The Role of Antiangiogenetic Agents in the Treatment of Breast Cancer

Single-cell RNA sequencing reveals small extracellular vesicles derived from malignant cells that contribute to angiogenesis in human breast cancers

BACKGROUND

Breast cancer is the most common cancer affecting women across the world. Tumor endothelial cells (TECs) and malignant cells are the major constituents of the tumor microenvironment (TME), but their origin and role in shaping disease initiation, progression, and treatment responses remain unclear due to significant heterogeneity.

METHODS

Tissue samples were collected from eight patients presenting with breast cancer. Single-cell RNA sequencing (scRNA-seq) analysis was employed to investigate the presence of distinct cell subsets in the tumor microenvironment. InferCNV was used to identify cancer cells. Pseudotime trajectory analysis revealed the dynamic process of breast cancer angiogenesis. We validated the function of small extracellular vesicles (sEVs)-derived protein phosphatase 1 regulatory inhibitor subunit 1B (PPP1R1B) in vitro experiments.

RESULTS

We performed single-cell transcriptomics analysis of the factors associated with breast cancer angiogenesis and identified twelve subclusters of endothelial cells involved in the tumor microenvironment. We also identified the role of TECs in tumor angiogenesis and confirmed their participation in different stages of angiogenesis, including communication with other cell types via sEVs. Overall, the research uncovered the TECs heterogeneity and the expression levels of genes at different stages of tumor angiogenesis.

CONCLUSIONS

This study showed sEVs derived from breast cancer malignant cells promote blood vessel formation by activating endothelial cells through the transfer of PPP1R1B. This provides a new direction for the development of anti-angiogenic therapies for human breast cancer.

Gallbladder Cancer: Current Multimodality Treatment Concepts and Future Directions

Gallbladder cancer (GBC) is the most common primary tumor site of biliary tract cancer (BTC), accounting for 0.6% of newly diagnosed cancers and 0.9% of cancer-related deaths. Risk factors, including female sex, age, ethnic background, and chronic inflammation of the gallbladder, have been identified. Surgery is the only curative option for early-stage GBC, but only 10% of patients are primary eligible for curative treatment. After neoadjuvant treatment, up to one-third of locally advanced GBC patients could benefit from secondary surgical treatment. After surgery, only a high-risk subset of patients benefits from adjuvant treatment. For advanced-stage GBC, palliative chemotherapy with gemcitabine and cisplatin is the current standard of care in line with other BTCs. After the failure of gemcitabine and cisplatin, data for second-line treatment in non-resectable GBC is poor, and the only recommended chemotherapy regimen is FOLFOX (5-FU/folinic acid and oxaliplatin). Recent advances with the PD-L1 inhibitor durvalumab open the therapy landscape for immune checkpoint inhibition in GBC. Meanwhile, targeted therapy approaches are a cornerstone of GBC therapy based on molecular profiling and new evidence of molecular differences between different BTC forms and might further improve the prognosis of GBC patients.

Melatonin is a potential oncostatic agent to inhibit HepG2 cell proliferation through multiple pathways

Context

Chemotherapy is a cornerstone in the treatment of hepatocellular carcinoma (HCC). Melatonin is a pineal hormone that targets various cancers, however, its antitumor pathways are still not fully elucidated.

Objective

This study investigated melatonin's antitumor molecular mechanisms to inhibit the proliferation of HepG2 cells.

Materials and methods

HepG2 Cells were classified into cells without treatment as a control group and cells treated with melatonin (5.4 mmol/L) for 48 h. Proliferating cell nuclear antigen (PCNA) and marker of proliferation Ki-67 were estimated using immunohistochemical analysis. Apoptosis and cell cycle were evaluated using flow cytometric analysis. Apoptotic markers were detected using RT-qPCR assay. Antioxidants and oxidative stress biomarkers were performed using a colorimetric assay.

Results

Melatonin produced a remarkable steady decrease in the viability of HepG2 cells at a concentration range between 5-20 mmol/L. Melatonin suppressed cell proliferation in the G2/M phase of the cell cycle (34.97 ± 0.92%) and induced apoptosis (12.43 ± 0.73%) through up-regulating p21 and p53 that was confirmed by the reduction of PCNA and Ki-67 expressions. Additionally, melatonin repressed angiogenesis evidenced by the down-regulation of angiopoietin-2, vascular endothelial growth factor receptor-2 expressions (0.42-fold change), and the level of CD133. Moreover, melatonin augmented the oxidative stress manifested by a marked increase of 4-hydroxynonenal levels with a reduction of glutathione content and superoxide dismutase activity.

Discussion and conclusion

Melatonin inhibits proliferation and angiogenesis and induced apoptosis and oxidative stress in HepG2 cells. These results indicate the oncostatic effectiveness of melatonin on liver cancer.

Usefulness of melatonin as complementary to chemotherapeutic agents at different stages of the angiogenic process

Chemotherapeutics are sometimes administered with drugs, like antiangiogenic compounds, to increase their effectiveness. Melatonin exerts antitumoral actions through antiangiogenic actions. We studied if melatonin regulates the response of HUVECs to chemotherapeutics (docetaxel and vinorelbine). The inhibition that these agents exert on some of the processes involved in angiogenesis, such as, cell proliferation, migratory capacity or vessel formation, was enhanced by melatonin. Regarding to estrogen biosynthesis, melatonin impeded the negative effect of vinorelbine, by decreasing the activity and expression of aromatase and sulfatase. Docetaxel and vinorelbine increased the expression of VEGF-A, VEGF-B, VEGF-C, VEGFR-1, VEGFR-3, ANG1 and/or ANG-2 and melatonin inhibited these actions. Besides, melatonin prevented the positive actions that docetaxel exerts on the expression of other factors related to angiogenesis like JAG1, ANPEP, IGF-1, CXCL6, AKT1, ERK1, ERK2, MMP14 and NOS3 and neutralized the stimulating actions of vinorelbine on the expression of FIGF, FGFR3, CXCL6, CCL2, ERK1, ERK2, AKT1, NOS3 and MMP14. In CAM assay melatonin inhibited new vascularization in combination with chemotherapeutics. Melatonin further enhanced the chemotherapeutics-induced inhibition of p-AKT and p-ERK and neutralized the chemotherapeutics-caused stimulatory effect on HUVECs permeability by modifying the distribution of VE cadherin. Our results confirm that melatonin blocks proangiogenic and potentiates antiangiogenic effects induced by docetaxel and vinorelbine enhancing their antitumor effectiveness.

Potential Therapeutic Strategies for Lung and Breast Cancers through Understanding the Anti-Angiogenesis Resistance Mechanisms

Breast and lung cancers are among the top cancer types in terms of incidence and mortality burden worldwide. One of the challenges in the treatment of breast and lung cancers is their resistance to administered drugs, as observed with angiogenesis inhibitors. Based on clinical and pre-clinical findings, these two types of cancers have gained the ability to resist angiogenesis inhibitors through several mechanisms that rely on cellular and extracellular factors. This resistance is mediated through angiogenesis-independent vascularization, and it is related to cancer cells and their microenvironment. The mechanisms that cancer cells utilize include metabolic symbiosis and invasion, and they also take advantage of neighboring cells like macrophages, endothelial cells, myeloid and adipose cells. Overcoming resistance is of great interest, and researchers are investigating possible strategies to enhance sensitivity towards angiogenesis inhibitors. These strategies involved targeting multiple players in angiogenesis, epigenetics, hypoxia, cellular metabolism and the immune system. This review aims to discuss the mechanisms of resistance to angiogenesis inhibitors and to highlight recently developed approaches to overcome this resistance.

Melatonin Enhances the Usefulness of Ionizing Radiation: Involving the Regulation of Different Steps of the Angiogenic Process

Radiotherapy is a part of cancer treatment. To improve its efficacy has been combined with radiosensitizers such as antiangiogenic agents. Among the mechanisms of the antitumor action of melatonin are antiangiogenic effects. Our goal was to investigate whether melatonin may modulate the sensitivity of endothelial cells (HUVECs) to ionizing radiation. Melatonin (1 mM) enhanced the inhibition induced by radiation on different steps of the angiogenic process, cell proliferation, migration, and tubular network formation. In relation with the activity and expression of enzymes implicated in estrogen synthesis, in co-cultures HUVECs/MCF-7, radiation down-regulated aromatase mRNA expression, aromatase endothelial-specific promoter I.7, sulfatase activity and expression and 17β-HSD1 activity and expression and melatonin enhanced these effects. Radiation and melatonin induced a significant decrease in VEGF, ANG-1, and ANG-2 mRNA expression. In ANG-2 and VEGF mRNA expression melatonin potentiated the inhibitory effect induced by radiation. In addition, melatonin counteracted the stimulatory effect of radiation on FGFR3, TGFα, JAG1, IGF-1, and KDR mRNA expression and reduced ANPEP expression. In relation with extracellular matrix molecules, radiation increased MMP14 mRNA expression and melatonin counteracted the stimulatory effect of radiation on MMP14 mRNA expression and increased TIMP1 expression, an angiogenesis inhibitor. Melatonin also counteracted the stimulatory effect of radiation on CXCL6, CCL2, ERK1, ERK2, and AKT1 mRNA expression and increased the inhibitory effect of radiation on NOS3 expression. In CAM assay, melatonin enhanced the reduction of the vascular area induced by radiation. Melatonin potentiated the inhibitory effect on the activation of p-AKT and p-ERK exerted by radiation. Antiangiogenic effect of melatonin could be mediated through AKT and ERK pathways, proteins involved in vascular endothelial (VE) cell growth, cell proliferation, survival, migration, and angiogenesis. In addition, radiation increased endothelial cell permeability and melatonin counteracted it by regulating the internalization of VE-cadherin. Radiation has some side effects on angiogenesis that may reduce its effectiveness against tumor growth and melatonin is able to neutralize these negative actions of radiation. Additionally, melatonin potentiated radiation-induced antiangiogenic actions on several steps of the angiogenic process and enhanced its antitumor action. Our findings point to melatonin as a useful molecule as adjuvant to radiotherapy in cancer treatment.

Melatonin inhibits angiogenesis in SH-SY5Y human neuroblastoma cells by downregulation of VEGF

Vascular endothelial growth factor (VEGF) produced from tumor cells plays a crucial role in the pathogenesis and neovascularization of neuroblastoma. Inhibition of VEGF secretion by tumor cells, as well as VEGF-regulated signaling in endothelial cells, are important to reduce the angiogenesis and growth of neuroblastoma. Since melatonin has anti-angiogenic effects in tumor cell lines, the aim of the present study was to study melatonin modulation of the pro-angiogenic effects of VEGF in neuroblastoma cells (SH-SY5Y). We used co-cultures of SH-SY5Y and endothelial cells. VEGF expression and protein levels were analyzed by quantitative RT-PCR and ELISA, respectively. Endothelial cell migration was assessed by wound-healing assay and endothelial angiogenesis by a tube formation assay. Melatonin inhibited the pro-angiogenic effects of SH-SY5Y cells. The conditioned medium collected from the neuroblastoma cells was angiogenically active and stimulated proliferation, migration and tube formation in endothelial cells. This effect was significantly counteracted by the addition of either anti-VEGF or melatonin. Melatonin inhibited VEGF expression and secretion in SH-SY5Y cells, decreasing the levels of VEGF available for endothelial cells. Melatonin has anti-angiogenic effects at different steps of the angiogenic process in SH-SY5Y neuroblastoma cells, through the downregulation of VEGF.

Disrupting Tumor Angiogenesis and "the Hunger Games" for Breast Cancer

Angiogenesis, one of the hallmarks of cancers, has become an attractive target for cancer therapy since decades ago. It is broadly thought that upregulation of angiogenesis is involved in tumor progression and metastasis. Though tumor vessels are tortuous, disorganized, and leaky, they deliver oxygen and nutrients for tumor development. Based on this knowledge, many kinds of drugs targeting angiogenesis pathways have been developed, such as bevacizumab. However, the clinical outcomes of anti-angiogenesis therapies are moderate in metastatic breast cancer as well as in metastatic colorectal cancer and non-small cell lung cancer, even combined with traditional chemotherapy. In this chapter, the morphologic angiogenesis patterns and the key molecular pathways regulating angiogenesis are elaborated. The FDA-approved anti-angiogenesis drugs and current challenges of anti-angiogenesis therapy are described. The strategies to overcome the barriers will also be elucidated.

In vitro and in vivo models for analysis of resistance to anticancer molecular therapies

The efficacy of classical and molecular therapies in cancer is hampered by the occurrence of primary (intrinsic) and secondary (acquired) refractoriness of tumours to selected therapeutic regimens. Nevertheless, the increased knowledge of the genetic, molecular and metabolic mechanisms underlying cancer results in the generation of a correspondingly increasing number of druggable targets and molecular drugs. Thus, a current challenge in molecular oncology and medicinal chemistry is to cope with the increased need for modelling, both in cellular and animal systems, the genetic assets associated to cancer resistance to drugs. In this review, we summarize the current strategies for generation and analysis of in vitro and in vivo models, which may reveal useful to extract information on the molecular basis of intrinsic and acquired resistance to anticancer molecular agents.

Suppression of laser-induced choroidal neovascularization by intravitreal injection of tristetraprolin

AIM

To examine the effect of intravitreal adenoviral vector-mediated tristetraprolin (Ad-TTP) on VEGF mRNA expression in a rat model of laser-induced choroidal neovascularization.

METHODS

Ad-TTP was prepared using a commercial kit. Retinal laser-induced photocoagulation (10 spots per eye) was performed on rats in this experimental choroidal neovascularization (CNV) model. Rats were divided into four groups: control (single intravitreal injection of balanced salt solution, n=10), laser-induced CNV (photocoagulation only, n=20), laser-induced CNV plus Ad-TTP injection (photocoagulation plus a single intravitreal Ad-TTP injection, n=20) and Ad-TTP injection only (n=10). Changes in choroidal morphology were evaluated in ten rats in the laser only and the laser plus Ad-TTP groups. Two weeks after laser injury, the size of CNV was calculated by perfusion with high-molecular-weight fluorescein isothiocyanate (FITC)-dextran. VEGF mRNA expression in retina-choroid tissue from ten rats in each group was measured by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Two weeks after treatment, the area of laser-induced CNV was reduced by approximately 60% in the rats given the Ad-TTP injection compared with that in the laser-only group. There was a tendency toward decreased VEGF mRNA expression in the Ad-TTP injection groups.

CONCLUSION

A single intravitreal injection of Ad-TTP significantly suppressed CNV size in this experimental laser-induced CNV model. Ad-TTP injection also decreased VEGF mRNA expression compared with that in the laser-induced CNV group. The present study is meaningful as the first study to investigate the effect of tristetraprolin delivered via intravitreal injection.

Cell adhesion molecules and their relation to (cancer) cell stemness

Despite decades of search for anticancer drugs targeting solid tumors, this group of diseases remains largely incurable, especially if in advanced, metastatic stage. In this review, we draw comparison between reprogramming and carcinogenesis, as well as between stem cells (SCs) and cancer stem cells (CSCs), focusing on changing garniture of adhesion molecules. Furthermore, we elaborate on the role of adhesion molecules in the regulation of (cancer) SCs division (symmetric or asymmetric), and in evolving interactions between CSCs and extracellular matrix. Among other aspects, we analyze the role and changes of expression of key adhesion molecules as cancer progresses and metastases develop. Here, the role of cadherins, integrins, as well as selected transcription factors like Twist and Snail is highlighted, not only in the regulation of epithelial-to-mesenchymal transition but also in the avoidance of anoikis. Finally, we briefly discuss recent developments and new strategies targeting CSCs, which focus on adhesion molecules or targeting tumor vasculature.

Identification of a cytoplasmic linker protein as a potential target for neovascularization

OBJECTIVE

Atherosclerosis and other cardiovascular diseases are serious threats to human health and become the leading cause of death in the world. Emerging evidence reveals that inhibition of plaque neovascularization could be an effective approach for the treatment of atherosclerosis. This study was conducted to identify cytoplasmic linker protein 170 as a potential target for cardiovascular diseases through modulation of neovascularization.

METHODS AND RESULTS

Immunofluorescence microscopy revealed that cytoplasmic linker protein 170 was ubiquitously expressed in mouse kidney, liver, lung, normal non-atherosclerotic aorta, and atherosclerotic aorta and was partly localized in the vascular endothelium. siRNAs were introduced to human umbilical vein endothelial cells (HUVECs) and the effect of knockdown was confirmed by Western blotting. Vascularization study was assessed with matrigel-based capillary assembly, branching, and in vivo matrigel plug assays. The data showed that siRNA-mediated knockdown of the cytoplasmic linker protein remarkably compromised the assembly and branching of capillary-like blood vessels and neovascularization in vivo. Cell motility and polarity properties were then analyzed using scratch wound repair, boyden chamber, and immunofluorescence assays, and the results revealed that the cytoplasmic linker protein was critical for the motility abilities of HUVECs through its actions on cell polarity.

CONCLUSION

Both in vitro and in vivo studies demonstrate the significance of the cytoplasmic linker protein for blood vessel formation. Mechanistic investigation reveals that its effect on neovascularization is orchestrated through its regulation of vascular endothelial cell polarity and motility. These findings provide the basis for exploring effective approaches to regulate neovascularization in cardiovascular diseases.

Breast cancer in systemic sclerosis: results of a cross-linkage of an Italian Rheumatologic Center and a population-based Cancer Registry and review of the literature

OBJECTIVE

Increased frequency of few types of cancer in systemic sclerosis (SSc) has been reported in the literature; in particular, breast carcinoma has been proposed as one of the most frequent malignancy in SSc patients, even though data are not univocal. The aim of the present study was to retrospectively evaluate the prevalence of breast cancer in our SSc series, compared with sex-/age-matched general population of the same geographical area, and the possible correlations with SSc features, including X-ray exposure for clinical investigations. A review of the world literature about this topic was also done.

METHODS

Clinical records of 318 consecutive SSc patients, 31 M and 287 F, age 51.5±14.5 SD years, disease duration 10±6.5 SD years, referred to our Rheumatology Unit between January 2002 and December 2012 were evaluated.

RESULTS

Twelve (3.8%) cases of breast cancer were recorded, including 11/287 females (3.8%) and 1/31 (3.2%) male patients. Considering the subgroup of 202 SSc patients resident in the Province of Modena compared with data of the local Tumor Registry, the incidence of breast cancer observed in our SSc series is significantly higher than expected (SIR 2.1; 95% interval of confidence: 1.13-3.90; p<0.01). On the whole, the comparison between SSc patients with cancer and those without did not show any significant differences with regard to SSc clinical features, including the X-ray exposure. Of note is the relatively shorter disease duration at the time of breast cancer detection (median 2.5years, range 1-21; disease duration of mean 10±6.5 SD years in the entire cohort). The review of the literature revealed that the observed incidence of breast cancer in our case series is comparable to the few studies reporting the highest percentages of this malignancy.

CONCLUSIONS

A significant increase of breast cancer incidence compared to sex-age-matched general population from the same geographic area was observed. Moreover, a close temporal relationship between SSc and breast cancer onset was found, independently from clinical, serological, and instrumental features of SSc. The possible pathogenetic link between this systemic autoimmune disease and complicating breast cancer, as well as the results of previous studies, are discussed.

Bevacizumab in advanced breast cancer: a new model for the assessment of activity in non-first-line treatment regimens

The activity of bevacizumab (BVZ) in advanced lines is not well known. In the treatment of metastatic breast cancer, the response rate and time to treatment failure (TTF) decrease with progression through successive therapeutic lines. The objective of this study was to compare BVZ activity in advanced treatment lines with that achieved in the previous line in routine clinical practice. Ninety-six patients who had received BVZ treatment in second or subsequent treatment lines were selected from five Spanish hospitals. Analysis was carried out of the differences in TTF and response rate in the lines with BVZ and those in earlier lines. Data analysis was carried out in two different ways: (a) by comparing treatment groups according to the treatment line received, using a Cox regression model with random effects, and the McNemar test to analysis the response rate, and (b) by comparing intrapatient data, using the Wilcoxon signed-rank test. In 62 patients, the TTF (adjusted for treatment line) was longer in the BVZ treatment line than that in the previous line. In the BVZ lines, there was a significant reduction in the probability of treatment failure [hazard ratio 0.52; 95% confidence interval (CI) 0.38-0.71]. The median TTF was 4.27 months (95% CI 3.7-5) in the previous line and 6.18 months (95% CI 5.5-7.93) in the BVZ line. The percentage of patients with an objective response was 33.3% in the previous lines and 52.1% (P=0.005) in the BVZ line. Contrary to expectation, more patients showed better results with the BVZ line than with the previous line. BVZ treatment in advanced lines improves the results obtained in previous treatment lines. This suggests that BVZ is active in advanced lines and that it produces favourable changes in the natural history of patients with metastatic breast carcinoma.

Regulation of vascular endothelial growth factor by melatonin in human breast cancer cells

Melatonin exerts oncostatic effects on breast cancer by interfering with the estrogen-signaling pathways. Melatonin reduces estrogen biosynthesis in human breast cancer cells, surrounding fibroblasts and peritumoral endothelial cells by regulating cytokines that influence tumor microenvironment. This hormone also exerts antiangiogenic activity in tumoral tissue. In this work, our objective was to study the role of melatonin on the regulation of the vascular endothelial growth factor (VEGF) in breast cancer cells. To accomplish this, we cocultured human breast cancer cells (MCF-7) with human umbilical vein endothelial cells (HUVECs). VEGF added to the cultures stimulated the proliferation of HUVECs and melatonin (1 mM) counteracted this effect. Melatonin reduced VEGF production and VEGF mRNA expression in MCF-7 cells. MCF-7 cells cocultured with HUVECs stimulated the endothelial cells proliferation and increased VEGF levels in the culture media. Melatonin counteracted both stimulatory effects on HUVECs proliferation and on VEGF protein levels in the coculture media. Conditioned media from MCF-7 cells increased HUVECs proliferation, and this effect was significantly counteracted by anti-VEGF and 1 mM melatonin. All these findings suggest that melatonin may play a role in the paracrine interactions between malignant epithelial cells and proximal endothelial cells through a downregulatory action on VEGF expression in human breast cancer cells, which decrease the levels of VEGF around endothelial cells. Lower levels of VEGF could be important in reducing the number of estrogen-producing cells proximal to malignant cells as well as decreasing tumoral angiogenesis.

Antiangiogenic effects of melatonin in endothelial cell cultures

Endothelial cells represent one of the critical cellular elements in tumor microenvironment playing a crucial role in the growth and progression of cancer through controlling angiogenesis. Vascular endothelial growth factor (VEGF) produced from tumor cells is essential for the expansion of breast cancer and may function in both paracrine and autocrine manners to promote proliferation, growth, survival and migration of endothelial cells. Since melatonin regulates tumor microenvironment by decreasing the secretion of VEGF by malignant epithelial cells and also regulates VEGF expression in human breast cancer cells, the aim of the present study was to investigate the anti-angiogenic activity of melatonin against the pro-angiogenic effects of breast cancer cells. In this work, we demonstrate that melatonin strongly inhibited the proliferation as well as invasion/migration of human umbilical vein endothelial cells (HUVECs). Melatonin disrupted tube formation and counteracted the VEGF-stimulated tubular network formation by HUVEC. In addition, conditioned media collected from human breast cancer cells were angiogenically active and stimulated tubule length formation and this effect was significantly counteracted by the addition of anti-VEGF or melatonin. Melatonin also disintegrated preformed capillary network. All these findings demonstrate that melatonin may play a role in the paracrine interactions that take place between malignant epithelial cells and proximal endothelial cells. Melatonin could be important in reducing endothelial cell proliferation, invasion, migration and tube formation, through a downregulatory action on VEGF. Taken together, our findings suggest that melatonin could potentially be beneficial as an antiangiogenic agent in breast cancer with possible future clinical applications.

Mechanisms of resistance to endocrine therapy in breast cancer: focus on signaling pathways, miRNAs and genetically based resistance

Breast cancer is the most frequent malignancy diagnosed in women. Approximately 70% of breast tumors express the estrogen receptor (ER). Tamoxifen and aromatase inhibitors (AIs) are the most common and effective therapies for patients with ERα-positive breast cancer. Alone or combined with chemotherapy, tamoxifen significantly reduces disease progression and is associated with more favorable impact on survival in patients. Unfortunately, endocrine resistance occurs, either de novo or acquired during the course of the treatment. The mechanisms that contribute to hormonal resistance include loss or modification in the ERα expression, regulation of signal transduction pathways, altered expression of specific microRNAs, balance of co-regulatory proteins, and genetic polymorphisms involved in tamoxifen metabolic activity. Because of the clinical consequences of endocrine resistance, new treatment strategies are arising to make the cells sensitive to tamoxifen. Here, we will review the current knowledge on mechanisms of endocrine resistance in breast cancer cells. In addition, we will discuss novel therapeutic strategies to overcome such resistance. Undoubtedly, circumventing endocrine resistance should help to improve therapy for the benefit of breast cancer patients.