Molecular subtypes of triple-negative breast cancer: understanding of subtype categories and clinical implication

MicroRNAs Associated with Androgen Receptor and Metastasis in Triple-Negative Breast Cancer

It is crucial to identify novel molecular biomarkers and therapeutic targets for triple-negative breast cancer (TNBC). The androgen receptor (AR) is a regulator of TNBC, acting partially via microRNA molecules (miRNAs). In this study, we used PCR arrays to profile the expression of 84 miRNAs in 24 TNBC tissue samples, which were equally classified according to AR expression and/or metastasis. Several bioinformatics tools were then utilized to determine the potentially affected protein targets and signaling pathways. Seven miRNAs were found to be significantly more highly expressed in association with AR expression, including miR-328-3p and miR-489-3p. Increased expression of miR-205-3p was found to be significantly associated with metastasis. Certain miRNAs were specifically found to be differentially expressed in either metastatic or non-metastatic AR-positive tumors. A gene ontology (GO) analysis indicated biological roles in the regulation of transcription, cellular response to DNA damage, and the transforming growth factor-beta (TGF-beta) signaling pathway. The GO analysis also showed enrichment in kinase and transcription factor activities. The TGF-beta and a number of kinase-dependent pathways were also retrieved using the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. This study offers an understanding of the role of AR in TNBC and further implicates miRNAs in mediating the effects of AR on TNBC.

A case report and literature review on a rare subtype of triple-negative breast cancer in children

BACKGROUND

Triple-negative breast cancer (TNBC) is a type of breast tumor with a poor prognosis because it lacks or expresses low levels of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER-2). TNBC is more common in middle-aged and older women, and cases of TNBC in children are rarely reported. This is the only case of childhood SBC in our hospital in more than 70 years, and the disease is extremely rare internationally. We analyzed and studied the disease and TNBC from both clinical and pathological aspects and found that SBC is very different from TNBC.

CASE PRESENTATION

We report a case of secretory breast cancer (SBC), a subtype of TNBC, in an 8-year-old girl from our institution. The child presented with a single mass in the left breast only, with no skin rupture and no enlargement of the surrounding lymph nodes. The child underwent two surgeries and was followed up for one year with a good prognosis.

CONCLUSIONS

SBC is highly prevalent among the multiple pathological types of pediatric breast cancer. Almost all pediatric SBC patients are characterized by the ETV6-NTRK3 fusion gene, which has a good prognosis and a 10-year survival rate of more than 90% when compared with other TNBC subtypes. According to the patient, we performed local mass resection and a postoperative pathological diagnosis of SBC (a subtype of BL-TNBC). The TNBC case had a good prognosis and differed from basal TNBC in several aspects, including clinical presentation, treatment, and prognosis. It is necessary to exclude SBC from BL-type TNBC, enhance understanding of the disease, and individualize the treatment plan, so as to avoid medical errors.

New Biomarkers and Treatment Advances in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a specific subtype of breast cancer lacking hormone receptor expression and HER2 gene amplification. TNBC represents a heterogeneous subtype of breast cancer, characterized by poor prognosis, high invasiveness, high metastatic potential, and a tendency to relapse. In this review, the specific molecular subtypes and pathological aspects of triple-negative breast cancer are illustrated, with particular attention to the biomarker characteristics of TNBC, namely: regulators of cell proliferation and migration and angiogenesis, apoptosis-regulating proteins, regulators of DNA damage response, immune checkpoints, and epigenetic modifications. This paper also focuses on omics approaches to exploring TNBC, such as genomics to identify cancer-specific mutations, epigenomics to identify altered epigenetic landscapes in cancer cells, and transcriptomics to explore differential mRNA and protein expression. Moreover, updated neoadjuvant treatments for TNBC are also mentioned, underlining the role of immunotherapy and novel and targeted agents in the treatment of TNBC.

The inhibition of steroid hormones determines the fate of IPC-366 tumor cells, highlighting the crucial role of androgen production in tumor processes

Inflammatory mammary cancer (IMC) is a disease that affects female dogs. It is characterized by poor treatment options and no efficient targets. However, anti-androgenic and anti-estrogenic therapies could be effective because IMC has a great endocrine influence, affecting tumor progression. IPC-366 is a triple negative IMC cell line that has been postulated as a useful model to study this disease. Therefore, the aim of this study was to inhibit steroid hormones production at different points of the steroid pathway in order to determine its effect in cell viability and migration in vitro and tumor growth in vivo. For this purpose, Dutasteride (anti-5αReductase), Anastrozole (anti-aromatase) and ASP9521 (anti-17βHSD) and their combinations have been used. Results revealed that this cell line is positive to estrogen receptor β (ERβ) and androgen receptor (AR) and endocrine therapies reduce cell viability. Our results enforced the hypothesis that estrogens promote cell viability and migration in vitro due to the function of E1SO4 as an estrogen reservoir for E2 production that promotes the IMC cells proliferation. Also, an increase in androgen secretion was associated with a reduction in cell viability. Finally, in vivo assays showed large tumor reduction. Hormone assays determined that high estrogen levels and the reduction of androgen levels promote tumor growth in Balb/SCID IMC mice. In conclusion, estrogen levels reduction may be associated with a good prognosis. Also, activation of AR by increasing androgen production could result in effective therapy for IMC because their anti-proliferative effect.

Triple-negative breast cancer: epidemiology, molecular mechanisms, and modern vaccine-based treatment strategies

Long-standing scarcity of efficacious treatments and tumor heterogeneity have contributed to triple-negative breast cancer (TNBC), a subtype with a poor prognosis and aggressive behavior that accounts for 10-15% of all new cases of breast cancer. TNBC is characterized by the absence of progesterone and estrogen receptor expression and lacks gene amplification or overexpression of HER2. Genomic sequencing has detected that the unique mutational profile of both the somatic and germline modifications in TNBC is staggeringly dissimilar from other breast tumor subtypes. The clinical utility of sequencing germline BRCA1/2 genes has been well established in TNBC. Nevertheless, reports regarding the penetrance and risk of other susceptibility genes are relatively scarce. Recurring mutations (e.g., TP53 and PI3KCA mutations) occur together with rare mutations in TNBC, and the shared effects of genomic modifications drive its progression. Given the heterogeneity and complexity of this disease, a clinical understanding of the genomic modifications in TNBC can pave an innovative way toward its therapy. In this review, we summarized the most recent discoveries associated with the underlying biology of developmental signaling pathways in TNBC. We also summarize the recent advancements in genetics and epidemiology and discuss state-of-the-art vaccine-based therapeutic strategies for TNBC that will enable tailored therapeutics.

A bibliometric analysis of 16,826 triple-negative breast cancer publications using multiple machine learning algorithms: Progress in the past 17 years

Background

Triple-negative breast cancer (TNBC) is proposed at the beginning of this century, which is still the most challenging breast cancer subtype due to its aggressive behavior, including early relapse, metastatic spread, and poor survival. This study uses machine learning methods to explore the current research status and deficiencies from a macro perspective on TNBC publications.

Methods

PubMed publications under "triple-negative breast cancer" were searched and downloaded between January 2005 and 2022. R and Python extracted MeSH terms, geographic information, and other abstracts from metadata. The Latent Dirichlet Allocation (LDA) algorithm was applied to identify specific research topics. The Louvain algorithm established a topic network, identifying the topic's relationship.

Results

A total of 16,826 publications were identified, with an average annual growth rate of 74.7%. Ninety-eight countries and regions in the world participated in TNBC research. Molecular pathogenesis and medication are most studied in TNBC research. The publications mainly focused on three aspects: Therapeutic target research, Prognostic research, and Mechanism research. The algorithm and citation suggested that TNBC research is based on technology that advances TNBC subtyping, new drug development, and clinical trials.

Conclusion

This study quantitatively analyzes the current status of TNBC research from a macro perspective and will aid in redirecting basic and clinical research toward a better outcome for TNBC. Therapeutic target research and Nanoparticle research are the present research focus. There may be a lack of research on TNBC from a patient perspective, health economics, and end-of-life care perspectives. The research direction of TNBC may require the intervention of new technologies.

Anti-Androgenic Therapies Targeting the Luminal Androgen Receptor of a Typical Triple-Negative Breast Cancer

Triple-negative tumors are progressively delineating their existence over the extended spectrum of breast cancers, marked by intricate molecular heterogeneity, a low overall survival rate, and an unexplored therapeutic approach. Although the basal subtype transcends the group and contributes approximately 80% to triple-negative breast cancer (TNBC) cases, the exceptionally appearing mesenchymal and luminal androgen receptor (LAR) subtypes portray an unfathomable clinical course. LAR with a distinct generic profile frequently metastasizes to regional lymph nodes and bones. This subtype is minimally affected by chemotherapy and shows the lowest pathologic complete response. The androgen receptor is the only sex steroid receptor that plays a cardinal role in the progression of breast cancers and is typically overexpressed in LAR. The partial AR antagonist bicalutamide and the next-generation AR inhibitor enzalutamide are being assessed in standard protocols for the mitigation of TNBC. There arises an inevitable need to probe into the strategies that could neutralize these androgen receptors and alleviate the trajectory of concerning cancer. This paper thus focuses on reviewing literature that provides insights into the anti-androgenic elements against LAR typical TNBC that could pave the way for clinical advancements in this dynamic sphere of oncology.

Correlation of TROP-2 expression with clinical-pathological characteristics and outcome in triple-negative breast cancer

Limited data exist regarding the associations between TROP-2 protein expression, clinical-pathological characteristics, and outcome in triple-negative breast cancer (TNBC). TROP-2 expression was determined for patients diagnosed with TNBC between 2000 and 2017 by immunohistochemistry (IHC) (ab227689, Abcam) on whole slide tumor sections, and assessed as continuous and categorical variables (H-score high, 201-300, medium 100-200 and low < 100). We investigated the prognostic value of TROP-2 expression for relapse and survival, associations between TROP-2 expression and baseline patient and tumor characteristics, stromal tumor-infiltrating lymphocytes (sTILs), androgen receptor (AR), standardized mitotic index (SMI) and pathological complete response (pCR, in patients with neoadjuvant chemotherapy) were assessed. We included 685 patients with a median age at diagnosis of 54 years (range 22-90 years). After median follow-up of 9.6 years, 17.5% of patients experienced distant relapse. TROP-2 expression was high, medium and low in 97 (16.5%), 149 (25.3%) and 343 (58.2%) of patients, respectively. The presence of LVI, associated DCIS, nodal involvement, apocrine histology and AR expression were correlated with higher TROP-2 levels. There were no associations between TROP-2 expression and sTILs, time-to-event outcomes, or pCR rate after neoadjuvant chemotherapy. TROP-2 expression is not associated with sTILs level and has no prognostic value in our cohort of stage 1-3 TNBC. However, an association with histotype and AR expression was found, suggesting a histotype specific TROP-2 expression pattern with highest expression in apocrine subtype, warranting further research.

Genomic mapping of copy number variations influencing immune response in breast cancer

Identification of genomic alterations that influence the immune response within the tumor microenvironment is mandatory in order to identify druggable vulnerabilities. In this article, by interrogating public genomic datasets we describe copy number variations (CNV) present in breast cancer (BC) tumors and corresponding subtypes, associated with different immune populations. We identified regulatory T-cells associated with the Basal-like subtype, and type 2 T-helper cells with HER2 positive and the luminal subtype. Using gene set enrichment analysis (GSEA) for the Type 2 T-helper cells, the most relevant processes included the ERBB2 signaling pathway and the Fibroblast Growth Factor Receptor (FGFR) signaling pathway, and for CD8+ T-cells, cellular response to growth hormone stimulus or the JAK-STAT signaling pathway. Amplification of ERBB2, GRB2, GRB7, and FGF receptor genes strongly correlated with the presence of type 2 T helper cells. Finally, only 8 genes were highly upregulated and present in the cellular membrane: MILR1, ACE, DCSTAMP, SLAMF8, CD160, IL2RA, ICAM2, and SLAMF6. In summary, we described immune populations associated with genomic alterations with different BC subtypes. We observed a clear presence of inhibitory cells, like Tregs or Th2 when specific chromosomic regions were amplified in basal-like or HER2 and luminal groups. Our data support further evaluation of specific therapeutic strategies in specific BC subtypes, like those targeting Tregs in the basal-like subtype.

Iron Overload and Breast Cancer: Iron Chelation as a Potential Therapeutic Approach

Breast cancer has historically been one of the leading causes of death for women worldwide. As of 2020, breast cancer was reported to have overtaken lung cancer as the most common type of cancer globally, representing an estimated 11.3% of all cancer diagnoses. A multidisciplinary approach is taken for the diagnosis and treatment of breast cancer that includes conventional and targeted treatments. However, current therapeutic approaches to treating breast cancer have limitations, necessitating the search for new treatment options. Cancer cells require adequate iron for their continuous and rapid proliferation. Excess iron saturates the iron-binding capacity of transferrin, resulting in non-transferrin-bound iron (NTBI) that can catalyze free-radical reactions and may lead to oxidant-mediated breast carcinogenesis. Moreover, excess iron and the disruption of iron metabolism by local estrogen in the breast leads to the generation of reactive oxygen species (ROS). Therefore, iron concentration reduction using an iron chelator can be a novel therapeutic strategy for countering breast cancer development and progression. This review focuses on the use of iron chelators to deplete iron levels in tumor cells, specifically in the breast, thereby preventing the generation of free radicals. The inhibition of DNA synthesis and promotion of cancer cell apoptosis are the targets of breast cancer treatment, which can be achieved by restricting the iron environment in the body. We hypothesize that the usage of iron chelators has the therapeutic potential to control intracellular iron levels and inhibit the breast tumor growth. In clinical settings, iron chelators can be used to reduce cancer cell growth and thus reduce the morbidity and mortality in breast cancer patients.

Kinesin Family Member 2A Serves as a Potential Biomarker Reflecting More Frequent Lymph Node Metastasis and Tumor Recurrence Risk in Basal-Like Breast Cancer Patients

Background

Kinesin family member 2A (KIF2A) is reported as an oncogene and a potential biomarker for progression and prognosis in several cancers such as cervical, ovarian, and gastric. However, its clinical value in basal-like breast cancer (BLBC) is unclear. This study aims to evaluate KIF2A expression and its correlation with clinical features and survival rates in BLBC patients.

Methods

KIF2A mRNA and protein expressions in tumor and adjacent tissues from 89 BLBC patients are assessed by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry assays, respectively.

Results

Both KIF2A protein (p < 0.001) and mRNA expressions (p < 0.001) were higher in tumor than in adjacent tissue. Besides, tumor KIF2A protein expression was positively correlated with N (p = 0.028) and TNM (p = 0.014) stages; meanwhile, tumor KIF2A mRNA expression was positively correlated with N stage (p = 0.046), TNM stage (p = 0.006), and tumor size (p = 0.043). Additionally, both tumor KIF2A protein (p = 0.035) and mRNA (p = 0.039) high expressions were correlated with worse disease-free survival (DFS) but not with overall survival (both p > 0.05). Moreover, tumor KIF2A protein expression was higher in relapsed patients than in non-relapsed patients within 3 years (p = 0.015) and 5 years (p = 0.031), whereas no difference was found between the dead and survivors within 3 years (p = 0.057) or 5 years (p = 0.107). Lastly, after adjustment, tumor KIF2A mRNA high exhibited a trend that correlated with DFS but without statistical significance (p = 0.051).

Conclusion

KIF2A correlates with more frequent lymph node metastasis and worse DFS in BLBC patients, shedding light on its potency as a biomarker for BLBC.

Molecular Subtyping of Cancer Based on Robust Graph Neural Network and Multi-Omics Data Integration

Accurate molecular subtypes prediction of cancer patients is significant for personalized cancer diagnosis and treatments. Large amount of multi-omics data and the advancement of data-driven methods are expected to facilitate molecular subtyping of cancer. Most existing machine learning–based methods usually classify samples according to single omics data, fail to integrate multi-omics data to learn comprehensive representations of the samples, and ignore that information transfer and aggregation among samples can better represent them and ultimately help in classification. We propose a novel framework named multi-omics graph convolutional network (M-GCN) for molecular subtyping based on robust graph convolutional networks integrating multi-omics data. We first apply the Hilbert–Schmidt independence criterion least absolute shrinkage and selection operator (HSIC Lasso) to select the molecular subtype-related transcriptomic features and then construct a sample–sample similarity graph with low noise by using these features. Next, we take the selected gene expression, single nucleotide variants (SNV), and copy number variation (CNV) data as input and learn the multi-view representations of samples. On this basis, a robust variant of graph convolutional network (GCN) model is finally developed to obtain samples’ new representations by aggregating their subgraphs. Experimental results of breast and stomach cancer demonstrate that the classification performance of M-GCN is superior to other existing methods. Moreover, the identified subtype-specific biomarkers are highly consistent with current clinical understanding and promising to assist accurate diagnosis and targeted drug development.

Enzalutamide Overcomes Dihydrotestosterone Induced Chemo-Resistance In Triple-Negative Breast Cancer Cells via Apoptosis

Background:

Triple-negative breast cancer is challenging to treat due to its heterogeneity and lack of therapeutic targets. Hence, systemic chemotherapy is still the mainstay in TNBC treatment. Unfortunately, patients commonly develop chemo-resistance. Androgen signalling through its receptor is an essential player in breast cancer where it has been shown to confer chemo-resistance to TNBC cells

Objective:

To elucidate the mechanistic effects of enzalutamide in the chemoresponse of TNBC cells to doxorubicin through the apoptosis pathway.

Results:

Enzalutamide decreased the viability of MDA-MB-231 and MDA-MB- 453 cells and reduced DHT-induced chemo-resistance of both cell lines. It also increased the chemo-sensitivity towards doxorubicin in MDA-MB-231 cells. Increasing DNA degradation and caspase 3/7 activity were concomitant with these outcomes. Moreover, enzalutamide downregulated the expression of the anti-apoptosis genes, mcl1 and bcl2, in MDA-MB-231 cells. Moreover, increase the pro-apoptotic gene bid. On the other hand, DHT upregulated the expression of the anti-apoptosis genes, mcl1 and bcl2, in both cell lines.

Conclusion:

DHT increases the expression of the anti-apoptosis mcl1 and bcl2 in the TNBC cells, presumably leading to cell survival via the prevention of doxorubicin-induced apoptosis. On the other hand, enzalutamide may sensitize the cells to doxorubicin through downregulation of the bid/bcl2/mcl1 axis that normally activates the executive caspases, caspase 3/7. The activities of the latter enzymes were apparent in DNA degradation at the late stages of

Safety and Efficacy Evaluation In Vivo of a Cationic Nucleolipid Nanosystem for the Nanodelivery of a Ruthenium(III) Complex with Superior Anticancer Bioactivity

Simple Summary

The availability of selective, effective, and safe anticancer agents is a major challenge in the field of cancer research. As part of a multidisciplinary research project, in recent years our group has proposed an original class of nanomaterials for the delivery of new anticancer drugs based on ruthenium(III) complexes. In cellular models, these nanosystems have been shown to be effective in counteracting growth and proliferation of human breast cancer cells. Compared to conventional metallochemotherapeutics such as platinum-based agents whose clinical practice is associated with serious undesirable effects, ruthenium complexes share improved biochemical profiles making them more selective towards cancer cells and less cytotoxic to healthy cells. Their combination with biocompatible nanocarriers further enhances these promising features, as here showcased by our research carried out in an animal model which underscores the efficacy and safety in vivo of one of our most promising ruthenium-based nanosystems.

Abstract

Selectivity and efficacy towards target cancer cells, as well as biocompatibility, are current challenges of advanced chemotherapy powering the discovery of unconventional metal-based drugs and the search for novel therapeutic approaches. Among second-generation metal-based chemotherapeutics, ruthenium complexes have demonstrated promising anticancer activity coupled to minimal toxicity profiles and peculiar biochemical features. In this context, our research group has recently focused on a bioactive Ru(III) complex—named AziRu—incorporated into a suite of ad hoc designed nucleolipid nanosystems to ensure its chemical stability and delivery. Indeed, we proved that the structure and properties of decorated nucleolipids can have a major impact on the anticancer activity of the ruthenium core. Moving in this direction, here we describe a preclinical study performed by a mouse xenograft model of human breast cancer to establish safety and efficacy in vivo of a cationic Ru(III)-based nucleolipid formulation, named HoThyRu/DOTAP, endowed with superior antiproliferative activity. The results show a remarkable reduction in tumour with no evidence of animal suffering. Blood diagnostics, as well as biochemical analysis in both acute and chronic treated animal groups, demonstrate a good tolerability profile at the therapeutic regimen, with 100% of mice survival and no indication of toxicity. In addition, ruthenium plasma concentration analysis and tissue bioaccumulation were determined via appropriate sampling and ICP-MS analysis. Overall, this study supports both the efficacy of our Ru-containing nanosystem versus a human breast cancer model and its safety in vivo through well-tolerated animal biological responses, envisaging a possible forthcoming use in clinical trials.

MicroRNA-495/TGF-β/FOXC1 axis regulates multidrug resistance in metaplastic breast cancer cells

Triple-negative metaplastic breast carcinoma (MBC) poses a significant treatment challenge due to lack of targeted therapies and chemotherapy resistance. We isolated a novel MBC cell line, BAS, which showed a molecular and phenotypic profile different from the only other metaplastic cell model, HS578T cells. To gain insight behind chemotherapeutic resistance, we generated doxorubicin (HS-DOX, BAS-DOX) and paclitaxel (HS-TX, BAS-TX) resistant derivatives of both cell lines. Drug sensitivity assays indicated a truly multidrug resistant (MDR) phenotype. Both BAS-DOX and BAS-TX showed up-regulation of FOXC1 and its experimental down-regulation re-sensitized cells to doxorubicin and paclitaxel. Experimental modulation of FOXC1 expression in MCF-7 and MDA-MB-231 cells corroborated its role in MDR. Genome-wide expression analyses identified gene expression signatures characterized by up-regulation of TGFB2, which encodes cytokine TGF-β2, in both BAS-DOX and BAS-TX cells. Pharmacological inhibition of the TGF-β pathway with galunisertib led to down-regulation of FOXC1 and increase in drug sensitivity in both BAS-DOX and BAS-TX cells. MicroRNA (miR) expression analyses identified high endogenous miR-495-3p levels in BAS cells that were downregulated in both BAS MDR cells. Transient expression of miR-495-3p mimic in BAS-DOX and BAS-TX cells caused downregulation of TGFB2 and FOXC1 and re-sensitized cells to doxorubicin and paclitaxel, whereas miR-495-3p inhibition in BAS cells led to increase in resistance to both drugs and up-regulation of TGFB2 and FOXC1. Together, these data suggest interplay between miR-495-3p, TGF-β2 and FOXC1 regulating MDR in MBC and open the exploration of novel therapeutic strategies.

The Roles of DNA Demethylases in Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBCs) are very heterogenous, molecularly diverse, and are characterized by a high propensity to relapse or metastasize. Clinically, TNBC remains a diagnosis of exclusion by the lack of hormone receptors (Estrogen Receptor (ER) and Progesterone Receptor (PR)) as well as the absence of overexpression and/or amplification of HER2. DNA methylation plays an important role in breast cancer carcinogenesis and TNBCs have a distinct DNA methylation profile characterized by marked hypomethylation and lower gains of methylations compared to all other subtypes. DNA methylation is regulated by the balance of DNA methylases (DNMTs) and DNA demethylases (TETs). Here, we review the roles of TETs as context-dependent tumor-suppressor genes and/or oncogenes in solid tumors, and we discuss the current understandings of the oncogenic role of TET1 and its therapeutic implications in TNBCs.

MiR-21 Is Required for the Epithelial-Mesenchymal Transition in MDA-MB-231 Breast Cancer Cells

Breast cancer (BCa) is one of the leading health problems among women. Although significant achievements have led to advanced therapeutic success with targeted therapy options, more efforts are required for different subtypes of tumors and according to genomic, transcriptomic, and proteomic alterations. This study underlines the role of microRNA-21 (miR-21) in metastatic MDA-MB-231 breast cancer cells. Following the knockout of miR-21 from MDA-MB-231 cells, which have the highest miR-21 expression levels compared to MCF-7 and SK-BR-3 BCa cells, a decrease in epithelial-mesenchymal transition (EMT) via downregulation of mesenchymal markers was observed. Wnt-11 was a critical target for miR-21, and the Wnt-11 related signaling axis was altered in the stable miR-21 knockout cells. miR-21 expression was associated with a significant increase in mesenchymal markers in MDA-MB-231 BCa cells. Furthermore, the release of extracellular vesicles (EVs) was significantly reduced in the miR-21 KO cells, alongside a significant reduction in relative miR-21 export in EV cargo, compared with control cells. We conclude that miR-21 is a leading factor involved in mesenchymal transition in MDA-MB-231 BCa. Future therapeutic strategies could focus on its role in the treatment of metastatic breast cancer.