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BACKGROUND: Anthracyclines are a widely used and effective class of chemotherapy. However, a major limitation for their use is cardiotoxicity, manifesting as systolic dysfunction, congestive heart failure, and arrhythmias. The objective of this study was to identify genes and genetic risk variants for doxorubicin-induced arrhythmia. METHODS: We performed genome-wide association studies and meta-analysis across 2 independent nonoverlapping, genetically homogenous data sets from the Molecular Epidemiology Resource (cases N=77, controls N=1184) and Tapestry (cases N=13, controls N=172). Doxorubicin-related arrhythmia was the primary cardiac outcome, followed by investigation of a broader phenotype of cardiac events. Effects of doxorubicin on top-associated genes were assessed by quantitative polymerase chain reaction on RNA extracted from human cardiomyocytes following treatment with doxorubicin and by echocardiography in a zebrafish model of doxorubicin-induced cardiomyopathy. RESULTS: In the meta-analysis, rs12151014 at the KCTD15 locus was associated with doxorubicin-related arrhythmia at the genome-wide significance (minor allele frequency in Molecular Epidemiology Resource cases 0.195 versus 0.069 in controls; Tapestry cases 0.192 versus 0.079 in controls) P =9.01×10 −9 ; odds ratio, 3.61. MMP 16 rs1094199 was associated with the broader phenotype of arrhythmia and heart failure (minor allele frequency in Molecular Epidemiology Resource cases 0.079 versus 0.019 in controls; Tapestry cases 0.038 versus 0.015) P =1.98×10 − 8 ; odds ratio=6.15. In human cardiomyocytes, MMP16 and KCTD15 gene expression was significantly downregulated by doxorubicin, and in a zebrafish MMP16 knockout was protective of doxorubicin-induced decline in left ventricular ejection fraction. CONCLUSIONS: Genetic variants at KCTD15 and MMP16 are associated with doxorubicin-related arrhythmia and cardiac events. MMP16 is a potential cardioprotective therapeutic target.

PURPOSE Incorporation of structured data elements within the electronic health record generates real-time data for many potential uses. However, this requires a change in documentation practices, which may increase documentation effort. The best strategies to support structured documentation interventions have not been thoroughly investigated. Herein, we report the results of extending a data capture tool across multiple disease sites and practice locations. METHODS A note-based data capture tool was developed to collect five data elements using minimum common oncology data elements language. Soft-stop close visit validation (CVV), offloading of data entry tasks to allied health staff, group education, individualized e-mails, and one-on-one assistance were used to support utilization. Baseline and follow-up surveys were collected. For each provider, we compared data capture in the 6 months before and after their CVV go-live. RESULTS Forty-five providers participated (31 physicians, 14 nurse pracationers and physician assistants [NPPAs]), resulting in 23,274 encounters pre-CVV go-live and 23,146 post-CVV go-live visits. Median percentage of all data elements captured increased from 69.5% to 82.6% across all providers. The effect of CVV was immediate and sustained. When surveyed, most respondents agreed with the value propositions of understanding practice population, outcomes, selecting trials to open, and identifying patients for trial enrollment. Most respondents (15/20, 75%) felt the soft stop was a helpful reminder. CONCLUSION Structured data can be successfully collected in provider notes with >80% data capture. Personalized assistance incorporating the structured data elements into users' preexisting templates and soft-stop CVV, along with monitoring the results of implementation and personalized follow-up, was used to support the structured data capture intervention.

Summary Functional ex vivo assays using live tumor tissues have demonstrated strong predictive accuracy for response to immune checkpoint inhibitors (ICIs) but are not scalable, requiring manual processing of large resections collected at academic centers. Here, an ex vivo live tumor fragment (LTF) platform was developed using standard-of-care biopsies from 228 patients with suspected malignancy collected across prospective, multicenter observational trials and biobanks. Hierarchical clustering of ICI-mediated changes in cytokine production identified two groups: responders and nonresponders. A binary classifier (elive index) using 8 cytokines achieved an AUC of 0.99 for cluster prediction. elive index correctly predicted clinical benefit in 93% (26/28) of patients ( P = 3.2x10 -5 ) and accurately identified 83% (10/12) of objective responders. Critically, elive responders were identified among biomarker-negative patients, highlighting the platform as a scalable approach that complements existing companion diagnostics and expands the population of patients identified to benefit from ICI therapy.

Background: The current guidelines recommend that women at elevated risk for breast cancer (BC), defined as lifetime BC risk ≥ 20%, undergo annual screening with breast magnetic resonance imaging (MRI) and mammogram. However, limited evidence exists in the literature to guide the optimal timing of the MRI relative to the mammogram. Our study evaluated women undergoing high-risk BC screenings to determine the impact of timing for supplemental MRI on BC detection. Methods: Patients who completed high-risk screening MRI at a single institution from January 2019 through June 2022 were included. Baseline characteristics and clinical outcomes were collected through retrospective chart review. MRI exams were divided into two groups based on timing of MRI: concurrent (<90 days from mammogram) and staggered (≥90 days from mammogram). Results: Of 1115 patients initially identified, 770 met inclusion criteria, with a total of 3707 screening exams performed (2073 mammograms and 1634 MRIs). The final analysis included 1355 MRI exams for 712 patients, where a prior mammogram and MRI were available. Of the MRIs included, 784 (57.9%) were concurrent and 571 (42.1%) were staggered. Additional imaging was performed for 12.5% (98/784) of concurrent MRIs and 9.6% (55/571) of staggered MRIs. Biopsy rates were 9.8% (77/784) for concurrent and 7.0% (40/571) for staggered MRIs. In this high-risk population, there were surprisingly low BC detection rates, with a BC incremental detection rate of 0.5% in both the concurrent and staggered groups (p = 1.0), with the median size of detected invasive BCs equaling 5 mm in the concurrent group and 4 mm in the staggered group (p = 0.72). Conclusions: When comparing concurrent and staggered MRI regimens, there were no significant differences in incremental cancer detection rate, tumor size, rates of additional imaging, or negative biopsies. Further investigation with prospective analysis is needed to validate these findings.

TPS655 Background: Early (14-28 day) on-treatment suppression of tumor proliferation during neoadjuvant endocrine therapy (NET) is strongly associated with favorable long-term outcomes in estrogen receptor–positive (ER+) HER2– breast cancer. In premenopausal women, tamoxifen with or without ovarian function suppression (OFS) results in suboptimal Ki-67 suppression compared with aromatase inhibitor + OFS. (Z)-endoxifen (ENDX), the active metabolite of tamoxifen, dually inhibits ER signaling and PKCβ1-mediated AKT activation, supporting its evaluation as an alternative NET strategy in this population. Methods: EVANGELINE (NCT05607004) is an ongoing, multicenter, open-label Phase 2 study evaluating daily 40 mg ENDX plus goserelin administered every 28 days as neoadjuvant therapy in premenopausal women with ER+/HER2–, cT2–3, cN0–1 breast cancer. The primary objective is to determine the proportion of patients with baseline Ki-67 >10% who achieve Ki-67 ≤10% after 4 weeks of therapy. A Simon two-stage design is used to test whether the Week 4 Ki-67 ≤10% rate is at least 65%, with 20 patients enrolled into the first stage and, if promising, another 25 patients enrolled into the second stage (cohort A). A parallel cohort of 20 patients with baseline Ki-67 ≤10% (cohort B) is enrolled to assess objective response rate (ORR) at 24 weeks per RECIST v1.1. Secondary objectives include examining safety and tolerability, residual cancer burden, and PEPI score. Correlative analyses include examining effect of treatment on select tumor and plasma biomarkers. Clinical trial information: NCT05607004 .

e13082 Background: Human epidermal growth factor receptor 2 (HER2)–low breast cancer, defined as HER2 immunohistochemistry (IHC) 1+ or IHC 2+/in situ hybridization–negative, represents a newly targetable subtype comprising nearly half of all breast cancers. Brain metastases are a common and morbid complication of metastatic breast cancer, yet patients with active central nervous system (CNS) disease are frequently excluded from clinical trials. Trastuzumab deruxtecan (T-DXd), an antibody–drug conjugate with a cleavable linker and potent topoisomerase I inhibitor payload, has demonstrated substantial intracranial activity in HER2-positive disease. However, the intracranial efficacy of T-DXd in patients with HER2-low breast cancer remains incompletely characterized. Methods: A systematic literature search was conducted across PubMed/MEDLINE, Embase, CENTRAL, ClinicalTrials.gov, and Web of Science from database inception through January 1, 2025. A total of 2,275 records were identified and screened. Eligible studies included randomized controlled trials and prospective or retrospective clinical studies evaluating trastuzumab deruxtecan in patients with HER2-low metastatic breast cancer and measurable brain metastases. Studies were required to report intracranial objective response rate (IC-ORR), defined as complete or partial intracranial response among CNS-evaluable patients, assessed by study-defined criteria (RECIST 1.1 or RANO-BM). Results: Five studies comprising 62 patients with HER2-low metastatic breast cancer and brain metastases were included. Using a random-effects proportional meta-analysis with Freeman–Tukey double arcsine transformation, the pooled intracranial objective response rate (IC-ORR) was 46% (95% CI, 27–65%). Between-study heterogeneity was moderate (I² = 47.7%, p = 0.11), with consistent directionality of intracranial activity observed across included cohorts. Conclusions: Across five studies, T-DXd demonstrated clinically meaningful intracranial activity in HER2-low metastatic breast cancer with brain metastases, yielding a pooled IC-ORR of 46%. This provides one of the first quantitative benchmarks of CNS response in HER2-low disease, where evidence has been limited to small, heterogeneous cohorts. These findings support dedicated prospective trials in HER2-low patients with active CNS disease and standardized intracranial endpoints to refine patient selection and expected benefit. Summary of outcomes. Study Year CNS-Evaluable Patients (N) Intracranial Responders (CR+PR) IC-ORR (%) Zhou et al. 2025 15 7 46.7 (21.0–73.0) Batista et al. 2024 6 3 50.0 (12.0–88.0) Lazaratos et al. 2024 6 4 66.7 (22.0–96.0) Duan et al. 2025 9 6 66.7 (30.0–93.0) Burnside et al. 2024 26 6 23.1 (9.0–44.0) Pooled estimate (random effects) — 62 26 46.0 (27.0–65.0)*

e12707 Background: Anthracycline-based chemotherapy remains a cornerstone of breast cancer treatment but is limited by dose-dependent cardiotoxicity. Sodium-glucose cotransporter-2 inhibitors (SGLT2i) have demonstrated cardioprotective effects across diverse populations. Preclinical models suggest they may mitigate anthracycline-induced cardiotoxicity. However, clinical data evaluating this association remain limited. Methods: We conducted a retrospective cohort study using the TriNetX real world data platform, including adults with breast cancer who received anthracycline within one year of diagnosis. Patients were stratified by SGLT2i use within one year of diagnosis into the SGLT2i group and the non-SGLT2i group. Propensity score matching (PSM) was performed to balance baseline demographics and comorbidities. Outcomes included 3-year all-cause mortality, heart failure, myocardial infarction, atrial fibrillation, mean left ventricular ejection fraction (LVEF), mean Troponin I, and mean brain natriuretic peptide level (BNP), analyzed using risk ratios (RR) and Kaplan-Meier survival analysis. Results: After PSM, 2912 patients were included in each group, with a mean follow-up of 630.3 days in SGLT2i group and 756.7 days in non-SGLT2i group. Mean age was 61.5 years vs 62.3 years (SGLT2i group vs non-SGLT2i group), with more than 98% of females in both groups. Most patients were White (49.0% in SGLT2i group and 48.6% in non-SGLT2i group), followed by African American (23.7% vs. 23.4%), unknown races (14.0% vs 14.0%), and Asian (9.5% vs. 9.8%). At baseline, the SGLT2i group had lower mean LVEF (53.4% vs 61.9%), higher mean Troponin I (0.992 vs 0.0849), and higher mean BNP levels (778 vs 240). SGLT2i group was associated with significantly lower 3-year all-cause mortality (Hazard ratio 0.52, 95% CI 0.44–0.61). Heart failure incidence (9.5% vs 6.0%; p = 0.0005) was significantly higher in the SGLT2i group. Mean LVEF in SGLT2i group was significantly lower (51.7% vs 58.9; p < 0.0001) and mean BNP level was significantly higher in SGLT2i group (685.5 vs 383.0; p = 0.0336). No significant differences were observed in myocardial infarction (3.9% vs 3.4%; p = 0.4459), atrial fibrillation (3.4% vs 4.5%; p = 0.0799), and mean troponin I (0.085 vs 0.113, p = 0.5191). Conclusions: In this real-world cohort, SGLT2i use was associated with lower 3-year all-cause mortality despite higher rates of heart failure. Notably, patients receiving SGLT2i had worse baseline cardiac function yet demonstrated more favorable trends in cardiac biomarkers, including smaller declines in LVEF, reductions in BNP, and lower mean troponin I levels, suggesting a slower progression of cardiac dysfunction. These findings support a potential cardioprotective and survival benefit of SGLT2i in patients with breast cancer receiving anthracycline therapy and warrant confirmation in future studies.

e12601 Background: Mammography remains the standard modality for breast cancer (BC) screening but has several limitations. There is a critical need for minimally invasive markers that can aid in distinguishing benign, non-invasive lesions from those likely to progress to invasive BC. Platelets are nature’s transport mechanism for delivery of growth factors and inhibitors. Assaying the platelet proteome, Hessian Labs developed HeLP (Hessian Labs Personalized) test designed to identify early malignancy, as well as its grade, and invasiveness. The test is based on a discovery that platelets sequester oncogenic regulators against a concentration gradient in plasma early in tumor development. Hence, it has the potential to differentiate benign from invasive BC at various stages, stratifying the need for intervention. Methods: Platelet samples from 120 women with BC were analyzed using a discovery data-independent acquisition mass spectrometry (DIA-MS). The identified differentially expressed platelet-associated proteins, were prioritized using ClariaIQ , a proprietary computational platform that ranks proteins based on their relevance to stage-specific oncogenic pathways and established Cancer Hallmarks, to identify stage- and grade-associated proteomic signatures and create the HeLP panel. Results: DIA-MS identified multiple platelet sequestered proteins that were differentially expressed between indolent disease and invasive BC. ClariaIQ prioritization resulted in the selection of 13 proteins for inclusion in the HeLP breast cancer assay. We present two examples: SAA1 and SERPIN proteins demonstrated differential expression between healthy, benign breast lesions and malignant invasive disease (Table 1). SAA1 peaks in early BC and SERPIN in advanced stages. With SAA1, in HER negative BC the levels rise to an average of 285,000 RE units when compared to HER2 positive BC. Conclusions: Platelet sequestered protein signatures provide clinically relevant information regarding breast cancer status, grade, and invasiveness. The findings support the robustness of the signal, and a more patient-specific signature than traditional plasma or serum biomarkers. It suggests a role for HeLP as a minimally invasive adjunct to mammography to improve diagnostic stratification and therapeutic decision-making. Disease Group SAA1 Mean (RE) SAA1 SD (RE) SERPIN A3 Mean (RE) SERPIN A3 SD (RE) Healthy Controls 119,592 206,349 490,231 279,017 Benign Breast Lesions 622,187 50,855 341,102 153,144 Stage I Breast Cancer 1,223,865 1,878,654 742,409 466,468 Stage II Breast Cancer 663,369 1,970,265 922,381 844,512 Stage III Breast Cancer 437,853 662,211 705,994 597,399 Stage IV Breast Cancer 225,265 384,826 1,068,874 1,415,934 RE=Relative Expression units. N=20 subjects included in each group.

522 Background: Tumor-associated macrophages (TAMs) drive immune evasion and chemotherapy resistance in breast cancer through tumor microenvironment reprogramming. We developed a composite TAM score integrating transcriptional programs with spatial IHC polarization markers to stratify recurrence risk and enrich macrophage-modulating trials, hypothesizing it would improve prognostic accuracy in treatment-naïve disease and predict neoadjuvant chemotherapy (NACT) response. Methods: TAM score was derived from scRNA-seq atlases (n=4), filtering survival-associated genes in METABRIC/TCGA (n=2,509), and weighting IHC markers CD163/CD206 normalized to CD68/CSF1R via Cox coefficients. Validation: treatment-naïve invasive carcinomas (n=83; follow-up 57 months; 24 events). Primary endpoint: recurrence-free survival (RFS); multivariable Cox adjusted for age, tumor size, nodal status, grade, subtype, treatment. Predictive utility assessed in matched primary/post-NACT residual tumors (n=45) correlating TAM dynamics with RCB. Results: High TAM score (≥median) independently predicted worse RFS (HR 3.8, 95% CI 1.6-9.1, p<0.05) and outperformed CD163/CD68 alone (HR 2.1, p<0.05); 5-year RFS was 68% vs 91% (TAM-high vs TAM-low). Prognostic value persisted in node-negative (HR 4.2, p=0.02) and luminal B (HR 3.5, p=0.01) subsets. In the NACT cohort, baseline TAM score inversely correlated with pCR (12% vs 38%, p=0.04). Among residual disease (RCB-II/III, n=34), persistent TAM-high post-NACT identified 3-year RFS 52% vs 85% in TAM-low/normalized cases (HR 4.1, p=0.01), independent of RCB; CD163+/CD206+ expansion occurred in 76% of RCB-III vs 29% of RCB-I (p=0.008). Conclusions: This TAM score predicts recurrence from pre-treatment tissue and identifies macrophage-driven resistance persisting post-NACT, nominating TAM-high residual disease for macrophage-modulating trials. Translational evidence supports this: CSF1R inhibition reduced immunosuppressive TAMs, increased M1-like programs, decreased PD-L1/PD-L2, and enhanced anti-PD-1 efficacy preclinically with ex vivo confirmation. Early-phase data (rebastinib plus chemotherapy in HER2-negative metastatic disease) demonstrate feasibility, supporting prioritization of TAM-high patients with residual disease for trials combining TAM modulation with checkpoint therapy. TAM score performance in treatment-naïve and NACT cohorts. Endpoint TAM-High TAM-Low HR scores (95% CI) p-value Treatment Naïve cohort 5 year RFS (Overall) 68% 91% 3.8 (1.6-9.1) <0.05 RFS (node-negative) 4.0 0.02 RFS (luminal B)-- 3.5 0.01 CD163/CD68 alone 2.1 <0.05 NACT Cohort (n=45) Baseline pCR rate 12% 38%- 0.04 3-year RFS(RCB-II/III n=34) 52% 85% 4.1 0.01 CD163+/CD206+ expansion 76% (RCB-III) 29%(RCB-I)- 0.008