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Background: When missing data are present in clinical outcomes studies, complete-case analysis (CCA) is often performed, whereby patients with missing data are excluded. While simple, CCA analysis may impart selection bias and reduce statistical power, leading to erroneous statistical results in some cases. However, there exist more rigorous statistical approaches, such as single and multiple imputation, which approximate the associations that would have been present in a full dataset and preserve the study’s power. The purpose of this study is to evaluate how statistical results differ when performed after CCA analysis versus imputation methods. Methods: This simulation study analyzed a sample dataset consisting of 2204 shoulders, with complete datapoints from a larger multicenter total shoulder arthroplasty database. From the sampled dataset of demographics, surgical characteristics, and clinical outcomes, we created five test datasets, ranging from 100 to 2000 shoulders, and simulated 10–50% missingness in the postoperative American Shoulder and Elbow Surgeons (ASES) score and range of motion in four planes in missing completely at random (MCAR), missing at random (MAR), and not missing at random (NMAR) patterns. Missingness in outcomes was remedied using CCA, three single imputation techniques, and two multiple imputation techniques. The imputation performance was evaluated relative to the native complete dataset using the root mean squared error (RMSE) and the mean absolute percentage error (MAPE). We also compared the mean and standard deviation (SD) of the postoperative ASES score and the results of multivariable linear and logistic regression to understand the effects of imputation on the study results. Results: The average overall RMSE and MAPE were similar for MCAR (22.6 and 27.2%) and MAR (19.2 and 17.7%) missingness patterns, but were substantially poorer for NMAR (37.5 and 79.2%); the sample size and the percentage of data missingness minimally affected RMSE and MAPE. Aggregated mean postoperative ASES scores were within 5% of the true value when missing data were remedied with CCA, and all candidate imputation methods for nearly all ranges of sample size and data missingness when data were MCAR or MAR, but not when data were NMAR. When data were MAR, CCA resulted in overestimates of the SD. When data were MCAR or MAR, the accuracy of the regression estimate (β or OR) and its corresponding 95% CI varied substantially based on the sample size and proportion of missing data for multivariable linear regression, but not logistic regression. When data were MAR, the width of the 95% CI was up to 300% larger when CCA was used, whereas most imputation methods maintained the width of the 95% CI within 50% of the true value. Single imputation with k-nearest neighbor (kNN) method and multiple imputation with predictive mean matching (MICE-PMM) best-reproduced point estimates and intervariable relationships resembling the native dataset. Availability of correlated outcome scores improved the RMSE, MAPE, accuracy of the mean postoperative ASES score, and multivariable linear regression model estimates. Conclusions: Complete-case analysis can introduce selection bias when data are MAR, and it results in loss of statistical power, resulting in loss of precision (i.e., expansion of the 95% CI) and predisposition to false-negative findings. Our data demonstrate that imputation can reliably reproduce missing clinical data and generate accurate population estimates that closely resemble results derived from native primary shoulder arthroplasty datasets (i.e., prior to simulated data missingness). Further study of the use of imputation in clinical database research is critical, as the use of CCA may lead to different conclusions in comparison to more rigorous imputation approaches.

TPS11585 Background: Soft tissue sarcomas (STS) with genomic complexity are often aggressive but may be sensitive to further genotoxic stress. Leiomyosarcoma (LMS), a common STS, frequently harbors genomic complexity and DNA damage response (DDR) dysregulation. Preclinical data showed hyper-dependency on DNA-PK-mediated non-homologous end joining (NHEJ) DDR, and low-dose liposomal doxorubicin (LD-LPD) synergized with the DNA-PK inhibitor peposertib to inhibit tumor growth in LMS models. We hypothesize that a low, sensitizing dose of LPD enhances DNA damage and safely synergizes with peposertib in LMS and other genomically complex STS. Methods: This phase 1, open label, multicenter dose escalation and dose expansion study (NCT05711615) evaluates LD-LPD given intravenously (IV) on day 1 of 28-day cycles with peposertib given orally (PO) twice daily (BID) continuously (Table). Up to 18 patients (pts) over 18 years-old with advanced or unresectable LMS, undifferentiated pleomorphic sarcoma, myxofibrosarcoma, dedifferentiated liposarcoma, and synovial sarcoma, ECOG performance status ≤2, who received ≥1 prior line of systemic therapy (including anthracycline ≤300 mg/m 2 ) are eligible for dose escalation. Dose expansion will include 12 pts with LMS. The primary objective is to determine the recommended phase 2 dose of LPD+peposertib based on the dose limiting toxicity rate. The Bayesian Optimal Interval (BOIN) design will inform dose escalation decisions. Secondary endpoints for the expansion cohort include adverse event rate, progression-free survival, and objective response rate per RECIST v1.1. Potential predictive biomarkers and changes in DDR biomarkers will be evaluated on biopsies during screening and at cycle 1 day 7. Circulating tumor DNA (ctDNA) collected at baseline (dose escalation and dose expansion), on treatment and at progression (dose expansion) will be correlated with disease activity and response. This trial activated on 8-May-2023 through the Experimental Therapeutics Clinical Trials Network (ETCTN) and is enrolling at select sites in the United States. Dose escalation is ongoing as of January 2025. Clinical trial information: NCT05711615 . Planned dose levels for dose escalation. Dose Escalation Schedule Dose Level Dose Liposomal doxorubicin Peposertib (tablet) -1 10 mg/m 2 IV 50 mg PO BID 0* 10 mg/m 2 IV 100 mg PO BID +1 10 mg/m 2 IV 150 mg PO BID +2 10 mg/m 2 IV 200 mg PO BID +3 15 mg/m 2 IV 200 mg PO BID +4 20 mg/m 2 IV 200 mg PO BID *Starting dose.

TPS11580 Background: Gastrointestinal stromal tumor (GIST) is the most common sarcoma of the gastrointestinal tract. KIT and platelet-derived growth factor receptor α ( PDGFRA ) mutations remain the key oncogenic drivers in the majority of patients with advanced GIST, with acquired secondary drug-resistant mutations contributing to the heterogeneity and complexity of the disease. The diversity of these resistance mutations allows escape from standard-of-care tyrosine kinase inhibitor (TKI) therapy, creating an unmet need for novel therapies that inhibit all clinically relevant GIST-driving mutations. DCC-3009 is an investigational, highly potent, and selective switch-control KIT and PDGFRA inhibitor designed to act against known clinically relevant primary and secondary GIST-driving mutations while limiting off-target effects. Preclinical data showed that DCC-3009 has strong antitumor effects in xenograft models driven by resistant KIT mutations, optimized solubility and oral bioavailability, and low risk of cytochrome P450 inhibition. Here, we describe an ongoing phase 1/2 study evaluating DCC-3009 as a monotherapy in patients with advanced GIST. Methods: This study is a multicohort, open-label, phase 1/2 trial evaluating the safety, tolerability, and efficacy of DCC-3009 in patients with advanced GIST (NCT06630234). This trial uses a modular approach, with each module defined according to the therapy (DCC-3009 alone or in combination with other anticancer agents) and divided into 2 parts (dose escalation and dose expansion). For inclusion in the DCC-3009 monotherapy dose escalation, adult patients (≥18 years) must have histologically or cytologically confirmed advanced GIST with documented KIT or PDGFRA mutation and progression on or intolerance to at least 1 approved TKI regimen in the advanced setting (imatinib if KIT -mutant). Patients must have at least 1 measurable lesion per modified Response Evaluation Criteria in Solid Tumors version 1.1 (mRECIST v1.1) and an Eastern Cooperative Oncology Group Performance Status of 0 or 1 at screening. Exclusion criteria include receiving systemic anticancer therapy (encompassing investigational agents) within 14 days or less than 5 half-lives, radiotherapy within 14 days prior to first dose of study drug, prior or concurrent malignancy requiring treatment or expected to need treatment for active cancer, known allergy or hypersensitivity to the study drug components or any of its excipients, and impaired oral absorption or malabsorption syndrome. Enrolled patients across monotherapy dose escalation will receive DCC-3009 orally in 28-day cycles. The primary outcome measures for monotherapy dose escalation include safety assessment. Secondary outcome measures include objective response rate, duration of response, and progression-free survival by mRECIST v1.1, as well as overall survival and pharmacokinetics. Clinical trial information: NCT06630234 .

TPS11579 Background: Gastrointestinal stromal tumors (GIST) are commonly driven by mutations in the receptor tyrosine kinase KIT . Resistance to approved tyrosine kinase inhibitors (TKIs) arises from additional KIT mutations in the ATP-binding pocket (AP) and activation loop (AL). No single approved TKI broadly suppresses all resistant clones, and overlapping VEGFR inhibition and toxicity limits TKI combinations. The type I TKI bezuclastinib (“BEZ,” CGT9486) inhibits KIT AL resistance mutations, does not inhibit VEGFR, and has complimentary activity with sunitinib (“SUN,” inhibitor of KIT AP resistance mutations). The first-in-human study (PLX121-01) and ongoing Peak trial (NCT05208047) evaluated BEZ+SUN showing promising safety and efficacy in GIST. SARC044 investigates BEZ+SUN in patients (pts) with SUN-resistant, KIT-mutant GIST, and correlatives aim to determine mechanisms of response and resistance (NCT06208748). Methods: SARC044 is a multi-center, open label, single-arm phase II trial enrolling up to 40 adult pts with KIT exon 9 or 11-mutant GIST resistant to imatinib and SUN. After TKI washout (baseline, “b/l”), pts initiate BEZ 600 mg daily for 2 weeks, then add SUN 37.5 mg daily, taking both drugs continuously (28-day cycles) until mRECISTv1.1 progression or unmanageable toxicity. Response evaluations (RE) are performed every 8 weeks (wk) through 15 months (mo) on study, then every 12 wk. Circulating tumor DNA (ctDNA) is collected at b/l, cycle 1 day 15 (C1D15), C2D1, C3D1, and progression. Targeted exome sequencing (TES) of ctDNA will track primary/resistant KIT mutation dynamics across therapy. 18 FDG PET/CTs are performed in 20 pts at b/l, C1D15, and C2D1, which guide a biopsy of a resistant tumor. TES, allele-specific and long-read PCR (to detect AP+AL mutation phasing), and immunoblotting (evaluating KIT pathway activation) will be performed on tissue. EORTC QLQ-C30 surveys collect pt-reported outcomes (PRO) at b/l, on treatment, and at progression. The primary endpoint is median progression-free survival (mPFS) and secondary endpoints include overall survival at 1 and 2 years, clinical benefit rate at 16 wk, adverse event rate, PRO, and KIT mutation profile in ctDNA and tissue. 35 evaluable pts achieves 83% power (p<0.05, one-sided) in a one-sample log-rank test to detect a mPFS of 6.5 mo vs 4 mo (historic control). Expected accrual is 12 mo across 4 sites in the United States with ~36 mo to study completion. Clinical trial information: NCT06208748 .

e21573 Background: In melanoma, biomarkers such as lactate dehydrogenase (LDH), circulating tumor DNA (ctDNA), and the neutrophil-lymphocyte ratio (NLR) have been linked to disease progression. This study aims to compare survival outcomes in melanoma patients based on high versus low levels of these biomarkers, assessing their impact on survival within their respective groups. By evaluating these biomarkers, we hope to identify potential prognostic indicators that could guide treatment decisions and improve personalized care in melanoma management. Methods: We conducted a retrospective survival analysis of 43 melanoma patients, excluding 16 due to incomplete data at Dignity Health Cancer Institute in Phoenix, Arizona. Kaplan-Meier survival analysis was used to compare survival between groups with high vs low levels of biomarkers. Patients were stratified by median values for LDH, NLR, and the presence of detectable ctDNA. Patients included in the analysis were treated systemically with pembrolizumab, encorafenib/binimetinib, nivolumab, or ipilimumab/nivolumab. Survival curves were generated, and statistical significance was assessed using log-rank tests. Data was sourced from our electronic medical record and Signatera™ assay to obtain the primary endpoints. Specimens were standardized in accordance with Natera’s™ specifications. All analyses were executed in GraphPad Prism software. Results: When stratifying by ctDNA, 18 patients had undetectable ctDNA, while 9 had detectable ctDNA with an average level of 1330 (SD = 2067). The median survival for the high ctDNA group was 220 days, whereas the low ctDNA group had significantly longer survival, with only two deaths observed (p = 0.006) within the time period. For LDH, using a cutoff of 204 (IQR = 90.5), patients with high LDH had a median survival of 220 days, while those with low LDH had a significantly longer survival (p = 0.004). When comparing NLR with a cutoff at 2.94 (IQR = 3.7), no significant difference in survival was found between high and low NLR groups (p = 0.72). Conclusions: Our findings show that patients with higher levels of ctDNA and LDH have significantly shorter survival compared to those with low levels of these biomarkers. While NLR did not show a significant survival difference, the study suggests that higher ctDNA and LDH could be important markers for identifying patients at greater risk of poor outcomes. These results underscore the potential value of monitoring these biomarkers to assess disease progression and survival in melanoma patients. Further studies with larger cohorts are needed to validate these findings and refine melanoma prognostic models.

e14551 Background: Extracellular vesicles (EVs) are microscopic particles released by all cell types with a distinct fingerprint reflecting the cell of origin. In patients with prostate cancer, PSMA+EVs have been associated with clinical outcomes. In this study, we investigated tumor-derived EVs (tdEVs) using the tumor-specific CD326 marker as a novel biomarker for pancreas ductal adenocarcinoma (PDAC). Methods: The study included patients with localized PDAC treated on a prospective phase 2 clinical trial evaluating a 15-fraction chemoradiation (CRT) regimen. Blood samples were obtained after induction chemotherapy (C) (prior to CRT) and in follow-up. 20 healthy controls were included. High-resolution flow cytometry enumerated levels of fluorescent antibody labelled tumor-specific CD326 (EpCAM)-positive EVs. All samples were de-identified and randomly coded. The technologist responsible for EV analysis was blinded to patient information and clinical data. Each sample was run in triplicate. Flow cytometry data was analyzed with custom-built software to automatically determine and apply gates and generate reports with scatter plots and EV concentrations for each combination of markers and data summaries. Results: tdEV data were analyzed from 70 patients with pre-CRT samples. Patients had mean age 66 years (9.0 standard deviation), with 60% ECOG 0, 43% borderline resectable and 48% locally advanced. Patients had a median 8 cycles of C prior to CRT, and 70% proceeded to surgery after CRT. 2-year overall survival (OS) was 54%. Patient samples showed elevated total CD326 EVs compared to the healthy controls (p = 0.0005). Furthermore, patient CD326 EVs revealed two distinct subpopulations: small (120-1,000nm) and large (1,000-3,000nm) size CD326 EVs. No large CD326 subpopulation was found in healthy donor samples. Higher pre-CRT levels of total CD326 and large CD326 EVs were associated with decreased progression-free survival (PFS) (hazard ratio (HR) = 2.38, p = 0.013 and HR = 2.017, p = 0.021) on multivariable models with surgical resection. Resection was associated with increased PFS (p < 0.0001), and the interaction terms did not meet significance (p = 0.083 and p = 0.21). No differences in pre-CRT total or large CD326 EVs were identified between patients with or without surgical resection (p = 0.72 and p = 0.83). CA19-9 levels were not predictive of clinical outcomes in this trial and showed no association with EV levels. Conclusions: We present an association between clinical outcomes and tdEVs in PDAC, highlighting their potential as a novel, independent biomarker. If validated, tdEVs may offer an opportunity to personalize care and improve risk stratification.

8618 Background: Telisotuzumab vedotin (Teliso-V) is a c-Met–directed antibody-drug conjugate comprising the mAb telisotuzumab and the microtubule polymerization inhibitor monomethyl auristatin E. In the phase 2 LUMINOSITY trial (NCT03539536), Teliso-V monotherapy 1.9 mg/kg showed durable responses and a generally manageable safety profile in patients (pts) with c-Met protein–overexpressing (OE) non-squamous (NSQ) EGFR -wildtype (WT) non-small cell lung cancer (NSCLC). Herein we present an analysis of efficacy outcomes according to prior platinum or prior platinum and immune checkpoint inhibitor (ICI)-based therapies. Methods: Pts (≥18 years) with locally advanced/metastatic c-Met protein–OE NSQ EGFR -WT NSCLC who had ≤2 prior lines of therapy, including ≤1 line of chemotherapy, were treated with 1.9 mg/kg Teliso-V Q2W. c-Met protein overexpression (by immunohistochemistry clinical trial assay for MET [SP44] [Roche]) was defined as ≥25% tumor cells with 3+ staining intensity (high: ≥50% 3+; intermediate [int]: 25 to <50% 3+). The primary endpoint was overall response rate (ORR) by independent central review per RECIST v1.1. Results: As of 21 Feb 2024, 172 pts received ≥1 dose of Teliso-V and 168 pts were included in efficacy analyses (c-Met high, n=84; c-Met int, n=84). In the c-Met OE total population, 97.6% of pts received prior platinum and 78.6% received prior platinum + ICI. Efficacy data for pts with prior platinum and platinum + ICI therapies are shown in the Table. Among the 172 dosed pts, the most common any-grade treatment-related adverse events (TRAEs) were peripheral sensory neuropathy (31%), peripheral edema (16%), and fatigue (14%). The most common grade ≥3 TRAE was peripheral sensory neuropathy (7%). Conclusions: This analysis demonstrated that Teliso-V elicited durable responses in pts with c-Met protein–OE NSQ EGFR -WT NSCLC regardless of whether they had received prior platinum or platinum + ICI therapies; the efficacy outcomes in these subgroups were consistent with those in the overall pt population. Clinical trial information: NCT03539536 . Platinum Platinum + ICI Overall ORR, a n/N (%) [95% CI] c-Met OE total c-Met high c-Met int 48/164 (29.3) [22.4, 36.9]28/81 (34.6) [24.3, 46.0]20/83 (24.1) [15.4, 34.7] 38/132 (28.8) [21.2, 37.3]22/67 (32.8) [21.8, 45.4]16/65 (24.6) [14.8, 36.9] 49/168 (29.2) [22.4, 36.7]29/84 (34.5) [24.5, 45.7]20/84 (23.8) [15.2, 34.3] Median DOR, a mo [95% CI] c-Met OE total c-Met high c-Met int 7.2 [5.5, 11.3]9.0 [3.8, 12.0]7.2 [4.7, 11.5] 7.2 [5.5, 11.0]9.0 [3.8, 11.3]7.2 [5.3, 11.5] 7.2 [5.5, 11.0]7.2 [4.2, 12.0]7.2 [4.7, 11.5] a Per independent central review. DOR, duration of response.

8513 Background: The MET pathway is a known mediator of EGFR-TKI resistance and represents a therapeutic vulnerability to select MET-TKIs. Savo is an oral, highly selective MET-TKI that, when combined with osi, has the potential to overcome MET-driven resistance after progressive disease (PD) on osi. The Phase 2 SAVANNAH study has demonstrated clinically meaningful activity with the combination of savo + osi in patients (pts) with EGFR-mutated (EGFRm) advanced NSCLC and MET overexpression/amplification (NCT03778229). Isolating the efficacy of savo in the use of savo + osi is a key question for this combination. Methods: A subset of SAVANNAH included eligible pts who had EGFRm advanced NSCLC with MET overexpression (IHC 3+ intensity in ≥90% of tumor cells [IHC3+/≥90%]) and/or amplification (≥10 MET gene copies by FISH [FISH10+]) after PD on first-line (1L) osi; asymptomatic stable brain metastases (treated/untreated) were allowed. Pts were randomized 2:1 (double-blind) to savo 300 mg BID + osi 80 mg QD, or savo 300 mg BID + PBO (stratified by investigator [INV] assessed baseline [BL] brain metastases [yes/no]), until INV-assessed PD per RECIST 1.1. Brain imaging occurred at BL and PD; pts with brain metastases were re-imaged at each tumor assessment to PD. Endpoints included objective response rate (ORR), duration of response (DoR), and progression-free survival (PFS) by BICR and INV; CNS PFS, and presence/absence of CNS lesions at PD by BICR. Results: Overall, 73 pts were randomized (savo + osi n=48; savo + PBO n=25). At BL, median age: 67 vs 65 years, female: 73% vs 64%, White: 73% vs 52% in the savo + osi and savo + PBO arms, respectively. Efficacy outcomes (ORR, DoR, and PFS) were higher with savo + osi than savo + PBO (Table). CNS PFS events by CNS BICR occurred in 5/14 (36% savo + osi) and 2/4 pts (50% savo + PBO). In pts without BL brain metastases, none of the 13 pts (savo + osi) with RECIST PD by BICR had a new CNS lesion; 6/11 pts in the savo + PBO arm developed a new CNS lesion. Conclusions: In EGFRm advanced NSCLC with MET IHC3+/≥90% and/or FISH10+ status after PD on 1L osi, efficacy of savo 300 mg BID + osi was numerically greater than savo + PBO and showed promising CNS activity. To date, this is one of the largest randomized data sets presented evaluating an oral MET-TKI in EGFRm NSCLC. Efficacy findings from SAVANNAH suggest that targeting both EGFR and MET is key and support further investigation of savo + osi and CNS activity in the Phase 3 SAFFRON study. Clinical trial information: NCT03778229 . Assessment Savo + osi (n=48) Savo + placebo (n=25) ORR, % (95% CI) BICR 58 (43, 72) 16 (5, 36) INV 54 (39, 69) 24 (9, 45) DoR, mo, median (95% CI) BICR 11.8 (6.0, NC) 4.5 (2.6, NC) INV 8.0 (4.9, 11.7) 4.2 (2.6, NC) PFS, mo, median (95% CI) BICR 8.3 (5.8, 15.1) 3.6 (1.4, 5.7) INV 7.6 (5.6, 11.0) 2.7 (1.4, 4.1) BICR, blinded independent central review; CI, confidence interval; mo, months; NC, not calculable.

TPS3644 Background: Currently, there are no biomarkers validated prospectively in randomized studies for resected colon cancer (CC) to determine need for adjuvant chemotherapy (AC). However, circulating tumor DNA (ctDNA) represents a highly specific and sensitive approach (especially with serial monitoring) for identifying minimal/molecular residual disease (MRD) post-surgery in CC patients (pts), and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. CC pts who do not have detectable ctDNA (ctDNA-) are at a much lower risk of recurrence and may be spared the toxicities associated with AC. Furthermore, for CC pts with detectable ctDNA (ctDNA+) who are at a very high risk of recurrence, the optimal AC regimen has not been established. We hypothesize that for pts whose CC has been resected, ctDNA status may be used to risk-stratify for making decisions about AC. Methods: In this prospective phase II/III trial, up to 1,912 pts with resected stage IIB, IIC, and III CC will be enrolled. Based on the post-operative ctDNA status using personalized and tumor-informed assay (Signatera™, bespoke assay), those who are ctDNA- (Cohort A) will be randomized to immediate AC with fluoropyrimidine (FP)+oxaliplatin (Ox) for 3-6 mos per established guidelines v serial ctDNA monitoring. Patients who are ctDNA+ post-operatively, or with serial monitoring (Cohort B), will be randomized to FP+Ox v more intensive AC with addition of irinotecan (I) for 6 mos. One cycle of chemotherapy is allowed while awaiting ctDNA testing results for cohort assignment. The primary endpoints for Cohort A are time to ctDNA+ status (phase II) and disease-free survival (DFS) (phase III) in the immediate v delayed AC arms. The primary endpoint for Cohort B is DFS in the FP+Ox v FP+Ox+I arms for both phase II and phase III portions of the trial. Secondary endpoints include prevalence of detectable ctDNA post-operatively, time-to-event outcomes (overall survival and time to recurrence) by ctDNA status, and the assessment of compliance to adjuvant therapy. Biospecimens including archival tumor tissue, as well as post-operative plus serial matched/normal blood samples, will be collected for exploratory correlative research. Active enrollment across the NCTN started in June 2022 with CCTG sites joining in August 2023. Current accrual (as of 1-27-2025): 647/1,912. NCT: 05174169. Support: U10 CA180868, -180822; -180888; UG1 CA189867; Natera, Inc. Clinical trial information: NCT05174169 .

11506 Background: Catequentinib Hydrochloride (AL3818, Anlotinib, Catequentinib) is a novel, orally administered, small molecule tyrosine kinase inhibitor. There remains an unmet need for effective, well tolerated therapies for patients (pts) with advanced/ metastatic leiomyosarcoma (LMS). We performed a randomized, double blind trial of Catequentinib monotherapy versus placebo in advanced/metastatic LMS. Methods: Patients with a diagnosis of LMS requiring third or further line treatment were eligible. Catequentinib was administered in a 21-day cycle with 14 days on and 7 days off regimen. In this double blind phase 3 trial, patients were randomized 2:1 to Catequentinib or placebo, with the option of crossover to Catequentinib after confirmed Progression Disease (PD) on placebo. Progression-free survival (PFS) with Log Rank test was the primary endpoint and the trial was conducted at multiple sites in the US, UK and EU. Results: Total N = 111 patients were enrolled, and N = 110 were treated and evaluated, 74 randomized to Catequentinib (C), and 36 to placebo (P). In arms (C)/(P) median ages were 59.0/60.5 (range: 33-91) years respectively and 59/29 (79.7%/80.6%) were female. Median PFS by Blinded Independent Central Review (BICR) met the primary endpoint at 3.42 months (95% CI: 2.60, 6.83) for (C) and 1.41 months (95% CI: 1.35, 4.86) for (P) with a p-value of 0.0265 and a HR of 0.536 (95% CI: 0.307, 0.936). Median PFS for patients stratified at ≤ 3 prior lines was 4.86 months (95% CI: 2.04, 8.94) for (C) and 1.41 months (95% CI: 1.31, 4.86) for (P) with a p-value of 0.0046 and a HR of 0.386 (95% CI: 0.196, 0.760). The 6-month progression-free rate was 42.37% for (C) and 20.71% for (P). OS was 17.45 months (95% CI: 13.57, 19.32) for (C) and 16.33 months (95% CI: 11.27, NE) for crossover patients in the (P) arm. 30 (40.5%) of patients have experienced grade 3 treatment-related adverse events in the (C) arm compared to 3 (8.3%) of patients in the (P) arm. The most common TEAE for (C) vs (P) were diarrhea (50.0% vs 22.2%), stomatitis (31.1% vs 8.3%), fatigue (64.9% vs 41.7%), and hypertension (47.3% vs 19.4%). Conclusions: This phase 3 trial met the primary PFS endpoint and demonstrates superior PFS for Catequentinib vs placebo in metastatic/advanced LMS. This study confirms the acceptable benefit-risk profile of Catequentinib in LMS. Catequentinib is an effective and well tolerated treatment option for patients with LMS. Clinical trial information: NCT03016819 .