Citations

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 .

e20629 Background: Lung cancer (LC) and respiratory failure (RF) are major contributors to mortality in adults globally. Understanding long-term mortality trends across demographic, racial, geographic, and socio-economic groups is crucial to addressing disparities and improving outcomes. This study examines national mortality patterns for LC and RF in the United States from 1999 to 2023, providing critical insights into changes over time and identifying key disparities in age-adjusted mortality rates (AAMRs). Methods: A descriptive analysis of mortality data from the CDC WONDER database (1999-2023) identified deaths due to LC (ICD-10 code C34) and RF (ICD-10 code J96) in adults aged 25+. AAMRs per 100,000 population were calculated and stratified by gender, race/ethnicity, region, state, and urban-rural classification. Temporal trends were analyzed with Joinpoint regression to compute APCs and 95% CIs. Statistical significance was set at p<0.05. The study followed STROBE guidelines. Results: From 1999 to 2023, a total of 456,325 adult deaths (age 25-85+) were attributed to Lung cancer and Renal failure. Age-adjusted mortality rates (AAMRs) for lung cancer (LC) and respiratory failure (RF) decreased from 1999 to 2010 (APC = -1.2, 95% CI: -1.6 to -0.9), followed by an increase from 2010 to 2023 (APC = 1.4, 95% CI: 1.1 to 1.7). Gender trends revealed a steady decline for men, while women's Age-Adjusted Mortality Rates (AAMr) initially decreased, then increased from 2011-2023 (APC: 2.0, 95% CI: 1.7 to 2.5). Non-Hispanic White populations experienced a rapid increase in age-adjusted mortality rates from 2014 to 2017 (APC: 2.7; 95% CI: 0.9 to 3.3), while other racial/ethnic groups exhibited varied trends with declines, increases, and stabilizations. Geographically, AAMRs were highest in the Northeast (8.6; 95% CI: 8.5 to 8.7) and lowest in the Midwest (7.1; 95% CI: 7.0 to 7.1). Metropolitan areas saw declining trends until 2006, stabilizing briefly, and increasing thereafter. Non-metropolitan areas experienced notable increases post-2009 (APC = 2.3, 95% CI: 1.8 to 3.1). State-level disparities revealed Mississippi with the highest AAMR (14.0; 95% CI: 13.7 to 14.4) and Wisconsin with the lowest (3.7; 95% CI: 3.5 to 3.8). These findings highlight significant demographic, racial, and geographic variations in LC and RF mortality trends. Conclusions: LC and RF-related mortality rates initially declined from 1999 to 2010 but increased significantly from 2010 onward, with notable demographic, racial, and geographic disparities. These findings highlight the urgent need for targeted interventions and resource allocation to address these rising trends and reduce inequities across vulnerable populations.

e20615 Background: Patients with Stage IV NSCLC have a poor prognosis, with approximately 25-30% succumbing to the disease within the first three months. However, survival outcomes can vary significantly depending on individual factors and advancements in treatment options. Therefore, it is crucial to identify patients at high risk of poor survival outcomes to tailor personalized treatment strategies and optimize clinical management. An international study has been conducted to generate prognostic scores for patients with Stage IV NSCLC. Methods: A retrospective observational study was conducted using real-world data (RWD) from South Korea (ROOT-HEALTH database from Samsung Medical Center), the USA (COTA NSCLC dataset) and France (CIAN lung cohort from Centre Léon Bérard). Patients with stage IV NSCLC between January 2008 and December 2023 were included. The study's primary objective was to learn from patients ‘baseline characteristics affecting overall survival (OS) and progression-free survival (PFS) to derive a prognostic score reflecting relative risk of death for given patient. A partition strategy was used, with 70% of the cohort for training and 30% for validation. Data-driven feature elimination has been applied to avoid overfitting of the models. Nested cross-validation reduced selection bias in hyperparameter tuning and model selection. Results: A total of 7,805 patients with NSCLC were included in the final analysis (USA: n=610, France: n=271, Korea: n=6,924). In the Korean dataset, the model achieved a C-index of 0.872 for OS using 35 selected variables. For the USA dataset, the model, based on 15 selected variables, demonstrated a C-index of 0.707 for OS. For PFS, the Korean dataset demonstrated a C-index of 0.823, the USA dataset achieved a C-index of 0.664, and the French dataset reported a C-index of 0.64, using 15 selected variables. The important predictors for OS included albumin, neutrophil/lymphocyte ratio, bilirubin, and druggable mutations. For PFS, important predictors included LDH, albumin, hemoglobin, MET mutation, bilirubin, and BMI. The prognostic scores derived from these models allowed to identify patients with higher risk of death, than average, in each country. Conclusions: This study generates prognostic scores for OS and PFS in stage IV NSCLC using longitudinal international data from the USA, France, and South Korea throughout the cancer journey. It has the potential to support better treatment strategy for severe patients in clinical practice and early decision-making in clinical studies. Further research utilizing diverse international cohorts is essential to refine prognostic scores and enhance personalized treatment strategies for stage IV NSCLC patients.

e20520 Background: Cancer and respiratory failure (RF) are amongst leading causes of mortality in adults. This study investigates national trends in age-adjusted mortality rates (AAMRs) for cancer and RF in the United States from 1999 to 2023, focusing on disparities by gender, race, region, and rural-urban residence to inform public health strategies. Methods: This descriptive study analyzed data from the CDC WONDER database, of adults aged 25 and older. Mortality data were identified using ICD-10 codes C00–C97 (cancer) and J96 (RF). AAMRs per 100,000 population were calculated and stratified by gender, race/ethnicity, census region, urban-rural classification, and state. Temporal trends were analyzed using Joinpoint regression to estimate annual percent changes (APCs) with 95% confidence intervals (CIs). Statistical significance was set at p < 0.05. Results: From 1999 to 2023, total deaths of 1,263,368 attributed to cancer and RF (682,141 men, 581,227 women). AAMRs declined from 1999 to 2004 (APC = -1.5, 95% CI: -4.0 to -0.4), stabilized from 2004 to 2012 (APC = 0.8, 95% CI: 0.1 to 2.4), and increased from 2012 to 2023 (APC = 3.2, 95% CI: 2.9 to 3.8). Men experienced a greater initial decline (APC = -2.1, 1999–2004) but significant increases thereafter (APC = 3.0, 2012–2023), while women showed a slower decline followed by sharper increases (APC = 3.5, 2013–2023). Non-Hispanic Black populations initially declined (APC = -1.7, 1999–2003) but later increased significantly (APC = 3.0, 2014–2020). Hispanic/Latino populations declined (APC = -1.2, 1999–2009) before rising sharply (APC = 3.1, 2009–2020). American Indian or Alaska Native populations showed consistent increases (APC = 1.7, 1999–2020). Urban areas experienced initial declines (APC = -1.7, 1999–2004), followed by increases (APC = 2.4, 2011–2020). Non-metropolitan areas exhibited steeper increases (APC = 4.6, 2014–2020). Regionally, the West recorded the highest AAMR (24.0), followed by the Northeast (23.6), South (20.9), and Midwest (18.0). Mississippi had the highest state-level AAMR (36.3), while Wisconsin had the lowest (10.0). States in the top 90th percentile included Mississippi, Arkansas, and California, while Wisconsin, Minnesota, and Oregon were among the lowest. Conclusions: Cancer and RF mortality declined initially but have significantly increased in recent years. Disparities persist across gender, racial, and regional groups, underscoring the need for focused public health efforts and equitable resource distribution to address these trends.

e19531 Background: Effective treatment and elimination of clonal plasma cells (PC) in multiple myeloma (MM) are typically associated with recovery of polyclonal (normal) plasma cells (PPC). Studies suggest that robust PPC recovery is associated with better outcomes. However, it is unclear if this remains valid in the context of monoclonal antibodies, such as Daratumumab, that selectively target plasma cells, and in turn, may adversely impact PPC recovery. Methods: We identified patients with MM who underwent MRD testing using Euroflow method at 6-12 months after treatment initiation. Eight patients had disease progression prior to MRD testing and were excluded from further analysis. PPC was quantitated by the proportion of total events acquired during flow examination. Patients were considered MRD-negative if they had <1 clonal PCs in 10 5 cells, as detected in the marrow. We first examined the impact of initial therapy (Daratumumab vs. non-Daratumumab based regimens) and MRD status on PPC recovery. Subsequently, we analyzed impact of PPC recovery on patient outcomes in terms of progression-free survival (PFS) and overall survival (OS). Results: We identified 572 patients who had MRD testing by flow at a median of 9 months (range 6-12) after treatment initiation. The median age was 63 years, 58% were male. Daratumumab was part of initial therapy in 17% of patients; the most common induction therapies were PI-IMiD triplets (73%), and dara-PI-IMiD quads (15%). In our cohort, 74% of patients were MRD-negative. In our practice, only samples with no monotypic PCs identified on initial low-sensitivity flow proceed to MRD testing, hence, the proportion of MRD-negative patients appears higher in our study than previously reported. Median PPC was 0.02% and was similar between MRD-negative and -positive patients. We found the median PPC was significantly low in patients who received Daratumumab compared to the non-Daratumumab treated cohort (0.011% vs. 0.023%; p<0.01). There was a trend towards lower PFS and OS among the lowest PPC quartile group compared to the upper 3 quartiles, although this was not significant (p=0.07 for PFS and OS, Wilcoxon). This trend was more evident among patients who did not receive Daratumumab. Conclusions: Our study demonstrates negative impact of anti-CD38 therapy with Daratumumab on recovery of PPCs after initial treatment, consistent with the persistent hypogammaglobulinemia seen in clinical practice among these patients. However, unlike the observation with the non-Daratumumab treated cohort, the low proportion of PPCs does not significantly impact patient outcomes among patients who received Daratumumab.

3553 Background: Vilastobart (XTX101) is tumor-activated, high affinity, Fc-enhanced aCTLA-4 designed to focus activity toward the tumor and minimize systemic adverse events. Fc-enhancement augments FcγR co-engagement on antigen presenting cells and has been linked with efficacy of aCTLA-4 combinations in patients (pts) with microsatellite stable (MSS) colorectal cancer (CRC) and other tumors [Fakih ASCO GI 2025]. Vilastobart was generally well-tolerated and demonstrated evidence of anti-tumor activity in pts with immunologically “cold” advanced solid tumors, both as a monotherapy and in combination with atezolizumab [Davar SITC 2024]. Methods: Phase 2 of the NCT04896697 study evaluated the initial recommended Phase 2 dose of vilastobart 100 mg Q6W in combination with atezolizumab 1200 mg Q3W in pts with MSS CRC who had at least 1 prior chemotherapy regimen in the metastatic setting, excluding pts with prior immune checkpoint inhibitors. Pts with (LM) and without liver metastasis (NLM) were eligible. Tumor biopsies were obtained before and during treatment for translational analyses. Results: As of January 13, 2025, 40 pts were dosed in Phase 2. Median age was 55 (25-82) and 70% of pts had 3 or more prior lines of therapy. Of the 24 enrolled NLM pts, 11 were response-evaluable with an available on-treatment scan as of the data cut. In these 11 pts, two confirmed and one unconfirmed partial response (PR) were reported, all accompanied by significant decreases in ctDNA and serum tumor marker CEA and with each pt ongoing on therapy, for a preliminary ORR of 27%. One additional pt (with peritoneal metastasis) had a 24% reduction in target lesions (first scan) and was ongoing on therapy. Of the 16 enrolled LM pts, 7 were response evaluable, with one stable disease and another pt reporting a mixed response with significant serum tumor marker reductions, both ongoing on therapy. Of note, one LM pt in Phase 1C dose escalation treated with vilastobart (150 mg Q6W) combination had a confirmed PR with LM resolution. Six pts (15%) reported G3+ treatment-related adverse events (TRAEs), with two G4 laboratory TRAEs and no G5 TRAEs. Only three pts discontinued therapy for TRAEs. TRAEs occurring in ≥10% (all grade) or ≥5% (G3) of pts are summarized in the Table. Conclusions: The combination of vilastobart, a novel tumor-activated, Fc-enhanced a-CTLA-4, and atezolizumab demonstrated initial evidence of anti-tumor activity in late line, metastatic MSS CRC where immune checkpoint blockade has historically been relatively ineffective. Vilastobart was observed to have a differentiated safety profile distinct from systemically active a-CTLA-4, consistent with tumor-selective activation. Clinical trial information: NCT04896697 . AE term All Graden (%) Grade 3n (%) Fatigue 12 (30%) 0 Diarrhea 8 (20%) 0 Infusion related reactions 5 (13%) 0 Pyrexia 4 (10%) 0 ALT increased 4 (10%) 0 AST increased 4 (10%) 1 (3%) Colitis 2 (5%) 2 (5%)

11507 Background: Advanced uterine leiomyosarcoma (uLMS) is an aggressive malignancy with poor prognosis. Standard-of-care treatments, including trabectedin (Tb) or pazopanib (P), provide median progression-free survival (PFS) of 3-4 months (mo) and objective response rates (ORR) of ~11%. Homologous recombination deficiency (HRD) in a subset of uLMS supports the use of PARP inhibitors combined with DNA-damaging agents. Preclinical studies demonstrated synergistic activity of olaparib and temozolomide (T+O), and a prior single-arm Phase II study of T+O showed promising efficacy independent of an established biomarker, warranting further investigation in a randomized setting. Methods: Alliance A092104 is a Phase II/III trial evaluating olaparib (200 mg BID) plus temozolomide (75 mg/m² daily, days 1-7, every 21 days) versus investigator’s choice of Tb or P in patients (pts) with advanced uLMS who progressed on ≥2 prior systemic therapies. Stratification factors included ECOG (0-1 vs. 2) and prior lines (2 vs. ≥3). The Phase II (Phase III) primary endpoint was PFS (OS), with a planned suspension of accrual at the end of Phase II. A total of 70 evaluable pts (58 PFS events) were needed to detect an improvement in PFS from 4 vs. 8 mo with power of 90% and 1-sided type I error of 10%, with futility assessed after 29 PFS events. Upon meeting the Phase II futility threshold for PFS, the trial was permanently closed. Data were released from the data and safety monitoring board. Pts continue to be followed for outcomes. Results: 74 pts enrolled (Arm 1: T+O, n = 37; Arm 2: investigator’s choice, n = 37 (Tb, 18; P, 13; 6 pts did not start treatment). The arms were balanced for baseline demographics except race, with the T+O arm having a higher proportion of black/African American (29.7% vs. 16.2%). 21 pts remain on treatment. Hematologic adverse events (AEs) were more frequent in the T+O arm, with Grade 4 neutropenia (19.5%) and thrombocytopenia (8.3%) both managed by dose reductions. Non-hematologic Grade 3 AEs were higher in the investigator’s choice arm (45.2% vs. 13.9%). No Grade 5 AEs were reported. In the first 70 pts, with a median follow-up of 5.9 mo, and 39 total PFS events, the median PFS was 3.2 mo (95% CI: 2.0-NE) for T+O versus 5.6 mo (95% CI: 2.8-NE) for investigator’s choice (HR = 1.00; 95% CI: 0.60-2.17; 1-sided stratified log rank p = 0.50). Within Arm 2, the median PFS for Tb and P were respectively 5.6 (95% CI: 3.1-NE) and 3.8 (95% CI: 1.5-NE) mo. 3 pts in the T+0 arm and 1 patient in the investigator’s choice arm (Tb) had a confirmed partial response. Conclusions: The trial did not meet its primary endpoint of PFS in Phase II. This suggests that a biomarker may be needed before there is further exploration of PARP inhibitor-based regimens in uLMS. Overall survival and analysis of tissue-based biomarkers will be presented. Clinical trial information: NCT05432791 .

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

TPS1138 Background: The SV-BR-1-GM breast cancer cell line activates anti-tumor immunity by expressing tumor associated antigens and secreting GM-CSF which enhances dendritic cell activation and promotes adaptive (T-cell mediated) and innate (dendritic and NK cell) immune responses. The cells are also engineered to optimize immune recognition through pt specific HLA antigen matching. SV-BR-1-GM acts through direct antigen presentation and CD4+ T-cell activation and, when combined w/ checkpoint inhibitors (CPIs), has demonstrated clinical benefit in 54 heavily pretreated metastatic breast cancer (MBC) pts. In pts w/ disease progression following CPI therapy, similar or improved progression free survival (PFS) compared to their prior treatment regimen. Disease control following antibody drug conjugates was observed in 40%of pts. Clinical benefit was seen in 5 out of 8 pts w/ untreated intracranial metastases. CD8+ Immuno-PET imaging suggests systemic activation, w/ increased CD8+ tumor infiltrating lymphocytes at both primary and metastatic tumor sites, as well as lymphoid organs. Optimized sequencing of CPI w/ SV-BR-1-GM and its latest phase 3 formulation have shown enhanced clinical outcomes, including improved overall survival (OS) (median 13.4 mos), PFS (3.6 mos), and clinical benefit rate (CBR; 61%).These findings have informed refinements to the ongoing pivotal, registration enabling Phase 3 trial, designed to optimize pt selection and treatment sequencing strategies. Methods: This ongoing multicenter, randomized, open label Phase 3 trial evaluates Bria-IMT + CPI vs. Treatment of Physician’s Choice (TPC) in MBC pts lacking approved curative therapies. Pts are randomized 1:1:1 to Bria-IMT + CPI, TPC, or Bria-IMT monotherapy (discontinued after 150 enrollments to prioritize combination arms). The Bria-IMT regimen consists of: Day -2: Cyclophosphamide 300 mg/m², Day 0: 20M irradiated SV-BR-1-GM cells, Day 2/3: 0.1 mcg pegylated α interferon at each inoculation site. CPI infusion is administered Day -3 to 3. Cycles q3w. TPC regimens follow site specific SOC. Imaging q6w (first 2 cycles), then q8w. Eligibility includes all MBC subtypes, including CNS mets, and permits prior CPI therapy ( >21 days pre-treatment). There will be 100 sites across the U.S., Canada, and ex-North America w/ an enrollment target of 404. The trial is currently active at 59 sites with 217 sub investigators. To date, 67 pts screened: 46 randomized (median age 56 yrs [34–83], median 6 [2–13] prior lines of therapy. The primary endpoint is OS, with an interim analysis at 144 events targeting a hazard ratio of 0.6. Secondary endpoints: PFS, overall response rate, CBR, CNS event free survival, and TWiST. Safety analyses ongoing; pt reported outcomes assess subjective treatment impact. Clinical trial information: NCT03328026 .