Aggressive Subtype Of Breast Cancer Research Articles

Exploring the prognostic significance of arm-level copy number alterations in triple-negative breast cancer.

Somatic copy number alterations (SCNAs) are prevalent in cancer and play a significant role in both tumorigenesis and therapeutic resistance. While focal SCNAs have been extensively studied, the impact of larger arm-level SCNAs remains poorly understood. Here, we investigated the association between arm-level SCNAs and overall survival in triple-negative breast cancer (TNBC), an aggressive subtype of breast cancer lacking targeted therapies. We identified frequent arm-level SCNAs, including 21q gain and 7p gain, which correlated with poor overall survival in TNBC patients. Further, we identified the expression of specific genes within these SCNAs associated with survival. Notably, we found that the expression of RIPK4, a gene located on 21q, exhibited a strong correlation with poor overall survival. In functional assays, we demonstrated that targeting Ripk4 in a murine lung metastatic TNBC model significantly reduced tumor burden, improved survival, and increased CD4+ and CD8+ T cell infiltration. RIPK4 enhanced the survival of triple-negative breast cancer cells at secondary sites, thereby facilitating the formation of metastatic lesions. Our findings highlight the significance of arm-level SCNAs in breast cancer progression and identify RIPK4 as a putative driver of TNBC metastasis and immunosuppression.

A comprehensive overview of metaplastic breast cancer: Features and treatments.

Metaplastic breast cancer is a rare, aggressive, and chemotherapy-resistant subtype of breast cancers, accounting for less than 1% of invasive breast cancers, characterized by adenocarcinoma with spindle cells, squamous epithelium, and/or mesenchymal tissue differentiation. The majority of metaplastic breast cancers exhibit the characteristics of triple-negative breast cancer and have unfavorable prognoses with a lower survival rate. This subtype often displays gene alterations in the PI3K/AKT pathway, Wnt/β-catenin pathway, and cell cycle dysregulation and demonstrates epithelial-mesenchymal transition, immune response changes, TP53 mutation, EGFR amplification, and so on. Currently, the optimal treatment of metaplastic breast cancer remains uncertain. This article provides a comprehensive review on the clinical features, molecular characteristics, invasion and metastasis patterns, and prognosis of metaplastic breast cancer, as well as recent advancements in treatment strategies.

A β-Carboline Derivate PAD4 Inhibitor Reshapes Neutrophil Phenotype and Improves the Tumor Immune Microenvironment against Triple-Negative Breast Cancer.

Triple-negative breast cancer is a highly aggressive and heterogeneous breast cancer subtype characterized by early metastasis, poor prognosis, and high recurrence. Targeting histone citrullination-mediated chromatin dysregulation to induce epigenetic alterations shows great promise in TNBC therapy. We report the synthesis, optimization, and evaluation of a novel series of β-carboline-derived peptidyl arginine deiminase 4 inhibitors that exhibited potent inhibition of TNBC cell proliferation. The most outstanding PAD4 inhibitor, compound 28, hindered the PAD4-H3cit-NET signaling pathway and inhibited the growth of solid tumors and pulmonary metastatic nodules in the 4T1 in situ mouse model. Furthermore, 28 improved the tumor immune microenvironment by reshaping neutrophil phenotype, upregulating the proportions of dendritic cells and M1 macrophages, and reducing the amount of myeloid-derived suppressor cells. In conclusion, our work offered 28 as an efficacious PAD4 inhibitor that exerts a combination of conventional chemotherapy and immune-boosting effects, which represents a potential therapy strategy for TNBC.

Mitomycin C in the treatment of early triple-negative locally advanced BRCA-associated breast cancer

Rationale. BRCA1 associated triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer. At the same time, carcinomas that develop in carriers of BRCA1 mutations are characterized by extremely high sensitivity to DNA-damaging chemotherapy. Mitomycin C alone or in combination with platinum agents has already demonstrated promising results in the treatment of BRCA-associated ovarian cancer (OC) and metastatic breast cancer. In this article, we present the results of a retrospective study aimed at comparing standard neoadjuvant chemotherapy regimens (NACT) with mitomycin-based regimens for primary locally advanced BRCA1-associated TNBC.The aim of the study is to determine the effectiveness of the combination of mitomycin and platinum compounds during neoadjuvant therapy in patients with primary locally advanced BRCA1 – associated TNBC.Materials and methods. The study included 89 patients diagnosed with primary locally advanced BRCA1-associated TNBC. Patients were divided into three groups depending on the therapy: 1) 4 cycles of anthracycline and cyclophosphamide followed by 12 weekly injections of paclitaxel (n = 48) (AC + T), 2) 4 cycles of anthracycline and cyclophosphamide followed by 12 weekly injections of paclitaxel and carboplatin (n = 27) (AC + TCbP), 3) mitomycin C plus platinum followed by 12 weekly injections of paclitaxel (n = 14) (MR + T). Pathological complete response (pCR) rates were compared.Results. The pCR rate in the MP+T group was 10/14 (71%). In patients with BRCA1-associated breast cancer who received AC + T and AC + TCbP regimens as NACT, the pCR rate was 17/48 (35%) and 19/27 (70%), respectively. The difference in pCR rate between mitomycin-containing therapy and the standard AC + T regimen was statistically significant (p = 0.03); the frequency of regressions was comparable to the frequency in the AC + TCbP group. During the 20-month follow-up period, no relapses were observed in the MR + T group. Relapses were more frequent in the AC + T group compared with the AC + TCbP group (16/48 (33%) vs 1/27 (4%), p = 0.003, Fisher’s exact test). The toxicity profile of the mitomycin-containing regimen included hematologic adverse events, the most common of which were anemia and leukopenia. Compared to standard regimens, nausea was significantly less pronounced. No patients reported alopecia with this regimen.Conclusions. The addition of mitomycin C to neoadjuvant therapy for BRCA1-associated TNBC may be a promising treatment option for this category of patients and merits further study.

Abstract PO5-21-07: Mitomycin: its developmental role in the treatment of patients with BRCA - associated triple-negative early and locally advanced breast cancer

Abstract Rationale. BRCA-associated triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer with high sensitivity to chemotherapy, which leads to increased interest in the development of new strategies for neoadjuvant treatment of patients with a triple-negative tumor phenotype. The aim of the study is to determine the role of adding platinum to standard neoadjuvant systemic therapy in patients with primary BRCA-associated TNBC, to evaluate the effect of platinum preparations on relapse-free survival in patients of this category, to determine the role of adding mitomycin to platinum in patients with primary BRCA-associated TNBC. Materials and methods. The study included 80 patients diagnosed with primary BRCA - associated TNBC, divided into 3 groups according to the treatment. Each group was subdivided depending on the final pathomorphological result and the presence of relapses. Results. 80 patients with primary BRCA-associated TNBC were divided into 3 groups depending on the ongoing neoadjuvant chemotherapy (NACT). Group I included 48 (60%) patients who received the AC-T regimen, in group II — NAC according to the AC-TCarb regimen, 27 (33.75%) patients, in group III — NAC with mitomycin in combination with cisplatin, 5 (6.25%) of patients. A comparative analysis of the results of the frequency of achieving complete pathomorphological regression (pCR), depending on the addition of a platinum drug to standard NAC, showed the advantage of group II compared to group I (73.7% vs. 41.2%, respectively, p = 0.0433). Taking into account the ongoing NAC regimens, with a median follow-up of 20.7 months, patients of group I had a slightly higher risk of relapse compared to patients of group II (p = 0.099). Patients of group III demonstrated the achievement of pCR in 66.6% of cases (2/3) during the full course of NAC, 2 patients of group III did not complete the planned course of NAC for medical reasons, due to the development of a pronounced nephrotoxic effect. During the observation period of group III, no cases of relapse were recorded. Conclusions.The addition of platinum drugs to the standard anthracycline/taxane NAPCT regimen in patients with primary BRCA-associated TNBC, results in a higher pCR rate, which entails a reduced risk of disease recurrence.The use of the new NAC regimen with mitomycin in combination with platinum compounds has promising results in patients with this oncopathology, which deserves a more detailed clinical evaluation.Performinga full course of planned NAC has a positive tendency in achieving pCR in patients of this category. Keywords: BRCA1/2 mutation; triple negative breast cancer; platinum preparations; mitomycin; neoadjuvant chemotherapy. Citation Format: Petr Krivorotko, Evgeniy Imyanitov, Diana Enaldieva, Elena Zhiltsova, Roman Donskih, Anna Sokolenko, Laysan Shaikhelislamova, Larisa Gigolaeva, Tengiz Tabagua, Alexander Komyakhov, Kirill Nikolaev, Konstantin Zernov, Sergey Yerechshenko, Roman Pesotsky, Nikolay Amirov, Alexander Emelyanov, Viktoria Mortada, Yana Bondarchuk, Vladislav Semiglazov. Mitomycin: its developmental role in the treatment of patients with BRCA - associated triple-negative early and locally advanced 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 PO5-21-07.

Abstract PO5-09-08: Cancer Health Disparities among non-Hispanic African women: A systematic review of the disparities, reasons and probable intervention

Abstract Health equity places health inequities in historical and social context and calls for action to address injustice and enhance health. As an ethical and human rights value that drives us to end health inequities, health equality is defined as everyone having a fair and just opportunity to be as healthy as feasible. According to this perspective, structural discrimination and marginalization cause health disparities that can be avoided. If these issues are not resolved, social and economic injustices, bias, and unfavorable outcomes that affect all of us will continue to exist. The idea of cancer health equality recognizes that there is still considerable work to be done to change the social structures and historical momentum that have contributed to different cancer outcomes, and that this work can only succeed if it is done. In USA, non-Hispanic black women experience a complicated and multifaceted disparity in breast cancer incidence and outcome. It's possible that social, economic, and behavioral variables contribute to discrepancies. Black women are less likely to breastfeed after childbirth, statistically more likely to have diabetes, heart disease, and obesity, all of which are risk factors for breast cancer. Compared to white women, they are more likely to lack adequate health insurance or access to medical facilities, which could have an impact on screening, follow-up treatment, and therapy completion. It has become evident via more study that biology also plays a part. Black women are more likely to be diagnosed at younger ages and at higher rates with more aggressive subtypes of breast cancer, such as triple-negative breast cancer (TNBC) and inflammatory breast cancer. The National Institute on Minority Health and Health Disparities (NIMHD) established a research framework to characterize the multiple domains of influence (biological, behavioral, physical environment, sociocultural environment, and health care system) that may act across various levels of influence to impact health. A literature search was conducted using the National Library of Medicine's PubMed search engine. Triple negative breast cancer (TNBC) is a common malignancy in African American women. The incidence of TNBC is higher in women of African ancestry and is associated with overall poor prognosis. This disparity is due to the presence/absence of oncogenes/tumor suppressor genes, mutations and altered signaling pathways that might predispose premenopausal African American women to TNBC. Multiple socioeconomic factors influence the access to standard care, novel treatments and inclusion in clinical trials and contribute to overall prognoses. This review focuses on the epidemiology, molecular alterations, and treatment-related disparities in African Americans with breast cancer. This poster will elaborate the racial disparity in terms of breast cancer among the African-American women in USA, the reasons and it's effects on health equity. Citation Format: Tasnuva Khan Efa. Cancer Health Disparities among non-Hispanic African women: A systematic review of the disparities, reasons and probable intervention [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 PO5-09-08.

Abstract PO2-08-09: Prevalence of germline genetic variants in breast cancer susceptibility genes among patients with metaplastic breast cancer

Abstract Background: Pathogenic or likely pathogenic variants (PV) in breast cancer (BC) susceptibility genes are present in approximately 5-10% of individuals with breast cancer and approximately 13-15% of those with triple-negative breast cancer (TNBC). Identifying patients with PV in BRCA1 and BRCA2 can inform selection of appropriate candidates for poly(ADP-ribose) polymerase inhibitors (PARPi), which have improved progression-free and overall survival in the metastatic and adjuvant settings, respectively. Metaplastic breast cancer (MpBC) is a rare, aggressive subtype of breast cancer that is often triple-negative and refractory to chemotherapy. To date, limited data describe germline genetic findings in patients with MpBC. Methods: We conducted a retrospective chart review including patients with pathology results at the Hospital of the University of Pennsylvania from 2021 through May 2023 demonstrating MpBC. Germline genetic test results and tumor histopathologic characteristics including estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status were evaluated. Descriptive statistics as well as two-tailed t tests were used for data analysis. Results: Of 89 patients identified with MpBC, 51 had germline genetic testing results available for review. Nine patients (17.6%) had MpBC with PV in BC predisposition genes (PV-MpBC) and 42 (82.4%) had PV-negative MpBC (PVneg-MpBC). Seven patients (13.7%) had a PV in BRCA1, 1 (2.0%) in BRCA2, and 1 (2.0%) in CHEK2. Median age at diagnosis was 45 years for patients with PV-MpBC and 56.5 years for those with PVneg-MpBC (p=0.005). Among patients with PV-MpBC, 6 (66.7%) had ER and PR negative disease by ASCO-CAP guidelines and 3 (33.3%) had ER and/or PR positive disease. Among patients with PVneg-MpBC, 31 (73.8%) had ER and PR negative disease and 11 (26.2%) had ER and/or PR positive disease. All 9 patients with PV-MpBC had HER2-negative disease, one (11.1%) of whom had HER2-low disease. Among patients with PVneg-MpBC, 40 (95.2%) had HER2-negative disease, two (4.8%) of whom had HER2-low disease, and 2 (4.8%) had HER2-positive BC. Conclusions: The frequency of PV in breast cancer susceptibility genes among patients with MpBC is comparable to, and possibly higher than, the reported rates of such PV in patients with TNBC, for whom genetic testing is recommended. If confirmed in a larger dataset, germline testing should be considered for all patients with MpBC regardless of ER, PR, and HER2 status, as findings may help identify candidates for PARPi therapy and genetically-directed clinical trials. Citation Format: Kaitlin Demarest, Anupma Nayak, Payal Shah. Prevalence of germline genetic variants in breast cancer susceptibility genes among patients with metaplastic 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 PO2-08-09.

Abstract PS16-08: Histologic Pattern and Outcomes in High-Grade Metaplastic Breast Cancer Compared to Triple-Negative Ductal Breast Cancer Counterparts: A Single Institution Retrospective Study

Abstract Background Metaplastic breast cancer (MpBC) is a rare and aggressive subtype of breast cancer that presents with high tumor stage and a poor prognosis. MpBC tumors tend to have worse outcomes compared to other non-metaplastic triple-negative breast cancers (TNBC). Although MpBC has been described as chemotherapy resistant, chemotherapy remains a mainstay of treatment. MpBC tumors can be further characterized by their specific histologic pattern. The existing literature on outcomes of MpBC by histologic pattern is limited, with varying results regarding response rate and overall survival (OS). Identifying a pattern of MpBC that has better response to treatment could help tailor treatment recommendations. Methods A retrospective chart review was performed and identified 106 patients with early-stage, high-grade MpBC who were diagnosed at Levine Cancer Institute between January 1, 2010 and September 1, 2021. A matched control cohort (n=106) of patients diagnosed with non-metaplastic TNBC was selected based on propensity score matching on diagnosis date, age at diagnosis, race, pathologic staging, and tumor grade. Patient demographics, tumor characteristics, therapeutic interventions, residual cancer burden (RCB), and outcomes were collected. The associations between the histologic patterns of MpBC and disease characteristics were evaluated using chi-squared tests for categorical variables and Wilcoxon tests for continuous variables. We also examined the differences in RCB scores between the MpBC cohort and the non-metaplastic TNBC cohort who received neoadjuvant chemotherapy. Additionally, Kaplan-Meier and Cox proportional hazard analysis was performed to assess differences in recurrence free survival (RFS) and OS between the spindle cell/sarcomatous pattern versus all other patterns. Results For the entire group (n=212), median age at diagnosis was 58 years (range, 24-92); all patients were female; 66% White, 29% Black, and 5% unknown race. Most tumors were triple-negative (91%); 19%, 56% and 14% with Clinical Stage I, II, and III disease, respectively. A total of 63% of patients underwent radiation treatment and 76% received chemotherapy (43% neoadjuvant and 57% adjuvant). Recurrence after treatment occurred in 16% of all patients. In the MpBC cohort (n=106), the histologic patterns included spindle cell/sarcomatous (34%), squamous (17%), heterologous mesenchymal (31%), mixed (17%), and other (1%). Of those with MpBC who received neoadjuvant chemotherapy (n=32), RCB among the different histologic patterns was assessed. When comparing spindle cell/sarcomatous versus the other histologic patterns combined, there was no significant difference in RCB (p = 0.81), although more RCB III scores were recorded in the spindle cell/sarcomatous pattern compared to the other MpBC patterns (40% versus 30%). When assessing RFS and OS by histologic pattern in the entire MpBC cohort, spindle cell/sarcomatous tumors had inferior RFS (p = 0.0194) and OS (p = 0.0039) compared to the other MpBC patterns combined. When comparing RCB values between MpBC and non-metaplastic TNBC, there were numerically more RCB-III classes in the MpBC cohort as compared to the non-metaplastic TNBC. Conclusion MpBC is an aggressive and difficult breast malignancy to treat. Based on our single institution review, no correlation between RCB and the histologic pattern of MpBC was found, however, RFS and OS were worse among the spindle cell/sarcomatous pattern. Furthermore, the MpBC cohort had numerically higher RCB-III scores than the TNBC control cohort, which is in line with historical data. Citation Format: Ashley Matusz-Fisher, Annabel Chen, Erin Donahue, Courtney Schepel, Michelle Wallander, Chad Livasy, Richard White, Antoinette Tan, Lejla Hadzikadic-Gusic. Histologic Pattern and Outcomes in High-Grade Metaplastic Breast Cancer Compared to Triple-Negative Ductal Breast Cancer Counterparts: A Single Institution Retrospective 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 PS16-08.

Abstract PO2-10-02: 'Sharing Our Own Experience': A Qualitative Study of Black Women Diagnosed with Triple-Negative Breast Cancer

Abstract Introduction: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that is disproportionately prevalent among U.S. Black women. Black women diagnosed with TNBC are less likely to receive the primary treatment options for TNBC, and more likely to die from the disease compared to white patients with the same diagnosis. Given TNBC’s impact on Black women, there is an urgent need to better understand their needs for information and support and any unique barriers to care they may face. Thus, this study explored the perspectives, needs, and lived experiences of Black women diagnosed with TNBC. Methods: Our study was guided by the transformative paradigm and used a multi-method approach. Study-eligible participants self-identified as: a) Black or African American; b) 18 years or older; c) being diagnosed with TNBC within the previous 5-7 years; d) receiving TNBC treatment in the U.S.; and e) English-speaking. From August-October 2022, SHARE Cancer Support (a national nonprofit focused on cancer) and 15 partner organizations used social media and listservs to recruit potential participants from their constituencies to complete a quantitative survey (n=49). From the survey participants, a stratified, purposeful sample of 20 Black women diagnosed with TNBC completed in-depth interviews from November 2022-February 2023. Two Black women researchers conducted virtual interviews with the participants via Zoom. The research team performed thematic analysis on the professionally transcribed data using NVivo 12. A Black Feminist lens was used to analyze codes and interpret emerging themes present across the interviews. The University of South Carolina's Institutional Review Board approved this study. Results: About half of those interviewed were between 35 and 44 years old, had a bachelor's degree or higher, and their annual household income ranged from less than $25,000 to $175,000. Eight major themes emerged from the personal stories of Black women diagnosed with TNBC. From diagnosis to survivorship, Black women discussed the importance of advocacy, including self-advocacy, others advocating on their behalf, and being motivated to become an advocate for others. The participants shared the significance of their identity as Black women and desired that cancer care team members acknowledge their identity and subsequently culturally tailor their care needs. Some participants also noted instances of racism and discrimination that occurred during their TNBC diagnosis or treatment experience. Participants overwhelmingly stressed the vital nature of having “someone who looks like me” to inform them about treatment options and existing resources, as well as to provide emotional support through their shared lived experiences with TNBC. Additionally, participants recognized the importance of embracing the uncertain yet inevitable future. They also emphasized that mental health support is not uniformly provided in care settings but should be an essential component of the TNBC treatment plan. Having support was essential to all the women, but they noted that support can look different for everyone and many existing support resources need to be improved. The themes were adapted into a list of recommended action steps for support organizations, clinical care team members, and TNBC patients to help improve the quality of life for Black women diagnosed with TNBC. Conclusions: The lived experiences of Black women diagnosed with TNBC can serve as a meaningful source of data and provide solutions to addressing persistent health disparities these women face. Findings from this study can inform future research and clinical practice about how to support the holistic needs of Black women diagnosed with TNBC. Recommendations for improving the quality of life for Black women diagnosed with triple-negative breast cancer. The 8 major themes that emerged in the qualitative study were adapted into a list of actionable recommendations for key interest groups to improve the lives of Black women diagnosed with triple-negative breast cancer. Citation Format: Tisha Felder, Lucy Ingram, Megan Austin, Victoria Burke, Stephanie Poland, Megan-Claire Chase, Christine Benjamin. 'Sharing Our Own Experience': A Qualitative Study of Black Women Diagnosed with 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 PO2-10-02.

Abstract PO4-03-09: Profile of circulating natural killer cells in stage III triple negative breast cancer before and after neoadjuvant chemotherapy

Abstract Background: Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer. The treatment for locally advanced disease is based on neoadjuvant chemotherapy and immunotherapy, with complete pathological response (pCR) serving as a predictor of disease-free survival. Although the presence of immune cell infiltration in the tumor has a favorable prognostic impact, there is a lack of predictive biomarkers for complete pathological response to neoadjuvant chemotherapy (NAC). Objective: to analyze the profile of circulating Natural Killer (NK) cells and NK subpopulations (NK FAS+ and NK PD1+) in association with the occurrence of complete pathological response after neoadjuvant chemotherapy in women with clinical stage III TNBC. Methods: This was a longitudinal prospective and translational cohort study, including women aged 18 to 60 years with stage III TNBC diagnosed between March 2015 and July 2017, with a follow-up of 24 months. A comparison control group consisted of 30 healthy women aged 18 to 60 years without prior or current cancer diagnosis and no family history of breast cancer. Peripheral blood samples were collected before NAC and before surgery. Flow cytometry was used to analyze the percentage levels of NK cells and NK subpopulations (NK FAS+ and NK PD1+). The Shapiro-Wilk test was initially applied to assess the normality of quantitative variables. The non-parametric Mann-Whitney test was used for comparison between two groups. The statistical significance level was set at p< 0.05. Overall survival (OS) was estimated using the Kaplan-Meier method. Statistical analysis was performed using GraphPad Prism v9.5.1. Results: The median age was 45 years. Stage IIIA was identified in 28% of the patients, while IIIB was observed in 72%. Regarding pathological response, 14 patients (48%) achieved pCR, while 15 patients (52%) had a non-complete pathological response (non-pCR). The 2-year OS was 86%, with no median reached. Higher percentage levels of NK cells, NK FAS+, and NK PD1+ were observed in the patient group compared to the control group, with significant differences. There was a significant increase in the percentage levels of NK cells after NAC compared to pre-NAC levels, and a reduction in NK PD1+ levels. NK cell levels were significantly higher in patients with stage IIIA compared to stage IIIB, while NK FAS+ levels were lower. NK cell and NK FAS+ subpopulation levels were significantly higher in patients who achieved pCR compared to non-pCR patients, with no difference in NK PD1+ cell levels. Conclusions: Elevated levels of circulating NK cells and NK FAS+ subpopulation collected from peripheral blood before NAC may serve as potential biomarkers for pCR in patients with TNBC. Citation Format: Luiz Jose de Barros Batista, Jurema Telles, Candice Santos, Ariani Souza, Marcelo Salgado, Leuridan Torres. Profile of circulating natural killer cells in stage III triple negative breast cancer before and after neoadjuvant chemotherapy [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 PO4-03-09.

Abstract PO3-24-10: Losartan enhances the radiosensitivity of triple-negative breast cancer by reshaping the tumor immune microenvironment

Abstract Triple-negative breast cancer (TNBC) represents the most aggressive subtype of breast cancer, and the therapeutic options available for TNBC are limited. In addition to surgery and chemotherapy, radiotherapy (RT) is a primary treatment modality for TNBC. However, radio-resistance poses significant challenges to TNBC treatment. Prior research has shown that losartan, an angiotensin receptor blocker, can improve vessel perfusion and drug delivery, thereby enhancing the efficacy of chemotherapy or radiotherapy in cancer. However, in our study, we found that losartan could enhance the radiosensitivity of TNBC in immunocompetent mice model, but not in immunodeficient mice model and TNBC cells. It suggested that losartan might enhance the radiosensitivity of TNBC in an immune system dependent way. Previous studies had noted that tumor immune microenvironment (TIME) played an important role in radio-resistance. Therefore, we focused on the TIME in our further study. For immune cells, it had reported that the recruitment and activation of immunosuppressive cells such as M2 phenotype tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs), could lead to the establishment of and immunosuppressive TIME and decreased the radiosensitivity. In this study, we found losartan facilitated the polarization of TAMs towards the M1 phenotype, and impeded the immunosuppressive function of MDSCs after RT in 4T1 TNBC mice model. Additionally, losartan also caused a significant increase of CD8+ T lymphocytes in the TIME, and also markedly enhanced the activity of infiltrated T cell. When the CD8+ T cells were eliminated by anti-CD8α antibody, the radiosensitization effect of losartan was significantly decreased. Therefore, T-cell mediated tumor suppression is essential for the radiosensitization caused by losartan in TNBC. For immune factors, we found that TNBC exhibited an increase in the expression of programmed death-ligand (PD-L1) and indoleamine-2,3-dioxygenase (IDO) upon exposure to irradiation, and the combination of losartan resulted in a significant reduction in their expression in vitro and in vivo. At the same time, the 4T1 TNBC transplantation tumors were significantly inhibited by losartan combined with PD-1 inhibitor after RT, which indicated that losartan might amplify the efficacy of radio-immunotherapy. Collectively, these findings suggest that losartan could reshape the TIME of TNBC through regulating immune cells (TAMs, MDCSs and CD8+ T cells) and immune factors (PD-L1 and IDO), which result in the enhancement of radiosensitivity of TNBC. In our investigation, losartan was innovatively found to increase the radiosensitivity of TNBC by reshaping the TIME rather than on the tumor stroma. As one of the most commonly prescribed drugs for hypertension, the safety and affordability of losartan have been extensively confirmed. In the future, losartan combined with radiotherapy might be a promising strategy for TNBC treatment. Citation Format: Cuiwei Liu, Xu Wang, Zihan Xia, Yuxi Ma, Yanxia Zhao. Losartan enhances the radiosensitivity of triple-negative breast cancer by reshaping the tumor immune microenvironment [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 PO3-24-10.

Abstract PO3-15-01: Overexpression of N-glycosylation related gene OST4 promotes chemotherapy resistance in triple-negative breast cancer

Abstract Triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer, with high malignancy and poor outcome. Resistance to chemotherapy leads to treatment failure. How to overcome drug resistance is the key point in TNBC treatment. Previously, we initiated a prospective multicenter single-arm NeoPath clinical study (ClinicalTrial.gov identifier: NCT03907800) to assess the efficacy and safety of nab-paclitaxel combined with carboplatin in the neoadjuvant therapy of triple negative and HER2-positive early breast cancer. A total of 99 TNBC patients were enrolled and the pCR rate in TNBC was 33.78%. Samples before and after treatment were collected. RNA-sequencing results showed that OST4 was of high-expression in drug-resistant TNBC tumor tissues compared with chemo-sensitive samples. To verify the clinical significance of OST4 expression levels in TNBC, we tested the expression of OST4 by immunohistochemical technique on a tissue microarray including 87 TNBC cases treated with chemotherapy. We found that high expression of OST4 was associated with poor tumor differentiation, and patients with high OST4 expression had more relapse after chemotherapy. Ex-vivo proliferation assay and foci formation assay further confirmed that over-expression of OST4 promoted chemo-resistance, whereas down-regulating OST4 could reverse resistance in TNBC cell lines. As an oligosaccharyltransferase, it is reported that OST4 played parts in N-glycosylation. So we try to elucidate the relationship between N-glycosylation and drug resistance. Glycoproteomics results verified the existence of differential N-glycosylation atlas in drug-resistant tumor tissues compared with drug sensitive samples. NGS1 was identified as a potential target of OST4 by co-immunoprecipitation and mass spectrometry. In conclusion, high expression of OST4 could promote chemotherapy resistance in TNBC trough N-glycosylation regulation. Targeting OST4 may help reverse drug-resistance and improve therapeutic effect in TNBC. Citation Format: Wei Wang, Deyue Liu, Shuning Ding, Yan Fang, Jiayi Wu, Li Zhu. Overexpression of N-glycosylation related gene OST4 promotes chemotherapy resistance in 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 PO3-15-01.

Abstract PO3-03-10: Race and neoadjuvant treatment of triple negative breast cancer (TNBC) in the US community oncology setting

Abstract Background: TNBC is an aggressive subtype of breast cancer with limited targeted therapies. Black women have twice the incidence of TNBC compared to White women and within TNBC, Black women have worse outcomes than White women. Differences in both tumor biology of TNBC and social determinants of health (SDOH) play a role in observed disparities. The focus of this study is to evaluate SDOH factors associated to differences in the use of neoadjuvant chemotherapy (NC) in Black and White women in the US community oncology setting. Methods: This study was a retrospective, observational, cross-sectional design and used iKnowMed SM EHR data from the The US Oncology Network. Patients diagnosed with TNBC between 03/31/2017 and 09/30/2021 with stages II-III disease of tumor size ≥ 2cm (T2 or higher) were included. The index date was date of TNBC diagnosis and records were assessed from 6 months pre- to 6 months post-diagnosis for NC initiation. Univariable and multivariable logistic regression was conducted to evaluate impact of self-reported race on NC. Age, stage, BMI, insurance, area deprivation index (ADI), size of practice represented by physician count and geographical region, were studied in their mediating and moderating effects1 on the relationship between race and NC treatment. Results: Of the 3321 patients with TNBC identified in this study, 1969 self-reported white and 494 self-reported black (80% and 20% respectively). In multivariable regression accounting for all variables, Black race (OR = 1.57, 95% CI [ 1.02, 2.44], p=0.04), younger age, more advanced stage, obesity, non-Medicaid insurance, and West region, were all found to be positively associated with use of NC. Higher physician count was nominally associated, (p = 0.07). ADI was not found to be associated to NC. Mediator and moderator analysis for the relationship between race and NC showed that only stage and ADI variable inclusion in the model are required for the positive association between black race and NC. This is driven by a significant interaction between ADI and stage (p = 0.027) which differed for Black and White women. Mainly, for Black women ADI is positively associated to NC treatment in stage IIA, but negatively associated in all other stages (interaction term, p = 0.033). For White women, ADI is negatively associated to NC treatment in all stages. Only Black women with stage IIA tend to be treated more instead of less with NC in areas of greater deprivation (greater ADI). BMI presents nominal interactions with both race and stage, where obesity was more strongly associated with NC treatment in Black women (p = 0.088) and in stage IIA (p = 0.086). All other variables presented association to NC treatment without mediation or moderation of the race effect and without detectable differences across stages. Conclusions: Black women with stage IIA appear to be a special subgroup of TNBC patients for whom treatment with NC increases with ADI. Increased ADI generally results in less standard of care treatment; this is observed in this study for White women overall and for Black women in stages > IIA. Black women in areas of greater deprivation with stage IIA disease, may be perceived to be presenting with more aggressive disease and thus offered NC preferentially. This result lends support to the hypothesis that young black women present with a distinct, more aggressive subtype of TNBC in the early stages. Mediator and moderator analyses are important tools in elucidating the relationships between factors underlying racial disparities in both care and outcomes. 1. Hayes AF, Rockwood NJ. Regression-based statistical mediation and moderation analysis in clinical research: Observations, recommendations, and implementation. Behav Res Ther. 2017 Nov;98:39-57. Odds ratios for multivariable analysis –insert figure image– Race, stage and ADI –insert figure image– Race and BMI in stage IIA –insert figure image– Citation Format: Paola Raska, Joseph Dye, Nicholas J Robert, Angel Kidd, Michael Danso. Race and neoadjuvant treatment of triple negative breast cancer (TNBC) in the US community oncology setting [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 PO3-03-10.

Abstract PO3-06-13: A novel stable 6-aryl-2-benzoyl-pyridine colchicine-binding site inhibitor targeting microtubules (60c) is effective against taxane-resistant, metastatic breast cancer

Abstract Background: Improving survival for patients diagnosed with metastatic disease and treating spontaneous chemoresistance remain major clinical challenges in treating breast cancer. Triple negative breast cancer (TNBC), characterized by a lack of therapeutically targetable receptors (ER/PR/HER2), is an aggressive subtype of breast cancer. TNBC therapy relies on a combination of systemically administered chemotherapies, including microtubule-targeting agents (MTAs) like paclitaxel (taxane class) or eribulin (vinca class); however, there are currently no FDA approved MTAs that bind to the colchicine-binding site. Approximately 70% of patients who initially respond to paclitaxel, a first-line MTA, will develop taxane resistance (TxR) within 6 months. We have previously reported that an orally bioavailable colchicine-binding site inhibitor (CBSI), sabizabulin (formerly known as Veru-111), not only inhibits TNBC tumor progression but also treats pre-established metastatic disease in a taxane-refractory PDX model, HCI-10-Luc2. Sabizabulin is currently in phase II/III trials for advanced prostate cancer. To further improve potency and metabolic stability, we created next-generation derivatives of the sabizabulin scaffold, including 60c. Results: 60c shows improved potency compared to sabizabulin against taxane-sensitive and TxR TNBC models, inhibiting proliferation and clonogenicity at low nanomolar concentrations, and inducing apoptosis in a dose-dependent manner. In vivo, 60c therapy significantly suppressed primary tumor growth and lung metastasis in an orthotopic MDA-MB-231-TxR xenograft model without gross toxicity, and with equivalent efficacy to combrestatin A4 phosphate (CA-4P), another CBSI in clinical trials. In the taxane-refractory HCI-10-Luc2 PDX model, 60c significantly suppressed both the growth of the primary tumor (by ~3.5 fold) and the expansion of pre-established axillary metastases (by ~26 fold) whereas paclitaxel had no effect. Analysis of total photon flux of organs excised at study endpoint showed that 60c had distinct anti-metastatic tropism as compared to sabizabulin. Whereas 60c completely suppressed metastases to the spleen (0/9 mice had signal), and significantly reduced metastatic burden in the leg bones (only 3/9 mice had signal) and in the kidney (only 2/9 mice had signal), 60c had no statistically significant effect on liver metastases. In contrast, we had previously reported that sabizabulin strongly repressed liver metastases in the same PDX model (0 mice with detectable liver metastases), with less potent effects on bone. Unlike 60c, sabizabulin showed no improvement relative to the vehicle control for spleen and kidney metastases. Together, our data positions 60c as a promising candidate for TNBC therapy, particularly for patients with TxR disease. Our results also suggest that different CBSI scaffolds may preferentially inhibit metastasis to specific organs, which requires further investigation. Citation Format: Damilola Oluwalana, Kelli Hartman, Raisa Krutilina, Hao Chen, Hilaire Playa, Shanshan Deng, Deanna Parke, Duane Miller, Tiffany Seagroves, Wei Li. A novel stable 6-aryl-2-benzoyl-pyridine colchicine-binding site inhibitor targeting microtubules (60c) is effective against taxane-resistant, metastatic 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 PO3-06-13.

Abstract PO2-28-02: ROR1 regulates CREB3L1 via a novel signaling pathway in triple negative breast cancer

Abstract Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer; it is highly metastatic and incredibly difficult to treat due to its lack of the hormone receptors (estrogen, progesterone, and human epidermal growth factor receptor 2) that are used as therapeutic targets to treat breast cancer patients. TNBC patients are left with limited treatment options besides potent chemotherapy drugs that often leave them with undesirable side effects. My work intends to reveal a novel oncogenic signaling pathway that could be used to specifically target and eliminate TNBC in patients. Our lab is focused on a surface receptor that is found to be highly expressed only in cancerous tissue and during fetal development, Receptor tyrosine kinase-like orphan receptor 1 (ROR1). TNBC patients with high ROR1 expression are found to have poor prognosis and decreased overall survival rate compared to patients with low expression. ROR1 is thought to be a good drug target because it activates various oncogenic pathways such as PI3K/AKT and STAT3 in order to increase TNBC metastasis and chemoresistance. Previous single cell RNA sequencing data showed that TNBC tumors with high ROR1 expression also had reduced expression of cAMP responsive element binding protein 3 like 1 (CREB3L1). Often TNBC patients are found to have low CREB3L1 expression, a transcription factor is thought to play a tumor suppressive role in TNBC by increasing the expression of genes associated with the unfolded protein response (UPR) when ER stress occurs. CREB3L1 silencing in TNBC is due to hypermethylation of its promoter region by DNA methyltransferases (DNMTs). We hypothesize that ROR1 regulates CREB3L1 by influencing DNMT activity. This project aims to reveal the tumor suppressors that are downregulated in TNBC by ROR1 activation. Citation Format: Victoria Reed, Eric Lalu, Bela Peethambaran. ROR1 regulates CREB3L1 via a novel signaling pathway in 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 PO2-28-02.

Abstract PO2-28-08: A spatial transcriptomic study of a triple-negative breast cancer (TNBC) patient-derived xenograft (PDX) model of residual disease refractory to conventional chemotherapy

Abstract TNBC is one of the most aggressive subtypes of breast cancer. Combating chemotherapy resistance is critical to improving quality of care and reducing fatality among TNBC patients. In order to understand the mechanisms of chemoresistance in TNBC tumors, it has been proposed that the spatial interactions between cell types in the tumor microenvironment (TME) could offer insights into the differential response to therapy among tumors, and metastatic potential of certain tumors over others. Thus, this study utilizes spatially resolved transcriptomic (SRT) technology to profile the spatial interactions in the TNBC TME. With the goal of better understanding chemoresistance in TNBC and providing a proof-of-concept for new technology, we have launched a longitudinal SRT study of a TNBC PDX of residual disease before, during, and after adriamycin and cyclophosphamide (AC) treatment (Tx). SRT by 10X Genomics Visium was performed on vehicle, AC-treated residual tumor (21 days post-Tx), and AC-treated regrown tumor (50 days post-Tx when tumors regrew to starting tumor volume). This study is divided into two parts: 1) development of a computational pipeline; 2) spatial colocalization analysis of residual and regrown tumors to understand chemoresistance. PART 1: Due to the lack of specialized tools for processing and sorting xenograft reads from SRT data, we developed the Xenomake pipeline, which combines a xenograft sorting algorithm (Xengsort) and spatial barcode demultiplexing pipeline to assign reads into the host and graft organisms for each spatial spot. RESULTS: Xenomake permits clustering the spatial spots into stroma-rich (enriched for mouse mRNAs), and epithelial-rich (enriched for human mRNAs) regions. We show that Xenomake can find differential cytokine production in the stroma and epithelium. Since PDX data separate the tumor into stroma and epithelium by organism, the pipeline enables fine-tuned downstream analysis such as stromal-stromal and stromal-epithelial interactions. Xenomake is thus generally applicable for SRT involving PDX samples. PART 2: Previously we detailed patterns of tumor regression into a residual tumor state, followed by uncontrolled regrowth in the absence of treatment in multiple PDX models of TNBC. Although using PDX models necessitates immune-compromised mice, several types of stromal populations are present and analyzable in these models. Thus, using organism-assigned reads processed by Xenomake, we computationally inferred the localization pattern of stromal cell types in Visium spots including cancer associated fibroblasts (CAF), macrophages (MP), endothelial cells (ENDO), monocytes, and perivascular-like cells. We compared the spatial localization profiles (SLP) of stromal cell types across samples. With human reads, we computed the spatial pathway activity map (SPAM) for the ~30 HALLMARK pathways across samples. We correlated the patterns of SPAM with stroma cell-type SLP to survey the stroma-epithelial interactions across samples. RESULTS: Stroma cells are generally distributed in the tumor periphery in vehicle and AC50, while in AC21 there is a notable increase in stroma abundance and stroma infiltration within tumor mass. SLP of MP (Cd68+ and Csf1r+) is correlated with ENDO (Pecam1+), and with CAF (Acta2+ and Pdgfrb+). Additionally, all 3 cell types are correlated with Vim and Cd44 expression. Although all samples show enrichment of MP, ENDO, and CAF, they interact differently with pathway activities of adjacent epithelial cells. In vehicle and AC50, the 3 cell types are colocalized with OXPHOS, MYC targets, E2F pathway, while in AC21, a switch to colocalization with EMT is observed. Furthermore, hypoxia response and glycolysis display anti-correlation with stroma cell types, meaning that these pathway activities are further away from stroma and occupy distinct territories. The results suggest stroma-tumor metabolic crosstalk and ways of targeting residual disease. Citation Format: Benjamin Strope, Katherine Pendleton, William Bowie, Gloria Echeverria, Qian Zhu. A spatial transcriptomic study of a triple-negative breast cancer (TNBC) patient-derived xenograft (PDX) model of residual disease refractory to conventional chemotherapy [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 PO2-28-08.

Abstract PO1-26-06: The effect of localized radiotherapy in combination with chemoimmunotherapy in a humanized triple-negative breast cancer mouse model

Abstract Background: Metastatic triple-negative breast cancer (TNBC) is an aggressive sub-type of breast cancer that is challenging to treat. While the addition of immunotherapy (IT) with pembrolizumab (pembro) to chemotherapy prolongs overall survival in patients with programmed death-ligand 1 positive (PD-L1+) TNBC, few patients obtain long-term benefit. Radiotherapy (RT) can stimulate cellular damage, release of tumor antigens and promote the T cell anti-tumor response including at distant sites (abscopal response) when used with IT. The purpose of this study was to investigate the combination of RT with pembro and paclitaxel (pac) in a TNBC humanized mouse model. Methods: Human Immune System BRGS (BALB/c, Rag2-/-, IL2RγC-/-, NODSIRPa ) mice were engrafted with TNBC MDA-MB-231 cells in bilateral flanks. Treatments included: vehicle, pac 10 mg/kg intra-peritoneal (IP) weekly, pembro 15 mg/kg IP weekly, and RT 8 Gy x 3 fractions every other day the first week of treatment to one-sided tumors (contralateral tumors received no RT). Mice were treated and analyzed in the following groups: vehicle, pac + pembro, RT + pac, and RT + pac + pembro. Treatments began when tumors reached 100-300 mm3 and tumors were measured twice weekly. At the end of study, sera, lymph nodes (LNs), spleen, and tumor tissue were collected for immunohistochemistry, single cell suspensions, and flow cytometry analysis for immune cell populations. Results: All treatment arms resulted in a decrease in tumor volume when compared to vehicle with the greatest reduction in the RT + pac and RT + pac + pembro arms. Combination therapy with RT + paclitaxel (p=0.0002) and RT + pac + pembro (p=0.008) resulted in a statistically significant decrease in specific growth rate (SGR) when compared to vehicle. An abscopal effect was not observed in the non-RT tumors compared to RT-tumors in either group. RT + pembro was associated with an increase in hCD45 T cells in LNs and spleens but not in tumors. In mice that received RT, a decrease was noted in HLA-ABC class I and Intermediate Class II major histocompatibility complex (MHC). In addition, RT-tumors had reduced expression of PD-L1 and polio virus receptor (PVR) and increased expression of PD-1. The percentage of interferon gamma (IFNg+), tumor necrosis factor alpha (TNFa+) CD8+ T cells increased with radiation. This percentage was the highest in the triplet therapy with RT+ pembro + pac. Conclusion: Combination treatment with RT + immunochemotherapy resulted in a significant increase in anti-tumor activity when compared to immunochemotherapy alone, however, an abscopal effect was not observed in contralateral non-RT tumors. RT resulted in down-regulation of immune inhibitory receptors and tumor MHC. Citation Format: Anna Schreiber, Stacey Bagby, Stephen Smoots, Adrian Dominguez, Christine Fisher, Julie Lang, Todd Pitts, Jennifer Diamond. The effect of localized radiotherapy in combination with chemoimmunotherapy in a humanized triple-negative breast cancer mouse model [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 PO1-26-06.

Abstract PS18-09: The DARC side of Breast Cancer - DARC, Duffy-null and African ancestry influence in the Triple Negative Breast Cancer tumor microenvironment

Abstract Background. Despite a recent convergence of breast cancer (BC) incidence rates between African American (AA) and European American (EA) women, AA women continue to have ~40% higher mortality rates. BC is a heterogeneous collection of diseases, where African ancestry women are disproportionately burdened with the most aggressive subtype of BC, triple negative BC (TNBC). We have previously reported that the African ancestry-specific Duffy-null allele (FY-) is a risk factor for TNBC diagnoses. FY- is a promoter variant that removes expression of the Duffy Antigen Receptor for Chemokines (DARC/ACKR1), from red blood cells (RBCs). DARC serves as a portal of entry for Plasmodium vivax malaria parasite, and FY- confers immunity, leading to fixation of FY- among Sub-Saharan African populations. DARC is an atypical chemokine receptor that functions to modulate chemokine levels in circulation and tissues to aid immune cell recruitment. DARC is also expressed on breast tumor epithelial cells, however the significance of DARC in the TNBC tumor microenvironment (TME) has not fully been explored. Leveraging our African ancestry enriched International Study for the Center of Breast Cancer Subtypes cohort and in vivo murine models, we employed multi-omics approaches to explore the function of FY- and DARC expression across cell types in the TNBC TME. Genomics. Using transcriptomic data from the TCGA BC cohort, we have previously reported that DARC expression is highly correlated with deconvoluted immune cell abundance using CIBERSORT. To build upon this finding among TNBC patients, we have analyzed RNAseq data from two cohorts of African ancestry women to explore correlation of DARC expression status and immune cell abundance. Among TNBC cases, we report that higher DARC expression was significantly associated with increased immune cell abundance, with increases in B cell, T cell and monocyte populations. Using whole genome sequencing data across 86 African ancestry cases, we are currently investigating germline FY- status with mutational signatures. Circulating biomarkers. Patient plasma was collected prior to surgery, where Luminex multiplex assays were performed to quantify levels of >40 circulating chemokines and cytokines. FY- status has been determined for ~550 patients using single-plex or multiplex PCR genotyping methods from germline saliva DNA. Our univariate analyses show several circulating chemokines, including CCL2, CXCL2, CXCL6 and CXCL11, have significant differences between FY- and non-FY- BC patients. Curation of clinicopathological variables for multivariate analysis is ongoing. Murine models. We crossed C3(1)Tag BC transgenic mice with a DARC knock-out (KO) line to generate mice lacking DARC expression that spontaneously develop tumors in the mammary fat pads. The C3(1)Tag model is reported to have similar gene expression profiles to basal-like TNBC tumors. Tumors were collected at pre-determined time points of 25 and 30 weeks, where DARC KO mice had increased tumor size and tumor burden at 30 weeks. Initial fluorescent staining revealed an increase in immune cell infiltration in the TME of DARC expressing mice compared to DARC KO mice. To further explore this, we employed multiplex staining across a representative cohort of DARC expressing and KO mice at 25 and 30 weeks to capture the specific immune cell populations infiltrating the TME. Conclusions. TNBC tumors have worse prognosis due to lack of targeted therapeutic options. Increased immunogenicity of TNBC tumors, especially among African ancestry women may be driven in part by DARC expression. Characterization of FY- status, in coordination with DARC among other cell types in the TNBC TME could present new opportunities for biomarker and/or therapeutic development to improve prognosis for these underserved populations. Citation Format: Rachel Martini, Stevens Patino, Emma Guyonnet, Brian Stonaker, Isra Elhussein, Julie Sahler, Avery August, Nancy Manley, Rick Kittles, Clayton Yates, Lisa Newman, Melissa Davis. The DARC side of Breast Cancer - DARC, Duffy-null and African ancestry influence in the Triple Negative Breast Cancer tumor microenvironment [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 PS18-09.

Abstract PO3-17-08: SAFETY AND TOLERABILITY OF SUBCUTANEOUS TRASTUZUMAB AS A TREATMENT IN PATIENTS WITH EARLY HER 2 POSITIVE BREAST CANCER : EXPERIENCE OF A CANCER CENTER IN PERU

Abstract BACKGROUND: About 15% to 20% of breast cancers express positivity for human epidermal growth factor receptor 2 (HER2), a more aggressive breast cancer subtype with shorter survival. Trastuzumab, a humanized monoclonal antibody was approved by the U.S. Food and Drug Administration (FDA) for therapeutic use in metastatic breast cancer in 1998 and HER2-positive early breast cancer in 2006. HER2 overexpression is associated with more aggressive tumor growth and worse prognosis compared to HER2-negative tumors. HER2-positive tumors occur more frequently in younger women and node-positive women and are often less responsive to cytotoxic therapies. The primary objective of this study was to evaluate the tolerability of the subcutaneous formulation of trastuzumab in real life at the national institute of neoplastic diseases LIMA-PERU in patients with epidermal growth factor receptor 2 (HER2)-positive early breast cancer; efficacy was a secondary objective. METHOD: Female patients aged 18 years or older diagnosed between 2018-2019 with early epidermal growth factor receptor 2 (HER2)-positive breast cancer who received at least 1 dose of trastuzumab subcutaneously in a neo/adjuvant setting with or without chemotherapy were included. The treatment indication is 600 mg at a fixed dose every 3 weeks for 18 cycles. RESULTS: A total of 70 patients who received treatment with subcutaneous trastuzumab were included in the analysis. The mean age of the population was 52.6 ± 12.4 years, with the majority of patients being older than 50 years (54.29%). The mean number of subcutaneous trastuzumab cycles received was 11.4 ± 4.2. Adverse effects such as arthralgia (47.62%), diarrhea (9.52%), fatigue (9.52%) and injection site reaction (9.52%) occurred in 30% of patients. The mean number of cycles received until the first occurrence of adverse effects was 5.2 ± 2.1. It was observed that 97.14% completed treatment with trastuzumab subcutaneously, and 2.86% had to discontinue treatment. Cardiotoxicity and hypertension were the reasons why patients discontinued treatment. Of the patients included in the study, 63.77% received subcutaneous trastuzumab in the neoadjuvant setting, while the remaining 36.23% received it in the adjuvant setting. Of the patients, 45.71% started treatment with trastuzumab intravenously and received an average of 6 ± 3 cycles before switching to the subcutaneous presentation. After 3 years of follow-up, 7.14% developed disease progression; 57.1% had progression at the cerebral level, 28.6% at the local level and 14.3% at the pulmonary/hepatic level. 98.57% of patients are alive. CONCLUSIONS: In a real-life setting, subcutaneous trastuzumab is a well-tolerated and effective treatment option for patients even in patients who started treatment with the intravenous presentation and made the switch during treatment. Table 1: General clinical characteristics of patients XX XX Citation Format: Iris Otoya, Natalia Valdivieso, Zaida Morante, Carlos Castañeda, Silvia Neciosup, Mónica Calderón, Henry Gómez. SAFETY AND TOLERABILITY OF SUBCUTANEOUS TRASTUZUMAB AS A TREATMENT IN PATIENTS WITH EARLY HER 2 POSITIVE BREAST CANCER : EXPERIENCE OF A CANCER CENTER IN PERU [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 PO3-17-08.

Abstract PO1-24-05: EZH2 histone methyltransferase activity promotes spindle metaplastic breast carcinoma metastasis and is induced by CCN6 knockout/b-catenin/TCF axis

Abstract Background: Metaplastic breast carcinomas (mBrCAs) are a highly aggressive subtype of triple negative breast cancer with histological evidence of deregulated differentiation towards non-glandular components. Previous studies have demonstrated that human mBrCA often exhibit activation of differentiation pathways, including canonical Wnt/b-catenin and EZH2-mediated transcriptional repression. Our lab has identified CCN6 as a tumor suppressor in mBrCA. MMTV-Cre;Ccn6fl/fl (CCN6KO) mice develop spindle mBrCAs and CCN6 is reduced/lost in 68% of human mBrCAs. Recently, we have demonstrated that the tumor suppressor function of CCN6 in spindle mBrCA requires activation of Wnt/b-catenin signaling pathway. Here, we tested the hypothesis that CCN6 KO leads to the upregulation of EZH2 histone methyltransferase promoting mBrCA. Furthermore, we investigated the requirement for the activation of the Wnt/b-catenin pathway in this mechanism. Methods: To test the effect of CCN6/b-catenin on EZH2 gene and protein expression we performed IHC, IF, qRT-PCR, ChIP-Seq, RNA-seq, invasion and adhesion assays, EZH2 reporter assay and immunoblots in mBrCA cell lines and MMTV-Cre;Ccn6fl/fl tumors. To investigate the role of CCN6KO-induced b-catenin activation on EZH2 activity and neoplastic functions we employed three independent approaches: i) Expression of a dominant-negative Tcf4 (dnTcf4) rescued with EZH2-WT, dSET and dNLS domain mutants versus vector in MMTV-Cre;Ccn6fl/fl tumor-derived cells; ii) Expression of a constitutively active mutant (S33Y) b-catenin in concert with treatment with recombinant human CCN6 (rhCCN6; 500 ug/ml) versus control; iii) Syngeneic orthotopic mammary tumor transplants of MMTV-Cre;Ccn6fl/fl were used for in vivo rescue experiments with rhCCN6 or BSA. To assess the therapeutic benefit of inhibiting EZH2 methyltransferase activity, MMTV-Cre;Ccn6fl/fl tumor cells (CCN6KO cells) were implanted orthotopically or intracardially in FVB mice, followed by treatment with EPZ-6438 (a selective EZH2 methyltransferase inhibitor) or vehicle. We tested CCN6, b-catenin, and EZH2 expression by IHC in a cohort of 27 human mBrCA tumor samples. Results: CCN6KO-induced b-catenin/TCF activation mediates EZH2 transcriptional upregulation and the deposition of repressive H3K27me3 in spindle mBrCAs. We found that the invasion program triggered by CCN6KO-induced Wnt/b-catenin requires EZH2 catalytic activity as WT-EZH2 (but not dSET-EZH2) rescued the reduced invasion of CCN6KO-dnTcf4 cells. RNA-seq and 3H3K27 ChIP-seq of CCN6KO-dnTcf4 cells transduced with EZH2-WT or dSET-EZH2 identify specific CCN6KO-b-catenin/Tcf targets that require EZH2 transcriptional repressor function. In vivo, administration of CCN6 protein to MMTV-Cre;Ccn6fl/fl tumor transplants reduces tumor growth and nuclear b-catenin, EZH2 and 3H3K27 in the tumors. Pharmacologic inhibition of EZH2 reduces the growth and metastasis of CCN6KO mBrCA tumors and improves survival. We identify a subset of human spindle mBrCA (54%) that display a CCN6Low/nuclear b-cat/EZH2High phenotype. Conclusion: We found a critical role for EZH2 activation in CCN6-deficient mBrCA tumor phenotypes via b-catenin/TCF Wnt canonical signaling. We demonstrate the effectiveness of pharmacological inhibition of EZH2 methyltransferase activity in reducing primary tumor growth and distant metastasis in mouse models of spindle mBrCA. In clinical samples, low CCN6 is significantly associated with activated b-catenin and high EZH2 in spindle mBrCAs compared to other subtypes. These data reveal a novel tumor suppressor mechanism of CCN6 and provide compelling evidence supporting the potential therapeutic value of CCN6 restoration, b-catenin or EZH2 inhibition as promising approaches for the treatment of spindle mBrCAs. Citation Format: Maria Gonzalez, Ahmad Eido, GIUSEPPINA AUGIMERI, Celina Kleer. EZH2 histone methyltransferase activity promotes spindle metaplastic breast carcinoma metastasis and is induced by CCN6 knockout/b-catenin/TCF axis [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 PO1-24-05.