Hormone-positive Breast Cancer Research Articles

Abstract ED08-02: Next generation therapeutics in hormone positive breast cancer: balancing efficacy and tolerability

Abstract The past several years have brought a wealth of new and emerging novel agents for the management of both early and advanced hormone repcetor positive breast cancer, including inhibitors of PIK3CA, mTOR, AKT, CDK4/6, PARP, as well as oral SERDs. These agents have significantly improved survival outcomes for many patients, but progress may come at the cost of specific and sometimes challeging side effects, whcih may threaten the ability to keep a patient on a therapy that is providing benefit. We will review a spectrum of agents, the expected side effect profiles, and strategies to mitigate toxicity and maximize therapeutic index. Citation Format: E. Mayer. Next generation therapeutics in hormone positive breast cancer: balancing efficacy and tolerability [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 ED08-02.

Abstract PO4-16-11: De-escalation of anthracyclines during adjuvant therapy based on Oncotype RS: A single institution experience in Mexico City

Abstract Introduction: In Mexico, hormone positive HER2 negative breast cancer is the most frequent subtype, accounting for 76.6% of cases. For patients undergoing local control management through surgery; adjuvant chemotherapy is usually followed depending on different risk factors. In order to avoid overtreatment, different genomic firms have been approved aiding in a more objective decision. One of these genomic firms is the Oncotype Recurrence score. The TAILORx and RxPONDER trials have provided guidance in determining which patients are candidates for chemotherapy depending on their menopausal status. However, it has not yet been determined whether patients requiring chemotherapy can receive an anthracycline-free regimen. In the Plan B clinical trial, a non-inferiority analysis was conducted on early-stage breast cancer patients who received anthracycline-based or non-anthracycline-based chemotherapy, with the non-anthracycline regimen being non-inferior, including patients with a RS > 25. We intend to reevaluate these findings in our Mexican population. Methods: We evaluated 217 patients with early stage hormone sensitive HER2 negative breast cancer who had an Oncotype Recurrence score (RS) result. This retrospective cohort study took place by analyzing electronic records from January 2011 to December 2017 with patients treated at the National Cancer Institute in Mexico City. We included patients 18 years of age or older, any sex with an Oncotype RS ≥ 16 in premenopausal patients or ≥ 26 in postmenopausal patients who received adjuvant chemotherapy with or without anthracyclines. Our primary endpoint was iDFS comparing TC vs AC-T. Overall survival was set as a secondary endpoint. Results: Of the 217 patients with an Oncotype recurrence score, only 46 patients received adjuvant chemotherapy of which 71.7% were premenopausal with a median age of 45 years. Stage II was the most common stage with 91.3% of the population, as well as ductal carcinoma with 82.6%. All patients had positive lymph nodes, 54.3% at least 1 lymph node. Most patients received AC-T adjuvant chemotherapy (60.9%), and only 39.1% received TC. Of the 46 patients analyzed, only 19.6% (9) had a recurrence upon follow-up (Table 1). Median time of follow up was 87.5 months. Difference in Disease free survival could not be established between patients receiving AC-T with 105 months (CI 95% 94.36-117.43 months) vs TC with 94.09 months (CI 95% 83.85-104.34 months, < p.918) (Figure 1). Overall survival did not have a statistical difference between both chemotherapy regimens, p< 0.649 (Figure 2A), when comparing Oncotype RS, overall survival was better in those with Oncotype OS < 26, p< 0.023 (Figure 2B). Discusion As described previously in the Plan B trial, TC was non inferior to the conventional adjuvant regimen of AC-T in Hormone positive HER2 negative early-stage breast cancer. Our results tend to show similar results when compared to the Plan B. An important aspect to our study was that 71.7% of our patients were premenopausal, where in the Plan B trial only 35% were premenopausal, considered a higher risk group of patients. Although a statical difference couldn´t be established due to our small sample size, in DFS or OS when comparing the chemotherapy regimen. Premenopausal patients with an Oncotype RS < 26 could receive an anthracycline free regimen, without impact in their overall survival. Larger prospective studies are necessary to assure this conclusion. Figure 1 DFS (TC vs AC-T) Figure 2 A and B Overall Survival Table 1 (Baseline characteristics) Citation Format: Carlos Arturo González Núñez, Paula Cabrera-Galeana, Juan Enrique Bargalló Rocha, Rafael Vazquez-Romo, Sergio Aguilar-Villanueva, Alexandra Garcilazo, Areli Velazquez-Martinez, Andrea Maliachi, Ruben Rodriguez, Esmeralda Romero-Bañuelos. De-escalation of anthracyclines during adjuvant therapy based on Oncotype RS: A single institution experience 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 PO4-16-11.

Abstract PO5-20-10: Treatment with CDK4/6 Inhibitor in a Patient with Metastatic Breast Cancer Causing Myelophthisis

Abstract Background: Symptomatic bone marrow metastasis causing myelophthisis is a rare manifestation of metastatic breast cancer, indicating a poor prognosis due to significant cytopenias. CDK4/6 inhibitors are first-line therapies for metastatic hormone-positive breast cancer but remain an unclear choice in breast cancer patients with significant cytopenias due to associated hematological adverse effects. We present a case of biopsy-proven hormone-positive breast cancer with bone marrow infiltration causing profound pancytopenia. CDK4/6 inhibitors were safely administered despite their cytopenic effects. Case Presentation: A 59-year-old female presented after an abnormal annual mammogram and biopsy showed calcifications stromal fibrosis, cyst formation, and usual ductal hyperplasia in the right upper outer quadrant. One month later, she presented to an outside hospital with gingival bleeding, epistaxis, progressive dyspnea on exertion, and generalized weakness. Labs showed severe anemia with a hemoglobin of 4.8 g/dL (baseline 12.1 g/dL), thrombocytopenia with platelets of 5 K/mm (baseline 215 K/mm), LDH of 879, reticulocyte count of 5%, and negative direct Coombs test. Peripheral smear showed no schistocytes, but showed nucleated RBCs, severely reduced platelets, and occasional giant platelets. The patient was treated for presumed ITP, and the presence of nucleated RBCs prompted bone marrow biopsy which confirmed metastatic invasive lobular carcinoma breast cancer (ER 90-95%, PR 90-95%, HER2 1+). She was discharged on letrozole 2.5 mg daily with close outpatient oncologic follow-up. One week later, she presented to our institution with persistent symptomatic anemia and thrombocytopenia. Inpatient systemic therapy was begun using dose-reduced Palbociclib (75mg) and letrozole with close CBC monitoring while also receiving packed red blood cells (goal >6.5) and platelet transfusions (goal >10). Repeat bone marrow biopsy showed extensive marrow fibrosis, but no significant hematopoietic elements. ADAMTS13 was 134%, ruling out TTP, and she was treated again for presumed ITP with dexamethasone and IVIG, Throughout the 4-week admission, her right breast mass decreased in size and she was discharged after completing 3 weeks of Palbociclib with biweekly outpatient transfusions. During follow-up, the patient’s hemoglobin and platelets slowly started to respond allowing her to become transfusion-independent and allowing dose escalation. Restaging scans 2 months after hospitalization showed an overall improvement of disease burden. The patient continued to do well for almost 18 months, however, later redeveloped visceral crisis and is responding to chemotherapy. Discussion: There is limited data on the management of breast cancer with bone marrow infiltration at presentation. A wide range of survival data in different case reports exists, ranging from 5 to 44 months. However, chemotherapy was used in these studies rather than CDK4/6 inhibitors. By far, cytopenias are the most concerning grade 3 and 4 side effect of Palbociclib. Data from the PALOMA-1 trial suggest that hematologic toxicities, specifically neutropenia, were different from those associated with cytotoxic chemotherapies and are more transient and reversible in nature. Studies have examined the in vitro mechanism of bone marrow suppression in Palbociclib versus cytotoxic chemotherapy, and its cytostatic effect on neutrophil precursors allows for hematological toxicities to be transient. With strong supportive care measures, patients in bone marrow visceral crisis can be safely treated with cytopenic CDK4/6 inhibitors. Citation Format: Nikita Dahake, Jordan Senchak, Jalil Nasibli, Jason Incorvati. Treatment with CDK4/6 Inhibitor in a Patient with Metastatic Breast Cancer Causing Myelophthisis [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 PO5-20-10.

Abstract PO3-18-04: MBRC-101: a novel antibody-drug conjugate (ADC) targeting the membrane-associated tyrosine kinase receptor EphA5 in breast cancer

Abstract Objectives: ADCs have emerged as a major advance in contemporary medical oncology. The receptor tyrosine kinase (RTK) EphA5 possesses the classical receptor kinase topology with an extracellular-binding domain, a single-pass transmembrane domain, and a cytoplasmic kinase domain. We have previously shown that EphA5 is highly expressed in non-small cell lung cancer and contributes to DNA-damage repair and radiation therapy resistance. Others have reported EphA5 expression in gastric, ovarian, and pancreatic cancers. Here, we investigated the expression of EphA5 in breast cancer (BC) and assessed EphA5 as a potential cancer-specific target using a novel ADC designated MBRC-101. Methods: MBRC-101 is composed of a humanized anti-EphA5 IgG1 kappa monoclonal antibody conjugated to the small molecule microtubule-disrupting agent monomethyl auristatin E (MMAE) via a protease cleavable valine-citrulline (vc) ThioBridge linker (ThioBridge™-Glu-[Val-Cit-PAB-MMAE] PEG [24u]). MBRC-101 averages a drug-to-antibody ratio (DAR)=4. The specificity profile of the anti-EphA5 monoclonal antibody was characterized using a Membrane Proteome Array (MPA). Receptor-mediated antibody internalization was determined by real-time live-cell analysis; cell killing assays used both live-cell analysis of cell confluence and the CellTiter-Glo® luminescent cell viability assay. Expression of EphA5 in archival human breast tumor tissue sections was evaluated by immunohistochemistry (IHC) using a commercial polyclonal antibody against human EphA5. In vivo efficacy studies used patient-derived xenograft (PDX) models of BC. Results: IHC demonstrated robust and selective EphA5 expression in 87% (20 of 23) of triple negative breast cancer (TNBC) and 88% (23 of 26) of hormone receptor-positive (HR+) patient tumors tested. EphA5 expression was not detected in adjacent, non-malignant breast tissue. Antibody-specificity profile testing showed that the anti-EphA5 antibody bound exclusively to EphA5 and did not cross-react with other members of the Eph receptor/ephrin ligand family. Binding of the anti-EphA5 antibody to EphA5 on the cell surface triggered rapid internalization and processing of the EphA5/antibody complex through the endosomal-lysosomal system. Consistently, MBRC-101 was cytotoxic to EphA5-expressing cells and its activity was concentration-dependent and commensurate to the levels of EphA5 on the cell surface. In PDX murine models of TNBC, once weekly administrations of intravenous (IV) MBRC-101 showed dose-dependent, robust, and reproducible anti-tumor activity in vivo. Partial tumor responses were observed at doses of 2.5 mg/Kg IV and complete and nearly complete tumor responses starting at 5 mg/Kg IV. Doses up to 10 mg/Kg IV were well-tolerated in tumor-bearing mice with no observable weight loss. Pre-clinical safety confirmed MBRC-101 is also well tolerated in rats and in cynomolgus monkeys. Conclusions: These results support EphA5 as a new and promising membrane-associated molecular target for the design and development of ADC-based therapies against hormone-positive breast cancer and TNBC and support the conduct of a Phase 1/1b study of MBRC-101 in patients with breast cancer. Citation Format: Fernanda Staquicini, Fenny Tang, Vanessa de Oliveira, Daniela Staquicini, Yongjian Wu, Kirstin Barnhart, J Kellogg Parsons, Wadih Arap, Isan Chen, Renata Pasqualini. MBRC-101: a novel antibody-drug conjugate (ADC) targeting the membrane-associated tyrosine kinase receptor EphA5 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 PO3-18-04.

Abstract PO5-20-09: LOCOREGIONAL MANAGEMENT OF DE NOVO STAGE IV HORMONE-POSITIVE BREAST CARCINOMA AFTER CDK 4/6 INHIBITOR TREATMENT

Abstract Systemic therapy remains the backbone for treatment of metastatic breast carcinoma. Locoregional treatment of the primary tumor remains controversial. While it has an established role in the palliative setting, its survival benefit remains unclear. The rationale behind locoregional approach is the reduction of tumor burden and the removal of cancer stem cells which may propagate the disease. In previous literature, hormone-positive breast cancer seems to be the best candidate for locoregional treatment in the presence of synchronous metastases. We present a case of a 43 year-old, female, with no known comorbidities, who sought consult due to note of a hard lump on her right breast. Core needle biopsy of the right breast mass was performed which showed invasive breast carcinoma, no special type, Nottingham histologic grade 2. On immunohistochemistry, tumor was ER +8, PR +8, Ki 67 90%, Her-2 neu negative. Baseline positron emission tomography/CT (PET/CT) scan showed hypermetabolic, heterogeneously-enhancing lobulated right breast mass, 3 × 6.7 × 7.7 cm, with smaller hypermetabolic adjacent nodules. There was also note of multiple enhancing, hypermetabolic lung and pleural nodules, and lymphadenopathies in the mediastinal, right axillary, right cardiophrenic and perigastric areas. Well-defined, hypermetabolic heterogeneously hypoenhancing masses were also seen in segments II and VII of the liver. There was also note of right-sided pleural effusion. Ultrasound-guided thoracentesis was done which turned positive for malignant cells on pleural fluid analysis. She underwent 4 cycles of chemotherapy with Doxorubicin and Paclitaxel. Reevaluation PET-CT scan revealed partial response. Patient was then started on Ribociclib plus Letrozole with ovarian function suppression for 18 months. On latest reevaluation PET/CT scan, there was no evidence of hypermetabolic metastatic disease, with demonstration of hypermetabolic activity only in the right breast. The patient then underwent right total mastectomy, with histopathologic findings of residual invasive carcinoma, Nottingham histologic grade 3, residual tumor size of 3.5 cm, with 95% tumor cellularity and lymphovascular invasion identified, ypT2. All surgical margins were negative for tumor. Currently, the patient has no evidence of disease, with ribociclib and letrozole continued until disease progression or unacceptable toxicity. In this case, surgery of the primary tumor was performed in the presence of a responsive metastatic disease, with the primary tumor being the only evidence of disease. With the advent of newer therapy options like cyclin-dependent kinase 4/6 inhibitors offering outstanding survival benefit for metastatic disease, a more aggressive and synergistic approach with locoregional therapy may be done to eradicate the tumor burden, translating to better long-term survival. Locoregional management of the primary tumor should be discussed in the context of a multidisciplinary team approach and should be individualized based on the individual patient’s need. Citation Format: Raye Angeli Abella, Rubi Li. LOCOREGIONAL MANAGEMENT OF DE NOVO STAGE IV HORMONE-POSITIVE BREAST CARCINOMA AFTER CDK 4/6 INHIBITOR TREATMENT [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 PO5-20-09.

Abstract PO2-19-01: A Single-Arm Prospective Study of the Neurocognitive Changes Occurring in Breast Cancer Patients on Aromatase Inhibitors. Is There a Difference Between Objective and Perceived Neurocognition?

Abstract Background: Estrogen (ER) and Progesterone (PR) receptors are rich in regions of the brain involved in cognitive functions, like the hippocampus and cerebral cortex. Animal models have shown that estradiol regulates neurocognition and plays an important role in the normal brain development. Hormone positive (HR+) breast cancers (BC) comprise 70% of the disease and the standard of care in the post-menopausal group is the use of Aromatase Inhibitors (AI) for at least 5 years. While “chemo brain” is a well-recognized term, neurocognitive changes from estrogen inhibition by AI have not been clearly defined. As neurocognition is multi-faceted, information on specific aspects affected by AI use is unclear. We hope to answer this through our trial. Design: The study is a single arm, self-controlled prospective observational cohort study in which, post-menopausal BC patients who are to be started on AIs will undergo a battery of neurocognitive tests just before starting AI, at 6 months and at 12 months after being on AI. The changes at 6 and 12 months will be compared to baseline. The tests will involve objective [Hopkins verbal learning test revised (HVLT), Controlled Oral Word Association Test from Multilingual Aphasia Examination, Trial Making Test A and B, and Recall and Recognition of Word List encoded from the HVLT] and subjective/patient-reported [The Functional Assessment of Cancer Therapy - Cognitive Function (FACT-Cog)] components. Tests for anxiety [Generalized Anxiety Disorder (GAD)–7], depression [Patient Health Questionnaire (PHQ)-9] and working memory (Working Memory Tasks from the Wechsler Adult Intelligence Scale) will also be assessed. While the objective tests involve providing patients with specific instructions and asking them to complete the tasks, the FACT Cog questionnaire uses a self-reported 37-item questionnaire enabling assessment of their perceived symptoms. The tests have been summarized in the table. Eligibility criteria: ER/PR+ post-menopausal BC and DCIS patients who are English speaking and are planning to start AIs will be included. Patients who have received hormonal therapy or chemotherapy in the past, those who are scheduled to receive chemotherapy, those who have undergone Whole brain Radiation therapy (RT), those with a premenopausal status, and those having comorbid conditions that could affect cognitive functioning (like any form of dementia or brain metastasis) will be excluded. Specific aims: Our aim is to see if there are progressive neurocognitive changes compared to an age-appropriate baseline and to see if changes to both objective and perceived cognitive changes occur over the course of AI use, in post-menopausal HR+ BC patients. Statistical methods: The T-test and McNemer test will be used. The normal values provided from the test may be used as a standard to justify normal or abnormal values from the collected data. Therefore, a percentage of normal (or abnormal) subjects in each time point can be derived and compared using the McNemar's test. Present accrual and target accrual: 4 patients have been accrued as of June 2023 with a target accrual of 80 patients [80% power to detect a significant change, at a p of 0.05]. Contact information for people with a specific interest in the trial: Dr Abirami Sivapiragasam (abisiva2019@yahoo.com), Dr Sam Benjamin (benjamis@upstate.edu), Dr Prashanth Ashok Kumar (ashokkup@upstate.edu), Amy Bubb (bubbam@upstate.edu). Summary of the neurocognitive tests employed in the trial. Citation Format: Prashanth Ashok Kumar, Erinn McDowell, Amy Bubb, Danning Huang, Susan Sperry, Sam Benjamin, Abirami Sivapiragasam. A Single-Arm Prospective Study of the Neurocognitive Changes Occurring in Breast Cancer Patients on Aromatase Inhibitors. Is There a Difference Between Objective and Perceived Neurocognition? [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 PO2-19-01.

Abstract PO1-02-07: HER2 Low Non-Metastatic Breast Cancer in Qatar: A Nationwide Retrospective Cohort Study to Evaluate the Response to Neoadjuvant Chemotherapy: A Real-World Analysis

Abstract Background: Breast Cancer is the most diagnosed cancer type worldwide and the second leading cause of cancer-related death among women. HER2-low breast cancer is a newly defined molecular subtype of breast cancer in which tumors exhibit a minimal overexpression of HER2 or no gene amplification. To illustrate, HER2-low tumors typically have an IHC score of 1+ or a score of 2+ with negative amplification. However, emerging evidence suggests that even a minimal amplification of HER2 may significantly impact the response to therapy and prognosis. Our study aims to unveil the impact of HER2-low expression on the response to anthracycline and taxane-based neoadjuvant chemotherapy (NACT) in comparison to the HER2-negative group in non-metastatic breast cancer. The primary objective was evaluating the response to NACT comparing the favorable response (complete and partial response) in each of the two groups of HER2-low and HER2-negative patients. Methods: This is a retrospective cohort study. All patients’ profiles with non-metastatic, HER2-Low, and HER2-negative breast cancers who received neo-adjuvant chemotherapy and underwent surgery between the 1st of January 2018 and the 30th of August 2022 were included. Patients' response was evaluated using surgical pathology reports to compare the two study groups (HER2-low and HER2-negative). Results: The total number of patients included was 262 patients, the majority were HER2-low 89% (233/262) vs. 11% (29/262) HER2-negative. A favorable response to NACT was shown in 71% (185/262) of all patients. The favorable response rate was similar in both groups, 70% (164/233) in the HER2-low group vs. 72% (21/29) in the HER2-negative group, OR: 1 (95% CI: 0.8-1), p-value 0.8. Similarly, the pathological complete response (pCR) rate was the same in both study groups at 14%, OR: 0.7 (95% CI: 0.2-3), p-value: 0.6. Interestingly, patients with hormone-positive tumors across both study groups had a higher response rate as compared to hormone-negative patients. However, statistical significance was shown in the HER2-low group only. In the HER2-low cohort, 73% of the patients (119/164) with hormone-positive tumors showed a favorable response OR: 0.8 (95% CI: 0.8- 1), p-value: 0.001. Comparatively, in the HER2-negative cohort, 52% of the patients (11/21) with hormone-positive tumors had a favorable response OR: 2 (95% CI: 1– 5), p-value: 0.05. Conclusion: Our results did not show any significant impact of HER2-low expression on neoadjuvant chemotherapy response. Nonetheless, a statistically significant difference in response was observed in the hormone-positive HER2-low breast cancer patients. Further studies are needed to evaluate the influence of hormonal expression on the response rate to NACT in the HER2-low patient population. Citation Format: Ahmed Kardousha, Wafaa Shehada, Ahmed Basha, Sahar Nasser, Mufid el Mistiri, Anas Hamad, Salha Al-Bader, Shereen Elazzazy. HER2 Low Non-Metastatic Breast Cancer in Qatar: A Nationwide Retrospective Cohort Study to Evaluate the Response to Neoadjuvant Chemotherapy: A Real-World Analysis [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 PO1-02-07.

Abstract PO1-01-12: A retrospective cohort study on the effect of adding adjuvant ovarian function suppression to endocrine therapy in premenopausal women with T1-T2 tumor hormone-positive breast cancer on survival and disease recurrence

Abstract Background: Breast cancer is the most common diagnosed cancer in women and is the leading cause of cancer death. Young women diagnosed with breast cancer are at higher rates of adverse outcomes in terms of survival and recurrence. Hormone sensitive breast cancer is the commonest subtype of breast cancer in this group. To date, the standard adjuvant treatment is endocrine therapy for both pre and post-menopausal women. Recent published studies have recommended adding ovarian function therapy to premenopausal women who are at high risk of recurrence. In this study we evaluated the impact of adding adjuvant ovarian function suppression for premenopausal women with small (T1 and T2) hormone receptor positive node negative breast cancer who did not receive any form of chemotherapy on overall survival and disease-free recurrence. Methods: We performed a retrospective study where we evaluated the electronic medical records of 4431 premenopausal women diagnosed with breast cancer in Asan Medical Center in Seoul, South Korea. All the analyzed patients were operated from the period of January 2006 till December 2019. The inclusion criteria were age of 55 and below, T1 and T2 tumors with N0 disease who received selective estrogen receptor modulators (SERM - Tamoxifen) and didn’t receive neo or adjuvant chemotherapy. We compared patients who received SERM (Tam Only) only to patients who received SERM and ovarian function suppression (Tam + OFS) medications. The primary endpoint was overall survival (OS), and the secondary endpoint was mortality and disease-free survival (DFS). We used chi-square test for categorical variables and t-test for continuous variables. The p-value was set as p< 0.05 as statistically significant. Kaplan Meier curve and log rank test were used to analyze the data for overall survival, disease-free survival and mortality. We performed an additional subgroup analysis adjusted to age, tumor size, Ki67%, progesterone receptor, HER2 status and type of operation. Results: There was equal distribution of cases between tamoxifen only group and tamoxifen + OFS group (2121 versus 2310 respectively). The median age in each group was 45 years of age. Tumor size of ≤0.5cm was the commonest in the tamoxifen only group whereas tamoxifen + OFS group had majority of cases with tumor size of 1 - 2cm. Both groups had a Ki-67% of 10-20%. Histologic grade of 2 and nuclear grade of 2 were most commonly representative in the comparing groups. Invasive ductal carcinoma was the most common histological subtype (93-94%) and invasive lobular carcinoma accounted for 5-6% of cases. Regarding immunohistochemistry results, 91-93% of patients were progesterone receptor positive and 68-73% were HER2 negative. The majority underwent breast conserving surgery compared to mastectomy. We have also looked at the pattern of prescribing OFS treatment in the Tamoxifen + OFS group regarding the length of treatment. Nearly 80% of patients received OFS treatment for a period of 1-2 years whereas only 5.2% received < 1 year and 1.8% >2years. After adjusting to age, tumor size, Ki67%, PR receptor and HER2 status, the result was only significant for higher risk of DFS in the TAM + OFS group in Ki67 < 20%. The OFS+TAM had more DFS and mortality events compared to TAM only group. However, the only significant result was the overall survival favoring tamoxifen only group with a p-value of 0.039 and HR of 1.05-7.99. Conclusion: Adding ovarian function suppression to tamoxifen in premenopausal hormone positive node negative T1-T2 tumors didn’t show any benefit in terms of disease-free interval and overall survival. Further studies are advised to assess the benefit of adding ovarian function suppression to this group of patients Table 1: baseline characteristics of Table 2: Disease Free Survival Subgroup Analysis Citation Format: Sarah Al Safi, Hee Jeong Kim, Seonok Kim, Sae Byul Lee, Jisun Kim, Tae-Kyung Yoo, Il-Yong Chung, Beom Seok Ko, Byung Ho Son. A retrospective cohort study on the effect of adding adjuvant ovarian function suppression to endocrine therapy in premenopausal women with T1-T2 tumor hormone-positive breast cancer on survival and disease recurrence [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 PO1-01-12.

Abstract 5715: CDK7 modulation of Hippo-YAP activity by RNAPII phosphorylation regulates CDK4/6 inhibitor resistance in hormone positive breast cancer

Abstract Breast cancer is the leading cause of cancer in women and poses a massive social economic burden worldwide. CDK4/6 inhibitors have roles as standard of care in advanced and adjuvant setting for hormone positive (HR (+)), HER2 negative breast cancer. CDK6 amplification has been proposed to confer resistance to CDK4/6 inhibitors. By a small molecule screen, we discovered a multi-kinase inhibitor PIK-75 that suppressed the Hippo-YAP pathway and significantly downregulated CDK6, resulting in reversal of CDK6 amplification mediated CDK4/6 inhibitor resistance. To further probe the mechanism, we discovered that PIK-75 suppressed phosphorylation of the C-terminal domain (CTD) of RNA polymerase II (RNAPII) which then resulted in downregulation of YAP expression and the Hippo pathway. Chromatin immunoprecipitation (ChIP) confirmed suppression of RNAPII Ser5 occupancy at YAP promoter after PIK-75 or shCDK7 treatment. Integrating results from RNA sequencing and proteomic analysis in breast cancer cells treated with PIK-75 revealed widespread transcription suppression and substantial spliceosome defect. Alternative splicing analysis by PIK-75 treated cells revealed a widespread splicing defect affecting multiple genes, including YAP, providing an alternative pathway for PIK-75-CDK7 mediated transcriptional regulation. We then investigated the phenotypic impact mediated by PIK-75 and CDK7 inhibition. We discovered that CDK7 silenced cells showed downregulation of YAP intranuclear translocation, impairment of cell migration, and cell cycle progression. ChiP-sequencing of RNAPII was also performed to investigate changes in global RNAPII occupancy and impact on promoter proximal pausing. In vivo studies confirmed that PIK-75 treatment demonstrated tumoricidal efficacy in CDK6 amplified HR (+) breast cancer cells, while the CDK4/6 inhibitor abemaciclib showed minimal cytotoxicity. In conclusion, we discovered a novel CDK7-RNAPII phosphorylation-Hippo/YAP-CDK6 regulation axis that when perturbed, could regulate CDK4/6 inhibitor resistance in HR (+) breast cancer. Molecular studies and multi-omic profiling elucidated the role of CDK7 in hippo pathway and characterizes multiple roles of PIK-75. Our study provides intriguing novel insights into the link between "transcriptional CDKs" and the hippo pathway that could potentially be further probed for therapeutics in HR (+) breast cancer. Citation Format: Chung-Jen Yu, Yong-Ji Zhuang, Chih-Yi Lin, Yi-Ru Tseng, Ting-Yi Lin, Hsiu-Man Shih, Chun-Yu Liu, Ta-Chung Chao, Ling-Ming Tseng, Chi-Cheng Huang, Yi-Fang Tsai, Feng chiao Tsai, Jiun-I Lai. CDK7 modulation of Hippo-YAP activity by RNAPII phosphorylation regulates CDK4/6 inhibitor resistance in hormone positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5715.

MMP-11 expression in early luminal breast cancer: associations with clinical, MRI, pathological characteristics, and disease-free survival

BackgroundEarly hormone-positive breast cancers typically have favorable outcomes, yet long-term surveillance is crucial due to the risk of late recurrences. While many studies associate MMP-11 expression with poor prognosis in breast cancer, few focus on early-stage cases. This study explores MMP-11 as an early prognostic marker in hormone-positive breast cancers.MethodsIn this retrospective study, 228 women with early hormone-positive invasive ductal carcinoma, treated surgically between 2011 and 2016, were included. MMP-11 expression was measured by immunohistochemistry, and its association with clinical and MRI data was analyzed.ResultsAmong the patients (aged 31–89, median 60, with average tumor size of 15.7 mm), MMP-11 staining was observed in half of the cases. This positivity correlated with higher uPA levels and tumor grade but not with nodal status or size. Furthermore, MMP-11 positivity showed specific associations with MRI features. Over a follow-up period of 6.5 years, only 12 oncological events occurred. Disease-free survival was linked to Ki67 and MMP-11.ConclusionMMP-11, primarily present in tumor-surrounding stromal cells, correlates with tumor grade and uPA levels. MMP-11 immunohistochemical score demonstrates a suggestive trend in association with disease-free survival, independent of Ki67 and other traditional prognostic factors. This highlights the potential of MMP-11 as a valuable marker in managing early hormone-positive breast cancer.

175 (PB-082) Poster - The role of macrophages in hormone positive breast cancer

175 (PB-082) Poster - The role of macrophages in hormone positive breast cancer

Adjuvant Chemotherapy in Premenopausal Patients With Hormone-Positive Breast Cancer With a Recurrence Score of 16-25: A Retrospective Analysis Using the National Cancer Database.

Results from the TAILORx trial revealed that the use of adjuvant chemotherapy along with endocrine therapy had no survival advantage in patients with estrogen receptor (ER)-positive, human epidermal growth factor receptor 2-negative (HER2-), node-negative (N0) breast cancer (BC) with an intermediate (11-25) 21-gene recurrence score (RS) in the overall population. However, in patients under age 50 years, adjuvant chemotherapy demonstrated a progression-free survival benefit when the RS ranged from 16-25. We studied this cohort with the population-based national database. The 2010-2018 National Cancer Database was used to include patients with BC age 18-50 years, N0, M0, RS 16-25, ER+/progesterone receptor±, and HER2-. Patients were divided into two groups on the basis of adjuvant chemotherapy use, and the survival between them was compared. Adjuvant chemotherapy use was noted in 4,808/15,792 (30.45%) patients. Median RS was 18 and 21 in patients without and with adjuvant chemotherapy, respectively. Factors associated with adjuvant chemotherapy use were higher T stage, poor and moderately differentiated tumors, age <40 years, care at an academic center, Caucasian race, patients undergoing mastectomy, regional lymph node surgery, and radiation therapy. Kaplan-Meier survival at 10 years was better with adjuvant chemotherapy (96.2% v 91.6%). Patients without adjuvant chemotherapy had more adverse outcomes (hazard ratio [HR], 1.683 [95% CI, 1.392 to 2.036]; P < .0001). Subgroup analysis showed that the benefit was significant in patients with RS scores 21-25 (HR, 1.953 [95% CI, 1.295 to 2.945]), ductal histology (HR, 1.521 [95% CI, 1.092 to 2.118]), Caucasian race (HR, 1.655 [95% CI, 1.180 to 2.322]), and 41-50 years age group (HR, 1.732 [95% CI, 1.244 to 2.411]). Our study showed an overall survival benefit for adjuvant chemotherapy use in patients with ER-positive, N0 premenopausal BC patients, age less than 50 years, with an intermediate RS score, particularly 21-25.

Abstract A015: Mutations in mismatch repair genes that alter subcellular localization of the protein predict resistance to standard therapy but response to cell cycle inhibitors

Abstract Hormone positive breast cancer is one of the most common cancer types in U.S. Every year, over 150,000 patients are detected with this cancer type of which, &amp;gt;40,000 patients will go on to die of their disease. We recently identified defects in a principal mismatch repair (MMR) gene, MLH1, as a driver of resistance to standard-care treatment and poor patient outcomes. Moreover, we demonstrated increased sensitivity to palbociclib, a CDK4/6 inhibitor, in experimental model systems in vitro and in vivo and in clinical trial data. MLH1 is mutated in 5-10% of treatment-resistant tumors, i.e., 4,000 patient tumors every year. However, most of these mutations are missense and variants of unknown significance (VUS). The impact of these mutations on mismatch repair capability and on treatment resistance remains uncertain. Here, we use experimental model systems (ER+/HER2- breast cancer cells, organoid models, and patient tumors) to study how variants of MLH1 and its subcellular localization predicts resistance to standard endocrine therapy but sensitivity to cell cycle inhibitors. We also assessed the ability of nuclear MLH1 to induce activation of G1/S cell cycle checkpoints by activating Chk2. Currently, there are few tests available in the clinic to predict response to therapies early in the timeline of hormone positive breast cancer patients. Due to the nature of the disease, this can result in years of overtreatment. Overtreatment comes at great financial, physical, and emotional cost to patients and their families. We for the first time show that stalling nuclear translocation of MLH1 inhibits Chk2 activation which counterbalances CDK4/6 activity. Therefore, cytoplasmic Mlh1 may be first in-class biomarker for CDK4/6 response in cancer types. Citation Format: Aloran Mazumder, Svasti Haricharan. Mutations in mismatch repair genes that alter subcellular localization of the protein predict resistance to standard therapy but response to cell cycle inhibitors [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr A015.

Epiretinal membrane formation associated with letrozole therapy – Two case reports

Letrozole, an aromatase inhibitor, is being increasingly used for adjuvant endocrine therapy in hormone-positive postmenopausal breast cancer. Although aromatase inhibitors are thought to increase vitreoretinal traction by causing estrogen reduction, posterior segment complications of letrozole are sparsely reported. We report two cases of presumed epiretinal membrane formation in postmenopausal, hormone receptor–positive breast cancer patients on adjuvant letrozole therapy.

Role of ovarian suppression in adjuvant treatment of breast cancer

Adjuvant endocrine therapy is an integral component of treatment for resectable luminal breast cancer. Tamoxifen or aromatase inhibitors monotherapy has been the standard of practice for many years. However, recent studies have shown that the addition of ovarian suppression statistically significantly increases survival rates in patients at high risk for recurrence and with poor prognosis factors. In this literature review, we summarized recent data regarding the role of ovarian suppression in adjuvant therapy for hormone-positive breast cancer. Suppression of ovarian function was most effective in young patients (&lt; 35 years) in the premenopausal stage when adverse prognostic factors were present (indications for (neo)adjuvant CT, G3, etc.) The authors noted that using of aromatase inhibitors instead of tamoxifen in this subgroup significantly reduced the risk of breast cancer recurrence. Ovarian suppression, especially in combination with aromatase inhibitors, was accompanied by an increase in the incidence of adverse side effects, particularly osteoporosis and bone fractures, which can be reduced by prescribing adequate accompanying therapy with OMA. The optimal duration of ovarian function suppression has also not been determined, but a two-year course seems optimal, given the results of large clinical trials. In the protocols performed, there was no significant effect of temporary ovarian suppression on the likelihood of subsequent pregnancy.

Abstract A083: Initiation and persistence of hormone therapy in endocrine positive breast cancer at an urban safety-net hospital

Abstract Background: Evidence demonstrates inequities in receipt and persistence of hormone therapy among breast cancer patient populations based on race, ethnicity, insurance, and language. Institutions where patients seek cancer care may have an impact on receipt of treatment. It is unknown whether safety net hospitals, servicing a vulnerable patient population, exhibit inequities in receipt of hormone therapy for breast cancer. Study Design: We performed a retrospective study of patients diagnosed with all stages of hormone positive (ER+ and/or PR +) breast cancer treated at a safety net institution over the five year period from January 1, 2009 to December 31, 2013. The initiation of and persistence of hormone therapy were assessed by race, ethnicity, insurance status, and primary language. Persistence of therapy was defined as defined as at least 3 prescriptions (90 day supply) or more than 1 visit after start of treatment documenting taking treatment. Results: A total of 599 women were identified. The median age was 59 years, 58% were non-White, 32% were non-English-speaking, and 35% had Medicaid or no insurance. A total of 506 (84%) were started on hormone therapy. In multivariate regression analysis, the rate of endocrine therapy initiation was associated with higher stage at diagnosis, post-menopausal status, and HER2 negative status. Non-white race, Hispanic/Latino ethnicity, non-English-language, and Medicaid/no insurance were not significantly associated with or without initiation of hormone therapy. 93% of patients started on hormone therapy had evidence of continued treatment, 91% had evidence of continued treatment at 1 year, 75% finished their recommended course of hormone therapy. Conclusion: At an urban safety-net hospital, we do not observe inequities in the initiation of endocrine therapy for breast cancer by race, ethnicity, insurance, or language. Persistence of therapy was similar to nationally reported data. Additional research by hospital type, and granular reasons for non-adherence are warranted. Citation Format: Quinn S. Solfisburg, Brendin R. Beaulieu-Jones, Michael R. Cassidy, Naomi Y. Ko. Initiation and persistence of hormone therapy in endocrine positive breast cancer at an urban safety-net hospital [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr A083.

Evaluation of the effect of CYP2D6*3, *4,*10, and *17 polymorphisms on the pharmacokinetic of tamoxifen and its metabolites in patients with hormone-positive breast cancer

Background and objectiveA high rate of interindividual variability in response to tamoxifen (TAM) in breast cancer patients with CYP2D6 polymorphism has been reported, which affects the patient’s therapeutic outcome. The objective of this study was to investigate the pharmacogenomics of CYP2D6 genotyping in Iranian patients with breast cancer treated with adjuvant TAM. MethodsA peripheral blood sample was obtained to determine the steady-state plasma concentrations of TAM and its metabolites (Endoxifen (EN) and 4-Hydroxytamoxifen (4-OHT)) using high-performance liquid chromatography with fluorescence detection (HPLC-FLU) assay. We detected CYP2D6 * 3, * 4, * 10, and * 17 single nucleotide polymorphisms via polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method. ResultsA total of 84 Iranian estrogen receptor‑positive breast cancer patients receiving the daily dose of 20 mg tamoxifen were recruited. Although a consequent decrease in the median EN and 4-OHT concentrations was observed by comparing poor or intermediate metabolizer patients with an extensive metabolizer population, this difference did not reach a significant level. The mean plasma EN concentrations in poor and intermediate metabolizers were 46.1% (95% CI, 7.4–27.8%) and 59.4% (95% CI, 11.9–37.3%) of extensive metabolizer subjects, respectively. Poor and intermediate metabolizers had the mean plasma 4-OHT concentrations that were 46.6% (95% CI, 0.9–61.7%) and 73.2% (95% CI, 2.7–93.1%) of those of subjects who were extensive metabolizer, respectively. ConclusionsThe possible role of genotyping in Iranian patients' response to treatment may explain inter-individual differences in the plasma concentrations of active metabolites of TAM.

MO9-3 Triple-negative and hormone-positive breast cancer: The association with reproductive factors among Bangladeshi women

MO9-3 Triple-negative and hormone-positive breast cancer: The association with reproductive factors among Bangladeshi women

Trastuzumab deruxtecan in the treatment of patients with advanced breast cancer with HER2-low expression: Recent studies review

The review gives the definition of HER2-low status, shows its clinical and biological role in patients with advanced breast cancer. A unique mechanism of action of trastuzumab deruxtecan and potential for its use in advanced breast cancer with HER2-low expression are described. The key results of the open multicenter phase III DESTINY-Breast04 (DB-04) trial including safety data are presented. Results on the effectiveness of the drug in patients with markers of hormone resistance first presented in 2023 and the place of trastuzumab deruxtecan in the updated ESMO 2023 algorithm of hormone-positive breast cancer treatment are considered.

The role of the tumor microenvironment in endocrine therapy resistance in hormone receptor-positive breast cancer.

Endocrine therapy is the prominent strategy for the treatment of hormone-positive breast cancers. The emergence of resistance to endocrine therapy is a major health concern among hormone-positive breast cancer patients. Resistance to endocrine therapy demands the design of newer therapeutic strategies. The understanding of underlying molecular mechanisms of endocrine resistance, components of the tumor microenvironment (TME), and interaction of resistant breast cancer cells with the cellular/acellular components of the intratumoral environment are essential to formulate new therapeutic strategies for the treatment of endocrine therapy-resistant breast cancers. In the first half of the article, we have discussed the general mechanisms (including mutations in estrogen receptor gene, reregulated activation of signaling pathways, epigenetic changes, and cell cycle alteration) responsible for endocrine therapy resistance in hormone-positive breast cancers. In the latter half, we have emphasized the precise role of cellular (cancer-associated fibroblasts, immune cells, and cancer stem cells) and acellular components (collagen, fibronectin, and laminin) of TME in the development of endocrine resistance in hormone-positive breast cancers. In sum, the article provides an overview of the relationship between endocrine resistance and TME in hormone-positive breast cancers.