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TPS650 Background: The TAILORx and RxPONDER trials showed that recurrence score (RS) identifies many postmenopausal pts who do not benefit from addition of ACT to endocrine therapy (ET); however, RS also identifies subsets who do benefit (node-neg/high clinical risk/RS 16-20, node-neg/RS 21-25, and node-pos/RS ≤25). Most premenopausal pts in these trials did not receive ovarian function suppression (OFS) as part of their ET regimen. Given the observed benefit from OFS in high-risk premenopausal pts with HR+/HER2– BC in SOFT/TEXT, we question whether the ACT benefit in TAILORx/RxPONDER was due to chemotherapy-induced OFS. To address this, we developed OFSET, a phase III clinical trial comparing OFS+ET to ACT+OFS+ET. Methods: We hypothesize that addition of ACT to OFS+ET is superior to OFS+ET in improving invasive breast cancer-free survival (IBCFS) among premenopausal pts with early-stage HR+/HER2– tumors, and a 21-gene RS between 16-25 (for pN0 pts) and 0-25 (for pN1 pts). Secondary objectives include invasive disease-free survival, overall survival, distant recurrence-free interval, breast cancer-free interval, and health-related quality of life (HRQOL). Pts must be node-neg with RS 16-20 (plus high clinical risk), RS 21-25, or have 1-3 positive nodes with RS ≤25. Stratification is by nodal status/RS status (pN0 RS 16-25; pN1 RS 0-15; pN1 RS 16-25), intent to receive CDK4/6 inhibitor (yes; no), and age (18-39; ≥40). Pts are randomized after surgery to either OFS+ET or ACT+OFS+ET. ET is an aromatase inhibitor (AI) per physician discretion; or tamoxifen if AI is not tolerated or if OFS is incomplete. Radiotherapy will be administered per protocol guidelines. An HRQOL sub-study will assess severe menopausal symptoms (measured by FACT ESS-19) and pain severity (PROMIS) between arms. Blood and tumor specimens will be collected for future research. We anticipate accrual of 3,960 pts in 7 yrs, 7 mos. Per NSABP B-28/RxPONDER data, 5-yr IBCFS of pN1 pts on the ACT+OFS+ET arm is estimated at 92.3%. Per TAILORx data, 5-yr IBCFS of pN0 pts on the ACT arm is ~95%. Assuming 56% of pts to be pN0 and 44% pN1, and a 0.5% annual loss-to-follow-up rate, the definitive analyses to detect a hazard ratio: 0.75 with ACT+OFS+ET v OFS+ET, with 1-sided α of 0.025 and 80% power, will require 380 IBCFS events, expected to occur ~11 yrs after study initiation. Accrual is 496/3,960 (from 8/2023 to 1/2026). NCT #: NCT05879926. Clinical trial information: NCT05879926 .

TPS2673 Background: The main challenge for developing CAR T therapies for solid tumors is the lack of targets that distinguish tumor from normal cells, resulting in on-target, off-tumor toxicity. Tmod logic-gated CAR T therapy addresses this challenge by incorporating 2 CARs on the same T cell: an activator targeting a marker on both tumor and normal cells, and a blocker targeting HLA-A*02 that inhibits CAR T activity against normal cells while allowing activation against tumor cells (with HLA-A*02 LOH), improving tumor selectivity and decreasing toxicity. Early safety results from 3 ongoing phase 1/2 clinical trials of logic-gated, Tmod CAR T therapy (EVEREST-1, EVEREST-2, and DENALI-1) have demonstrated manageable safety and tolerability in patients with advanced solid tumors (Grierson et al, SITC , 2024; Ward et al, SITC 2025; Specht et al, SABCS , 2025). Early efficacy results include the first ever reported complete response in a patient with non-small cell lung cancer following treatment with a CAR T-cell therapy (A2B694). A2B543 is an autologous Tmod CAR T therapy that contains the same Tmod construct as A2B694 with an added membrane-tethered IL-12 (memIL12) booster. Specifically, A2B543 is comprised of autologous Tmod cells transduced with 2 lentiviral vectors: one expressing both the HLA-A*02-targeted blocker and the mesothelin-targeted CAR activator; and a second expressing the memIL12 booster. Interleukin 12 (IL-12) is a potent, pro-inflammatory cytokine that plays a crucial role in inducing antitumor immune responses; however, systemic IL-12 can be prohibitively toxic (Jia et al, Front Immunol , 2022). In A2B543, expression of the memIL12 cassette is under the control of an NFAT promoter and is induced during antigen engagement or T cell activation. This inducible memIL12 is designed to reduce the toxicity associated with systemic IL-12 while enhancing the long-term potency and persistence of Tmod (Zhang et al, J Immunother Cancer , 2025). Methods: EVEREST-2 (NCT06051695) is a phase 1/2, open-label, nonrandomized study evaluating the safety and efficacy of A2B543 in adults with recurrent/metastatic mesothelin-expressing cancers with tumor-associated HLA-A*02 LOH, including mesothelioma, colorectal, non-small cell lung, pancreatic, or ovarian cancer. Patients are enrolled through BASECAMP-1 (NCT04981119), a master prescreening study that identifies patients with HLA LOH via next-generation sequencing and cryopreserves leukapheresis product. Upon progression, A2B543 is manufactured and then administered after lymphodepletion. The phase 1 primary objective is to evaluate the safety and tolerability of A2B543 and identify a recommended phase 2 dose (RP2D). The phase 2 primary objective is to assess overall response rate. Clinical trial information: NCT06051695 .

TPS11592 Background: Epithelioid hemangioendothelioma (EHE) is an ultra-rare vascular sarcoma with about 120 cases diagnosed in the US per year. Although it is commonly considered an indolent disease, in its aggressive form clinical outcomes are poor. Molecularly, EHE is characterized by the presence of oncogenic fusions with HIPPO pathway effectors TAZ or YAP; TAZ-CAMTA1 or YAP-TFE3. YAP/TAZ are modulators of mTORC1 in preclinical models, suggesting that mTOR inhibition may be an effective treatment mechanism for EHE. Nab-sirolimus is albumin bound sirolimus, which achieves higher intratumoral accumulation compared to oral sirolimus and has demonstrated increased antitumor activity in preclinical cancer models compared to the oral mTOR inhibitors sirolimus and everolimus. This is an open label, multi-center, single arm, phase II clinical trial with a two-stage design, testing nab-sirolimus for progressing or symptomatic EHE. The primary objective is to determine ORR of nab-sirolimus in patients with EHE who require systemic treatment. We hypothesize that nab-sirolimus will have significant clinical efficacy for EHE as measured by the primary endpoint of objective response rate, as well as by secondary outcomes including progression free survival benefit over historical controls and by improvement in patient reported outcomes (PROs). If positive, this trial could lead to a new standard of care for treating EHE. Methods: This is a single arm, multi-center, phase 2 study with a two-stage design. Key inclusion criteria include histologically or cytologically confirmed EHE that is either progressing or clinically symptomatic, not a candidate for curative intent surgery, and requires systemic therapy in the opinion of the investigator, radiographically evaluable disease by RECIST v1.1, age ≥18 years, ECOG performance status ≤ 2, and adequate end organ function. With a Simon two-stage optimal design with one sided alpha 0.10, power 90%, assuming a historical control ORR 5% to detect an ORR of 20% (alternative hypothesis), 12 patients will be included in the first stage. If there is ≥ 1 response, an additional 25 patients will be enrolled to a total of 37 patients. ≥ 4 responses are needed for a significant result. The total planned accrual is 41 patients to account for unevaluable patients who may be enrolled, 10% above the required evaluable patients. Planned post hoc subgroup analyses will include outcomes by fusion type and presence of serosal effusions at the time of study enrollment. The trial is registered at clinicaltrials.gov NCT07104331. Clinical trial information: NCT07104331 .

TPS10628 Background: Despite advances in cancer treatment, a lack of established population-level cancer screening strategies for early detection across cancer types contributes to cancer-related mortality. Emerging MCED liquid biopsy tests represent a screening approach with potential to enable detection of multiple malignancies at earlier stages in the disease process. We previously showed that an initial classifier based on a genome-wide methylome enrichment platform detected 12 cancer types, including early-stage, low-shedding tumors (Park et al. AACR 2023. Abs 1030). However, clinical performance of the platform has not been evaluated prospectively. Thus, the CAMPERR study (NCT05366881) was designed to train and validate a cell-free methylated DNA immunoprecipitation and high throughput sequencing (cfMeDIP-seq)-based test for detection and differentiation of 20 pre-selected cancer types, representing 93% of annual cancer incidence and 88% of annual cancer deaths. Longitudinal follow-up for a subset of participants with lung cancer will enable training and validation for MRD-based recurrence prognostication. Methods: This case-control study is enrolling participants with 20 different pre-specified cancer types (n=2400) and those without known cancer (n=3900). Eligible participants are ≥40 years of age and not receiving treatment for cancer at the time of enrollment or taking any demethylating/hypomethylating agents. Cases include individuals with newly diagnosed (≤120 days), untreated cancer or recurrence of a cancer originally diagnosed >5 years ago. Cancers of interest are stage I-IV bladder, brain, breast, cervical, colorectal, endometrial, esophageal, gastric, head and neck, hepatobiliary, leukemia, lung, lymphoma, multiple myeloma, ovarian, pancreatic, prostate, renal, sarcoma, and thyroid. Participants with stage I-III lung cancer will have clinical follow-up and blood draws after completion of first-line treatment, every 3 mo for the first year thereafter, and every 6 mo for an additional 2 years. Eligible control participants have not been diagnosed with invasive cancer in the last 5 years and will have clinical follow-up ≥12 mo from enrollment to evaluate cancer status. Liquid biopsy results will not be returned to clinicians or participants. The primary objective is cancer detection. Secondary objectives include detection of specific cancer types, identification of the tissue of origin, and prognostication of clinical outcomes (eg, recurrence-free survival, overall survival). CAMPERR is currently enrolling at 15 sites. As of December 3, 2025, 2108 of 2400 cancer cases have been enrolled, including prostate (n=225), lung (n=216), colorectal (n=211), breast (n=193), and pancreatic (n=192); controls are fully enrolled. Clinical trial information: NCT05366881 .

e23510 Background: There is minimal data comparing the prognostic models (PM) developed to predict recurrence of Gastrointestinal stromal tumors (GIST). Current PM include tumor size, location, and mitotic index (MI) but lack genotypic data. This analysis compares the performance of the National Institute of Health, Armed Forces Institute of Pathology, and Memorial Sloan Kettering Cancer Center models for predicting tumor recurrence with and without adjustment for c-kit Exon 11 mutation status (MS). Methods: This is an IRB-approved single-institution retrospective analysis. Adults with GIST mentioned in their medical records from 2014 – 2025 at the authors’ institution were identified. 330 patients with documented biopsy-proven GIST were included. Data was collected by manual review. PM were evaluated using multivariate analysis, adjusting for surgical resection, systemic therapy, and c-Kit exon 11 MS. Predictive performance was measured by area under the curve (AUC) and receiver operating characteristics (ROC) analysis. Results: Mean age at diagnosis was 64.6 years (SD =13.1 years). 46.7 % of patients were male. Primary GIST was most common in the stomach (63.9%) and small bowel (23.6%). Primary tumors were an average of 6.5 cm (SD 5.6 cm) with a MI of 6.6/50 HFU (SD = 13.4 50/HFU). Patients received resection (80.9%) and first-line systemic therapy with imatinib (43.3%). Recurrence occurred in 17.9% of patients. 19.4% of patients completed genetic testing, of which 51.6% were c-Kit exon 11 mutation positive. The predictive performance of all PM was not statistically different with (p value = 0.16) or without (p value = 0.18) adjustment for c-Kit exon 11 MS (Table 1). However, adjusting for c-Kit exon 11 MS improved AUC for all PM. Conclusions: Adjusting PM for c-KIT exon 11 status improved the predictive performance of all PM, although the results were not significant. This study found no significant difference in the performance of PM that predict GIST recurrence, which aligns with the one other study on this topic. Lack of significance may be due to a small sample size, which also limited the multivariate analysis. Including genotypes in PM that predict GIST recurrence should be further explored with larger multi-center datasets that can adjust for multiple mutations. Multivariate analysis comparing prognostic models for gastrointestinal stromal tumors at predicting recurrence with and without adjustment for c-KIT exon 11 genotypes using receiver operating characteristic. Without c-Kit exon 11 AUC (95% Confidence Interval) P value NIH 0.86 (0.81,0.90) 0.18 AFIP 0.87 (0.82,0.91) MSKCC 0.89 (0.84,0.94) With c-Kit exon 11 genotype NIH 0.80 (0.67,0.93) 0.16 AFIP 0.84 (0.73,0.95) MSKCC 0.90 (0.80,0.99) NIH: National Institute of Health, AFIP: Armed Forces Institute of Pathology, MSKCC: Memorial Sloan Kettering Cancer Centre. AUC: Area under the curve.

ABSTRACT Early identification of patients with treatment‐responsive rapidly progressive dementia (RPD) is important as early treatment improves outcomes. The STAM 3 P score identifies treatment‐responsive RPD using “high risk” presenting features. We optimized performance by adding a time component (i.e., dementia within 3 months) and validated the modified “STAM3 m P score” in two independent cohorts ( n = 302). A STAM3 m P score ≥ 1 identified 96% of patients with treatment‐responsive RPD; ≥ 3 features were highly specific (98%). These data suggest that ≥ 1 STAM3 m P features effectively identifies treatment‐responsive RPD and may be used to prioritize investigations, whereas ≥ 3 STAM3 m P features are highly specific and may inform early treatment decisions.

8001 Background: The ALCHEMIST clinical trial platform, launched by the National Clinical Trials Network (NCTN) in 2014, screened patients with resected non-small cell lung cancer (NSCLC) for molecular markers and tailored post-operative adjuvant therapy trials. A081105 evaluated whether adjuvant erlotinib improved overall survival (OS) following complete resection in patients with early stage EGFR mutated lung adenocarcinoma. Methods: A081105 was a randomized phase III trial enrolling patients with completely resected stage IB (≥4 cm), II, or IIIA non-squamous NSCLC (per the 7 th TNM staging classification) harboring EGFR exon 19 deletion or L858R mutations. Patients were randomized 1:1 to erlotinib 150 mg daily for up to 2 years or placebo/observation, stratified by stage, prior chemotherapy, EGFR mutation subtype, and ECOG performance status. The primary endpoint was OS in the per-protocol (PP) population with centrally confirmed EGFR mutations, designed to detect a hazard ratio (HR) of 0.67 in favor of erlotinib with a power of 86% and one sided type I error rate of 5%. Secondary endpoints included OS and disease free survival (DFS) in a modified intent-to-treat (mITT) population with local or centrally confirmed EGFR mutations, and safety. A prespecified backstop analysis was conducted after a minimum of 5 years of follow-up on all patients. Results: Trial enrollment was discontinued when 390 of the intended 450 patients had been enrolled due to the proven benefit of adjuvant osimertinib. Among 390 enrolled patients, the arms were balanced for age (median: 67.0 years), sex (70% female), race (70% white), stage (II: 51%, IIIA: 37%), prior chemotherapy (82%), ECOG PS 0 (60%), and exon 19 deletion (57%). Adjuvant erlotinib did not significantly improve OS compared with placebo/observation in the overall PP population (364 patients, 108 events, HR 0.89; 95% CI, 0.59–1.34; 1-sided P = 0.29) or within exon 19 deletion (HR: 0.94) or L858R mutation (HR: 0.82) subgroups. Five-year OS rates were 78.6% versus 77.9%, respectively. Results were consistent in the mITT analysis (379 patients, 113 events, HR 0.86; 95% CI, 0.58–1.28). Erlotinib improved DFS (mITT: 181 events, median: 68 vs 50 months, HR 0.74; 95% CI, 0.55–1.01). Across both arms, 11% of patients started non-protocol treatment (Osimertinib: 9%) prior to disease progression, and 9% withdrew consent for all follow-up prior to recurrence. In the erlotinib arm, 3 deaths on study were reported; grade 3 or higher adverse events were reported on 39% of patients. Median duration of treatment on Erlotinib arm was 16 months; only 37% of patients completed the planned treatment. Conclusions: In resected EGFR -mutant NSCLC, adjuvant erlotinib did not improve overall survival but improved DFS. Additional studies are exploring efficacy in selected subsets of patients using genomics and proteomic analyses. Clinical trial information: NCT02193282 .

7062 Background: MCL is a rare and aggressive subtype of B-cell non-Hodgkin lymphoma that remains incurable. Bruton tyrosine kinase (BTK) inhibitors are an established standard of care for R/R MCL. However, comparative effectiveness data for different BTK inhibitors for R/R MCL are limited. This study evaluated the real-world effectiveness of zanu and acala in US patients with R/R MCL based on overall survival (OS) and time to next treatment (TTNT). Methods: A retrospective cohort study was conducted using Komodo health administrative claims data. Eligible patients were adults (aged ≥18 years) with ≥2 MCL diagnoses and continuous enrollment or activities within 1 year prior to and 3 months following the index date. Patients were required to initiate monotherapy with zanu (index period: November 2019 to August 2025) or acala (index period: October 2017 to August 2025) as a second-line or later (2L+) treatment, with index date defined as the first observed claim for zanu or acala. Patients with evidence of clinical trial participation, end stage renal disease or prior stem cell transplant were excluded. Outcomes included OS (time from index date to all-cause mortality) and TTNT (time from index date to subsequent therapy with an allowable gap of 120 days). If an outcome was not observed, patients were censored at the date of last activity or enrollment end date. Survival analyses were conducted using Kaplan-Meier estimates and Cox proportional hazards models. Inverse probability of treatment weighting (IPTW) was adjusted for age, sex, US region, treatment initiation year and Charlson Comorbidity Index (CCI). Results: In total, 2219 patients (zanu, n=931; acala, n=1288) were eligible and included in the study. The mean age was higher in the zanu (72.3 years; SD, 9.4) vs acala cohort (71.4 years; SD, 9.7). Most patients were male (zanu, 71%; acala, 75%), non-Hispanic white (zanu, 73%; acala, 74%), and the mean CCI was 3.5 (SD, 3.2) and 3.6 (SD, 3.1) in the zanu and acala cohorts, respectively. Median follow-up was 14.8 and 18.2 months in zanu and acala cohorts, respectively. Median TTNT was 26.7 months for zanu and 20.8 months for acala. Median OS was not reached for zanu and was 60.6 months for acala. In the unadjusted model, zanu had a longer TTNT (HR, 0.86; 95% CI, 0.76-0.97; P =.012) and OS (HR, 0.74; 95% CI, 0.62-0.88; P <.001). After IPTW adjustment, TTNT and OS favored zanu treatment (TTNT: IPTW-adjusted HR, 0.86; 95% CI, 0.76-0.98; P =.025; OS: IPTW-adjusted HR, 0.81; 95% CI, 0.68-0.98; P =.03). Conclusions: In this real-world analysis of US health claims data, zanu monotherapy demonstrated significantly longer TTNT and improved OS compared with acala in patients receiving 2L+ therapy for MCL. These findings support zanu as an effective BTK inhibitor for R/R MCL.

632 Background: Prospective data on the risk of breast cancer (BC) recurrence among young BC survivors who have a subsequent pregnancy are limited. We sought to evaluate the long-term impact of pregnancy and live birth on BC outcomes in the Young Women’s Breast Cancer Study (NCT01468246), a prospective multicenter study of women aged ≤40 years at BC diagnosis. Methods: Women with stage 0-III BC without prior hysterectomy were included. The primary endpoint was breast cancer-free interval (BCFI) between patients with and without a (a) pregnancy and (b) live birth after BC. Secondary endpoints were distant recurrence-free interval (DRFI) and overall survival (OS). A time-varying Cox proportional hazards model was performed by estrogen receptor (ER) status, controlling for age at diagnosis, tumor stage, HER2 status, tumor grade, parity at diagnosis, and germline pathogenic variant status. Results: Among 1,016 BC survivors at a median follow-up of 12 (range, 0.5-18.5) years, 198 reported ≥1 pregnancy and 165 reported ≥1 live birth post-diagnosis. Among survivors who reported a post-diagnosis pregnancy, median age at diagnosis was 32 (range, 17-40) years; most had stage I (35%) or II (40%) BC, with 72% hormone receptor (HR)-positive and 25% HER2+; 42% were nulligravid and 60% were nulliparous at diagnosis. Among BC survivors who did not become pregnant post-diagnosis, median age at diagnosis was 37 (range, 21-40) years; most had stage I (35%) or II (43%) BC, with 75% HR-positive and 28% HER2+; 25% were nulligravid and 29% were nulliparous at diagnosis. Among BC survivors with ER-positive tumors (n = 737), pregnancy after BC was not associated with a difference in BCFI (adjusted hazard ratio [HR] 0.60, 95% CI 0.31-1.16, P = 0.130), DRFI (HR 0.73, 95% CI 0.35-1.55, P = 0.416), or OS (HR 0.58, 95% CI 0.24-1.40, P = 0.227). Similarly, live birth after BC did not impact BCFI (HR 0.83, 95% CI 0.45-1.55, P = 0.560), DRFI (HR 1.04, 95% CI 0.52-2.06, P = 0.923), or OS (HR 0.77, 95% CI 0.34-1.76, P = 0.541). Outcomes among BC survivors with ER-negative tumors (n = 278) were also not affected by post-diagnosis pregnancy (BCFI [HR 1.48, 95% CI 0.70-3.14, P = 0.304], DRFI [HR 1.59, 95% CI 0.68-3.75, P = 0.287], OS [HR 0.99, 95% CI 0.39-2.49, P = 0.975]) or live birth (BCFI [HR 1.02, 95% CI 0.41-2.53, P = 0.974], DRFI [HR 0.80, 95% CI 0.24-2.69, P = 0.722], OS [HR 0.39, 95% CI 0.09-1.69, P = 0.208]). Conclusions: In this multicenter, prospective study with 12 years of median follow-up, pregnancy and live birth after BC did not impact BC events or overall survival, irrespective of ER status. These long-term data from a modern cohort provide reassurance for young BC patients interested in future fertility. Clinical trial information: NCT01468246 .

4173 Background: [ 212 Pb]VMT-α-NET is an alpha-particle radiation-delivering agent targeted to somatostatin receptor type 2 (SSTR2)-expressing tumors. Here, we present safety and efficacy results from the dose-finding phase 1/2a clinical trial (NCT05636618). Methods: This phase 1/2a dose-escalation study uses a Bayesian algorithm to identify an optimal dose of [ 212 Pb]VMT-α-NET for participants with advanced, well-differentiated NETs expressing SSTR2. Eligible participants must have unresectable or metastatic disease, documented radiologic progression following at least one prior systemic treatment, and evidence of SSTR2 expression (Krenning Score ³2) in ≥1 lesion confirmed on an FDA-approved somatostatin receptor PET scan. Patients previously treated with systemic peptide receptor radionuclide therapy (PRRT) are excluded from enrollment. During the dose-finding phase, participants may receive up to four administrations of [ 212 Pb]VMT-α-NET at their assigned dose level, and they are monitored for dose-limiting toxicities (DLTs) for 42 days and safety throughout the study. Efficacy is evaluated by investigators according to RECIST criteria v1.1. Dosimetry is included as a supportive analysis. Results: As of the 10-Dec-2025 data cut-off (DCO), 56 participants had been enrolled across Cohorts 1, 2, and 3 and received at least one dose of [ 212 Pb]VMT-α-NET: 2 participants in Cohort 1 (2.5 mCi), 46 in Cohort 2 (5 mCi), and 8 in Cohort 3 (6 mCi). No dose-limiting toxicities, grade 5 adverse events, treatment-related discontinuations, serious renal events, dysphagia, or clinically meaningful treatment-related myelosuppression were observed. The median follow-up for all treated participants was 40 weeks (range 6–97). Efficacy has been summarized in this abstract for 25 participants (2 in Cohort 1 and 23 in Cohort 2). Nineteen of these 25 participants remained progression-free at the time of the DCO, with a median efficacy follow-up of 49 weeks (range 6–97). In Cohort 2, investigators observed RECIST v1.1 objective responses in 9 of 23 participants (39%), including 8 confirmed responses. Both participants in Cohort 1 continued to exhibit stable disease after two years of follow-up. Updated safety for all participants and updated efficacy for participants with sufficient maturity beyond the 25 summarized here will be presented at the congress. Conclusions: Treatment with [ 212 Pb]VMT-α-NET continues to demonstrate a favorable safety profile across all treated participants (n = 56) and shows signs of sustained efficacy at the 2.5 mCi and 5 mCi dose levels. The therapy has been well-tolerated with no observed dose-limiting toxicities or serious treatment-related adverse outcomes. Based on these encouraging safety and efficacy findings, the study is ongoing, and enrollment into Cohort 3 (6 mCi) remains active. Clinical trial information: NCT05636618 .