e13080 Background: Integrated DNA/RNA comprehensive genomic profiling (CGP) may expand therapeutic opportunities and support decision-making in metastatic breast cancer (mBC), yet real-world evidence for its clinical utility remains limited. We evaluated the impact of CGP-guided care on treatment decisions and outcomes in a heterogeneous mBC cohort. Methods: A retrospective, single-center analysis of 207 patients with mBC who underwent BostonGene’s Tumor Portrait test. Actionable alterations were defined per NCCN/FDA guidelines or clinical trial eligibility. Clinical utility is defined as CGP-driven treatment initiation or identification of guideline-supported future options was assessed in patients with ≥60 days of follow-up (n = 160). Subgroup analyses evaluated outcomes with trastuzumab deruxtecan (T-DXd), sacituzumab govitecan (SG), or immune checkpoint inhibitors using RNA-seq-based ADC biomarker thresholds, breast cancer classifier (BCC/PAM50), and tumor microenvironment subtypes. Progression-free survival (PFS) was analyzed using Kaplan–Meier methods and Cox regression. Results: The cohort included HR+/HER2− (58%), TNBC (35%), and HER2+ (7%) mBC, with a median of 2 prior therapy (range: 1–11). Overall, 65.5% of patients had actionable molecular alterations, of which 33.9% were supported by NCCN/FDA-approved indications, while the remaining alterations were potentially targetable within clinical trial settings. CGP directly informed treatment initiation in 10% of patients and identified potential future targeted therapy options in an additional 15%. Luminal B and Basal BCC subtypes were consistently associated with inferior PFS outcomes across the cohort. Among patients treated with T-DXd (n = 45), higher HER2 RNA expression was associated with reduced progression risk, whereas Basal and Luminal B subtypes demonstrated worse PFS (p = 0.006). Among patients receiving SG (n = 55), those with TNBC had longer PFS than those with HR-positive mBC, whereas TROP2 RNA expression was uniformly high and not predictive of outcome. Among patients treated with immunotherapy (n = 25), PD-L1 expression was not significantly associated with PFS. Conclusions: Integrated DNA and RNA CGP identified actionable alterations in most patients in our study cohort. It also either directly informed treatment decisions or identified new guideline-supported treatment options in 25% (total) of cases. Transcriptomic subtyping provided further prognostic insights, particularly among patients receiving T-DXd, that contextualize treatment selection and sequence when multiple therapeutic options are available, including scenarios in which more potent ADC-based regimens may be favored over alternative targeted approaches.

Importance:Breast cancer treatment is associated with cancer-related cognitive impairment (CRCI). However, the association of endocrine therapy (ET) vs chemotherapy plus endocrine therapy (CET) with CRCI is poorly understood. Objective:To compare patient-reported CRCI between women with breast cancer treated with ET vs CET and to consider whether menopausal status may be associated. Design, Settings, and Participants:This was a prespecified secondary analysis of RxPONDER (SWOG S1007), a multinational phase 3 randomized clinical trial of more than 5000 women with hormone receptor-positive ERBB2-negative (formerly HER2-negative) breast cancer with 1 to 3 involved lymph nodes and Oncotype DX (21-gene recurrence score) of 25 or less. Participants were enrolled from February 2011 to September 2017, with results first reported in December 2020. Participants were randomly assigned to CET or ET, with ongoing follow-up. This secondary analysis assessed cognitive function using the Patient-Reported Outcomes Measurement Information System Perceived Cognitive Function Concerns (PCF) questionnaire at baseline, 6, 12, and 36 months. Data were analyzed from July 2022 to August 2025. Intervention:Random assignment to CET or ET. Main Outcomes and Measures:Mean PCF standardized (T) scores by menopausal status over time using generalized estimating equations analysis for continuous outcomes. Results:Of the 568 patients who completed the baseline questionnaire and were included in the analysis, 139 (24%) were premenopausal (median [range] age, 47.8 [28.0-56.3] years) and 429 (76%) were postmenopausal (median [range] age, 62.3 [37.3-87.6] years). Among the 274 (48%) who received CET and the 294 (52%) who received ET alone, CET was determined to have a greater negative association with patient-reported CRCI in both the pre- and postmenopausal participants during the 36-month follow-up. In the ET alone group, PCF scores for premenopausal participants decreased from baseline to 6 and 12 months (53.53, 51.51, and 51.72, respectively) but recovered to baseline (54.36) at 36 months. For postmenopausal participants, mean PCF scores were essentially stable (51.72, 51.13, 51.11, and 51.70, respectively); however, in the CET group, PCF scores for both pre- and postmenopausal participants decreased from baseline to 6 and 12 months (premenopausal, 52.84, 49.27, 48.04; postmenopausal, 50.65, 48.39, 47.13, respectively) and did not return to baseline at 36 months (premenopausal, 49.25; postmenopausal, 48.44). The difference in longitudinal mean PCF scores over time between CET and ET groups was -3.02 (95% CI, -5.33 to -0.72; P = .01) for premenopausal and -2.37 (95% CI, -3.92 to -0.82; P = .003) for postmenopausal participants. Conclusions and Relevance:This secondary analysis of the RxPONDER found that CET had a greater negative association with patient-reported CRCI compared to ET alone in both pre- and postmenopausal participants over a 36-month follow-up period. Interventions to prevent or treat CRCI are needed to improve the long-term quality of life of these patients treated with chemotherapy. Trial Registration:ClinicalTrials.gov Identifier: NCT01272037.

589 Background: Lytic bone metastases develop in ~70% of breast cancer patients that lead to pain, functional decline, and skeletal-related events (SREs) that reduce quality of life (QoL) and survival. Prophylactic denosumab/bisphosphonate treatment offers limited protection, and current local palliative interventions, EBRT and surgery, don’t reverse lytic destruction. Zeta-BC-003 is a first-in-class intratumoral (IT) injectable biomaterial infused with N-allyl noroxymorphone, a small molecule drug that acts through the p21 pathway to drive bone healing and local tumor control. Reports on two Compassionate Use patients (7 lesions, 2-yr follow-up; Palma et al, Pain Manag 2023) showed no SREs/fractures or tumor activity coupled with neo-trabecular bone regeneration and therapeutic spread to other lesions within treated bone, which align with these Phase 2a results. Methods: ZGMBC (NCT05280067), an open-label Phase 2a study, enrolled women (N=10; 8/23-3/25) with MBC lytic lesions and a Spinal Instability Numeric Score (SINS) ≥3 - ≤9. A single intratumoral (IT) Zeta-BC-003 injection was administered via fluoroscopic guidance. CT & MRI were obtained at Days 0, 84, and 180. Primary endpoints: SREs/fractures; defect volume; pain via the Numeric Rating Scale (NRS); post-op pain control via the Morphine Equivalent Dose (MED); and AE/SAEs. Secondary endpoints: QoL (SF-12v2); SINS; and tumor response. Results: Subjects (mean age 52) had the following MBC subtypes: HR+ (N=6), HR+/HER2+ (N=2), HER2+/HR- (N=1), and TNBC (N=1). Breakthrough lesions were seen in 5 subjects despite bisphosphonate therapy and 1 subject died from pleural edema prior to study end. Zeta-BC-003 was injected into 10 subjects with 11 lesions with additional therapeutic effect seen in 4 adjacent untreated lesions. A CR was shown for all lesions and there were no SREs/fractures. The bone defect volume decreased 65.4% (±20.5%; p=0.0003) and 84.1% (±13.1%; p<0.0001) at Days 84 and 180. NRS pain scores decreased 4.2% (p<0.05) and MED decreased ≥33% in opioid-treated subjects. SINS scores improved 18.5% (p<0.05), indicating increased stability. Increased PCS (24%) and MCS (12%) scores showed increased QoL. There were no treatment emergent SAE/AEs. Conclusions: Zeta-BC-003 prevented SREs/fractures in all lesions, reduced lytic defect volume, improved spinal stability, decreased pain/opioid use, improved QoL, ceased tumor activity, and demonstrated therapeutic spread to untreated lesions in the same vertebral body. These findings contrast with historical SRE rates of 53% in MBC and align with the durable CR seen in our Compassionate Use patients. Zeta-BC-003 may represent a first-of-its-kind intratumoral drug that ceases lytic activity, stimulates neo-trabecular bone growth, and improves QoL by eliminating SREs/fractures while also increasing overall survival. Clinical trial information: NCT05280067 .

Background Metastases are a key cause of mortality in breast cancer patients. Heterogeneity of breast cancer makes treatment challenging and emphasizes the need to define drivers of metastasis that can be selectively targeted. We previously reported upregulation and phosphorylation of c-MET (MET) in breast cancer, with both being correlated with poor prognosis. We also detected MET-T1010I, a germline mutation in patients with metastatic breast cancer, and demonstrated that MET aberrations promoted tumor growth and invasion in an HGF-dominant environment in vitro and in vivo. However, direct evidence of MET aberrations driving breast cancer metastasis is lacking. Because mouse HGF does not bind human MET effectively, commonly used mouse models are unsuitable for studying the HGF-MET axis. Methods We created and used human HGF/MET-paired spontaneous metastatic breast cancer mouse models where human HGF was expressed in HGF-transgenic mice with a SCID background and different MET variants were expressed in mammary xenografts. Snap-frozen breast tumor tissues were analyzed by protein array, and the data were further analyzed for pathway scores. Phosphor protein arrays assessed the effect of the MET aberrations on the phosphorylation of receptor tyrosine kinases and protein kinases. Serum HGF was quantified by ELISA assay. Cytokine and chemokine chips assessed 60 serum cytokines and chemokines. Results The aberrations of MET drive breast cancer metastasis in a human HGF-dominant environment, with a higher rate and shorter latency in MET-T1010I than with MET overexpression. Circulating HGF is increased in breast cancer patients, compared to age-matched healthy women. The enhanced circulating HGF was strongly correlated with circulating IL-16 and eotaxin-2/CCL-24, which are implicated in cancer metastasis. Interestingly, functional proteomics analysis of tumor tissues revealed previously unrecognized crosstalk between the HGF-MET axis and FGFR3, accompanied by activation of the EMT pathway and immunosuppression. These results deepen our understanding of the mechanisms underlying breast cancer metastasis and highlight the potential of combination strategies targeting FGFR3 and MET. Conclusion Aberrations of the HGF-MET axis drive metastasis in breast cancer and crosstalk with FGFR3, suggesting combined targeting of FGFR3 and MET as a potential novel approach to treat MET-activated cancers.

BACKGROUND:The RxPONDER trial has guided adjuvant chemotherapy use in node-positive HR+/HER2- breast cancer; however, prior analyses showed poorer outcomes among non-Hispanic Black (NHB) women compared with non-Hispanic White (NHW) women despite similar 21-gene Recurrence Score® (RS) results. This suggests contributors to disparities may not be captured by the composite RS. We evaluated RS gene group components-proliferation, estrogen receptor (ER), HER2 (GRB7), and invasion-by ethnicity, body mass index, and menopausal status, and assessed associations with outcomes. METHODS:RxPONDER enrolled 5,083 women with HR+/HER2- breast cancer, 1-3 positive nodes, and RS ≤ 25, randomized to endocrine therapy ± chemotherapy. 3,102 participants with ethnicity and gene expression data were included. RS components were compared across subgroups, and associations with invasive disease-free survival (IDFS) and distant recurrence-free interval were evaluated using multivariable Cox models adjusted for clinicopathologic factors and treatment. RESULTS:Among 3,102 women (70.2% NHW, 15.5% Hispanic, 9.5% Asian, 4.7% NHB), RS distributions were similar across groups and prognostic overall. Tumors from NHB (p = 0.003) and Hispanic (p = 0.02) had higher proliferation scores versus NHW women, while Asian women had higher HER2 (p = 0.006) and ER scores (p = 0.028). IDFS differences were not statistically significant for NHB vs. NHW women (HR 1.41; 95% CI 0.98-2.03), whereas Asian women had improved IDFS (HR 0.63; 95% CI 0.43-0.91). CONCLUSIONS:Despite similar overall RS distributions, component pathways vary by ethnicity and may contribute to outcome differences. These findings support evaluating gene-specific biology beyond composite scores to better understand disparities and refine risk stratification. TRIAL REGISTRATION:ClinicalTrials.gov: NCT01272037.

e13109 Background: There is a significant unmet need among patients with PD-L1 low/negative metastatic triple-negative breast cancer (mTNBC). >95% of TNBCs are positive for C-C chemokine receptor 5 (CCR5). Leronlimab (LRM) is a humanized monoclonal antibody given subcutaneously which blocks CCR5 and in a preclinical model reduced TNBC metastasis by more than 98%. Methods: In this post hoc analysis LRM safety and efficacy data were pooled from 28 mTNBC patients from 3 clinical trials (NCT03838367; NCT04313075; NCT04504942). LRM was given weekly at a dose of 350 mg (N=10), 525 mg (N=15), or 700 mg (N=3) in combination with various chemotherapies ± immune checkpoint inhibitors (ICI). PD-L1 staining (LifetracDx) was measured on cancer-associated macrophage-like cells (CAMLs) and circulating tumor cells (CTCs) prior to and after (≈40 days) LRM treatment. Results: Median age was 48.5 years (range 32-83) with a median of 2 prior metastatic therapies (range 0 to 5). Ten patients (35.7%) had non-visceral metastases; 18 (64.3%) had visceral metastases, including 7 (25.0%) with brain metastases. The most common treatment-emergent adverse events (TEAEs), at a rate of ≥10%, were fatigue (21.4%), headache (21.4%), anemia (10.7%), constipation (10.7%), nausea (10.7%), and decreased neutrophil count (10.7%) but with no febrile neutropenia events. Overall, 21.4% (6/28) patients reported any LRM treatment-related TEAE; of these none were classified as CTCAE grade >2. No patients discontinued treatment due to a LRM treatment-related TEAE. Overall, 35.7% (10/28) reported any serious TEAE; none of the serious TEAEs were considered related to LRM treatment. The median overall survival (OS) was 7.1 months. Survival at 1, 2, 3, 4, and 5 years was 35.7%, 21.4%, 17.9%, and 17.9%, 17.9%, respectively. OS among the 7 patients treated with LRM with an ICI, or followed by an ICI, was longer than among the remaining 21 patients (HR 4.14, 95% CI: 1.7–10.2; P=0.0041). For patients with available data, upregulation from baseline of PD-L1 was observed on CAMLs/CTCs in 76% (16/21) of patients. All five patients treated with LRM [525 mg (N=4), or 700 mg (N=1)] with an ICI, or followed by an ICI, and who significantly upregulated PD-L1, remained alive at 5 years. Conclusions: In this post hoc analysis LRM was well tolerated with no LRM treatment-related TEAEs leading to treatment discontinuation and no LRM treatment-related TEAEs graded as CTCAE >2. A 5-year OS rate of 17.9% (5/28) in this advanced population is encouraging. All 5 patients with PD-L1 upregulation treated with LRM with an ICI, or followed by an ICI, remained alive at 5 years suggesting a correlation with durable responses. These findings support the hypothesis that LRM may enhance PD-L1 expression on CAMLs/CTCs, potentially priming tumors for improved responses to ICIs. Confirmatory phase 2 studies in mTNBC are planned. Clinical trial information: NCT03838367 (N=10); NCT04313075 (N=16); and NCT04504942 (N=2).

Strategies are needed to avoid chemotherapy in early stage HER2-positive (HER2 + ) breast cancer (BC). We conducted a neoadjuvant therapy trial with zanidatamab, a dual HER2-directed bispecific antibody, in patients with 1-3 cm, node-negative HER2 + BC. Primary endpoint was pathologic complete response (pCR). Secondary endpoints were radiographic response by ultrasound and magnetic resonance imaging. US and MRI, pathologic response by residual cancer burden (RCB), rate of adverse events, feasibility of accrual and biomarkers of response. Fifteen patients with HER2 IHC 3 + , and 5 with HER2 IHC 2 + /ISH + BC were enrolled. Patients received zanidatamab 20 mg/kg every 2 weeks for 6 (n = 11) or 10 doses (n = 9). Fourteen patients also received endocrine therapy. At 6 weeks, there was a significant decrease in tumor size and volume. At surgery, six patients (30%) had pCR, meeting the prespecified pCR target, and four had limited RCB (RCB-1; 20%). Treatment was well tolerated. All patients with pCR had HER2 IHC 3+ tumors, ERBB2 amplification on WES, PAM50 HER2-high subtype, and a trend towards higher HER2 mRNA expression (p = 0.06). In conclusion, de-escalation to HER2-targeted therapy alone may be feasible. Further research is needed to refine patient selection. This study is registered at ClinicalTrials.gov (NCT05035836). With the improvement of HER2-targeted therapy in patients with breast cancer, there is growing interest in whether chemotherapy can be eliminated from regimens completely. Here, the authors report a phase 2 clinical trial investigating neoadjuvant zanidatamab (HER2-targeting antibody) in patients with early-stage HER2-positive breast cancer.

QuestionHow does chemoendocrine therapy (CET) compared to endocrine therapy (ET) alone affect cancer-related cognitive impairment (CRCI) in pre- and postmenopausal patients?FindingsThis secondary analysis of the RxPONDER randomized clinical trial included 568 participants assessed at 6, 12, and 36 months and found that CET had a greater negative association with patient-reported cognitive function compared to ET alone in both the pre- and postmenopausal groups.MeaningThese findings indicate that cognitive impairment occurs and persists more frequently with CET than with ET alone among both pre- and postmenopausal patients; therefore, interventions to prevent and treat CRCI are needed. ImportanceBreast cancer treatment is associated with cancer-related cognitive impairment (CRCI). However, the association of endocrine therapy (ET) vs chemotherapy plus endocrine therapy (CET) with CRCI is poorly understood.ObjectiveTo compare patient-reported CRCI between women with breast cancer treated with ET vs CET and to consider whether menopausal status may be associated.Design, Settings, and ParticipantsThis was a prespecified secondary analysis of RxPONDER (SWOG S1007), a multinational phase 3 randomized clinical trial of more than 5000 women with hormone receptor-positive ERBB2-negative (formerly HER2-negative) breast cancer with 1 to 3 involved lymph nodes and Oncotype DX (21-gene recurrence score) of 25 or less. Participants were enrolled from February 2011 to September 2017, with results first reported in December 2020. Participants were randomly assigned to CET or ET, with ongoing follow-up. This secondary analysis assessed cognitive function using the Patient-Reported Outcomes Measurement Information System Perceived Cognitive Function Concerns (PCF) questionnaire at baseline, 6, 12, and 36 months. Data were analyzed from July 2022 to August 2025.InterventionRandom assignment to CET or ET.Main Outcomes and MeasuresMean PCF standardized (T) scores by menopausal status over time using generalized estimating equations analysis for continuous outcomes.ResultsOf the 568 patients who completed the baseline questionnaire and were included in the analysis, 139 (24%) were premenopausal (median [range] age, 47.8 [28.0-56.3] years) and 429 (76%) were postmenopausal (median [range] age, 62.3 [37.3-87.6] years). Among the 274 (48%) who received CET and the 294 (52%) who received ET alone, CET was determined to have a greater negative association with patient-reported CRCI in both the pre- and postmenopausal participants during the 36-month follow-up. In the ET alone group, PCF scores for premenopausal participants decreased from baseline to 6 and 12 months (53.53, 51.51, and 51.72, respectively) but recovered to baseline (54.36) at 36 months. For postmenopausal participants, mean PCF scores were essentially stable (51.72, 51.13, 51.11, and 51.70, respectively); however, in the CET group, PCF scores for both pre- and postmenopausal participants decreased from baseline to 6 and 12 months (premenopausal, 52.84, 49.27, 48.04; postmenopausal, 50.65, 48.39, 47.13, respectively) and did not return to baseline at 36 months (premenopausal, 49.25; postmenopausal, 48.44). The difference in longitudinal mean PCF scores over time between CET and ET groups was -3.02 (95% CI, -5.33 to -0.72; P = .01) for premenopausal and -2.37 (95% CI, -3.92 to -0.82; P = .003) for postmenopausal participants.Conclusions and RelevanceThis secondary analysis of the RxPONDER found that CET had a greater negative association with patient-reported CRCI compared to ET alone in both pre- and postmenopausal participants over a 36-month follow-up period. Interventions to prevent or treat CRCI are needed to improve the long-term quality of life of these patients treated with chemotherapy.Trial RegistrationClinicalTrials.gov Identifier: NCT01272037 This secondary analysis of the RxPONDER randomized clinical trial assesses patient-reported cognitive impairment by menopausal status among women with breast cancer treated with chemoendocrine therapy vs endocrine therapy alone.

Background: Obesity in breast cancer (BC) survivors is associated with higher BC recurrence risk and mortality, and weight loss in an important tenet of health promotion. Glucagon-like peptide-1 receptor agonists (GLP1-RA) are incretin mimetics with favorable metabolic effects and approved for type 2 diabetes (DM2) or weight loss. While drug utilization is increasing, the implications in cancer survivors are not well elucidated. This study evaluated treatment patterns of GLP1-RA, weight loss trends, and patient outcomes in a cohort of BC survivors. Methods: We retrospectively analyzed patients with non-metastatic (DCIS or invasive stage I-III) BC treated at MD Anderson Cancer Center (MDACC) who received at least 3 months of GLP1-RA from 2005 - 2024. Data was obtained from the MDACC BC and pharmacy databases. Linear regression models estimated the association between weight change and clinical factors. After excluding patients with DCIS, propensity score matching (1:2 ratio) was used to match patients who received GLP1-RA with those who did not, based on baseline body mass index (BMI), DM2, age, clinical stage, and BC receptor status. Kaplan-Meier estimates and log-rank tests estimated and compared overall survival (OS) and disease-free survival (DFS) between patients who received GLP1-RA and those who did not. Results: In total, 1,022 patients met inclusion criteria. Median age was 54 years (23-86) years, and 56.9% were postmenopausal; 79.0% had DM2. Most (91.4%) had stage I-III invasive BC and 8.6% had DCIS; 80.2% had hormone receptor positive BC and 65.9% received adjuvant endocrine therapy with an aromatase inhibitor (AI) or tamoxifen. GLP1-RA was started following definitive BC therapy (chemotherapy, surgery, radiation) in 87.6%; the median time from BC diagnosis to GLP1-RA initiation in these patients was 4.7 (0.0-34.0) years. The median duration of GLP1-RA use was 1.2 (0.3-8.1) years. Median BMI at BC diagnosis was 33.5 (20.1-56) kg/m2. Baseline median weight and median BMI at GLP1-RA initiation (within 90 days prior) was 86.8 (47.2-175.0) kg and 33.6 (18.9-61.8) kg/m2, respectively. In patients (n=442, 43.2%) who received the drugs approved for weight loss (semaglutide or tirzepatide), median weight loss at 3 (+/- 45 days), 6 (+-/45 days), and 12 (+/- 60 days) months was -1.9% (-13.2%-14.9%), -3.1% (-20.2%-19.0%), and -2.6% (-27.8%-11.5%), respectively. On multivariate regression analysis, no significant association was observed between the 6 month change in weight and clinical factors (DM2, metformin use, endocrine therapy use, duration of GLP1-RA, clinical stage); however, the 12 month change in weight was significantly associated with clinical stage (invasive BC was associated with more weight loss vs DCIS, p<0.01) and endocrine therapy (tamoxifen or AI use was associated with weight gain, p=0.019). Patients who received endocrine therapy experienced, on average, a 2.83 kg weight gain at 12 months compared to those who did not, after adjusting for other variables in the model. In those with invasive BC (DCIS excluded); there was no significant difference in DFS but there was a significantly improved OS in patients who received GLP1-RA compared with controls (median survival not reached (0-30.9) vs 27.0 years (0-57.3), p<0.0001). Conclusion: This is the largest study describing real world patterns of GLP1-RA use in BC survivors. These medications were associated with modest weight loss; however, endocrine therapy may decrease this impact. An improved all-cause survival was observed, but there was no difference in DFS. Clinical trials are needed to investigate the role of these agents for weight loss as an adjunct to lifestyle interventions in cancer survivors. Further exploration of potential anti-cancer biological effects for BC risk reduction and cancer control may also be warranted. Citation Format: Jasmine Sukumar, Akshara Raghavendra, Sarah Pasyar, Roland Bassett, Debu Tripathy, Carlos H Barcenas, Karen Basen-Engquist, Banu Arun. Retrospective study of GLP-1 Receptor Agonists in Breast Cancer Survivors: Weight Loss and Patient Outcomes [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr PS15-03.

Background: Brain metastasis is a frequent site of relapse in patients with inflammatory breast cancer (IBC) - a rare, highly aggressive and metastatic variant of breast cancer. We have discovered that soluble E-cadherin (sEcad), an 80-kDa proteolytic fragment of full-length E-cadherin, correlated with increased risk of brain metastasis and death in patients with metastatic IBC. Additionally, we demonstrated that sEcad promotes brain metastasis growth and progression in HER2+ and triple-negative IBC brain metastasis models. However, how sEcad promotes brain metastatic progression is unknown. We hypothesize that sEcad promotes the production of specific cytokines, which, upon extracellular release, promote the activation of astrocytes, priming the brain microenvironment for metastatic growth. Methods: Stable overexpression of sEcad in IBC cell lines (MDA-IBC3 (ER–/HER2+) and SUM149 (ER–/HER2–) was achieved using lentiviral vectors. We injected MDA-IBC3-sEcad and control cells (tail-vein) and SUM149-sEcad and control cells (intracardiac) into SCID/Beige mice to assess brain metastasis burden and survival in mice. Human cytokine array was used to examine conditioned medium from sEcad high and control cells. Clinical datasets were used to compare expression and percent risk of brain relapse. Mice were treated with brain-permeable CXCR2 inhibitor in both IBC brain metastasis models. Multiplex quantitative imaging was used to visualize cells of the brain metastatic microenvironment. Results: Higher serum sEcad levels were significantly associated with reduced OS, earlier metastasis onset, and increased brain metastasis incidence. sEcad is an independent predictor of OS on multivariate analysis (hazard ratio [HR]=2.07 [95% CI 1.19-3.60], p=0.01). Treatment of astrocytes with recombinant sEcad increased reactive astrocytosis, in vitro and in vivo. Cytokine array analysis showed increased levels of pro-inflammatory cytokine CXCL1, DKK1 and CXCL8 in conditioned medium from sEcad-overexpressing IBC cells compared with control cells, which was validated by ELISA. In patient samples, CXCL1, CXCL8 and CXCR2, the receptor for CXCL1 and CXCL8, were expressed higher in brain metastasis compared to other metastases. Additionally, patients with high CXCL1/CXCL8 or CXCR2 expression had reduced brain metastasis relapse. Inhibition of CXCR2 decreased sEcad-mediated induction of reactive astrocytes. Treatment of mice bearing MDA-IBC3-sEcad and SUM149-sEcad brain metastases with the brain permeable CXCR2 inhibitor reduced number of brain metastasis, metastasis burden and prolonged survival of mice. Multiplexed immunofluorescence staining showed a significant reduction of reactive astrocytes in brain metastasis lesions treated with the CXCR2 inhibitor. Conclusion: Our findings underscore that sEcad drives brain metastasis by promoting an inflammatory brain microenvironment via a targetable CXCL1/CXCL8-CXCR2 axis. Targeting this axis presents a promising therapeutic strategy to effectively block brain metastasis in aggressive breast cancers. Citation Format: Xiaoding Hu, Yun Xiong, Emilly S Villodre, Juhee Song, Maria Stenkamp, Natalie Fowlkes, Elizabeth Leigh, Jeffery, Savitri Krishnamurthy, Junjie Chen, Wendy A Woodward, Debu Tripathy, Bisrat G Debeb. Targeting CXCL1-CXCR2 axis blocks brain metastasis in inflammatory breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr PS14-08.

Supplementary Figure 1. Comparison of TROP2 membrane expression between patient tumors and matched patient derived xenografts. Supplementary Figure 2. Representative images of TROP2 IHC in the breast cancer xenografts shown in Figure 2. Images represent one of three cores of a TMA assessed, with IHC shown at 20X. Supplementary Figure 3. Genomic alterations in genes associated with DNA damage repair. Supplementary Figure 4 BRCAness in BCX models Supplementary Figure 5. Violin plot of BRCAness signature in responders and non-responders. Supplementary Figure 6. Homologous repair in BCX models Supplementary Figure 7. Antitumor activity of Datopotamab deruxtecan (Dato-DXd) and PARP inhibitor talazoparib Supplementary Figure 8. IHC of TROP2 Supplementary Figure 9. Necrosis analysis Supplementary Figure 10. Internalization assay Supplementary Figure 11. (A) Immunoblotting of TROP2 expression in xenografts of BCX.011CL-control and BCX.011-TROP2. The first two on the left are cell line samples as controls for immunoblotting. The remaining are PDX tumor samples. PDX tumors (treated as shown) were collected on day 25-day 28 of treatment. TROP2 IHC was perform and scored. All BCX.011CL-TROP2 tumors formed TROP2 positive xenograft except for a single tumor that grew back after regressing with the first 10 mg/kg Dato-DXd treatment (B). Supplementary Figure 12. Effect of exogenous TROP2 expression on Dato-DXd sensitivity. Supplementary Figure 13. TROP2 expression in isogenic cell lines Supplementary Figure 14. Conjugated DXd in BCXs Supplementary Figure 15. Additional immunohistochemistry analysis of pharmacodynamic changes associated with Dato-DXd treatment

The brain is a common site of relapse in inflammatory breast cancer (IBC), an E-cadherin positive, aggressive form of breast cancer. We found that elevated serum levels of soluble E-cadherin (sEcad), an 80-kDa fragment of E-cadherin, in patients with metastatic IBC correlated with poorer outcomes and increased rates of brain metastases. In our effort to understand the underlying mechanism, we discovered that sEcad binds to XIAP, an inhibitor of cell death, activating the pro-survival NF-kβ signaling in tumor cells. We also discovered that sEcad affects the tumor cell microenvironment by enhancing cancer cell adhesion to endothelial cells and inducing reactive astrocytosis in the brain. In addition, we found that sEcad-mediated reactive astrocytosis relies on the CXCL1/CXCL8-CXCR2 axis and treatment with a brain-permeable CXCR2 antagonist reduced brain metastatic burden and prolonged survival. These findings implicate sEcad in brain metastasis and provide new insights into potential therapeutic targets for IBC. Highlights:High serum sEcad levels correlate clinically with poor survival outcomes and development of brain metastasissEcad drives IBC brain metastasis growth in mouse modelssEcad binds XIAP to activate NFkB and promote anoikis resistance and invasion of IBC cells sEcad activates reactive astrocytes and induces CXCR2 expression on tumor cells in vitro and in vivo CXCR2-IN-1, a brain-permeable CXCR2 antagonist, reduces metastasis and improves survival in IBC brain metastasis models.

Background: Inflammatory breast cancer (IBC) is a rare, aggressive form of breast cancer but accounts for 10% of breast cancer-related deaths. Cancer stem cells (CSCs; tumor stemness) play a key role in tumor dormancy, progression, and treatment resistance, yet mechanisms that drive CSCs remain poorly defined. We recently identified that NDRG1 promotes tumor growth and progression in IBC mouse models, and that its depletion inhibits AKT phosphorylation. We hypothesized that NDRG1 is a key regulator of tumor stemness in IBC via activating AKT signaling. Methods: CSCs were assessed using surrogate markers including CD44+/CD24-, mammospheres, and in vivo limiting dilution assay experiments. To identify which AKT isoforms (AKT1, AKT2, or AKT3) or upstream kinases (SGK1, GSK3β) mediate NDRG1-induced CSCs, NDRG1-depleted cells were transfected with NDRG1 WT, AKT plasmids or SGK1/GSK3β phospho-site mutants or siRNA for SGK1/GSK3β. Results: NDRG1 depletion significantly reduced CD44+/CD24- subpopulation and mammosphere formation (p<0.001). Limiting dilution experiments demonstrated a significant reduction in tumor incidence and stemness frequency in mice transplanted with NDRG1 knockdown cells (p= 1 x 10-12). Each of the three AKT isoforms partially rescued tumor stemness in the NDRG1 knockdown IBC cells [CD44+/CD24-: NDRG1 KD vs AKT1 OE, p=0.008; vs AKT2 OE, p=0.005; vs AKT3 OE, p=0.001)]. Overexpression of known inactive SGK1 phospho-site mutants of NDRG1 restored tumor stemness in NDRG1-depleted cells (p≤0.005). While silencing GSK3β reduced CSCs in IBC cells SGK1 did not affect this subpopulation, indicating that the tumor stemness effect of NDRG1 is independent of SGK1 and its kinase activity and is regulated by GSK3β. Conclusions: Our findings underscore the critical role of NDRG1 as a regulator of IBC tumor stemness. We observed all three isoforms of AKT restored CSCs in NDRG1-depleted breast cancer cells, highlighting the significance of the NDRG1-AKT axis in governing stemness and tumor progression in IBC. Citation Format: Emilly Schlee Villodre, Xiaoding Hu, Wendy A. Woodward, Stefan Pusch, Debu Tripathy, Bisrat G. Debeb. NDRG1-AKT signaling promotes tumor stemness in inflammatory breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-06-23.

Background: Adjuvant endocrine therapy (ET) is the standard of care (SOC) for the treatment of estrogen receptor-positive (ER+) human epidermal growth factor receptor-2 negative (HER2-) early-stage breast cancer. Despite optimized adjuvant treatments for patients with high risk of recurrence, patients continue to experience local and distant relapses, and new therapies are warranted. In the phase 3 EMERALD trial, single-agent elacestrant was evaluated vs SOC ET in ER+/HER2− metastatic breast cancer. Elacestrant significantly prolonged progression-free survival (PFS) vs SOC ET in the overall population (HR = 0.70; 95% CI, 0.55-0.88; P = 0.0018) and in patients with ESR1-mut tumors (HR = 0.55; 95% CI, 0.39-0.77; P = 0.0005) (Bidard, JCO 2022). In those pts with ≥12 months of prior ET+ CDK4/6 inhibitor (CDK4/6i) and ESR1-mut tumors, median PFS with elacestrant was 8.6 vs 1.9 months with SOC ET (Bardia, SABCS 2022). In patients with tumors without detectable ESR1-mut, a numerical difference was observed (HR = 0.86; 95% CI: 0.63-1.19). As elacestrant significantly prolonged PFS in the metastatic setting relative to endocrine monotherapy, with more pronounced activity in patients with endocrine-sensitive tumors, it is hypothesized that elacestrant should prolong invasive breast cancer-free survival (IBCFS) in the earlier adjuvant setting among patients who received prior adjuvant ET with or without a CDK4/6i. In addition, elacestrant can antagonize the estrogen receptor in tumor cells with a non-degradative antagonist function. Unlike other oral SERDs in development, elacestrant exhibits both degradative and partial agonist properties (Wardell, ERC 2015). Elacestrant could offer a new class of medication in the adjuvant setting and merits further therapeutic evaluation for patients with ER+/HER2- breast cancer with a high risk of recurrence. Methods: ELEGANT (NCT06492616) is a global, multicenter, randomized, open-label phase 3 study designed to evaluate elacestrant compared with SOC ET (aromatase inhibitor or tamoxifen) in patients with early breast cancer and a high risk of recurrence. A total of 4,220 patients will be randomized 1:1 to continue SOC ET or switch to elacestrant therapy for a duration of 5 years. Eligible patients are women or men with ER+/HER2− node-positive breast cancer who have completed 24 months (but not more than 60 months) of adjuvant ET and have ECOG PS ≤1. Patients who received a prior CDK4/6i or a poly ADP-ribose polymerase (PARP) inhibitor must have already completed or discontinued these treatments. Exclusion criteria include inflammatory breast cancer, any history of prior invasive breast cancer, and >6 months continuous interruption of prior SOC adjuvant ET or discontinuation of adjuvant ET >6 months prior to randomization. The primary endpoint is IBCFS. Key secondary endpoints include distant relapse-free survival (DRFS) and overall survival (OS). Additional secondary endpoints include invasive disease-free survival (IDFS), safety, and patient-reported outcomes. Exploratory endpoints include PK and biomarker analyses. Time-to-event endpoints will be reported using Kaplan-Meier estimates. Baseline demographics and other characteristics will be descriptively summarized. Citation Format: Aditya Bardia, Virginia Kaklamani, Joyce O’Shaughnessy, Peter Schmid, J. Thaddeus Beck, Michelino De Laurentiis, Giuseppe Curigliano, Hope S. Rugo, Debu Tripathy, William J. Gradishar, Michail Ignatiadis, David A. Cameron, Giulia Tonini, Simona Scartoni, Jennifer Crozier, Leo Viana Nicacio, Tomer Wasserman, Sara M. Tolaney. ELEGANT: Elacestrant versus standard endocrine therapy in women & men with node-positive, estrogen receptor-positive, HER2-negative, early breast cancer with high risk of recurrence in a global, multicenter, randomized, open-label phase 3 study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P2-08-21.

Background: ADCs combine the tumor specificity of monoclonal antibodies with the cytotoxic effects of chemotherapeutic drugs, allowing for targeted delivery of potent anticancer agents while minimizing systemic toxicities. Sacituzumab govitecan (SG) and trastuzumab deruxtecan (T-DXd) are antibody drug conjugates with topoisomerase 1 payloads targeting TROP2 and HER2, respectively. Defects in homologous recombination repair through gBRCA1/2 alterations have been postulated as a potential biomarker of response to DNA damaging agents such as topoisomerase I inhibitors. Consequently, we sought to assess the impact of gBRCA1/2 status and clinical outcomes in metastatic breast cancer patients treated with SG or T-DXd. Methods: We estimated the distribution of progression-free survival (PFS) and overall survival (OS) using the Kaplan-Meier method. Differences in survival curves between gBRCA-positive and BRCA-negative patients were assessed using the log-rank test. Cox proportional hazards regression models were employed to evaluate the association between each survival outcome and BRCA status, and Fisher exact test was used to assess the association with the clinical benefit rate (CBR). Results: The analysis included a total of 322 breast cancer patients treated with SG or T-DXd with a median follow-up time 30.1 months (Range: 0.5 – 299 months). Of these, 49 (15%) were gBRCA positive (gBRCA1 n=27 and gBRCA2 n=22). gBRCA1/2-positive patients were more likely to be younger, with 43% aged 18-40 compared to 22% in BRCA-negative patients. The median age at the start of either ADC was 49 years (range: 20-83). gBRCA-positive patients had received more prior lines of treatment, with 49% having three or more prior treatments compared to 40% of BRCA-negative patients. Out of the gBRCA1/2 positive patients, 39(80%) received PARP inhibitors, with 15(31%) of them receiving it as first-line treatment.53% of gBRCA-positive patients received SG, while 47% received T-DXd, similar to the BRCA-negative group (56% and 44%, respectively). 45% of BRCA-positive patients had hormone receptor (HR) positive cancers compared to 37% of BRCA-negative patients, and 88% of gBRCA-positive patients had HER2 negative cancers compared to 77% of BRCA-negative patients. Among the gBRCA-positive cohort, 51% had died by the last follow-up compared to 34% of BRCA-negative patients. Additionally, 80% of gBRCA-positive patients experienced disease progression or death, compared to 72% of BRCA-negative patients. The median PFS was 3.9 months (95% CI: 2.9-6.4 months) in gBRCA1/2 positive compared to 5.6 months (95% CI: 5.1-6.7 months) (hazard ratio 1.48 (1.05 – 2.10), p = 0.025) in BRCA1/2 negative patients. Median OS was 64.5 months (95% CI: 39.8 – Not estimable) in gBRCA positive patients compared to 71.4 months (range 63.5 – 99.6 months) in BRCA1/2 negative patients (HR 1.39 (0.89 – 2.16), p = 0.15). No statistically significant difference in CBR was noted between gBRCA positive and negative patients (p = 0.23). Conclusions: There is very limited data describing the survival outcomes of BRCA-tested patients receiving topoisomerase based ADCs. In our study, significant difference in PFS, favoring BRCA1/2 negative patients was noted compared to gBRCA1/2 positive patients treated with SG or T-DXd; while no differences in OS and CBR was observed between the two groups. Further study regarding the impact of DNA repair pathway defects and clinical outcomes with DNA damaging agents are warranted. Citation Format: Akshara Singareeka Raghavendra, Zhongya Wang, Roland Bassett Jr, Debu Tripathy, Banu Arun, Senthil Damodaran. Impact of gBRCA1/2 Status on Survival Outcomes in Metastatic Breast Cancer Patients Treated with Topoisomerase 1 based Antibody-Drug Conjugates (ADCs) [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P5-10-03.

Purpose: To develop deep learning models for predicting the pathologic complete response (pCR) to neoadjuvant systemic therapy (NAST) in patients with triple-negative breast cancer (TNBC) based on pretreatment multiparametric breast MRI and clinicopathological data. Methods: The prospective institutional review board-approved study [NCT02276443] included 282 patients with stage I–III TNBC who had multiparametric breast MRI at baseline and underwent NAST and surgery during 2016–2021. Dynamic contrast-enhanced MRI (DCE), diffusion-weighted imaging (DWI), and clinicopathological data were used for the model development and internal testing. Data from the I-SPY 2 trial (2010–2016) were used for external testing. Four variables with a potential impact on model performance were systematically investigated: 3D model frameworks, tumor volume preprocessing, tumor ROI selection, and data inputs. Results: Forty-eight models with different variable combinations were investigated. The best-performing model in the internal testing dataset used DCE, DWI, and clinicopathological data with the originally contoured tumor volume, the tight bounding box of the tumor mask, and ResNeXt50, and achieved an area under the receiver operating characteristic curve (AUC) of 0.76 (95% CI: 0.60–0.88). The best-performing models in the external testing dataset achieved an AUC of 0.72 (95% CI: 0.57–0.84) using only DCE images (originally contoured tumor volume, enlarged bounding box of tumor mask, and ResNeXt50) and an AUC of 0.72 (95% CI: 0.56–0.86) using only DWI images (originally contoured tumor volume, enlarged bounding box of tumor mask, and ResNet18). Conclusions: We developed 3D deep learning models based on pretreatment data that could predict pCR to NAST in TNBC patients.