7 days). The cohort of pts who did not receive CAR-T had a higher proportion of females (48.6%/31.8%), were more likely to have Medicaid (29.5%/7.8%), had higher NCI comorbidity index (scores 0.55/0.47), and most commonly received care in the Northeast (35.5%/11.7%) while pts who received CAR-T most commonly received care in the Midwest (23.0%/42.2%). The most common first classes of multiple myeloma medications after leukapheresis but prior to CAR-T infusion in pts who did/did not receive CAR-T were an alkylating agent (65.6%/36.1%), proteasome inhibitor (40.3%/30.6%), steroid (38.3%/39.3%), immunomodulatory drug (22.7%/27.3%), anti-CD38 (20.8%/20.8%), and stem cell transplant (0%/17.5%). Conclusions: Over half of pts receiving leukapheresis did not receive CAR-T infusion, highlighting a persistent gap between eligibility and treatment delivery. These data emphasize an urgent need for broadly accessible BCMA-targeted therapies that provide deep and durable responses.

7546 Background: MRD assessment informs relapse risk in MM but is typically bone marrow-based and invasive. We therefore compared two minimally invasive MRD assays: BM-informed cfDNA whole-genome sequencing (cfWGS) and plasma proteomic MRD (EasyM). Methods: 71 longitudinal plasma samples (22 diagnosis, 49 follow-up) from 22 newly diagnosed MM patients across 8 Canadian sites (TFRIM4) had paired cfWGS and EasyM (Rapid Novor Inc). cfWGS MRD used patient-specific mutation lists from diagnostic BM WGS (Abelman et al., medRxiv 2025). EasyM used mass spectrometry to quantify residual M-protein from baseline. The primary endpoint was progression-free survival (PFS). Results: Among 22 MM patients (8 male, 14 female; median age at diagnosis 62 years), 8 progressed at a median follow-up of 52.6 months (range: 10-79 months). At 1-year maintenance (n = 18 available), cfWGS MRD+ (6/18) predicted inferior PFS (HR 20.12, 95% CI 2.23-181.60, p = 0.007). EasyM any-detect positivity was frequent (16/18, reflecting delayed clearance) and not prognostic (p = 0.99), with poor agreement vs cfWGS (44.4%, κ = 0.118). An exploratory EasyM clearance threshold of 0.93% (hypothesis-generating) classified 5/18 patients as MRD+ and stratified PFS (HR 8.78, 95% CI 1.55-49.82, p = 0.004), improving agreement with cfWGS (17/18, 94.4%, κ = 0.870). Progression clustered in cfWGS+/EasyM-high patients (EasyM >0.93%; 4/5; median 11.9 months post-collection [1.9–22.8]) and occurred once in cfWGS−/EasyM-low patients (1/12, 27.6 months). The only discordant case (cfWGS+/EasyM−) progressed 8.7 months after collection. Higher quantitative MRD burden was associated with inferior PFS (cfWGS: HR 2.92 per 1 SD, 95% CI 1.29-6.59, p = 0.01; EasyM: HR 5.48 per 1 SD, 95% CI 0.79-37.90, p = 0.085). At ~100 days post-autologous stem cell transplantation (ASCT; n = 16 available), EasyM was uniformly MRD+ (16/16) while cfWGS was MRD+ in 7/16 patients. Applying an EasyM clearance threshold (2.13%; 9 cleared vs 7 residual) improved agreement with cfWGS (14/16; 87.5%; κ = 0.746). Of two discordant cases, one cfWGS+/EasyM-cleared patient relapsed 38.6 months post-collection and one cfWGS−/EasyM-residual patient remained progression-free at last follow-up. At post-ASCT, both assays showed consistent but underpowered associations with PFS (cfWGS HR 6.32, 95% CI 0.70–56.76, p = 0.100; EasyM-clearance HR 2.36, 95% CI 0.39–14.18, p = 0.335). Across all post-treatment samples (n = 49), continuous cfWGS burden correlated with EasyM residual M-protein (rho = 0.535, p < 0.001). Conclusions: BM-informed cfWGS MRD strongly stratified PFS, whereas EasyM required a clearance definition due to near-universal early positivity. Concordant plasma burdens support complementary MRD information. Future work will validate these findings in larger cohorts and quantify the incremental value of combined cfWGS and proteomic MRD for early relapse prediction.

7029 Background: Mosun, a CD20xCD3 T-cell engaging bispecific antibody, is approved for relapsed/refractory follicular lymphoma after ≥2 prior lines of therapy. We report an interim analysis and PROs with Mosun SC in elderly/unfit patients with previously untreated DLBCL. Methods: MorningSun (NCT05207670) is a Phase 2, basket study of Mosun SC in patients with B-cell non-Hodgkin lymphoma. In the DLBCL cohort, eligible patients (aged ≥80 years, or 65–79 years and ineligible for chemoimmunotherapy) received outpatient Mosun SC: Day (D) 1 (5 mg), D8 (45 mg) and D15 (45 mg) of Cycle (C) 1, then 45 mg on D1 for up to 17 21-day cycles. Primary endpoint was progression-free survival (PFS) rate at 24 months. Other endpoints included overall survival (OS), objective response rate (ORR), complete response (CR) rate, change from baseline (CfB) in lymphoma symptoms as assessed by the Functional Assessment of Cancer Therapy-Lymphoma subscale (FACT-Lym LYMS; higher scores indicate improvement, a ≥3-point increase is considered clinically meaningful) and safety. Results: Forty-nine patients were enrolled, primarily from community sites (n=34). Median age was 83 years (range: 71–101). International Prognostic Index was 3–5 in 53.1% patients and 18.4% of patients had bulky disease. As of February 10, 2025, the median duration of follow-up was 12.5 months (range: 1.4–30.8). PFS and OS rates at 12 months were 71.3% (95% confidence interval [CI]: 54.8–82.7) and 74.7% (95% CI: 58.5–85.4), respectively. ORR was 73.5% and CR rate was 59.2%. Completion rates for FACT-Lym LYMS were ≥95% at baseline and remained ≥87% at each subsequent timepoint. Patients reported improvement in health-related quality of life (HRQoL) over time, demonstrated by increased mean CfB (standard deviation [SD]) in FACT-Lym LYMS scores: C4D1, 5.1 (9.8); C9D1, 5.6 (11.8); C17D1, 9.8 (11.4). Clinically meaningful improvements in lymphoma symptoms were observed in 53.1% (95% CI: 38.3–67.5) of patients. The most common any-grade adverse event (AE) was injection site reaction (53.1%; all Grade [Gr] 1/2). Gr 3/4 AEs were reported in 65.3% of patients and 8.2% experienced a Gr 5 AE (no Gr 5 AEs were Mosun related, per investigator assessment). Serious AEs occurred in 42.9% of patients. Infection AEs occurred in 49.0% of patients (Gr 1: 4.1%; Gr 2: 28.6%; Gr 3: 16.3%) and resolved in 91.7%. Cytokine release syndrome occurred in 12.2% of patients (Gr 1: 10.2%; Gr 2: 2.0%; all resolved). Updated data with around one additional year of follow-up will be presented. Conclusions: Mosun SC showed promising efficacy with manageable safety in elderly/unfit patients with previously untreated DLBCL in an outpatient setting. Clinically meaningful improvements in lymphoma symptoms suggest that Mosun SC improves aspects of HRQoL in this population. Clinical trial information: NCT05207670 .

5624 Background: Endometrial cancer (EC) is the most common gynecologic cancer and abnormal uterine bleeding (AUB) is the predominant presenting symptom. While <10% of AUB represents underlying EC, endometrial sampling is currently required to rule out EC. To develop an alternative, non-invasive rule-out strategy, we aimed to refine a previously reported EC-associated methylated DNA marker (MDM) panel in vaginal swabs. Methods: Patients ≥18 years old with AUB who met ACOG recommendations for endometrial sampling and those undergoing a hysterectomy for biopsy-proven EC or atypical hyperplasia (AH) were prospectively enrolled in a multicenter cohort study. A vaginal fluid specimen was collected via swab by a provider during a speculum exam. DNA was extracted from samples and bisulfite treated, followed by a target and signal amplification method to detect 8 previously identified MDMs. The cross-validated EC classification model used the mean of standardized MDMs. Clinical classification of benign endometrium (BE), EC, and AH was based on central pathology review. EC diagnoses were based on hysterectomy specimens. Endometrioid and mucinous constituted type 1 EC; serous, carcinosarcoma, clear cell, and mixed histology ECs were collectively analyzed as type 2. Results: Of 693 participants enrolled, 670 were evaluable with valid results: 524 in the AUB cohort and 146 in the suspected EC cohort. Within the AUB cohort, 16 had EC or AH. The final analysis cohort included 508 BE, 156 EC, and 6 AH. Of the evaluable participants 20% identified as Black, 3% Asian or Pacific Islander, 75% White, and 3% Other; 7% reported Hispanic ethnicity. Median age was 66 and 50 years for EC and BE AUB, respectively; 80% of those with EC and 43% with benign AUB reported being postmenopausal. Among participants with EC, 102 (65%), 17 (11%), 30 (19%), 6 (4%) were stage I, II, III, and IV, respectively; one EC was unstaged. Type 2 EC accounted for 42 (27%) of all EC cases. A 4-MDM panel yielded an AUC of 0.97 (0.96-0.99, 95% CI) for EC; models with 5-8 MDMs gave identical performance. All-stage EC sensitivity was 97, 97, 96, 95, and 92% at specificities ranging from 75, 80, 85, 90, and 95%, respectively. At the 85% (82-88%) specificity threshold, sensitivities across EC stage, type, and age were consistently high (Table). Sensitivity for AH was 33% (10-70%). Conclusions: An MDM panel demonstrated high sensitivity for EC across stage and EC type, supporting the potential for a non-invasive vaginal swab-based test to rule out EC. Future studies are necessary to finalize the panel and algorithm, prior to validating the test. Clinical trial information: NCT06294886 . EC Sensitivity (%, 95% CI) at 85% Specificity All Stages (n=156)* 96 (92-98) Stage I (n=102) 94 (88 - 97) II (n=17) 100 (82 - 100) III (n=30) 100 (89 - 100) IV (n=6) 100 (61 - 100) Type 1 (n=114) 95 (89 - 98) 2 (n=42) 100 (92 -100) Age ≤ 66 yrs (n=86) 95 (89 - 98) > 66 (n=70) 97 (90 - 99) *n=1 EC was un-staged.