DNA stabilization by the upregulation of estrogen signaling in BRCA gene mutation carriers

DNA Damage Responses in Tumors Are Not Proliferative Stimuli, but Rather They Are DNA Repair Actions Requiring Supportive Medical Care

BACKGROUND

In tumors, somatic mutagenesis presumably drives the DNA damage response (DDR) via altered regulatory pathways, increasing genomic instability and proliferative activity. These considerations led to the standard therapeutic strategy against cancer: the disruption of mutation-activated DNA repair pathways of tumors.

PURPOSE

Justifying that cancer cells are not enemies to be killed, but rather that they are ill human cells which have the remnants of physiologic regulatory pathways.

RESULTS

1. Genomic instability and cancer development may be originated from a flaw in estrogen signaling rather than excessive estrogen signaling; 2. Healthy cells with genomic instability exhibit somatic mutations, helping DNA restitution; 3. Somatic mutations in tumor cells aim for the restoration of DNA damage, rather than further genomic derangement; 4. In tumors, estrogen signaling drives the pathways of DNA stabilization, leading to apoptotic death; 5. In peritumoral cellular infiltration, the genomic damage of the tumor induces inflammatory cytokine secretion and increased estrogen synthesis. In the inflammatory cells, an increased growth factor receptor (GFR) signaling confers the unliganded activation of estrogen receptors (ERs); 6. In breast cancer cells responsive to genotoxic therapy, constitutive mutations help the upregulation of estrogen signaling and consequential apoptosis. In breast tumors non-responsive to genotoxic therapy, the possibilities for ER activation via either liganded or unliganded pathways are exhausted, leading to farther genomic instability and unrestrained proliferation.

CONCLUSIONS

Understanding the real character and behavior of human tumors at the molecular level suggests that we should learn the genome repairing methods of tumors and follow them by supportive therapy, rather than provoking additional genomic damages.

HR-positive/HER2-negative breast cancer arising in patients with or without BRCA2 mutation: different biological phenotype and similar prognosis

Background

BRCA2 plays a key role in homologous recombination. However, information regarding its mutations in Chinese patients with breast cancer remains limited.

Objectives

This study aimed to assess the clinicopathological characteristics of BRCA2 mutation breast cancer and explore the mutation's effect on hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative breast cancer survival in China.

Design

This hospital-based cohort study prospectively included 629 women with breast cancer diagnosed from 2008 to 2023 at Zhejiang Cancer Hospital in China.

Methods

We compared the clinicopathological characteristics and metastatic patterns and analysed the invasive disease-free survival (iDFS), distant relapse-free survival (DRFS) and first-line progression-free survival (PFS1) of patients with HR-positive/HER2-negative breast cancer according to BRCA2 mutations.

Results

Among the 629 patients, 78 had BRCA2 mutations (12.4%) and 551 did not (87.6%). The mean age at diagnosis was lower in the BRCA2 mutation breast cancer group than in the non-mutation breast cancer group (38.91 versus 41.94 years, p = 0.016). BRCA2 mutation breast cancers were more likely to be lymph node-positive than non-mutation breast cancers (73.0% versus 56.6%, p = 0.037). The pathological grade was higher in 47.1% of BRCA2 mutation breast cancers than in 29.6% of non-mutation breast cancers (p = 0.014). The proportions of patients with BRCA2 mutations who developed contralateral breast cancer (19.2% versus 8.8%, p = 0.004), breast cancer in the family (53.8% versus 38.3%, p = 0.009) and ovarian cancer in the family (7.6% versus 2.4%, p = 0.022) were higher than those of patients without the mutation. The median follow-up time was 92.78 months. Multivariate analysis showed that BRCA2 mutation was not associated with poorer iDFS [hazard ratio = 0.9, 95% confidence interval (CI) = 0.64-1.27, p = 0.56] and poorer distant relapse-free survival (DRFS) (hazard ratio = 1.09, 95% CI = 0.61-1.93, p = 0.76). There was no significant difference between the two groups with regard to metastatic patterns in the advanced disease setting. In the first-line metastatic breast cancer setting, PFS1 expression was broadly similar between the two groups irrespective of chemotherapy or endocrine therapy.

Conclusion

HR-positive/HER2-negative breast cancer with BRCA2 mutations differs from those without mutations in clinical behaviour and reflects more aggressive tumour behaviour. Our results indicate that BRCA2 mutations have no significant effect on the survival of Chinese women with HR-positive/HER2-negative breast cancer.

ER-positive and BRCA2-mutated breast cancer: a literature review

BRCA2-mutated carriers have a high lifetime risk of breast cancer (BC), an early age of onset, and an increased risk of other cancers (including ovarian, pancreatic, and prostate cancer). Almost 70-80% of BRCA2-mutated BC are estrogen receptor (ER)-positive, which is a particular type of ER-positive BC that differs from sporadic ER-positive BC. This article reviews the clinicopathological features, treatment, and prognosis of ER-positive and BRCA2-mutated BC to provide a reference for clinical decision-making.

Rosetta Stone for Cancer Cure: Comparison of the Anticancer Capacity of Endogenous Estrogens, Synthetic Estrogens and Antiestrogens

This work presents the history of the recognition of principal regulatory capacities of estrogen hormones having been mistakenly regarded as breast cancer promoting agents for more than 120 years. Comprehensive analysis of the results of clinical, epidemiological, immunological and molecular studies justified that endogenous estrogens are the principal regulators of embryonic development, survival and reproduction via orchestrating appropriate expression and even edition of all genes in mammalians. Medical use of chemically modified synthetic estrogens caused toxic complications; thromboembolic events and increased cancer risk in female organs as they proved to be endocrine disruptors deregulating estrogen receptors (ERs) rather than their activators. Synthetic estrogen treatment exhibits ambiguous correlations with cancer risk at different sites, which may be attributed to an inhibition of the unliganded activation of estrogen receptors (ERs) coupled with compensatory liganded activation. The principle of estrogen induced breast cancer led to the introduction of antiestrogen therapies against this tumor; inhibition of the liganded activation of estrogen receptors and aromatase enzyme activity. The initial enthusiasm turned into disappointment as the majority of breast cancers proved to be primarily resistant to antiestrogens. In addition, nearly all patients showing earlier good tumor responses to endocrine therapy, later experienced secondary resistance leading to metastatic disease and fatal outcome. Studying the molecular events in tumors responsive and unresponsive to antiestrogen therapy, it was illuminated that a complete inhibition of liganded ER activation stimulates the growth of cancers, while a successful compensatory upregulation of estrogen signal may achieve DNA restoration, tumor regression and patient's survival. Recognition of the principal role of endogenous estrogens in gene expression, gene edition and DNA repair, estrogen treatment and stimulation of ER expression in patients may bring about a great turn in medical practice.

Towards Unravelling the Role of ERα-Targeting miRNAs in the Exosome-Mediated Transferring of the Hormone Resistance

Hormone therapy is one of the most effective breast cancer treatments, however, its application is limited by the progression of hormonal resistance, both primary or acquired. The development of hormonal resistance is caused either by an irreversible block of hormonal signalling (suppression of the activity or synthesis of hormone receptors), or by activation of oestrogen-independent signalling pathways. Recently the effect of exosome-mediated intercellular transfer of hormonal resistance was revealed, however, the molecular mechanism of this effect is still unknown. Here, the role of exosomal miRNAs (microRNAs) in the transferring of hormonal resistance in breast cancer cells has been studied. The methods used in the work include extraction, purification and RNAseq of miRNAs, transfection of miRNA mimetics, immunoblotting, reporter analysis and the MTT test. Using MCF7 breast cancer cells and MCF7/T tamoxifen-resistant sub-line, we have found that some miRNAs, suppressors of oestrogen receptor signalling, are overexpressed in the exosomes of the resistant breast cancer cells. The multiple (but not single) transfection of one of the identified miRNA, miR-181a-2, into oestrogen-dependent MCF7 cells induced the irreversible tamoxifen resistance associated with the continuous block of the oestrogen receptor signalling and the activation of PI3K/Akt pathway. We suppose that the miRNAs-ERα suppressors may act as trigger agents inducing the block of oestrogen receptor signalling and breast cancer cell transition to an aggressive oestrogen-independent state.

Nonhomologous end joining repair pathway molecules as predictive biomarkers for patients with oral squamous cell carcinoma

Purpose

Nonhomologous end-joining (NHEJ) is critical for the repair of either pathologic double-strand breaks (DSBs) and/or for the repair of physiologic DSBs created during radiotherapy to kill the tumor cell. Therefore, patients with higher expression of NHEJ repair proteins might develop resistance to ionizing radiation, allowing the disease to recur. As cancer of the oral cavity is a serious health problem globally, the present study aimed to examine the expression of Ku70/80, X-ray repair cross-complementing protein 4 (XRCC4) and DNA ligase IV-core molecules of the NHEJ pathway in patients with oral cancer.

Materials and Methods

Protein expression of Ku70/80, XRCC4, and DNA ligase IV were studied by Immunohistochemistry and mRNA expression of Ku70 and Ku80 were studied using reverse transcription polymerase chain reaction. Data were analyzed statistically using SPSS.

Results

A univariate survival analysis revealed an association of Ku70 mRNA with shorter overall survival (OS). While protein expression of XRCC4 showed an association with reduced relapse-free survival and shorter OS. Multivariate survival analysis demonstrated that XRCC4 and DNA ligase IV are independent prognosticators for predicting adverse disease outcomes.

Conclusion

Strong expression of repair proteins - XRCC4 and DNA ligase IV is associated with unfavorable disease outcome in patients with oral squamous cell carcinoma.

SARS-CoV-2 effects in the genitourinary system and prospects of sex hormone therapy

OBJECT

Corona virus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which leads to acute respiratory infection symptoms. SARS-CoV-2 infection is not always limited to the respiratory tract, and renal infection and dysfunction have been shown to be specific risk factors for death. In addition, COVID-19 has a higher incidence, severity and mortality in men than women. This disparity is due to biological rather than comorbid or behavioral sex differences. Because the male reproductive system is unique, the function of sex hormones in COVID-19 infection may explain the differences between males and females. Understanding these factors will provide appropriate prevention measures and adequate triage strategies and guide the drug discovery process.

METHODS

An electronic search was completed in PubMed, ARXIV, MEDRXIV and BIORXIV. The most relevant articles were systematically reviewed. In addition, single cell RNA sequencing analysis of tissue samples from human cell landscape was conducted.

RESULTS

The influence of SARS-CoV-2 on the urogenital system, the possibility of urinary tract transmission and the functions of sex hormones were discussed in this review.

CONCLUSION

Corona viruses can invade the genitourinary system, causing urological symptoms. Identifying the potential genitourinary organ impairments and protecting them from damage are necessary. Since sex hormones have potential as specific drugs, the gonadal hormones substitution therapy should be considered in both sexes in the COVID-19 pandemic.

A cross-sectional study of the association between perfluorinated chemical exposure and cancers related to deregulation of estrogen receptors

BACKGROUND

Environmental exposures acting through different mechanisms have been linked with a number of cancers. Perfluoroalkyl chemicals (PFCs) are endocrine disrupting chemicals affecting estrogen homeostasis.

OBJECTIVES

We examined the association between PFCs and a group of estrogen related cancers and explored if increased non-occupational exposure was associated with increased odds of developing these cancers. We also explored which of these chemical exposures was more correlated with each cancer.

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES), we selected participants ≥ 20 years of age. Our outcome variable was presence or absence of breast, prostate, ovarian and uterine cancer (yes/no); our exposure variables were serum PFCs. Logistic regression models were used in investigating the association between PFCs and cancer types and between quartiles of PFCs exposure concentrations and presence or absence of cancer while adjusting for covariates. Discriminant analysis was used to assess the correlation between individual PFCs compounds and individual cancer types.

RESULTS

PFCs were associated with increased odds of ovarian cancer; PFOA: 1.02(1.01, 1.02), PFOS: 1.01 (1.012, 1.013), PFHS 1.031 (1.030, 1.033), PFDE: 1.29(1.27, 1.30) and increased odds of breast cancer; PFOA: 1.089(1.089, 1.09), PFOS: 1.011(1.011, 1.011), PFNA: 1.031(1.030, 1.033), PFHS: 1.02 (1.02, 1.02), PFDE: 1.19(1.18, 1.19). PFCs were not associated with increased odds of prostate or uterine cancers. Comparing the odds in quartile 4 to quartile 1 for ovarian cancer, PFOA: 1.77(1.75,1.79), PFOS: 2.25(2.22, 2.28), PFHS: 1.86(1.84, 1.88), PFDE: 2.11(2.09, 2.14). For breast cancer, PFOA: 2.30(2.28, 2.31), PFOS: 1.47(1.46, 1.48), PFNA: 1.04(1.03, 1.05), PFHS:7.07(6.97,7.17), PFDE: 1.38(1.37, 1.39). PFOA was more correlated with breast cancer (0.7) and PFHS was more correlated with ovarian cancer (0.9).

DISCUSSION

PFCs were associated with increased odds of ovarian and breast cancers with a positive dose-response relationship. PFOA was more correlated with breast cancer and PFHS more with ovarian cancer.

Investigation of structural, treatment and clinical characteristics of COVID-19 along with the challenges caused by its prevalence

In the late 2019, a report from China was published stating a disease with unknown cause. After that,the outbreak of the COVID-19 caused a pandemic in the world. On March 11, 2020, the outbreak of this virus was reported in 100 countries. The virus is currently spreading rapidly around the world.In the past, coronaviruses caused life-threatening diseases such as SARS and MERSsome areas.Although there is still a debate about the origin of this new coronavirus, it is most likely linked with some animals including bats, civet and pangolin. In this review, we try to simply describe the features of the new coronavirusas well as the recent diagnostic and therapeutic findings.

Key genes and drug delivery systems to improve the efficiency of chemotherapy

Cancer cells can develop resistance to anticancer drugs, thereby becoming tolerant to treatment through different mechanisms. The biological mechanisms leading to the generation of anticancer treatment resistance include alterations in transmembrane proteins, DNA damage and repair mechanisms, alterations in target molecules, and genetic responses, among others. The most common anti-cancer drugs reported to develop resistance to cancer cells include cisplatin, doxorubicin, paclitaxel, and fluorouracil. These anticancer drugs have different mechanisms of action, and specific cancer types can be affected by different genes. The development of drug resistance is a cellular response which uses differential gene expression, to enable adaptation and survival of the cell to diverse threatening environmental agents. In this review, we briefly look at the key regulatory genes, their expression, as well as the responses and regulation of cancer cells when exposed to anticancer drugs, along with the incorporation of alternative nanocarriers as treatments to overcome anticancer drug resistance.

Deregulated estrogen receptor signaling and DNA damage response in breast tumorigenesis

Carriers of BRCA1 mutations have a higher chance of developing cancers in hormone-responsive tissues like the breast, ovary and prostate, compared to other tissues. These tumors generally exhibit basal-like characters and do not express estrogen receptor (ER) or progesterone receptor (PR). Intriguingly, BRCA1 mutated breast cancers have a less favorable clinical outcome, as they will not respond to hormone therapy. BRCA1 has been reported to exhibit ligand dependent and independent transcriptional inhibition of ER-α; however, there exists a controversy on whether BRCA1 induces or inhibits ER-α expression. The mechanisms associated with resistance of BRCA1 mutated cancers to hormone therapy, as well as the tissue restriction exhibited by BRCA1 mutated tumors are still largely unknown. BRCA1 mutated tumors possess increased DNA damages and decreased genomic integrity, as BRCA1 plays a cardinal role in high fidelity DNA damage repair pathways, like homologous recombination (HR). The existence of cross regulatory signaling networks between ER-α and BRCA1 speculates a role of ER on BRCA1 dependent DDR pathways. Thus, the loss or haploinsufficiency of BRCA1 and the consequential deregulation of ER-α signaling may result in persistence of unrepaired DNA damages, eventually leading to tumorigenesis. Therefore, understanding of this cross-talk between ER-α and BRCA1, with regard to DDR, will provide critical insights to steer drug development and therapy for breast/ovarian cancers. This review discusses the mechanisms by which estrogen and ER signaling influence BRCA1 mediated DNA damage response and repair pathways in the mammalian system.

Compensatory Estrogen Signal Is Capable of DNA Repair in Antiestrogen-Responsive Cancer Cells via Activating Mutations

Cancer cells are embarrassed human cells exhibiting the remnants of same mechanisms for DNA stabilization like patients have in their healthy cells. Antiestrogens target the liganded activation of ERs, which is the principal means of genomic regulation in both patients and their tumors. The artificial blockade of liganded ER activation is an emergency situation promoting strong compensatory actions even in cancer cells. When tumor cells are capable of an appropriate upregulation of ER signaling resulting in DNA repair, a tumor response may be detected. In contrast, when ER signaling is completely inhibited, tumor cells show unrestrained proliferation, and tumor growth may be observed. The laboratory investigations of genomic mechanisms in antiestrogen-responsive and antiestrogen-unresponsive tumor cells have considerably enhanced our knowledge regarding the principal regulatory capacity of estrogen signaling. In antiestrogen-responsive tumor cells, a compensatory increased expression and liganded activation of estrogen receptors (ERs) result in an apoptotic death. Conversely, in antiestrogen resistant tumors exhibiting a complete blockade of liganded ER activation, a compensatory effort for unliganded ER activation is characteristic, conferred by the increased expression and activity of growth factor receptors. However, even extreme unliganded ER activation is incapable of DNA restoration when the liganded ER activation is completely blocked. Researchers mistakenly suspect even today that in tumors growing under antiestrogen treatment, the increased unliganded activation of estrogen receptor via activating mutations is an aggressive survival technique, whilst it is a compensatory effort against the blockade of liganded ER activation. The capacity of liganded ERs for genome modification in emergency states provides possibilities for estrogen/ER use in medical practice including cancer cure.

The clinical characteristics and prognosis of endometrial carcinomas that occur after breast cancer: does hormone receptor status of breast cancer matter?

OBJECTIVE

To evaluate the clinical and pathological features of endometrial cancer (EC) following breast cancer and to assess the effect of the breast cancer hormone receptor status on subsequent EC.

MATERIALS

A retrospective study based on SEER data of EC patients with a history of breast cancer.

RESULTS

A total of 2142 cases met the inclusion criteria. Compared to that of the general population, the incidence of EC following estrogen receptor-positive (ER+) breast cancer and hormone receptor-negative (HR-) breast cancer increased by approximately 16-fold and 15-fold, respectively. Histologically, the proportions of type II EC following ER+ breast cancer, HR- breast cancer and primary EC were 39.6%, 39.4% and 31.2%, respectively (P < 0.001). The proportions of G3 ECs were 26.9%, 28.2% and 19.8%, respectively (P < 0.001). The proportion of patients who died from miscellaneous malignant tumors among EC patients following breast cancer was significantly higher than the proportion of patients among primary ECs. The overall survival rate was worse for EC patients with a history of breast cancer (P < 0.001). There were no significant differences between patients with EC following ER+ breast cancer and those with EC following HR- breast cancer with regard to stage, lymphatic metastasis, outcome or cause of death.

CONCLUSIONS

Compared to the general population, the incidence of EC in patients with breast cancer was increased markedly. Patients with EC following ER+ or HR- breast cancer shared the same clinicopathological features and prognoses. All patients need close monitoring regardless of breast cancer hormone receptor status.

Novel role of sex-determining region Y-box 7 (SOX7) in tumor biology and cardiovascular developmental biology

The sex-determining region Y-box 7 (Sox7) is an important member of the SOX F family, which is characterized by a high-mobility-group DNA-binding domain. Previous studies have demonstrated the role of SOX7 in cardiovascular development. SOX7 expression could be detected in normal adult tissues. Furthermore, the expression levels of SOX7 were different in different tumors. Most studies showed the downregulation of SOX7 in tumors, while some studies reported its upregulation in tumors. In this review, we first summarized the upstream regulators (including transcription factors, microRNAs (miRNAs), long noncoding RNAs (lncRNAs) and some exogenous regulators) and downstream molecules (including factors in the Wnt/β-catenin signaling pathway and some other signaling pathways) of SOX7. Then, the roles of SOX7 in multiple tumors were presented. Finally, the significance of divergent SOX7 expression during cardiovascular development was briefly discussed. The information compiled in this study characterized SOX7 during tumorigenesis and cardiovascular development, which should facilitate the design of future research and promote SOX7 as a therapeutic target.

Identification of driver genes and somatic mutations in cell-free DNA of patients with pulmonary lymphangioleiomyomatosis

Next-generation sequencing of cell-free circulating DNA (cfDNA) has emerged as promising technique for identifying minimally invasive genomic profiling of tumor cells recently. However, it remains relatively unknown in LAM disease. In our study, paired cfDNA and genomic DNA (gDNA) in blood samples were obtained from 23 LAM patients and seven healthy controls to explore mutations profiles of targeted 70 cancer-related genes. As results, log2-based allele frequencies of mutations in cfDNA were significantly different from those of gDNA. By comparing the mutual mutations identified both in cfDNA and gDNA, a significant correlation was also observed. After removing mutations in gDNA, distinct somatic mutation profiles of cfDNA were observed in LAM patients. Forty of 70 targeted genes had recurrent mutations, of which ATM, BRCA2 and APC showed the highest frequency. Based on the mutation, correlation network constructed of 40 mutated genes, 11 hub genes bearing intensive interactions were highlighted, including BRCA1, BRCA2, RAD50, RB1, NF1, APC, MLH3, ATM, PDGFRA, PALB2 and BLM. Expression of the hub genes showed significant clusters between LAM patients and controls and that RAD50 and BRCA2 had the strongest associations with subject phenotypes. Myogenesis and estrogen response were confirmed to be positively regulated in LAM patients. Collectively, our study provided a landscape of genomic alterations in LAM and discovered several potential driver genes, that is, BRCA2 and RAD50, which shed a substantial light on the clinical application of key molecular markers and potential therapy targets for precision diagnosis and treatment in the future.

Causal Therapy of Breast Cancer Irrelevant of Age, Tumor Stage and ER-Status: Stimulation of Estrogen Signaling Coupled With Breast Conserving Surgery

Abstract: Background

Results of long-term studies justify that the rate of breast cancer recurrence and tumor-related mortality remains quite unpredictable, regardless of the use of any current therapeutic measures.

Objective

Since the application of standard therapies, such as surgery, radiation, chemotherapy and antiestrogen administration does not work as might be expected; our therapeutic practice requires thorough rethinking.

Method

Published long-term therapeutic results on breast cancer cases were analyzed in correlation with stage at diagnosis, ER-status of tumors and patients’ age. The effectiveness of current therapeutic measures was also compared by estimating the rate of tumor-free survival, breast cancer recurrence and breast cancer-specific mortality.

Results

Diagnosis and treatment of breast cancer at an early stage cannot improve the rate of tumor-free survival. Poor differentiation of tumors, ER-negativity in particular, defines poor prognosis even after applying aggressive therapies. In patients treated with in situ breast cancer, the recurrence-rate of invasive tumor increased directly with ageing irrespective of tumor size or ER-status at diagnosis. Women who underwent lumpectomy without adjuvant radiation or chemotherapy exhibited significantly better overall and breast cancer specific survival rates than those receiving mastectomy, regardless of stage and ER-status of tumors. Antiestrogen treatment exhibited unforeseeable effectiveness even on targeted ER-positive tumors. Recent patents propose the detection of ESR1-gene amplification or restoration of ER-alpha expression for prediction of effective antiestrogen treatment, suggesting a crucial inhibitory role of estrogen-signaling against tumor-growth.

Conclusion

Estradiol-induced upregulation of estrogen signaling coupled with sparing of the estrogen-rich mammary fatpad are the most effective strategies against breast cancer.

Linking DNA Damage and Hormone Signaling Pathways in Cancer

DNA damage response and repair (DDR) is a tightly controlled process that serves as a barrier to tumorigenesis. Consequently, DDR is frequently altered in human malignancy, and can be exploited for therapeutic gain either through molecularly targeted therapies or as a consequence of therapeutic agents that induce genotoxic stress. In select tumor types, steroid hormones and cognate receptors serve as major drivers of tumor development/progression, and as such are frequently targets of therapeutic intervention. Recent evidence suggests that the existence of crosstalk mechanisms linking the DDR machinery and hormone signaling pathways cooperate to influence both cancer progression and therapeutic response. These underlying mechanisms and their implications for cancer management will be discussed.

The pitfall of the transient, inconsistent anticancer capacity of antiestrogens and the mechanism of apparent antiestrogen resistance

Although antiestrogens have been available for breast cancer therapy since the early 1970s, neither their inconsistent anticancer capacity nor the developing antiestrogen resistance of tumors can be fully understood. Although clinical and experimental investigations revealed many tiny details concerning the link between estrogen signaling and tumor development, they yielded fairly controversial findings. Estrogen receptor (ER) overexpression in tumor cells induced by estrogen treatment was erroneously regarded as a promoter of DNA damage, genomic instability, and tumor growth. Similarly, compensatory ER overexpression caused by antiestrogen treatment or estrogen withdrawal was mistakenly evaluated as a key for rapid tumor growth attributed to acquired antiestrogen resistance. Nevertheless, ER upregulation induced by estrogen treatment is a physiologic process even in tumor cells, whereas in the case of antiestrogen administration, it is a contraregulatory action to defend the endangered estrogen signaling. Upregulation of estrogen signaling displays a unique dichotomy, ensuring the survival and safe proliferative activity of healthy cells, while inducing apoptotic death of malignant tumor cells. Analysis of the fairly controversial results justifies that whatever type of available endocrine therapies may be used, including estrogen, antiestrogen treatment, or oophorectomy, an extreme upregulation of ER signaling seems to be the crucial mechanism of successful prevention and treatment for breast cancer. The inconsistent therapeutic effects of antiestrogen administration may be explained by the different genetic capacities of patients for the compensatory upregulation of ER and aromatase enzyme expressions. The weaker the defensive counteraction against the inhibition of estrogen signaling, the poorer is the prognosis of the disease. De novo or acquired antiestrogen resistance of tumors may be associated with the missing capacity of patients for the extreme upregulation of estrogen signaling or with the exhaustion of defensive counteractions in cases that previously showed good reactivity. High-dose estrogen treatment is capable of restoring ER signaling and anticancer capacity even after heavy exposure to antiestrogen therapy.