Triple-negative breast cancer: current understanding and future perspectives

Multidisciplinary considerations in the treatment of triple-negative breast cancer.

Triple Negative Breast Cancer (TNBC) is a particular subtype of breast cancer accounting for 15% to 20% of all breast cancer. It is defined on immunohistochemistry (IHC) by negative estrogen receptor (ER) and progesterone receptors (PR) and negative human epidermal growth factor receptor 2 (HER2) and characterized by aggressive nature, distinct metastatic patterns, lack of targeted therapies and poor outcomes. Cytotoxic chemotherapy was the mainstay of treatment for long decades and the development of new treatments for selected patients was complicated because of the heterogeneity of TNBC. The good understanding of molecular and genomic mechanisms of TNBC has allowed the development of new targeted therapies more efficient. Although the heterogeneity of genetic alterations in TNBCs based on the ethnicity and the age, BRCA mutations are found in around 20% to 25% of patients and especially in those of the basal-like immune-phenotype. Thus, targeting the defects in the DNA repair pathway becomes a promising field of research for this selected category of TNBC patients. Poly (ADP-ribose) polymerase (PARP) inhibitors exploit this DNA defects through synthetic lethality and therefore represent a promising treatment especially in BRCA1/ BRCA2 mutation carriers. These findings have finally allowed bringing personalized treatment to this orphan disease. In this work we tried to explain the rationale and mechanisms of targeting the immune system in TNBC, to report the results from recent clinical trials that put immunotherapy as a new standard of care in TNBC.

Background: Triple Negative Breast Cancer (TNBC) is a biologically aggressive subtype of breast cancer characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2) expression. It accounts for 15–20% of breast cancers globally but is disproportionately prevalent in younger women, women of African descent, and patients in low- and middle-income countries (LMICs). TNBC is associated with rapid progression, early recurrence, and limited targeted treatment options. Objective:To provide a comprehensive review of TNBC, focusing on epidemiology, molecular biology, clinicopathological features, diagnostic approaches, management strategies, recent therapeutic advances, and regional disparities. Methods:A narrative review was conducted using PubMed, Scopus, Web of Science, and African Journals Online (2013–2025). Eligible studies addressing TNBC incidence, biology, clinical presentation, diagnostics, treatment, and emerging therapies were included, with emphasis on comparative global and Sub-Saharan African data. Results:TNBC exhibits marked geographic and ethnic variation, with prevalence rates of 12–15% in Western populations and up to 46% in West Africa. Molecular profiling reveals heterogeneity across basal-like, mesenchymal, immunomodulatory, and luminal androgen receptor (LAR) subtypes. Standard treatment remains chemotherapy, particularly in the neoadjuvant setting, where pathologic complete response predicts improved outcomes. Recent advances include PARP inhibitors in BRCA-mutated TNBC, immune checkpoint inhibitors for PD-L1–positive disease, and antibody-drug conjugates such as sacituzumab govitecan, which have demonstrated survival benefit. However, in LMICs, late presentation, limited access to immunohistochemistry, and high treatment costs remain major barriers. Conclusion:TNBC continues to represent a global oncological challenge. While novel therapies are improving outcomes in high-resource settings, substantial gaps in diagnosis and treatment persist in LMICs. Future efforts should prioritize equitable access to molecular diagnostics, affordable targeted therapies, and global collaborations to reduce disparities in TNBC outcomes.

Background: Specific biomarkers can be essential for developing effective treatments for aggressive breast cancers, especially triple negative subtypes, for which treatment options are limited. Folate receptor alpha (FRα), a critical membrane protein for DNA synthesis and cell metabolism, has been suggested to participate in the transformation of breast cancer into aggressive subtypes. It has been shown to be strongly associated with poor prognosis in triple negative breast cancers (TNBC) as well as estrogen receptor (ER) positive and progesterone receptor (PR) negative subtypes. SOX10 is a nuclear transcription factor that participates in neural crest development and in the differentiation of cells of melanocytic lineage. Data suggests that SOX10 may contribute in stem cell or progenitor cell maintenance. Recently, SOX10 expression has also been documented in benign breast myoepithelial cells and in aggressive breast cancers. The correlation of FRα and SOX10 in breast cancer is not fully known. This is the first study to compare FRα and SOX10 immunohistochemical profiles in breast cancers with emphasis in TNBC. Design: 166 cases of whole breast cancer tissues were classified according to their ER, PR, and HER2 immunohistochemical (IHC) status. These same cases were then IHC stained for mouse monoclonal SOX10 and FRα. Cut-off values of 1% and 5% for SOX10 and FRα, respectively, were used to determine positivity. Results: SOX10 achieved a sensitivity of 42.1% (8/19) in ER+/PR-/HER2- cases and was negative in all ER+/PR-/HER2+ cases (p<0.05). FRα was positive in 7.6% (7/92) of ER+/PR+/HER2- cases and was negative in all ER+/PR+/HER2+ cases. SOX10 identified more ER+/PR-/HER2- cases (42.1%, 8/19) than ER+/PR+/HER2+ cases (7.7%, 1/13) (p<0.05). Similarly, FRα stained 52.6% (10/19) of ER+/PR-/HER2- cases and was negative in all ER+/PR+/HER2+ cases (p<0.005). SOX10 and FRα were observed in 3.3% (1/30) and 20% (6/30) of HER2+ cases, respectively. In ER-/PR-/HER2- (triple negative) cases, both markers were highly expressed with 40.0% (10/25) and 52.0% (13/25) positive cases with SOX10 and FRα, respectively, with 24.0% (6/25) of cases positive with both markers. Approximately one half of TNBC cases expressed SOX10 and FRα; however, most SOX10 positive TNBC cases did not overlap with FRα positive TNBC cases. Table 1: SOX10 and FRα expression in breast cancer subtypesER/PR/HER2 ClassificationSOX10+ (%)FRα+ (%)Co-expression of SOX10 and FRα (%)ER+/PR+/HER2+ (n=13)1 (7.7%)0 (0.0%)0 (0.0%)ER+/PR+/HER2- (n=92)6 (6.5%)7 (7.6%)2 (2.2%)ER+/PR-/HER2+ (n=10)0 (0%)5 (50.0%)0 (0.0%)ER+/PR-/HER2- (n=19)8 (42.1%)10 (52.6%)5 (26.3%)HER2+ (n=30)1 (3.3%)6 (20.0%)0 (0.0%)ER-/PR-/HER2- (n=25)10 (40.0%)13 (52.0%)6 (24.0%) Conclusion: SOX10 and FRα were frequently expressed in triple negative breast cancers and in progesterone receptor negative breast cancers. Our data suggests that there may be different mechanisms by which SOX10 and FRα are implicated in aggressive breast cancers. These findings may help achieve a better understanding of the two different pathways involving stem cells (SOX10) and growth factors (FRα), their potential prognosis and their therapeutic management in the future. Citation Format: Laura L Hoang, Weimin Qi, Charlie Yu, David Tacha. SOX10 and folate receptor alpha are frequently expressed in triple negative and progesterone receptor negative breast cancers [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-01-13.

1511 Background: Triple-negative breast cancer (TNBC) is a type of aggressive breast cancer diagnosed in approximately 15% of total breast cancer patients. TNBCs are characterised by the lack of expression of estrogen receptors alpha (ER-α), progesterone receptors (PR) and human epidermal growth factor receptor 2 (HER2), and thus are unresponsive to currently available ER-targeted and HER2-based treatments. An intriguing characteristic of TNBC is its association with hereditary breast cancers, as TNBCs are over-represented in BRCA1 mutation carriers. The etiology behind this association is yet unclear but may ultimately provide avenues for prevention and targeted therapy. Screening for BRCA1 and BRCA2 mutations is now an established component of risk evaluation and management of hereditary breast cancer. Genetic testing is offered to a breast cancer patient usually according to her family history; however some women may qualify for testing solely because of an early age of onset and/or tumor pathology, such as the triple-negative phenotype. There is a lack of population studies that determine the frequency of BRCA1 mutations among TNBC patients. Methods: We studied 284 women who were diagnosed with triple-negative invasive breast cancer independently of their age or family history. The mean age for the total cohort was 50.4 years (range: 21-76). The most prevalent BRCA1 mutations in the Greek population that account for 54% of all mutations detected in both genes (BRCA1 and BRCA2), were screened in all patients. Additionally, BRCA1 exons 5, 11 and 23 were also sequenced in cases with age of onset < 40 years. Results: Thirty deleterious BRCA1 mutations were identified in the 284 patients with triple-negative breast cancer (10.6%). Mean age of onset for all mutation carriers was 40.2 years (range: 28-57). Of the 30 carriers, 10 had no reported family history of breast or ovarian cancer. Among a total of 36 women with early-onset TNBC (< 40 years), 17 (47%) had a BRCA1 mutation. Conclusions: Women with early-onset triple-negative breast cancer are candidates for genetic testing for BRCA1, even in the absence of a family history of breast or ovarian cancer. No significant financial relationships to disclose.

Epigenetic Regulation of Cancer Stem Cell Genes in Triple-Negative Breast Cancer

Rationale and purpose: Triple negative breast cancers (TNBCs), characterized by lack of hormone receptors' expression in absence of HER2 amplification, partially overlap with the basal-like subtype, with frequent occurrence in BRCA1 mutation carriers (BRCA1+). TNBCs are often associated with earlier onset, interval cancer diagnosis, larger size and aggressive clinical course with peak risk of recurrence at 1-3 years and increased mortality rate in the first 5 years. Thus, when screening women at high risk of breast cancer, special attention should be paid to patient outcome for TNBCs in comparison with non-TNBCs. Our aim was to compare TNBCs and non-TNBCs diagnosed during a prospective, non-randomized, multimodality screening study – including clinical breast examination (CBE), mammography, ultrasound (US) and magnetic resonance imaging (MRI) – on women at familial/genetic high risk of breast cancer conducted in 18 centres from June 2000 to March 2008 (ISS-HIBCRIT-1; Sardanelli F et al, Invest Radiol 2011). Methods: Comparisons were performed using Mann-Whitney U, Fisher exact and χ2 tests. Results: Among the 44 patients diagnosed with invasive cancers, 14 (31%) were TNBCs and 30 (69%) non-TNBCs, the former being 13 invasive ductal (IDC) and 1 atypical medullary carcinoma, the latter also including 15/30 lobular subtypes and/or DCIS component (p=0.005). Of the 14 TNBCs, 10 (71%) were found in BRCA1+, 2 (14%) in BRCA2+ and 2 (14%) in BRCA-untested women with strong family history of breast/ovarian cancer; the same data for 30 non-TNBCs were 9 (30%), 6 (20%) and 15 (50%) respectively (p=0.028). We had only three interval cancers, all TNBCs. The median age at diagnosis was 49 years (range 36-62) for TNBCs and 53 years (range 35-72) for non-TNBCs (p=n.s). TNBCs presented a higher rate (11/14, 79%) of pathological grade 3 IDCs compared with non-TNBCs (8/30, 27%) (p=0.002). The mean tumor size was 1.6 cm for TNBCs and 1.2 cm for non-TNBCs (p=n.s). Nodal status was negative in 12/14 (86%) TNBCs and in only 16/30 (53%) non-TNBCs (p=0.038). MRI similarly outperformed CBE, mammography and US in both TNBCs and non-TNBCs. Clinical course and survival could be monitored for 40/44 patients (91%), 13 TNBCs and 27 non-TNBCs, with a follow-up of 5.8 and 6.3 years (p=n.s) respectively. The rate of disease-free patients for over 5 years was 8/13 (62%; mean disease-free interval 7.0 years, range 5.0-8.0) for TNBCs and 17/27 (63%; mean 7.2 years, range 5.2-9.9) for non-TNBCs. Death due to BC occurred for 2/13 TNBC (15%, at 3.5 and 4.2 years) and 3/27 non-TNBC patients (11%; at 2.0, 4.9 and 5.7 years). The rate of locoregional relapse was 1/13 (8%, at 4.4 years) and 5/27 (19%; mean time of 5.0 years, range 2.4-7.0) respectively. Distant recurrence was reported for only 2 non-TNBC patients. Conclusion: TNBCs showed stronger association with BRCA1+ status, lower rate of lobular subtypes or DCIS component, and less frequent nodal involvement. Despite a more frequent pathological grade 3 and the tendency to be diagnosed as interval cancers, under the current treatment protocols TNBCs showed relapse and BC-related death rates and over-5-year disease-free intervals similar to those of non-TNBCs. These data provide outcome evidence supporting the value of entering women at high risk of TNBC (in particular BRCA1+) in intensive screening programs including MRI. Citation Format: Franca Podo, Filippo Santoro, Siranoush Manoukian, Clelia de Giacomi, Laura Cortesi, Lorenzo Preda, Stefano Corcione, Francesco Sardanelli. High-risk patients found affected with breast cancer during a multimodality screening program: Triple negative versus non-triple negative breast cancers. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr B13.

The human epidermal growth factor receptor 2 (HER2)/erythroblastic oncogene B2 (ERBB2) is a tyrosine kinase receptor protein that plays an important role in the pathogenesis and aggressive nature of the tumors. It is well studied in various cancers, including breast, gastric, esophageal, ovarian, lung, and endometrial cancers. It is a well-known negative prognostic indicator in breast cancer associated with decreased disease-free survival and overall survival. Breast cancer treatment has been revolutionized with the invention of targeted monoclonal antibody therapies against the HER2 receptor, particularly trastuzumab and its antibody-drug conjugates (ADCs). HER2-targeted therapies have proven to improve progression-free survival and overall survival when added to chemotherapy in adjuvant, neoadjuvant, and metastatic settings in patients who are HER2-positive. ADCs approved for breast cancer include trastuzumab emtansine (Kadcyla, T-DM1) and trastuzumab deruxtecan (Enhertu, T-DXd). With enthusiasm and reported benefit, particularly in metastatic disease, HER2-targeted therapies are now widely used in breast cancer patients classified as HER2-negative based on binary classification but categorized as “HER2-low” with some degree of HER2 expression. HER2-targeted therapies are not approved for patients who have HER2 (ERBB2) mutation and have no HER2 expression of any degree (immunohistochemistry (IHC) 0+). We could not find any such reported cases, research studies, or clinical trials of HER2-targeted therapies being used in patients with HER2 mutation in our extensive search of the literature. We present a rare practice-changing case of a patient with triple negative metastatic breast cancer (estrogen receptor (ER), progesterone receptor (PR), and HER2 negative, HER2 0+ on IHC) and positive HER2 mutation, who achieved a disease-free survival of more than 2.5 years with trastuzumab deruxtecan monotherapy. This case makes a compelling argument for considering HER2-targeted therapies, mainly ADCs, in HER2-mutant breast cancer patients either as a monotherapy or in combination with other therapies, particularly in metastatic disease. This case report also indicates that further research and clinical trials looking into the efficacy and safety profile of anti-HER2 treatments in HER2-mutant breast cancers are warranted.

BACKGROUND: Triple negative breast cancer (TNBC), characterized by absence of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), is typically associated with aggressive tumor phenotype and poor prognosis. TNBC is also considered highly heterogeneous disease. Since TNBC lacks efficient therapeutic target, it is generally treated with nonspecific cytotoxic agents. A better understanding of molecular and histopathological features of TNBC is of great importance, in order to develop a new therapeutic strategy and to improve the prognosis of TNBC. TNBC has many similarities with basal-like breast cancer (BLBC), and is also associated with stemness and BRCAness. In addition, recent studies suggest links between TNBC and epithelial-mesenchymal transition (EMT). To identify prognostic biomarkers and novel therapeutic targets, we investigated the expression of the factors associated with EMT in TNBC. MATERIALS and METHODS: Sporadic invasive breast cancer specimens were obtained from 659 Japanese patients who underwent surgery in our department between 1994 and 2010, and 90(14%) cases were diagnosed as TNBC. The E-cadherin and vimentin mRNA expression was evaluated by quantitative RT-PCR. The E-cadherin, vimentin, CK5/6 and epidermal growth factor receptor(EGFR) protein expression was assessed by immunohistochemistry. In this study, we defined TNBC with positive expression of CK5/6 and/or EGFR as BLBC, and TNBC with low expression of E-cadherin and positive expression of vimentin as EMT-type. RESULTS: Compared with non-TNBC cases, E-cadherin mRNA expression was significantly lower in TNBC cases (p=0.0012). Immunohistochemically, E-cadherin expression was significantly lower (p=0.0001) and vimentin expression was significantly higher (p=0.0049) in TNBC cases. Vimentin expression was associated with younger age (&amp;lt;50 years old, p=0.021), high nuclear grade (p=0.017) and high Ki67 expression (p&amp;lt;.001) in TNBC. Among the patients with TNBC, vimentin expression was significantly associated with poor prognosis, in terms of disease free survival (p=0.0059) and overall survival (p=0.013). Multivariate analysis showed that vimentin expression was an independent prognostic factor for both disease free survival (p=0.017) and overall survival (p=0.012). Among TNBC cases, 52(63%) cases were BLBCs and 15(18%) cases were EMT-type. Among BLBC patients, vimentin expression was also associated with significantly shorter disease free survival (p=0.0085) and overall survival (p=0.0057). The patients with both BLBC and EMT-type features showed especially poor prognosis(P=0.05). CONCLUSION: These findings suggest that elevated expression of vimentin attributes to the aggressive phenotype in TNBC patients. Vimentin expression might be useful as a molecular marker for prognosis of TNBC, and vimentin may represent a novel therapeutic target of TNBC. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-02-10.

Female breast cancer (BC) became the most commonly diagnosed cancer globally in 2020. One of the hallmarks of BC is both intratumor and intertumor heterogeneity. Efforts have been made to categorize this heterogeneity based on the presence or absence of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2/ERBB2). Receptor expression patterns are used to stratify BC and the subsequent treatments. Much of the current knowledge of breast cancer comes from in vitro and in vivo studies using well established cell lines, some of which have been cultured since the 1950s. Given that serial passaging over many years has been reported to alter the mutational profile of cell lines and therefore their relevance to clinical decisions on the primary tumour, new near-tumor cell models need to be generated. In this study, tumour biopsies or ascitic fluids were obtained from a local cancer research biobank, as well as directly from metastatic BC patients across the globe. Using mechanical dissociation and cell separation techniques we isolated tumor cells and grew them in proprietary media. The resultant models were subjected to whole exome and RNA sequencing. In addition, the models were tested in a 3-day cell death assay against a library of more than 50 FDA-approved drugs. The models and four BC cell lines (HCC1937, ZR-75-1, MDA-MB-436 and HCC1428) were also tested in a longer term 7-day assay against a panel of four poly(ADP-ribose) polymerase (PARP) inhibitors. A total of 10 patient-derived cell (PDC) models were successfully established from biopsies or ascitic fluids taken from patients with primary (1/10) or metastatic (9/10) BC. Models were established from patients with ER+ BC, HER2+ BC and triple negative BC (TNBC) within an average of 23 days from sample arrival. All models displayed a greater sensitivity to the non-targeted drugs in the library compared with the targeted drugs. Mutations in breast cancer associated 1 (BRCA1) and BRCA2 genes that were not present in BC cell lines were identified in a subset of the PDCs. All models showed some sensitivity to PARP inhibitors, and most were exquisitely sensitive to talazoparib with IC50s of less than 100 nM. Determining cell death responses in near-tumour PDCs should thus be adopted to enable more informed clinical decisions for treatment pathways and in parallel will be promising tools for oncology drug discovery. Citation Format: Immaculate Nalubowa, Subir Singh, Yuen Ngan Fan, Rachel Howard-Jones, Albert Bezman, Dominic I. James, Geoff Muckle, Gareth J. Griffiths. Differential sensitivity to poly(ADP-ribose) polymerase inhibitors in patient-derived cell models of breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P119.

Triple-negative breast cancer (TNBC), which accounts for approximately 15% of breast cancers (BCs) is characterized by a lack of expression of the hormone receptors (HRs) (estrogen receptor (ER) and progesterone receptor (PR)), and human epidermal growth factor receptor 2 (HER2). TNBC reveals very aggressive behavior and often leads to poor prognosis. Unfortunately, standard chemotherapy (CHT) is related to low response rates and short progression-free survival (PFS) in patients with metastatic TNBC, creating an unmet need. However, recent recognition of different molecular subtypes and mutations within TNBC has allowed exploring some innovative targeted therapies, bringing new hope for women suffering from TNBC. Currently, some promising systemic treatment options in this area have been developed, including targeted therapies, such as poly(ADP-ribose) polymerase (PARP) inhibitors, immune checkpoint inhibitors, antibody-drug conjugates, and AKT inhibitors. The aim of this mini-review is to address these novel treatment modalities and highlight the main directions for further research and clinical practice in the advanced or metastatic forms of TNBC. This article presents poly(ADP-ribose) polymerase (PARP) inhibitors (e.g., olaparib, talazoparib, and valaparib for treatment of BRCA -mutated, HER2-negative metastatic BC), immune checkpoint inhibitors (atezolizumab and pembrolizumab), an antibody-drug conjugate (ADC) (sacituzumab govitecan), and AKT inhibitors (ipatasertib and capivasertib). A brief outline of the main clinical trials leading to the approval of these new medications has been provided. Moreover, this overview discusses the efficacy and safety of these innovative treatment options, focusing on women with metastatic TNBC. In addition, this paper comments on some recent considerations, regarding avenues of delivering care and conduct clinical trials in patients with BC, during the COVID-19 pandemic.

Introduction Triple-negative breast cancer (TNBC) is characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) expression. It accounts for ~15% of breast cancer diagnoses, and disproportionally affects young women and those of African and Hispanic ancestry. Areas covered This review encompasses recent advances in the management of early and advanced-stage TNBC. The identification of distinct molecular subtypes of TNBC has allowed for the optimization of systemic therapy. Distinct drivers of TNBC have been identified, resulting in the regulatory approval of targeted therapies for early and advanced stage disease, including immunotherapy, PARP inhibitors, and antibody-drug conjugates. Literature search was performed using PubMed, and included publications between 01/2010 to 11/2025. Expert opinion Until recently, the only treatment available for TNBC was chemotherapy. Advances in the molecular characterization of TNBC has revealed distinct subtypes, enabling the development and approval of targeted therapies, including PARP inhibitors, immunotherapy, and antibody-drug conjugates. Treatment options for both early and advanced-stage TNBC are improving, although it remains the subtype with the poorest outcomes. Ongoing trials are focused on personalizing treatment through predictive biomarkers, response-adaptive strategies, and novel agents, with the goal of maximizing efficacy while minimizing toxicity.

Breast cancer is the second most commonly diagnosed cancer in women in the United States. The most aggressive subtype is triple negative breast cancer (TNBC), which accounts for 15-20% of new cases on average each year. Histologically, it is characterized by the absence of estrogen receptors (ER), progesterone receptors (PR) and human epidermal growth factor receptor 2 (HER2), which are typically targeted by hormone therapies such as tamoxifen, fulvestrant, or letrozole. Standard of care for TNBC includes traditional chemotherapy and radiation, which are detrimental to both cancerous and normal cells. Therefore, the lack of all hormone receptors in TNBC calls for the investigation of novel anti-cancer compounds that specifically target TNBC with minimal damage to non-cancerous tissues. Receptor orphan tyrosine kinase-like receptor 1 (ROR1) is an oncoprotein that is overexpressed in several human malignancies such as lung, breast, prostate and pancreatic cancers, but not in normal tissues. Inhibition of ROR1 signaling has shown to repress proliferation and induce apoptosis of cancer cells. Through in-silico docking and isothermal titration calorimetry, we identified a novel compound CPD86 that interacts with and inhibits ROR1. We hypothesize that CPD86 selectively targets TNBC cells by reducing the phosphorylation of AKT/GSK3β via the inhibition of ROR1. Our in vitro results suggest that CPD86 inhibits cell viability and induces intrinsic apoptosis of TNBC cells at a half-maximal inhibitory concentration of 2-5 µM, but not in normal breast epithelial cells with minimal ROR1 expression. CPD86 also represses TNBC cell migration and invasion while leaving non-malignant cells unharmed. This study highlights that ROR1 inhibitors could be developed as a potential therapeutic for TNBC and the data would serve as proof-of-concept justification for evaluation in other ROR1-upregulated cancers. Citation Format: Tram Ta, Victoria Reed, Nikhil Chandra, Nick Dwyer, Norman Fultang, Shradheya Gupta, Indrakant Singh, Bela Peethambaran. A novel ROR1 inhibitor CPD86 suppresses Triple-Negative Breast Cancer cells via regulation of AKT/GSK3β pathway [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 PO5-27-07.

Introduction: Triple negative breast cancer (TNBC) is a highly aggressive form of breast cancer prevalent in African-American (AA) women defined as estrogen receptor- (ER), progesterone receptor- (PR), and human epidermal growth factor receptor 2- (HER2) negative. Because ER- and HER2-targeted therapies are ineffective in TNBC, systemic chemotherapy is the standard of care and there is a tremendous need for new effective therapies with less toxicity. Steroid hormone receptors are highly druggable targets, and orphan nuclear receptors, members of the nuclear receptor superfamily, are emerging as targets for cancer therapy. In fact, we have previously shown that treatment of TNBC cells with a small molecule agonist ligand (DY131) for estrogen related receptor beta (ERRβ), has growth inhibitory and anti-mitotic activity. We have also shown that increased mRNA expression of ERRβ, correlates with better recurrence- and distant metastasis-free survival in TNBC/basal-like breast cancer. The goal of our current work is to comprehensively characterize ERRβ copy number and mRNA status in TNBC and determine its association with patients' prognosis. Methods: ESRRB copy number was determined in 106 primary breast tumors (TNBC n=56, nonTNBC n=50) by array-CGH, using the Agilent SurePrint G3 Human CGH platform. ESRRB mRNA data and its association with overall survival was determined in systemically untreated patients from METABRIC using Illumina gene expression array data (probe ID ILMN_1707398). Results: Copy number alterations (CNAs). Copy number losses at the ESRRB locus (14q24.3) were observed in 10/56 (17.8%) of TNBC vs. 10/50 (20%) of nonTNBC, while copy number gains were detected in 43/56 (76.8%) of TNBC vs. 29/50 (58%) of nonTNBC (c2 *p=0.036). Interestingly, in both TNBC and non-TNBC, ESRRB loss was seen with markedly higher frequency in AA patients when compared to Caucasian (CA) patients (c2 *p=0.012 for TNBC, p=0.052 for non-TNBC). mRNA expression. Among patients not treated with systemic chemotherapy in the METABRIC dataset, low ESRRB mRNA was significantly associated with shorter overall survival in TNBC, but not ER+ or HER2+ patients (TNBC hazard ratio 0.24, 95% confidence interval 0.07-0.85, *p=0.016). Low ESRRB also correlated with reduced overall survival in TP53 mutant (but not wild type) tumors (hazard ratio 0.28, 95% confidence interval 0.1-0.82, *p=0.013). Conclusions: ESRRB presents significantly high levels of copy number losses in TNBC when compared to non-TNBC tumors. In breast tumors from AA women, both the TNBC and non-TNBC subtypes are significantly more likely to have reduced ESRRB copy number vs. CA women. Low ESRRB mRNA expression predicts for poor overall survival in TNBC and TP53 mutant tumors. These data advocate that ERRβ expression has prognostic value in breast cancer, particularly TNBC. Future goals include immunohistochemistry staining, and analysis, of a tissue microarray consisting of 150 primary breast tumors (50 TNBC, 50 ER+, 50 HER2+); as well as ERRβ overexpression and knock-down studies in TNBC cell lines to define the role it plays in TNBC. Citation Format: Fernandez AI, Graham G, Győrffy B, Cavalli L, Mahajan A, Riggins RB. ERRβ copy number and expression in triple negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-07-09.

Breast cancer is one of the most common malignancies among women. Triple-negative breast cancer (TNBC) is a distinct subtype of breast cancer characterized by the absence of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Consequently, patients with TNBC do not benefit from endocrine therapy or HER2-targeted therapy, leaving conventional chemotherapy as the primary treatment option. Unfortunately, less than 30% of patients with TNBC achieve a complete response to chemotherapy, and many develop resistance, highlighting the urgent need to identify novel therapeutic targets to overcome chemoresistance. In this study, we analyzed breast cancer data from The Cancer Genome Atlas (TCGA) and discovered that KPNA2 was significantly overexpressed in the basal subtype of the PAM50 classification. Furthermore, KPNA2 expression is strongly associated with the prognosis of TNBC patients undergoing chemotherapy. Through in vitro and in vivo experiments, we demonstrated that silencing of KPNA2 enhances TNBC sensitivity to chemotherapy by promoting multipolar division and suppressing homologous recombination repair (HR), a critical DNA damage repair mechanism. Mechanistically, immunoprecipitation mass spectrometry (IP-MS) identified KIFC1 as a downstream effector of KPNA2. KPNA2 not only binds to the nuclear localization signal (NLS) of KIFC1 to regulate its nuclear translocation but also influences the ubiquitination levels of the KIFC1 protein. Additionally, RNA-seq analysis revealed that KPNA2 and KIFC1 are involved in the NF-κB signaling pathway. The KPNA2/KIFC1/NF-κB pathway/HR-related genes axis provides a comprehensive explanation of how KPNA2 influences DNA damage repair. Overall, our findings shed light on the molecular mechanisms underlying chemoresistance in TNBC. This study provides compelling evidence supporting KPNA2 as a promising therapeutic target for overcoming chemoresistance in TNBC.