Estrogen Receptor Expression Research Articles

Abstract PO2-18-08: Identification of novel genetic/therapeutic vulnerabilities in breast cancer

Abstract Background: Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer death among women worldwide. Triple negative breast cancer (TNBC) is an aggressive subtype that is defined by the lack of expression of estrogen and progesterone receptors in the absence of HER2 amplification or overexpression. TNBC represents 15-20% of all breast cancers and occurs more frequently in young premenopausal women. TNBC often ends with a poor clinical outcome due to high histological grade, rapid recurrence in many patients combined with few treatment options. These realities highlight the urgent need to identify novel therapeutics vulnerabilities that can be leveraged to improve TNBC patient outcomes. Methods: We utilized the publicly available DepMap and Kaplan Meier datasets to identify essential genes that were unique to TNBC cells and whose expression levels were associated with worse patient outcomes. siRNA based approaches were used to confirm the relevance of top hits in mediating cancer cell phenotypes including viability, cell-cycle profiles and induction of apoptosis among others. A novel drug currently being developed was identified for the top hit in these studies and was subsequently employed in multiple in vitro approaches to characterize the mechanisms of action in TNBC as well as initial efficacy studies using clinically relevant ex vivo patient derived models. Results: Using the DepMap database, we interrogated genome-wide sgRNA knockout screens conducted in over 40 breast cancer cell lines to identify specific genes whose expression was required for cell viability in TNBC cells, but not other breast cancer cell lines. This endeavor identified 6 genes (CTPS1, HUS1, PRKRA, RAD1, RAD9A and RHOA) that were preferentially essential in TNBC cells. Further profiling of these genes revealed that CTPS1 expression is higher in cancer relative to normal tissue and that its expression is further upregulated in chemotherapy- and PARPi-resistant models. Knockdown of CTPS1 in TNBC cells was shown to decrease cell proliferation and viability with no effects observed in estrogen receptor+ cell lines. Using a first-in-class, highly selective and orally bioavailable CTPS1 inhibitor (STP938) developed by Step-Pharma, we identified IC50s in the low nM range for many TNBC cell lines, including cell models that are resistant to existing standard-of-care therapies. Inhibition of CTPS1 was shown to arrest cells in S phase. Conclusions: Our studies have identified CTPS1 as an essential gene in TNBC. CTPS1 encodes an enzyme responsible for the catalytic conversion of UTP (uridine triphosphate) to CTP (cytidine triphosphate), an essential step in the biosynthesis of nucleic acids. These findings are timely in light of the recent and ongoing development of the first-in-class CTPS1 inhibitor, STP938, for which first-in-human studies are underway for refractory B- and T-cell lymphomas. Based on our initial studies using this drug, we provide pre-clinical evidence of its efficacy in multiple models of primary and advanced TNBC. Efforts are currently underway to move this work toward a clinical trial for TNBC patients. Citation Format: Xiyin Wang, Michael Emch, Lauren Voll, Rebecca Russell, Esther Rodman, Philip Beer, John Hawse. Identification of novel genetic/therapeutic vulnerabilities in breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-18-08.

Abstract PO2-24-04: Exploring the role and therapeutic potential of Ubiquitin Specific Peptidase 11 (USP11) in estrogen receptor positive breast cancer

Abstract Dysregulated estrogen receptor (ER) function is a key feature of 70% of breast cancers. In this setting ER primarily functions as a growth-controlling transcription factor driving pro-tumorigenic properties, thus there is a need to identify novel modulators of ER transcriptional activity as alternative therapeutic options. Previously, we showed a significant association between high ubiquitin specific protease 11 (USP11) expression and poor survival in ER+ breast cancer patients, but not in ER- patients, indicating a role for USP11 in ER+ subtypes. However, the precise role of USP11 in controlling ER function remains undescribed. To interrogate USP11 function in ER+ breast cancer we generated a CRISPR USP11 knockout MCF7 breast cancer cell line. Our results showed for the first time that USP11 knockout significantly reduces proliferation, induces G2 cell cycle arrest and apoptosis, abrogates ERα transcriptional activity, significantly impairs cell migration and invasion, whilst also impairing MCF7 cancer stem-cell like properties and malignant transformation in vitro. In addition, we also observed significant dysregulation of epithelial-mesenchymal transition-related markers including E-cadherin, N-cadherin, Snail and Slug. Using RNA-seq of MCF7 cells +/- estradiol, +/- stable USP11 knockdown we identified dysregulated pathways in protein binding, cell adhesion molecule binding and cell cycle regulation following USP11 modulation. Of note, gene expression analysis indicated NCOA3 as the most differentially expressed coding gene. Further validation confirmed a significant reduction in NCOA3- encoded Steroid receptor coactivator- 3 (SRC-3) protein expression following USP11 modulation with immunocytochemical analysis also indicating co-localisation within the nucleus. Frequently upregulated in breast cancer and associated with poor outcome, SRC-3 promotes ER transcriptional activity and co-activates a wide range of additional pro-tumorigenic transcription factors. Thus, SRC-3 modulation offers an attractive therapeutic target in breast cancer. This finding may present a novel role for USP11 in controlling SRC-3 and therefore associated ER transcriptional activity. We then aimed to explore the therapeutic potential of USP11. Although rare in primary breast cancer, activating mutations in the ER ligand-binding domain have recently been linked to recurrent, anti-endocrine resistant disease and metastasis. As such cancers remain dependent on ER-signalling for proliferation, but are resistant to ER targeted therapies, we identified USP11 as a potential novel therapeutic target. Using CRISPR knock-in ER mutant MCF7 cell lines expressing the four most common ER activating mutations, we demonstrated that USP11 knockdown continues to significantly reduce proliferation and abrogates mutant ERα transcriptional activity. We then explored amphipathic cell penetrating peptide RALA encapsulation as a delivery method for siRNA targeting USP11. Optimisation of nanoparticle delivery in the Y537S ER-mutant MCF7 breast cancer cell line achieved significant knockdown of USP11 and ER- related target genes including TFF1, PgR, GREB1 and PKIB in 2D with minimal associated cellular toxicity. To overcome the siRNA-related issues of rapid clearance upon systemic delivery, we then explored the use of a freeze-dried collagen-based scaffold model as an in vitro 3D RALA-encapsulated siRNA delivery system. Here we observed successful delivery of nanoparticle to MCF7 breast cancer cells, with a significant reduction in USP11 mRNA expression. Bio-compatible scaffold- facilitated delivery may therefore offer a more feasible translation of this siRNA-based therapeutic. Overall, this study highlights a novel role for USP11 in various oncogenic pathways. USP11 may therefore offer a novel therapeutic target to be exploited for the management of ER-positive breast cancer, including ER mutant breast cancer. Citation Format: Rachel Moore, Anna Blümel, Elspeth Ward, Elizabeth Sainsbury, Emer Conroy, Fergal O’Brien, Caroline Curtin, Simak Ali, Helen McCarthy, William Gallagher, Darran O'Connor. Exploring the role and therapeutic potential of Ubiquitin Specific Peptidase 11 (USP11) in estrogen receptor positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-24-04.

Abstract PO1-01-11: Development and Validation of a Breast Cancer Recurrence Model Demonstrates Accurate Identification of Patients with Favorable Long-Term Outcomes

Abstract Background: The Oncotype DX (ODX) test is a 21-gene expression assay widely used for the prediction of risk recurrence in early-stage breast cancer, but it may be possible to identify patients who can forgo testing using only clinicopathologic variables. In 2018, the National Cancer Database (NCDB) began reporting quantitative histologic parameters for estrogen receptor (ER), progesterone receptor (PR), and Ki-67 expression in breast cancer patients. Inclusion of these variables may improve the development of nationally applicable models to predict ODX results using clinicopathologic variables alone. Methods: Using a cohort of patients from the NCDB diagnosed from 2018–2020 with hormone receptor (HR)-positive, HER2-negative, Stage I-III breast cancer, we trained machine learning models to predict high-risk (26-100) ODX score. A subset comprising 80% of patients was used for model training, while the remaining data were set aside for internal validation. An external validation cohort was selected from the University of Chicago Medical Center (UCMC), including patients diagnosed from 2009–2021. Feature selection, model architecture selection, and hyperparameter tuning were performed using 10-fold cross-validation within the NCDB training set. We compared a model with quantitative ER, PR, and Ki-67; a model with only quantitative ER and PR, and a model without quantitative immunohistochemistry – to best reflect the likely data available in a variety of practice patterns. The primary endpoint was the area under the receiver operating characteristic curve (AUROC) for prediction of high-risk ODX results in the UCMC validation cohort. Models were also evaluated as rule-out tests to identify low-risk patients who did not require further ODX testing, using a high (90%) sensitivity threshold, fit in the NCDB training dataset. Results: We identified 53,346 patients from the NCDB cohort meeting the inclusion criteria; 7% had a high risk ODX score, with a median follow-up time of 28 months. The UCMC validation cohort included 896 patients, and was more diverse, with 30% non-Hispanic Black patients (versus 8% in NCDB), more high-risk patients (18% with high ODX), and a longer median follow-up time of 55 months. In the NCDB validation cohort, models incorporating quantitative ER/PR (AUROC 0.78, 95% CI 0.77–0.80) and quantitative ER/PR/Ki-67 (AUROC 0.81, 95% CI 0.80–0.83) both performed better than the non-quantitative model (AUROC 0.70, 95% CI 0.68–0.72). These results were preserved in the external UCMC cohort, where the ER/PR model (AUROC 0.86, 95% CI 0.80–0.92, p = 0.032) and the ER/PR/Ki-67 model (AUROC 0.87, 95% CI 0.81–0.93) outperformed the non-quantitative model (AUROC 0.80, 95% CI 0.73–0.87, p = 0.009). The high sensitivity rule-out threshold of the ER/PR model predicted that 30% of patients in the UCMC cohort would be low ODX, and the ER/PR/Ki-67 model predicted 44% as low risk – negative predictive value was over 96% for prediction of high ODX. Of the patients predicted to be low risk by the quantitative models, none had a documented high ODX score, and recurrence was < 3% at 5 years. The hazard ratio for recurrence free interval, adjusted for age and comorbidity score, of patients predicted to be high risk by this threshold was 2.96 (95% CI 1.02–8.58) for the ER/PR model and 3.84 (95% CI 1.48–9.97) for the ER/PR/Ki-67 model. Conclusions: We present externally validated and nationally applicable models that identify approximately half of HR-positive/HER2-negative breast cancer patients who are unlikely to have high ODX results using widely available quantitative clinicopathologic variables. Patients identified as low risk by these models have excellent long-term outcomes and may be able to forgo adjuvant chemotherapy without further genomic testing. Citation Format: Asim Dhungana, Augustin Vannier, Fangyuan Zhao, Jincong Freeman, Poornima Saha, Megan Sullivan, Katharine Yao, Elbio Flores, Olufunmilayo Olopade, Dezheng Huo, Alexander Pearson, Frederick Howard. Development and Validation of a Breast Cancer Recurrence Model Demonstrates Accurate Identification of Patients with Favorable Long-Term Outcomes [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-11.

Abstract PO2-05-14: Prognosis and clinicopathological characteristics of HER2-negative metastatic breast cancers with low expression of hormone receptors: real world evidence from the French ESME cohort

Abstract Background: HER2-negative breast cancers expressing low (1-9 %) immunohistochemistry levels of hormone receptors (HR, estrogen and progesterone receptors), remain an uncertain category, being considered either as triple negative breast cancers (TNBC) or HR-positive (HR+) tumors across guidelines or approvals. The issues regarding this clinical subgroup are both prognostic, with the need of a better definition of their clinical outcome, as well as predictive. Methods: The ESME database is a French National cohort of all consecutive patients who initiated a first-line treatment for metastatic breast cancer (MBC) from 2008 on, in one of the 18 French Comprehensive Cancer Centers. Patients with HER2-negative (0 to 2+, ISH negative) MBC and known estrogen receptor (ER) and progesterone receptors (PR) expression levels were selected. Primary objective was to evaluate crude overall survival (OS) in HER2-/HR-low (ER and PR 0-9 and not TNBC) MBC pts compared with those with TNBC and HR+ disease defined by ER and PR < 1%, and ER ± PR ≥ 10%, respectively. In these 3 populations, predefined secondary objectives were to evaluate PFS under first line chemotherapy (CT), to describe clinical characteristics and the distribution of genetic abnormalities identified at the time of MBC diagnosis. Results: Out of 30,459 patients in the ESME database initiating their MBC treatment between 01/2008 and 01/2021, 19109 patients (2113 TNBC; 228 HR-low; 16768 HR+) were eligible for this analysis. Median follow-up was 58.0 months (95%CI [56.6; 59.0]). Median OS were 15.7 months [15.0-16.8], 19.1 months [15.5-22.4] and 44.6 months [43.8-45.5] in the TNBC, HR-low and HR+ subgroups, respectively. The multivariable analysis adjusted on age at MBC diagnosis, pathological grade and subtype, metastatic-free interval, number and sites of metastases and HER2 status (0 vs. 1-2+), identified no significant OS difference between HR-low and TNBC subgroups (HR=0.95, 95%CI 0.79-1.14), while HR+ patients had a better OS than TNBC patients (reference) (HR=0.50, 95%CI 0.47-0.53). Of these 19109 pts, 8910 received first-line CT regimen (1960 TNBC; 195 HR-low; 6755 HR+): taxanes-based: 66.7%, anthracyclines-based: 32.9%, capecitabine: 18%. Median PFS under first line CT were 5.3 (5.1-5.6), 5.1 (4.1-6.2) and 10.2 months (9.9-10.6) for TNBC, HR-low and HR+ subgroups, respectively. In the multivariable analysis adjusted on the same variables, the HR-low subgroup had a statistically poorer PFS compared to TNBC (HR=1.24, 95% CI 1.04-1.49). On the other hand, the HR+ subgroup had a better PFS than the TNBC (HR=0.74, 95%CI [0.70; 0.78]). Baseline germline BRCA1 mutations (at MBC diagnosis) were present in 4.5% of the TNBC cases, 2.6% of the HR-low cases, and 0.4% of the HR+ cases. The distribution of germline BRCA2 mutations was more homogeneous between the three groups (0.9% of TNBC cases, 1.3% of HR-low cases and 1.1 % of HR+ cases). Conclusions: In this large cohort, patients with HER2-negative, HR-low MBC seem to share similar general prognosis, oncogenetic features and PFS under standard chemotherapy treatment with TNBC patients. Citation Format: Marie Alexandre, Ludovic Gauthier, Audrey Mailliez, Thibault DE LA MOTTE ROUGE, Thomas Bachelot, Monica Arnedos, Florence Dalenc, Etienne Brain, Jean-Marc Ferrero, Vincent Massard, Isabelle Desmoulins, Marie-Ange Mouret-Reynier, Christelle Levy, Anthony Gonçalves, Marianne Leheurteur, Thierry Petit, Jean-Sébastien Frenel, Lise Bosquet, Suzette Delaloge, William Jacot. Prognosis and clinicopathological characteristics of HER2-negative metastatic breast cancers with low expression of hormone receptors: real world evidence from the French ESME cohort [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-05-14.

Abstract PO4-23-11: Resistance Mechanisms to CDK4/6 Inhibitors and/or Tamoxifen Using Comprehensive Thermostable Group II Intron Reverse Transcriptase Sequencing

Abstract Background Understanding the mechanisms of resistance to CDK4/6 inhibitors (CDK4/6i) and endocrine therapy (ET) is pivotal in exploring new therapeutic strategies for hormone receptor-positive (HR+), HER2-negative metastatic breast cancer. To decipher these resistance mechanisms, we analyzed the alterations in comprehensive RNA-seq (coding and non-coding RNAs) of HR+ HER2-negative BC cell lines via thermostable group II intron reverse transcriptase sequencing (TGIRT-seq). Methods We established Tamoxifen-resistant (TMR), Abemaciclib-resistant (ACR), Palbociclib-resistant (PCR), Tamoxifen/Abemaciclib double-resistant (TMR-ACR), and Tamoxifen/Palbociclib double-resistant (TMR-PCR) BC cell lines from MCF7 and T47D HR+/HER2- BC cell lines through stepwise dose-escalation continuous drug exposure. We performed a TGIRT-seq transcriptomic analysis using a protocol that allows the sequencing of both long and short non-coding and protein-coding RNAs in a single library. All libraries were sequenced using paired-end 150 bp on the Novaseq platform, resulting in an average of 50 million reads per library. For analysis, raw reads underwent adapter trimming, small RNA mapping, whole genome mapping, and the generation of annotated genes' read count. We used raw counts to detect differentially expressed genes (DEGs) with DESeq2 in R using the cut-off (log2 [fold change] > 1, FDR < 1e-3). We then used the selected DEGs for Gene Set Enrichment Analysis (GSEA) and Kaplan-Meier survival analysis from the TCGA database. Results The TGIRT-seq analysis identified 1171 to 3472 DEGs in different drug resistance and cell line combinations. Most DEGs in resistant cells were consistently downregulated compared to parent cells. Seventy-five percent of DEGs were protein-coding genes, with the rest being non-coding RNAs, such as small nucleolar RNAs, microRNAs, long non-coding RNAs, and transposable element RNAs, which conventional RNA-seq poorly detects. In principal component analysis (PCA) plots, replicates per drug resistance clustered clearly in both cell line backgrounds. PCA also indicated distinctive pathways for acquiring drug resistance in MCF7 and T47D cells. The estrogen receptor (ER) expression decreased, while HER2 increased in resistant cell lines. DEGs identified were enriched in ESR1-related pathways in all MCF7 and T47D cell lines resistant models. Several ER-regulating genes like IL-1R1 and RET were upregulated, while ADCY1 was consistently downregulated across different resistance types. A significant overlap with single-resistance DEGs was observed among the DEGs in double-resistance cell lines, but 20-50% of up/down-regulated DEGs in double-resistance cell lines were uniquely altered. Several previously identified DEGs (e.g., SALL4, TOP2A) and 21 novel candidate genes correlated with poor survival outcomes. Conclusion The analysis identified unique DEGs in double resistance cell lines, suggesting that double resistance mechanisms may not merely be a cumulative effect of single resistance mechanisms, necessitating further investigation and validation. CDK4/6i and/or ET-resistant BC cell lines displayed significant transcriptome reprogramming during the development of drug resistance. In previously published research, ESR1-related pathway alterations were proposed in tamoxifen resistance cell lines. Here we find that CDK4/6i-resistant cells also modify these ESR1-related pathways. Additionally, we identified several targetable genes, such as IL-1R1 and RET, involved in ESR1-related pathways that could pave the way for developing new treatment strategies. Citation Format: Toshiaki Iwase, Hengyi Xu, Nakyung Oh, Jangsoon Lee, Alan M Lambowitz, Naoto Ueno. Resistance Mechanisms to CDK4/6 Inhibitors and/or Tamoxifen Using Comprehensive Thermostable Group II Intron Reverse Transcriptase Sequencing [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-23-11.

Abstract PO4-01-08: Co-expression of estrogen receptor (ER), progesterone receptor (PR), and Ki67 in a single breast cancer cell indicates a favorable prognosis in ER-positive breast cancer

Abstract Background: ER-positive breast cancer is biologically and clinically divided into two subtypes: luminal-A and luminal-B. This classification is mainly based on the status of cellular proliferation. At least two different pathways drive cellular proliferation in ER-positive breast cancer. One is a classical pathway where ER binds to estrogen responsive element (ERE), which leads to the expression of downstream molecules, including PR. The other is a non-classical pathway where a complex of ER and relevant factors bind to different sites than ERE. Growth factor signaling has been suggested to potentiate a non-classical pathway. We hypothesized that examining PR status in ER-positive proliferating cells could tell which pathway is more dominant in ER-positive breast cancer. Methods: To test the hypothesis, we used a newly developed triplex immunohistochemistry (IHC) that detects three molecules simultaneously under bright-field microscopy. Postmenopausal patients who were treated with neoadjuvant endocrine therapy with aromatase inhibitors from January 2007 to September 2016 at Saitama Cancer Center were included in this study. ER, PR, and Ki67 expressions were assessed in a single slide using the triplex IHC assay with anti-ER antibody (clone SP1), anti-PR antibody (clone 1E2), and anti-Ki67 antibody (clone 30-9). ER, PR and Ki67 expression was assessed in a single cell nucleus of cancer cells (567 to 4871 cells) from multiple areas in each case. An ER-positive proliferating cell was defined as an ER-positive and Ki67-positive cell. PR status in ER-positive proliferating cells was assessed. When PR was expressed in more than 50% of ER-positive proliferating cells in a clinical case, the tumor was categorized as the PR-positive group. Luminal A and luminal B breast cancers were defined based on the pre-treatment Ki67 labeling index with a cut-off of 14 %. Statistical analyses included the Mann-Whitney test, the log-rank test, and the Cox proportional hazard model. Results: Pre-treatment tissues from 55 patients were evaluated. The median age was 62 (range: 54 to 80) years. The patients were grouped into PR-positive and PR-negative groups. The two groups had no differences in age and pre-treatment T and N stages. The median pre-treatment Ki67 labeling index was 5.9 % in the PR-positive group and 9.9 % in the PR-negative group, which showed a statistically significant difference (P = 0.01). Clinical response to neoadjuvant endocrine therapy was compared, and no difference was observed. The median post-treatment Ki67 labeling index was 3.6 % in the PR-positive group and 13.1 % in the PR-negative group with a significant difference (P = 0.035). The survival was compared between the two groups. The PR-positive group showed a significantly more favorable disease-free survival (DFS) than the PR-negative group (P = 0.0079). To adjust for the background differences including Ki67 and PR status, a multivariate analysis was performed and showed that the PR-positive group had a significantly better DFS than the PR-negative group independent of clinical stage, Ki67 labeling index, and PR status (P = 0.042). Breast cancer-specific survival (BCSS) was also better in the PR-positive group than in the PR-negative group after adjusting for clinical stage, Ki67 labeling index, and PR status (P = 0.043). Interestingly, among patients with luminal A tumors, those in the PR-positive group showed a better DFS than those in the PR-negative group (P = 0.022). Conclusion: PR status in ER-positive proliferating cells was an independent prognostic factor in DFS and BCSS and divided patients with luminal A tumors further into two prognostic groups. Citation Format: Takayuki Ueno, Rie Horii, Hiroshi Matsumoto, Makiko Ono, Yurina Maeshima, Hiroaki Nitta. Co-expression of estrogen receptor (ER), progesterone receptor (PR), and Ki67 in a single breast cancer cell indicates a favorable prognosis in ER-positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-01-08.

Abstract PO1-24-08: Targeting of HER3 potentiates the antitumor activity of paclitaxel against triple negative breast cancer

Abstract Background: Triple negative breast cancer (TNBC) is characterized by the absence of expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) overexpression. This aggressive form of breast cancer carries a higher risk of recurrence compared to other subtypes, presenting a significant clinical challenge. Although chemotherapy is commonly used as the primary treatment for a substantial number of TNBC patients, it is often accompanied by drug resistance and frequent tumor recurrence. Urgent efforts are needed to identify novel molecular targets specific to TNBC and develop effective therapies to combat this aggressive disease. The ultimate objective is to discover treatments capable of overcoming drug resistance and improving the overall survival of patients with TNBC. Methods: Immunohistochemistry was performed to examine the expression of HER3 in TNBC samples. Western blots were used to assess protein expression and activation. Cell proliferation and viability were determined by cell growth (MTS) assays. TCGA databases were analyzed to correlate HER3 mRNA expression with the clinical outcomes of TNBC patients. Specific shRNA was used to knockdown HER3 expression. LIVE/DEAD Cell Imaging was to detect live and dead cells. Orthotopic tumor models were established in nude mice to determine the capability of TNBC cells forming tumors and to test if our newly developed anti-HER3 monoclonal antibody (mAb) 4A7 could potentiate the antitumor activity of paclitaxel in vivo. Results: The chemo-resistant subline HCC1806-TR was obtained by subjecting TNBC HCC1806 cells to prolonged treatment with paclitaxel. In comparison to the parental cell line HCC1806-P, HCC1806-TR exhibited enhanced HER3 expression and activation. It is noteworthy that approximately half of the tested TNBC specimens and cell lines displayed elevated expression of HER3. Analyzing TCGA databases revealed that TNBC patients with high levels of HER3 mRNA expression in their tumors had significantly poorer overall survival (OS) and relapse-free survival (RFS) compared to those with low HER3 expression. Specifically knockdown of HER3 markedly inhibited TNBC cell proliferation and mammosphere formation in vitro and tumor growth in vivo. Blockade of HER3 signaling with our mAb (4A7) in combination with paclitaxel exerted significant antitumor activity against TNBC in vitro and in vivo. Conclusions: Our data demonstrate that increased HER3 is an effective therapeutic target for TNBC and our anti-HER3 mAb (4A7) may enhance the efficacy of paclitaxel in TNBC. Keywords: HER3, Anbibody, Chemotherapy, Triple Negative Breast Cancer Citation Format: Hui Lyu, Sanbao Ruan, Congcong Tan, Ann Thor, Bolin Liu. Targeting of HER3 potentiates the antitumor activity of paclitaxel against triple negative breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-24-08.

Abstract PO4-16-08: Prognostic factors for tumor recurrence after breast-conserving and radiotherapy treatment for early invasive breast cancer: ten years of results in a referral center in Mexico City

Abstract Background: Breast cancer is the most common malignancy in the world, reporting more than 2 million new cases in 2020. In early stages, patients undergo primary surgery. Breast-conserving surgery (BCS) has generally been accepted as a treatment for invasive breast cancer, findings at 20 years still show that lumpectomy and breast irradiation, as compared with mastectomy, have no significant difference in overall survival among the treatment groups. Approximately 10-15% of patients will develop local or systemic recurrence in 5 to 10 years. Factors such as young age (< 45 years), close/positive margins, no breast radiation, are associated with ipsilateral breast tumor recurrence. High grade has been related to distant metastasis. The mortality trend is upward due to a higher incidence of the disease and earlier detection. Methods: This is an observational and retrospective cohort study, which included patients with early breast cancer, who were treated with conserving surgery and received radiotherapy, at the Breast Oncology Service at the UMAE Gineco 4 "Luis Castelazo Ayala" during the period from January 2012 to December 2022. The aim of our study was to describe the prognostic factors associated with disease-free survival (DFS) and overall survival (OS) in patients with localized breast cancer treated with BCS. DFS was defined as time from surgery to recurrence event (local recurrence, distant recurrence, contralateral breast cancer, second primary cancer, or death from any cause) whichever occurred first. For statistical analysis, Kaplan Meier and Log-rank methods were used for survival analysis. Cox proportional hazard model was used for multivariate analysis. Results: We included 399 patients, the median follow-up was 88 months (95%CI 86-91). Median age was 59 years. The most common pathological stage was IA in 44.9%, the predominant immunophenotype was luminal A in 56.1% of patients, follow by luminal B in 19.3% and 13% were triple negative. Management of axilla with sentinel node biopsy occurred in 50.1% and 49.9% underwent to lymph node dissection. Regarding surgery outcomes 40.4% of the patients required widening of the margins, 5% of the patients remained with close surgical margins ≤2 mm, 7.5% had complications associated with the surgery, and none related death ocurred. All patients received adjuvant radiotherapy, the median time to initiation was 32 weeks (range 3-70) and 65.4% received adjuvant chemotherapy. Recurrence events occurred in 15.5% of patients, local 2.8%, systemic 8.8%, contralateral breast cancer 1.7%, and second primary 2.2%. Estimated disease-free survival at 5 and 10 years were 86.6% and 74.2%, respectively. In the multivariate analysis independent prognostic factors for DFS were: lobular histology HR 2.95 (95%IC 1.5-5.7), tumor size ≥ 2cm HR 1.95 (95%IC 1.1-3.6), close surgical margins HR 2.62 (95%IC 1-6.6), and ER low expression (1-10%) HR 4.39 (95%CI: 1.6-12.4). Estimated OS at 5 and 10 years for patients who experienced recurrence were 78.4% and 47.4% and for patients without recurrence were 96.8% and 93.5%, respectively (adjusted HR: 10.4, 95%CI: 5.2-20.6). Conclusion: These results suggest that patients with early breast cancer treated with conserving surgery and radiotherapy with risk factors such as lobular carcinoma, tumor size ≥2cm, close margins, and low expression of estrogen receptors have a high risk of recurrence and significantly decreased overall survival at 5 and 10 years. Citation Format: Nayeli Ortega-Avila, Yuly A. Remolina-Bonilla, Janett Caballero-Jasso. Prognostic factors for tumor recurrence after breast-conserving and radiotherapy treatment for early invasive breast cancer: ten years of results in a referral center in Mexico City [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-16-08.

Abstract PO2-01-13: Clinico-Pathological and Molecular Characterization of Early Hormone Receptor-Positive Breast Cancer in Young Women

Abstract Introduction Premenopausal women diagnosed with hormone receptor-positive (HR+)/HER2-negative (HER2-) early breast cancer (EBC) face a significantly higher risk of cancer recurrence and mortality compared to older women, particularly those diagnosed under the age of 40. The underlying causes behind this disparity remain largely unknown. Material and methods We retrospectively select tumour samples from patients (pts) diagnosed with HR+/HER2- EBC at Hospital Clinic (Barcelona, Spain) from May 2014 to March 2020 who had a PAM50/Prosigna assay (Veracyte) previously performed. This assay examines the expression of 50 genes involved in important breast cancer signaling pathways, as well as the intrinsic subtypes (IS) and the Risk of Recurrence (ROR) score. Our primary objective was to compare the distinct clinicopathological and molecular characteristics of HR+/HER2- EBC between two age groups: patients under 40 years old (Young EBC or YEBC) and those 40 years old and above (Older EBC or OEBC). Disease-free survival (DFS) was defined as the time between diagnosis and the first recurrence. Comparisons between groups were carried out using chi-square tests (categorical variables). Additionally, we performed a two-class unpaired Significance Analysis of Microarrays (SAM) with a false discovery rate (FDR) less than 5% to identify genes with significantly different expression between YEBC and OEBC. The statistical significance level was set at less than 0.05. Results A total of 441 tumor samples from 420 patients were included in the analysis, with 5% (22/441) corresponding to YEBC. With a median follow-up of 64.5 months, there were 20 breast cancer (BC) recurrences (4.8%), 12 second cancers (2.9%) and 5 BC-related deaths (1.2%), all occurring in the OEBC group. Table 1 provides an overview of the main clinico-pathological and molecular characteristics. YEBC tended to have larger tumors, with 45.5% (10/22) measuring over 2 cm compared to 36.1% (151/419) in OEBC (p=0.376). YEBC also had a higher proportion of grade 3 tumors (18.18% versus 3.1% in OEBC, p=0.418) and lower expression of estrogen receptor (ER) as determined by immunohistochemistry (mean of 72.28% vs 88.36%, p=0.004). Regarding the PAM50 IS, there was a difference observed between YEBC and OEBC (p < 0.001). Specifically, YEBC patients exhibited a tendency towards a higher proportion of Luminal B tumors (54.6% versus 38.9% in OEBC, p=0.144), as well as non-Luminal subtypes such as Basal-like (18.2% versus 0.95% in OEBC, p< 0.001) and HER2E (4.6% versus 0.7% in OEBC, p=0.186). YEBC tended to have higher ROR (p=0.167), and to receive chemotherapy in a higher proportion, especially in the intermediate-risk group (p=0.004). In YEBC tumours, SAM analysis (p < 0.05) showed an overexpression of genes mainly related with proliferation (i.e., RRM2, MELK, MIK67), cell cycle progression (i.e., KNTC2, CDC20, MYBL2) and apoptosis inhibition (i.e., BIRC5). In OEBC there were an overexpression of genes related with the oestrogen receptor-signalling pathway (i.e., ESR1, NAT1, FOXA1, PGR). Luminal B tumours in YEBC showed an upregulation of genes related to proliferation, migration, and poor prognosis (i.e., KRT17, KRT5) compared to OEBC. However, since there were no recurrences in the YEBC group, differences in terms of DFS between the groups could not be calculated. Principio del formulario Final del formulario Conclusions YEBC exhibited a more advanced stage and a more aggressive intrinsic phenotype compared to OEBC. Additionally, these tumors showed a tendency to upregulate genes involved in proliferation, cell cycle progression, and survival, while downregulating genes related to hormone signaling pathways. These molecular characteristics may help explain the worse prognosis of YEBC compared to OEBC. However, further research is necessary to delve into the differential genomic characteristics that contribute to the unfavorable prognosis observed in patients diagnosed with HR+ EBC before the age of 40. Key clinical and molecular features in 441 biopsies Citation Format: Francisco Javier Muñoz-Carrillo, José Antonio Sola, Carme Crous, Esther Sanfeliu, Isabel Garcia-Fructuoso, Elia Seguí, Teresa Gorría, Raquel Gómez-Bravo, Barbara Adamo, Tomás Pascual, Olga Martínez-Sáez, Francesco Schettini, Pablo Rivera, Rosalía Cayuela, Montserrat Muñoz, Núria Chic, Maria Vidal. Clinico-Pathological and Molecular Characterization of Early Hormone Receptor-Positive Breast Cancer in Young Women [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-01-13.

Abstract PO2-17-03: Patient reported outcomes (PROs) and survival with toremifene versus aromatase inhibitors (AI) in patients with moderate/high-risk premenopausal hormone receptor (HR)-positive breast cancer: A real-world study

Abstract Background: The selective estrogen receptor modulator (SERM) toremifene, a synthetic analogue of tamoxifen, has shown similar efficacy to tamoxifen in patients with HR-positive breast cancer and is widely used in China for the treatment of premenopausal women with breast cancer. Multiple studies have confirmed the benefit of ovarian function suppression (OFS) combined with AI and SERMs in premenopausal women with HR-positive breast cancer. However, to date, there are no data comparing the efficacy and safety of toremifene plus OFS versus AI plus OFS. In this real-world study, we compared PROs and survival with toremifene or AI combined with OFS in patients with moderate/high-risk premenopausal HR-positive breast cancer. Methods: We enrolled premenopausal female patients with HR-positive, moderate/high-risk breast cancer who received OFS combined with toremifene or AI between January 1, 2010 and December 31, 2017 at the Breast Cancer Center of Sun Yat-sen Memorial Hospital. The primary endpoint was PROs, which were collected from January 1 to March 31, 2023, including the SF-36 and five-level EuroQol five-dimensional (EQ-5D-5L) questionnaires. Disease-free-survival (DFS) and safety were secondary endpoints. Associations between treatment group and SF-36 scores were evaluated using a Student’s t test and between treatment group and EQ-5D-5L scores using nonparametric tests. DFS was assessed using the Kaplan–Meier method and Cox regression. Results: A total of 392 patients were enrolled; 171 (43.6%) received toremifene and 221 (56.4%) received AI. Mean ± standard deviation scores for the role physical and general health dimensions of SF-36 were higher in the toremifene group versus the AI group (7.44±1.21 vs 7.15±1.48, P=0.034 and 22.90±3.95 vs 21.78±4.33, P=0.009, respectively). Scores on the anxiety/depression (AD) dimension of EQ-5D-5L were significantly different between the toremifene and AI treatment groups (mean rank: 184.14 vs 206.07, P=0.038); ‘no problems’ was selected by 49.7% and 37.1% of patients in the toremifene and AI groups, respectively. There were no significant differences in the other dimensions of SF-36 and EQ-5D-5L between the toremifene and AI groups (P>0.05). Similar estimated 5- and 8-year DFS rates were reported for the toremifene and AI groups; 96.5% (95% CI: 93.7-99.2) and 91.9% (95% CI: 88.2-95.5), and 87.4% (95% CI: 81.1-93.8) and 87.8% (95% CI: 81.1-94.4), respectively, and the hazard ratio for DFS was 0.75 (95% CI: 0.38-1.46), P=0.39. DFS was also comparable in the two treatment groups when stratified by HER2 status, age (≤40y vs >40y) and estrogen receptor expression level (≤20% vs >20%). Adverse event rates were generally similar in the two treatment groups, except for a higher rate of endometrial thickening (17.5% vs 1.8%, p< 0.001) and a lower rate of morning stiffness (7.6% vs 14.5%, p< 0.001) in the toremifene versus the AI group. Conclusion: Patients who received toremifene plus OFS had better role physical and general health dimensions on SF-36 and AD dimensions of EQ-5D-5L than those receiving AI plus OFS. There were no significant differences in 5- or 8-year DFS between the toremifene and AI groups. Both treatments were generally well tolerated. Citation Format: Yaping Yang, Fengxia Gan, Wenqian Yang, Yuan Xia, Qiang Liu, Chang Gong. Patient reported outcomes (PROs) and survival with toremifene versus aromatase inhibitors (AI) in patients with moderate/high-risk premenopausal hormone receptor (HR)-positive breast cancer: A real-world study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-17-03.

Abstract PO1-01-13: Clinical characterization, prognostic and predictive values of HER2-low in early breast cancer in the PALLAS trial

Abstract Background: Low levels of HER2 expression (HER2-low) have recently emerged as a therapeutic target in patients (pts) with breast cancer (BC). The aim of this study was to evaluate clinical and demographic variables associated with HER2 expression, as well as the value of HER2-low as a prognostic and predictive biomarker for palbociclib benefit in pts enrolled in the PALLAS trial. Methods: The phase III PALLAS trial investigated the addition of palbociclib to adjuvant endocrine therapy (ET) in pts with stage II-III hormone receptor-positive BC. The aims of this analysis are (1) to assess the association between the presence of low levels of HER2 expression with demographic and clinicopathological parameters, (2) to test the prognostic value of HER2-low status on invasive disease-free survival (IDFS), distant relapse-free survival (DRFS), and overall survival (OS) and (3) to assess the value of HER2 expression as a predictive biomarker of response to palbociclib. HER2-low was defined as HER2 immunohistochemistry (IHC) 1+ or IHC 2+ with negative in situ hybridization; all pathologic evaluation was performed locally. Pts with HER2-0 and Her2-low BC were included in this analysis; those with HER2-positive BC or missing HER2 status were excluded. Association of HER2 with other baseline covariates were tested with Chi-squared tests. Prognostic and predictive power of HER2 were assessed with Cox Models. Multivariable models included age, T-stage, N-stage, grade and progesterone receptor (PR) expression. Hazard ratios (HR) and 95% Confidence intervals (CI) are reported. Results: From the original PALLAS intention-to-treat population (N = 5,753), 5304 pts (92.2%) were included in this analysis. Among these, 2,254 pts (42.5%) were classified as HER2 IHC 0 (HER2-0) and 3,050 (57.5%) as HER2-low (1,838 with IHC 1+ and 1,212 with IHC 2+). For this analysis, median follow-up was 59.8 months. Compared to HER2-0, pts with HER2-low tumors had statistically higher estrogen receptor expression levels (mean expression 89.2% vs 88.2%, p = 0.019), lower PR expression levels (65.9% vs 68.2%, p = 0.007). Importantly, HER2-low status varied significantly across 21 participating countries (range 16.7% to 75.6%; p< 0.001) and was more frequent in pts enrolled in North America (63.1%) than in Europe (53.4%) and other regions (53.4%) (p < 0.001). No differences in HER2 expression were observed according to anatomic stage, T-stage, N-stage, histological grade, age, menopausal status, primary surgery type, prior radiation, prior chemotherapy, or baseline performance status. There were no statistically significant differences in IDFS, DRFS or OS according to HER2 status in univariate or multivariable Cox models (prognostic value, HR provided in the Table). There was no significant interaction between the HER2 status and the benefit to palbociclib in IDFS, DRFS or OS (Table). Similar results were obtained when HER2-0 was compared to HER2 1+ and HER2 2+ separately. Conclusions: In this large, prospective and international cohort, no differences were observed in clinical parameters, prognosis, or differential benefit from palbociclib (predictive value) between HER2-0 and HER2-low tumors. Significant geographic variability was observed in the prevalence of HER2-low status, suggesting a high degree of variation in pathologic assessment of HER2 expression without impact on outcomes. Support: AFT, Abbvie Pfizer; Clinicaltrials.gov: NCT02513394 https://acknowledgments.alliancefound.org Citation Format: Guilherme Nader-Marta, Christian F. Singer, Dominik Hlauschek, Angela DeMichele, Paolo Tarantino, Georg Pfeiler, Miguel Martín, Justin Balko, Zbigniew Nowecki, Marija Balic, Adam Brufsky, Arlene Chan, Patrick G. Morris, Tufia Haddad, Sibylle Loibl, Yuan Liu, Lidija Sölkner, Christian Fesl, Erica Mayer, Michael Gnant. Clinical characterization, prognostic and predictive values of HER2-low in early breast cancer in the PALLAS trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-01-13.

Abstract PO5-07-07: The biological basis of breast MRI background parenchymal enhancement in women with high breast cancer risk

Abstract Introduction: The amount and degree of the fibroglandular tissue (FGT) enhancement on breast MRI, known as background parenchymal enhancement (BPE), is an emerging marker of breast cancer risk. Higher qualitative and quantitative BPE levels have been shown to correlate with both future risk of initial breast cancer diagnosis and breast cancer recurrence after treatment. Furthermore, adjuvant and preventative therapies such as radiation and endocrine therapy have been shown to lower BPE in many women, potentially serving as a marker of treatment efficacy. However, the biological basis of BPE remains unclear and elucidation of this mechanism could identify novel targeted prevention strategies. The goal of this study was to assess the association of BPE levels with markers of inflammation, vascularity, proliferation, and estrogen sensitivity in a cohort of high-risk women. Materials and Methods: In this IRB-approved retrospective study, we identified asymptomatic high-risk women who underwent at least one dynamic contrast-enhanced (DCE) breast MRI within one year of prophylactic bilateral mastectomy. Qualitative BPE assessments were obtained from clinical reports. Quantitative BPE measures were obtained using in-house semi-automated software: whole breast FGT was first segmented on pre-contrast images, percent enhancement (PE) was calculated for each voxel as (S1-S0)/S0 × 100%, where S0 and S1 are pre- and early post-contrast signal intensity, respectively, and quantitative BPE was then defined as the mean PE of the FGT. Additionally, the BPE volume ratio was calculated as the fraction of FGT that had a PE >50%. Histopathology markers of inflammation (COX-2), vascularity (VEGF), proliferation (Ki-67), and estrogen receptor status (ER) were prospectively measured on archived mastectomy specimens of each breast. BPE metrics were correlated with histopathological markers using Spearman’s rank correlation, with and without adjustment by menopausal status of the patient. All tests were based on generalized estimating equations models to account for the non-independence of the two breasts per patient. A p-value < 0.05 was considered significant. Results: We identified 56 women (median age: 39; range: 26-63 years) for this study, of which 39% were post-menopausal (N=22). Distribution of qualitative BPE levels were 41% minimal (N=23), 29% mild (N=16), 18% moderate (N=10), and 12% marked (N=7). Qualitative BPE and quantitative BPE markers were moderately positively correlated (r=0.37-0.54, p< 0.01). Table 1 lists the correlations between BPE metrics and histopathology markers. After adjusting for menopausal status, qualitative BPE was positively associated with ER (r=0.27, p=0.02) and VEGF (r=0.24, p< 0.01; r=0.21, p=0.02 adjusted). Quantitative BPE and BPE volume ratio were both positively correlated with VEGF (p< 0.04) and negatively correlated with COX2 (p< 0.05). No significant associations were observed between BPE and Ki-67. Discussion: Our study suggests that increased BPE on MRI positively correlates with increased vascularity and higher estrogen receptor expression but not inflammation or proliferation within normal breast tissue in high-risk women. These findings, along with established associations between BPE and cancer risk, could be useful to select and assess efficacy of targeted preventative treatments. Table. Spearman rank correlations between BPE metrics and histopathological markers. Citation Format: Pegah Khoshpouri, Anum Kazerouni, Sana Parsian, Daniel Hippe, Olivia Walsh, Lisa Koch, Savannah Partridge, Habib Rahbar. The biological basis of breast MRI background parenchymal enhancement in women with high breast cancer risk [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-07-07.

Abstract PO5-23-08: Adenylosuccinate lyase is essential for proliferation and mitochondrial function of endocrine therapy resistant breast cancer cells

Abstract Eighty percent of breast cancers express estrogen receptor alpha (ERα, ESR1) at the time of diagnosis. Endocrine therapy (ET) is the standard treatment that either block estrogen mediated ER activation (such as tamoxifen, fulvestrant) or suppress estrogen synthesis (such as exemestane, letrozole, or anastrozole). While ET is initially effective, emergence of ET-resistance is common and possess a major clinical challenge. Hence, there is an ongoing need to develop new treatments for ET-resistant-ERα positive breast cancer. In this study we investigated the role of adenylosuccinate lyase (ADSL), an enzyme of the de-novo purine biosynthesis pathway as a potential target of ET-resistant breast cancer. The protein level of ADSL in two independent ET-resistant cell line model LCC9 and T47D-4HT cells were significantly higher in comparison to its parental ET-sensitive cell lines, MCF7 and T47D cells, respectively. Transient knockdown of ADSL using two independent siRNA in both LCC9 and T47D-4HT cells results in a significant decrease of cell growth, colony, and spheroid formation. Notably, reduced ADSL levels in LCC9 cells prevented the cells from progressing from G1 to S phase of cell cycle with concurrent elevation of cyclin D1/D3, CDK2/4, and cyclin E. On the other hand, in T47D-4HT cells, ADSL reduction caused cells to accumulate in S-phase of cell cycle and showed lower levels of total cyclin D1 protein. Mechanistically, in LCC9 cells (but not in T47D-4HT cells), ADSL depletion induced DNA replication stress which activates (phosphorylate) ataxia-telangiectasia-mutated-and-Rad3-related kinase (ATR) and its major downstream effector checkpoint kinase 1 (Chk1) that in turn failed to de-phosphorylate the inhibitory-phospho-groups of cyclin-dependent kinase 2 (CDK2). In addition, ADSL depletion perturbed the mitochondrial function in both LCC9 and T47D-4HT cells. Oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) was lower in both the cells along with the mitochondrial membrane potential. Pertinently, lower concentration of AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside), a product of ADSL enzyme function, partially rescued the cell growth and restored mitochondrial membrane potential in ADSL-depleted LCC9 cells. To further understand the global effects of ADSL depletion we performed RNA-sequencing of LCC9 and T47D-4HT cells after ADSL depletion and compared with respective control siRNA transfected cells followed by gene set enrichment analysis. Intriguingly, diverse effect was observed in LCC9 and T47D-4HT cells as very few genes were found to be commonly regulated between these two cell lines. Analysis of clinical data sets revealed high level of ADSL transcript was associated with adverse progression free survival and overall survival in breast cancer patients treated with endocrine therapies. Overall, our findings demonstrate that ADSL-mediated de novo purine synthesis is critical for cellular growth, proliferation, and mitochondrial function of endocrine therapy-resistant breast cancer cells. Therefore, targeting ADSL is a novel potential therapeutic approach for ERα positive ET- resistant breast cancer. Citation Format: Anil Yadav, Lu Jin, Robert Clarke, Surojeet Sengupta. Adenylosuccinate lyase is essential for proliferation and mitochondrial function of endocrine therapy resistant breast cancer cells [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-23-08.

Abstract PO1-25-08: Evaluating the role of CDK4/6 inhibition on STAT3 activation in a transgenic mouse model of HER2-positive breast cancer

Abstract Background: The human epidermal growth factor receptor 2 (HER2) is a receptor tyrosine kinase overexpressed in approximately 20-25% of breast cancers with varying biological differences according to hormone receptor (HR) positive status. Combination of chemotherapy with dual HER2 blockade and endocrine therapy (adjuvant) or CDK4/6 inhibitor (CDK4/6i) therapy (metastatic) is standard of care for HER2-positive/HR-positive breast cancer. However, de-escalation of chemotherapy remains of significant interest given associated toxicities and, as a result, alternative therapeutic strategies are needed. One such strategy is targeting the signal transducer and activator of transcription 3 (STAT3) which is constitutively activated in the HER-2 positive setting. Moreover, there is preclinical evidence to suggest that phosphorylated STAT3 (pSTAT3) induces overexpression of cyclin D1 (CCND1), which along with CDK4 may mediate resistance to targeted therapy for HER2-positive breast cancer. However, it is unclear if pSTAT3 plays a significant role in tumorigenesis or the development of resistance to therapy in HER2-positive disease. We aim to evaluate the effect of CDK4/6i therapy with palbociclib on tumor growth in an inducible transgenic HER2-positive mouse model and the impact on pSTAT3 and cyclin D1 levels. Methods: Using an inducible transgenic mouse mammary tumor virus (MMTV) model of HER2-positive breast cancer, we evaluated STAT3 phosphorylation in tumors driven by HER2 expression in addition to the impact of CDK4/6 inhibition with palbociclib on tumorigenesis and pSTAT3 activation. To model tumor recurrence, doxycycline was withdrawn from tumor bearing mice and tumor regression was observed. Subsequently, the mice developed recurrent mammary tumors. Given recurrent tumors in this model are driven by a HER2-independent mechanism, we examined expression of cell cycle proteins together with STAT3 phosphorylation to determine association with recurrence. Result: In addition to expressing HER2, the primary tumors expressed estrogen receptor (ERα), Rb, cyclin D1, and CDK4/6 proteins. STAT3 phosphorylation was also observed. Treatment with palbociclib decreased Rb phosphorylation and decreased tumor growth compared to vehicle treated mice (%TGI 79.37% after 21 days). Furthermore, pSTAT3 levels were not altered with palbociclib therapy. When recurrent tumors were analyzed, they lacked HER2 expression but expressed cyclin D1 and CDK4/6 supporting that tumor growth is driven by cyclin D1/CDK4 pathway. Recurrent tumors also demonstrated pSTAT3 despite lack of HER2 expression suggesting that STAT3 phosphorylation in the recurrent tumors is mediated by an alternative mechanism, potentially the CDK4/6 pathway. Conclusion: We demonstrate STAT3 activation in a mouse model of HER2 driven breast cancer and show persistent activation in recurrent tumors lacking HER2 expression rendering them resistant to HER2-targeted therapy. We also demonstrate the anti-tumor effect of palbociclib in primary tumors with HER2-dependent proliferation. Taken together, our findings suggest that pSTAT3 is a viable therapeutic target and provides the rationale for combination therapy with CDK4/6 inhibition using palbociclib and STAT3 inhibition with a novel STAT3 inhibitor in HER2-positive breast cancer. This therapeutic approach may represent a potential chemotherapy de-escalation strategy. Citation Format: Taiwo Adesoye, Linjie Luo, Tuyen Bui, Serena Kim, Hannah Wingate, Debu Tripathy, Kelly Hunt, Khandan Keyomarsi. Evaluating the role of CDK4/6 inhibition on STAT3 activation in a transgenic mouse model of HER2-positive breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-25-08.

Abstract PO1-03-09: Transcriptomic profiling of ER-negative and ER-low, HER2-negative breast cancer and its implications on immune regulation

Abstract Background: The recommended cut-off of < 1% positive cells to define estrogen receptor (ER) negative status in breast cancer (BC) is highly debated. Few data exist on transcriptomic features of ER-low BC, suggesting no major differences vs ER-neg. Among HER2-negative BCs, we compared gene-expression profiling (including PAM50 intrinsic subtyping) according to ER status (ER-neg: 0% vs. ER-low: 1-9%) and assessed its impact on Tumor-infiltrating lymphocytes (TILs) levels. Methods: Across two cancer centers, stage I-III HER2-negative BCs FFPE samples were reviewed for ER status. All ER-low (ER 1-9%) samples were identified and a cohort of ER-neg BC samples, matched for age and stage, was also retrieved. A small cohort of pts with intermediate ER expression (ER-int: 10-50%) was included as a control cohort. Expression of 776 BC–related genes was evaluated by nCounter® (Breast Cancer 360TM Panel) and intrinsic molecular subtyping was determined using the PAM50 subtype predictor. A False Discovery Rate (FDR) corrected unpaired two-class SAM was used to identify genes differentially expressed in different subgroups. TILs were evaluated on archival H&E slides following guidelines. Results: Of 116 stage I-III HER2-neg BC pts included, 39 had ER-neg BC, 65 had ER-low BC, and 12 had ER-int disease. PAM50 intrinsic subtype distribution was similar in ER-neg and ER-low BCs, (with an enrichment in basal-like tumors), while both subgroups differed significantly from ER-int samples (Table). As compared to ER-neg tumors, ER-low BCs showed significantly higher expression of GATA3 gene and lower expression of EDN1 and PROM1 genes by SAM analysis (FDR< 5%); however, when the analysis was limited to PAM50 basal-like tumors (N=77) we only identified two genes that were downregulated in ER-low BCs (EDN1, PROM1) as compared to ER-neg BCs. On the contrary, significant differences in transcriptomic regulation were observed between ER-low and ER-int BCs, with ER-low BCs showing significantly higher expression of 53 genes and lower expression of 398 genes, as compared to ER-int (SAM analysis FDR< 5%). We previously reported similar TIL levels in ER-low and ER-neg tumors. In both ER-low and ER-int BCs, PAM50 basal-like subtype was associated with significantly higher TILs: median TIL levels 20 (range 0-80) and 6 (range 1-40) for PAM50 Basal-like BCs versus other PAM50 subtypes respectively in ER-low samples (p< 0.001); median TIL levels 53 (range 25-80) and 5 (range 0-10) for PAM50 Basal-like BCs versus other PAM50 subtypes respectively in ER-int samples (p=0.036). No significant difference in TIL levels according to PAM50 subtyping were observed in ER-neg tumors. No significant difference in mRNA levels for PD-1 (PDCD1) and PD-L1 (CD274) genes was observed between ER-low and ER-neg tumors. Conclusions: Among patients with HER2-neg BC, gene-expression profiling is similar in ER-neg (i.e., < 1%) vs. ER-low tumors with a high prevalence of PAM50 Basal-like tumors and few differentially expressed genes. In both ER-low and ER-int HER2-neg BCs, PAM50 Basal-like subtype is also associated with higher TIL levels. Our results strongly indicate that HER2-neg/ER-low BCs and HER2-neg/ER-neg BCs are similar biological entities, thus further supporting the use of similar treatments in patients with early-stage ER-low and triple-negative BC, including immune checkpoint inhibitors. PAM50 intrinsic subtype distribution according to ER levels Citation Format: Gaia Griguolo, Claudio Vernieri, Davide Massa, Lorenzo Nicolè, Claudia Pinato, Federica Miglietta, Andrea Vingiani, Silvia Brich, Riccardo Lobefaro, Francesca Schiavi, Matteo Fassan, Giancarlo Pruneri, Valentina Guarneri, Maria Vittoria Dieci. Transcriptomic profiling of ER-negative and ER-low, HER2-negative breast cancer and its implications on immune regulation [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-03-09.

Association Between Polymorphisms in DNA Damage Repair Pathway Genes and Female Breast Cancer Risk.

Breast cancer risk have been discussed to be associated with polymorphisms in genes as well as abnormal DNA damage repair function. This study aims to assess the relationship between genes single nucleotide polymorphisms (SNPs) related to DNA damage repair and female breast cancer risk in Chinese population. A case-control study containing 400 patients and 400 healthy controls was conducted. Genotype was identified using the sequence MassARRAY method and expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor-2 (HER-2) in tumor tissues was analyzed by immunohistochemistry assay. The results revealed that ATR rs13091637 decreased breast cancer risk influenced by ER, PR (CT/TT vs. CC: adjusted odds ratio [OR] = 1.54, 95% confidence interval [CI]: 1.04-2.27, p = 0.032; CT/TT vs. CC: adjusted OR = 1.63, 95%CI: 1.14-2.35, p = 0.008) expression. Stratified analysis revealed that PALB2 rs16940342 increased breast cancer risk in response to menstrual status (AG/GG vs. AA: adjusted OR = 1.72, 95%CI: 1.13-2.62, p = 0.011) and age of menarche (AG/GG vs. AA: adjusted OR = 1.54, 95%CI: 1.03-2.31, p = 0.037), whereas ATM rs611646 and Ku70 rs132793 were associated with reduced breast cancer risk influenced by menarche (GA/AA vs. GG: adjusted OR = 0.50, 95%CI: 0.30-0.95, p = 0.033). In a summary, PALB2 rs16940342, ATR rs13091637, ATM rs611646, and Ku70 rs132793 were associated with breast cancer risk.

Estrogenic re-mapping of the metabolic response to an energy deficit

Endothermy is an adaptation that can be traced back hundreds of millions of years and is critical for nearly every aspect of mammalian biology. Despite the advantages associated with a stable internal temperature, endothermy is energetically expensive. To conserve energy when food is scarce, mice have evolved the ability to reversibly enter a regulated state of hypothermia and hypometabolism, known as torpor. We have found that circulating 17β-estradiol, a potent estrogen, inhibits fasting-induced torpor in ovariectomized female mice, yet the signaling mechanisms underlying this estrogenic re-mapping of the metabolic response to an energy deficit remain largely unknown. Recent studies have identified the medial preoptic area of the hypothalamus (MPO) as the central regulator of torpor. MPO neurons that express estrogen receptor alpha have been identified as central coordinators of torpor, and MPO neurons that are activated during torpor broadly express estrogen receptors, suggesting that circulating estrogens may directly modulate torpor-driving neurons in the MPO. To test the hypothesis that circulating estrogens inhibit torpor by acting directly on estrogen-sensitive neurons in the MPO, we delivered 17β-estradiol (E2) directly to the MPO before inducing torpor with a 48-hour fast. Surprisingly, we found that E2 delivered to the MPO was suffcient to inhibit fasting-induced torpor in gonad-intact, but not ovariectomized, female mice. These data demonstrate that E2 signaling in the MPO is insuffcient to inhibit torpor on its own and that there are likely MPO-independent nodes in the body that circulating estrogens act on to inhibit torpor. However, our data also demonstrate that E2 signaling in the MPO does play a role in tuning the torpor response when endogenous gonadal hormones are present, suggesting that the MPO can sense estrogens and engage the appropriate effector circuits to inhibit torpor in certain physiological contexts. Together, these data advance our understanding of how circulating estrogens inhibit torpor in mice — a critical step towards the broader goal of understanding how circulating estrogens influence energy expenditure, and how these pathways can be manipulated to improve metabolic health. NIH RO1 (R01AG066821) - "Estrogenic modulation of neural circuits that control temperature" AHA Predoctoral Fellowship (23PRE1019923) - Estrogenic modulation of hypothalamic neurons that control energy expenditure. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Endometrial Hormonal Receptor Expression and Blood Vessel Density in Abnormal Uterine Bleeding: A Cross-sectional Descriptive Study

Introduction: Abnormal uterine bleeding (AUB) is bleeding which is abnormal in amount, duration, frequency, and cyclicity and differs from the normal pattern. The aim of the study is to evaluate the expression of endometrial estrogen (ER) and progesterone receptor (PR) immunohistochemically and blood vessel density in AUB patients. Furthermore, we will correlate hormonal receptor expression and blood vessel density with various endometrial pathologies presenting with AUB. Materials and Methods: A cross-sectional study of 60 cases with clinical diagnosis of AUB, (30 cases of cyclical endometrium and 30 cases of hyperplasia/carcinoma) was done. Histological typing of endometrial lesions was done. Microvessel density (MVD) was calculated by counting the average number of blood vessels/10 HPFs. Evaluation of MVD was done on hematoxylin and eosin (H and E) stain and also reticulin stain which highlighted the basement membrane. Immunohistochemistry for steroid hormone receptors, ER and PR was done as per avidin-biotin technique with Diaminobenzidine as the chromogen. Carcangiu scoring system for semiquantitative analysis of ER/PR expression in endometrial samples was adopted. Results: There was a significant difference in microvessel density between different histopathology microscopic diagnoses (P < 0.05). The mean value of microvessel density on reticulin stain was significantly higher as compared to the mean value of MVD on H and E. A decrease of the hormonal receptor expression, ER and PR was observed in parallel with the decreased histological degree of differentiation, the lowest values occurring in the case of endometrioid Grade 3 carcinomas. Conclusion: Angiogenesis is significantly correlated with increasing severity of the lesion. The correlation of immunohistochemical findings with histologic grade can be useful in predicting biological behavior in patients.

Tipping the balance — the move of aging females towards higher ERβ:ERα ratio and away from estrogen mediated vascular protection

Objective: The menopausal transition, marked by the cessation of endogenous estrogen production, is a hallmark of vascular aging in women, as the vascular function radically declines in the years hereafter (Parker et al. 2010). Primarily based on animal and in-vitro studies (Novella et al. 2012; Novensà et al. 2011; Park et al. 2017) it has been hypothesized that this is linked to menopause-dependent changes in the balance between the two dominant estrogen receptors, ERα and ERβ; as previous studies suggest that ERα favors NO-bioavailability whereas ERβ mediates increases in oxidative stress. However, it remains unresolved how aging actually influences changes in the balance between ERα and ERβ in skeletal muscle of females and how changes are related to downstream protein targets such as eNOS and NADPH oxidases. Study design: We measured skeletal muscle protein expression of estrogen receptors, androgen receptors, eNOS, SOD2, GPX1, gp91phox/-NOX2 and NOX4 in 82 females ranging from 20-70 yrs. of age. For age comparisons, data from the muscle biopsies were grouped by 5-year intervals. Statistical analyses were conducted by on one-way ANOVA and Pearson’s product moment correlations Results: The ERβ:ERα ratio was significantly higher in the 65+ yrs. compared to all other groups (p<0.01) and correlation analysis revealed that the ERβ/ERα ratio increased with aging (p=0.02, R2=0.07). The 65+ yrs. group presented a lower eNOS expression (p<0.05) than the 20-54 yrs. groups and correlation analysis showed a decrease in eNOS expression with aging (p=0.0002 R2=0.16). Gp91phox/-NOX2 expression correlated with ERβ and the expression of gp91phox/NOX2 (p=<0.0001 R2=0.4) was lower in the three middle groups, 45-59 yrs., compared with both the younger and older groups (p<0.05). ERα correlated with the antioxidants SOD2 and GPX1 (p=0.0001 R2=0.18 and p=<0.0001 R2=0.21, respectively). Conclusions: This study is the first to show that skeletal muscle expression of ERβ:ERα increases with age and that the expression of eNOS in skeletal muscle declines as a function of age in females. Our data also provides indirect support for that aging is associated with a shift from a more prominent ERα coupled antioxidant effect, through - SOD2/GPX1 related mechanisms, towards a more pro-oxidant environment through an ERβ mediated upregulation of Gp91phox/-NOX2. This shift, combined with the observation of an age induced decline in eNOS expression, could be mechanisms underlying reduced NO bioavailability in aging females. Further analyses are ongoing to throw light in these mechanisms and additional studies are warranted to fully elucidate the mechanistic pathways involved. Funding The study was funded by The Danish Ministry of Culture Fund for Research in Sports, The Independent Research Fund Denmark, Eva and Henry Frænkel Memorial Fund, and the Toyota Foundation. The study is part of The Copenhagen Women Study for which fi- nancial support was provided by the University of Copenhagen Excellence Programme for Interdisciplinary Research. The study was also supported by The Danish Ministry of Culture: Sports Research. Financial support is greatly appreciated from the Aarhus University Research Foundation (AUFF); the Hartmann Foundation; the A.P. Møller Foundation; the Toyota-Fonden, Denmark; and the Augustinus Foundation and Team Denmark. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Toxicity of bisphenol S on human normal ovarian epithelial cells mediated by ERβ-MAPK signaling pathway

To investigate the effects of long-term(7 days and 14 days) bisphenol S(BPS) exposure on the ERβ-MAPK signaling pathway, hormone secretion phenotype and cell cycle in human normal ovarian epithelial cells IOSE 80 at actual human exposure level. Physiologically based pharmacokinetic model combined with BPS levels in the serum of women along the Yangtze River in China was used to determine the dosing concentrations of BPS, and vehicle control and 17 β-estradiol(E_2) control were used. Complete medium with corresponding concentrations(0, 6.79×10~(-6), 6.79×10~(-4), 6.79×10~(-2), 6.79 μmol/L BPS and 10 nmol/L E_2) was replaced every 2 days. mRNA expressions of estrogen receptor(ERβ and GPR30), key genes in MAPK signaling pathway(P38/JNK/ERK signaling pathway) and gonadotropin-releasing hormone-related genes(GnRH-I, GnRH-II and GnRH-R) were measured by qPCR. The ERβ-MAPK signaling pathway inhibitors were employed to detect the effect of long-term exposure to BPS on the cell cycle by flow cytometry. Dose-response relationship analysis was performed to calculate the benchmark does lower confidence limits. Compared to the vehicle control, after 7 days exposure to BPS, the ratio of G_2/M phase was significantly increased(P<0.05), and the mRNA expressions of GnRH-I, GnRH-II and GnRH-R were significantly decreased(P<0.05); after 14 days exposure to BPS, the mRNA expressions of ESR2, MAPK3, and MAPK9 were significantly increased(P<0.05), and the mRNA expressions of GnRH-II and GnRH-R were significantly decreased(P<0.05). The GnRH-II mRNA expression level of BPS treatment for 7 days; the G_0/G_1 phase ratio, MAPK3 and MAPK8 mRNA expression level of BPS exposure for 14 days; and the GnRH-I mRNA expression level after BPS treatment for 7 days and 14 days showed a good dose-response relationship but with poor fit. Long-term low-dose exposure to BPS may cause cell cycle arrest by activating the ERβ-MAPK signaling pathway, and may lead to changes in the hormone secretion of IOSE 80 cells.