Estrogen receptor gene amplification is found in some estrogen receptor-positive human breast tumors

Currently Applied Molecular Assays for Identifying ESR1 Mutations in Patients with Advanced Breast Cancer

Approximately 70% of breast cancers, the leading cause of cancer-related mortality worldwide, are positive for the estrogen receptor (ER). Treatment of patients with luminal subtypes is mainly based on endocrine therapy. However, ER positivity is reduced and ESR1 mutations play an important role in resistance to endocrine therapy, leading to advanced breast cancer. Various methodologies for the detection of ESR1 mutations have been developed, and the most commonly used method is next-generation sequencing (NGS)-based assays (50.0%) followed by droplet digital PCR (ddPCR) (45.5%). Regarding the sample type, tissue (50.0%) was more frequently used than plasma (27.3%). However, plasma (46.2%) became the most used method in 2016-2019, in contrast to 2012-2015 (22.2%). In 2016-2019, ddPCR (61.5%), rather than NGS (30.8%), became a more popular method than it was in 2012-2015. The easy accessibility, non-invasiveness, and demonstrated usefulness with high sensitivity of ddPCR using plasma have changed the trends. When using these assays, there should be a comprehensive understanding of the principles, advantages, vulnerability, and precautions for interpretation. In the future, advanced NGS platforms and modified ddPCR will benefit patients by facilitating treatment decisions efficiently based on information regarding ESR1 mutations.

ESR1 alterations and metastasis in estrogen receptor positive breast cancer

Endocrine therapy is essential for the treatment of patients with estrogen receptor positive (ER+) breast cancer, however, resistance and the development of metastatic disease is common. Understanding how ER+ breast cancer metastasizes is critical since the major cause of death in breast cancer is metastasis to distant organs. Results from many studies suggest dysregulation of the estrogen receptor alpha gene (ESR1 ) contributes to therapeutic resistance and metastatic biology. This review covers both pre-clinical and clinical evidence on the spectrum of ESR1 alterations including amplification, point mutations, and genomic rearrangement events driving treatment resistance and metastatic potential of ER+ breast cancer. Importantly, we describe how these ESR1 alterations may provide therapeutic opportunities to improve outcomes in patients with lethal, metastatic breast cancer.

The evolving role of receptors as predictive biomarkers for metastatic breast cancer

INTRODUCTION

In breast cancer, estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2) are essential biomarkers to predict response to endocrine and anti-HER2 therapies, respectively. In metastatic breast cancer, the use of these receptors and targeted therapies present additional challenges: temporal heterogeneity, together with limited sampling methodologies, hinders receptor status assessment, and the constant evolution of the disease invariably leads to resistance to treatment. Areas covered: This review summarizes the genomic abnormalities in ER and HER2, such as mutations, amplifications, translocations, and alternative splicing, emerging as novel biomarkers that provide an insight into underlying mechanisms of resistance and hold potential predictive value to inform treatment selection. We also describe how liquid biopsies for sampling of circulating markers and ultrasensitive detection technologies have emerged which complement ongoing efforts for biomarker discovery and analysis. Expert commentary: While evidence suggests that genomic aberrations in ER and HER2 could contribute to meeting the pressing need for better predictive biomarkers, efforts need to be made to standardize assessment methods and better understand the resistance mechanisms these markers denote. Taking advantage of emerging technologies, research in upcoming years should include prospective trials incorporating these predictors into the study design to validate their potential clinical value.

Estrogen receptor alpha gene amplification in breast cancer: 25 years of debate

Twenty-five years ago, Nembrot and colleagues reported amplification of the estrogen receptor alpha gene (ESR1) in breast cancer, initiating a broad and still ongoing scientific debate on the prevalence and clinical significance of this genetic aberration, which affects one of the most important genes in breast cancer. Since then, a multitude of studies on this topic has been published, covering a wide range of divergent results and arguments. The reported prevalence of this alteration in breast cancer ranges from 0% to 75%, suggesting that ESR1 copy number analysis is hampered by technical and interpreter issues. To date, two major issues related to ESR1 amplification remain to be conclusively addressed: (1) The extent to which abundant amounts of messenger RNA can mimic amplification in standard fluorescence in situ hybridization assays in the analysis of strongly expressed genes like ESR1, and (2) the clinical relevance of ESR1 amplification: Such relevance is strongly disputed, with data showing predictive value for response as well as for resistance of the cancer to anti-estrogen therapies, or for subsequent development of cancers in the case of precursor lesions that display amplification of ESR1. This review provides a comprehensive summary of the various views on ESR1 amplification, and highlights explanations for the contradictions and conflicting data that could inform future ESR1 research.

Status of estrogen receptor 1 (ESR1) gene in mastopathy predicts subsequent development of breast cancer

Mastopathy is a common disease of the breast likely associated with elevated estrogen levels and a putative risk factor for breast cancer. The role of estrogen receptor alpha (ESR1) in mastopathy has not been investigated previously. Here, we investigated the prevalence of ESR1 gene amplification in mastopathy and its prediction for breast cancer. Paraffin-embedded tissues from 58 women with invasive breast cancer were analyzed. For all women, tissues with mastopathy taken at least 1.5 years before first diagnosis of breast cancer were available. Tissue from 46 women with mastopathy without a diagnosis of breast carcinoma in the observed time frame (12-18 years) was used as control. Fluorescence in situ hybridization analysis revealed that ESR1 was amplified in nine of 58 (15.5 %) breast cancers. All ESR1-amplified breast cancers were strongly positive for estrogen receptor with ER immunohistochemistry. Interestingly, in women with ESR1 amplification in breast cancer, the amplification was detectable in mastopathic tissues prior to the first diagnosis of breast cancer but was absent in tissues from women with mastopathy who did not develop breast cancer. Our study suggests that ESR1 gene amplification is an early event in breast pathology and might be a helpful predictive marker to identify patients at high risk of developing breast cancer.

Absence of estrogen receptor alpha (ESR1) gene amplification in a series of breast cancers in Taiwan

Immunohistochemical expression of ERα, encoded by the ESR1 (estrogen receptor 1) gene located at 6q25.1, is the most important determinant of responsiveness to endocrine therapy in breast cancer. The prevalence and significance of ESR1 amplification in breast cancer remain controversial. We set out to assess ESR1 status and its relevance in breast cancer in Taiwan. We tested tissue samples from 311 invasive carcinomas in a tissue microarray for ESR1 status by fluorescent in situ hybridization (FISH) and chromogenic in situ hybridization (CISH). In order to examine its association with ERα and ESR1 status, HER2 status was determined by FISH. Of the carcinomas, 58.8 % (183/311) was ERα positive. None of the carcinomas showed amplification of ESR1 by either method, whereas 24.1 % (75/311) of the carcinomas harbored HER2 amplification. Of the carcinomas, 9.6 % (26/301) showed ESR1 gain (1.3 ≤ ratio ESR1/chromosome 6 < 2) by FISH and 10 % (24/299) by CISH. FISH and CISH results showed a good correlation (κ-coefficient = 0.786). ESR1 gain by FISH and CISH was significantly associated with high-grade (P = 0.0294 and 0.0417, respectively) but not with ERα expression, HER2 status, or overall survival. ERα positivity was significantly associated with better overall survival (P = 0.039). HER2 amplification was significantly related with poor overall survival (P = 0.002). Our data confirm that in breast cancer, HER2 amplification is a frequent genetic aberration and a negative prognostic factor, and show that ESR1 amplification is not a key genetic abnormality in the tumorigenesis of breast cancer in Taiwan.

Amplification of ESR1 may predict resistance to adjuvant tamoxifen in postmenopausal patients with hormone receptor positive breast cancer

The estrogen receptor (ER) is the target of tamoxifen, but endocrine therapies do not benefit all patients with ER positive tumors. We therefore hypothesized that copy number changes in the ESR1 gene, encoding ER, confer resistance. Within a consecutive series of ER positive, postmenopausal patients allocated to 5 years tamoxifen, we identified 61 patients with recurrence less than 4 years and 48 patients without recurrence at least 7 years after initiation of adjuvant tamoxifen. Archival tissue containing primary tumor was collected from 97 patients (89%). Tumor samples were analyzed for ESR1 copy number changes using FISH with a probe covering the ESR1 gene at 6q25 and a reference probe covering the centromere of chromosome 6. The assay was validated in a material of 120 normal breast samples. FISH analysis for ESR1 was successful in 91 patients (94%). Amplification (ratio ESR1/CEN-6 ≥ 2.0) was observed in 11 of 50 (22%) patients with early recurrence, compared to two of 41 (5%) patients without recurrence. The difference is statistically significant (P = 0.033). In both groups, two patients with ESR1 deletion (ratio ESR1/CEN-6 < 0.8) were identified. ESR1 amplification was significantly associated with poor disease-free survival (P = 0.0054) and overall survival (P = 0.0004). This pilot study supports our hypothesis that ESR1 amplification is associated with a poorer outcome following adjuvant treatment with tamoxifen in ER positive early breast cancer. This study also revealed the existence of ESR1 deletions. The prognostic and predictive impact of ESR1 copy number changes needs further exploration in clinical trials.

Estrogen receptor alpha gene ESR1 amplification may predict endocrine therapy responsiveness in breast cancer patients

Estrogen receptor (ER) alpha plays a crucial role in normal breast development and has also been linked to mammary carcinogenesis and clinical outcome in breast cancer patients. However, the molecular mechanisms controlling the expression of ERalpha are as yet not fully understood. Gene amplification is one of the important factors regulating protein expression. Recent studies on the amplification of the ESR1 gene, which encodes ERalpha, have presented conflicting data. Using fluorescence in situ hybridization and real-time quantitative polymerase chain reaction analysis, we examined the ESR1 status in a series of breast cancer tissues and analyzed its clinical importance. ESR1 gene amplification and gain were found in 22.6 and 11.3% of samples, respectively, as determined by three-dimensional fluorescence in situ hybridization assay. Moreover, ESR1 amplification and amplification plus gain were significantly negatively correlated with tumor size, number of positive lymph nodes, negative ERalpha, and positive human epidermal growth factor receptor 2 status. It has also been shown that ESR1 amplification strongly correlates with higher expression levels of ER protein and that patients with ESR1 amplification in their tumors apparently experience longer disease-free survival than those without. Our data suggest that ESR1 amplification might prove to be helpful in selecting patients who may potentially benefit from endocrine therapy.

ESR1 amplification in endometrial carcinomas: hope or hyperbole?

The ESR1 gene maps 6q25 and encodes for oestrogen receptor alpha, which has been shown to play a pivotal role in the development of breast and endometrial cancer. It has recently been reported that oestrogen receptor alpha expression may be driven in some cases by ESR1 gene amplification and that this phenomenon may be an early event in breast and endometrial carcinogenesis. Although copy number gains of 6q have been reported by several groups, their prevalence, association with oestrogen receptor alpha expression, and clinical implications have been a matter of controversy. Here we discuss the key issues regarding the methods employed in the identification of ESR1 amplification, and briefly review the current literature and recent controversies on the subject of ESR1 amplification in endometrial and breast cancers.

A functional significance for codon third bases

Most amino acids are specified by more than one trinucleotide codon. Here we show that amino acids of differing functional importance may be distinguished by the pattern of synonymous codon usage. GC-rich genes tend to be of a greater transcriptional (p<0.01) and mitogenic (p<0.0001) significance than AT-rich genes, consistent with GC-->AT mutational drift in methylated genomic regions. Third-base GC retention also identifies critical amino acids within individual proteins, as indicated by non-random patterns of codon variation between gene homologs and also by differential sequelae of site-directed mutagenesis. Sequence analysis of human receptor tyrosine kinase genes confirms that functionally important transmembrane hydrophobic amino acids are specified by codons containing GC third bases more often than are transmembrane neutral amino acids (chi(2)=134.2). Amino acids encoded by GC third bases thus appear more tightly linked to cell function and survival than are those encoded by AT third bases.

Differential screening and suppression subtractive hybridization identified genes differentially expressed in an estrogen receptor-positive breast carcinoma cell line

Differences in gene expression are likely to explain the phenotypic differences between hormone-responsive and hormone-unresponsive breast cancer. We have identified differentially expressed cDNAs in the estrogen receptor (ER)-positive MCF7 breast carcinoma cell line compared with the ER-negative MDA-MB-231 breast carcinoma cell line. Differential screening isolated four differentially expressed genes: cytokeratin 8, cytokeratin 18, Hsp27 and GPCR -Br. To identify differentially expressed genes of lower abundance, suppression subtractive hybridization was utilized and 29 differentially expressed clones were isolated. Sequence analysis revealed that 11 clones were from previously described genes: HEK8, neuropeptide Y receptor Y1, p21 WAF-1, p55 PIK, cytokeratin 18 (cloned twice), fructose-1,6-biphosphatase, cytokeratin 8, TGFbeta1 binding protein, elongation factor 1alpha2 and pS2. The remaining 18 clones did not match sequences in the GenBank/EMBL database, indicating that they may be novel genes. Expression of pS2, neuropeptide Y receptor Y1 and three novel clones was induced by estradiol, indicating estrogen-responsiveness. The expression pattern of one novel gene, DEME -6, correlated with expression of ER and ERF -1/ AP -2gamma in a panel of breast carcinoma cell lines. A 2.6 kb cDNA of DEME -6 was sequenced and contains an open reading frame of 574 amino acids that demonstrates 62.4% similarity with a gene from Caenorhabditis elegans chromosome III. Expression of DEME -6 was also detected in primary breast carcinomas but not in normal breast tissue, as determined by RT-PCR. These findings support the hypothesis that a set of genes coordinately regulated with ER , but not necessarily estradiol-responsive, are characteristic of the hormone-responsive breast cancer phenotype.

Alterations and Polymorphisms of the Estrogen Receptor Gene in Breast Cancer

The existence of hormone-independent tumors is a substantial problem for the present endocrine treatment of breast cancers. Recently, numerous variant estrogen receptors (ERs) at the mRNA level have been detected with base pair insertions, transitions, and deletions, as well as alternative splicing, yielding deletion of exon 3, 5, or 7. It has been shown that the loss of hormone dependence in breast tumors is partly due to the presence of mutated or truncated ERs that can activate the transcription of an estrogen-regulatable gene in the absence of estrogen. The mechanism of the loss of hormone dependency is, however, still very complex. Thus, further work assessing the correlation between clinical behavior and ER variants is required to determine whether these variants play a role in hormone-resistant disease. Additionally, a possible linkage to the ER gene has been found in some breast cancer families, suggesting that either the ER gene itself or an adjacent gene may be breast cancer susceptibility genes.

Auto-regulation of the estrogen receptor promoter

The presence or absence of estrogen receptor (ER) plays a key role in the diagnosis and treatment of breast tumors. It is known that patients with breast tumors classified as ER-positive have a better prognosis. Observations such as this have led us to explore the question of what makes some breast tumors overexpress ER whereas others express either very low levels or none at all. To begin a study of ER regulation, we first chose to examine a 200 bp region of the ER promoter located immediately upstream from the transcribed sequence of the human ER gene. We found that this region of the ER promoter contained basal activity when transiently transfected into ER-negative HeLa cells. ER promoter activity was further increased by co-transfection of a wild-type ER expression vector, and this increased activity was hormone-dependent. Several ER deletion mutant constructs were also able to increase the activity of the ER promoter fragment, but none could support equivalent activity as was seen with the full-length ER. Therefore, we conclude that the ER can contribute to its own expression, and we hypothesize that this auto-regulation may contribute to its overexpression in some breast tumors.

The role of estrogen receptor mutations in tamoxifen-stimulated breast cancer

During the past 20 years, the hormonal therapy of choice for the treatment of breast cancer has been the antiestrogen, tamoxifen. The use of tamoxifen has been proved to produce a favorable response and survival advantage in patients whose tumors are classified as estrogen receptor-positive (ER+)/progesterone receptor-positive (PR+). Additionally, tamoxifen is the only drug known to reduce the incidence of contralateral disease. This drug produces relatively few harmful side effects, while exhibiting several beneficial effects such as maintaining bone density and reducing the incidence of myocardial infarction in the postmenopausal woman. However, tumors eventually acquire a tamoxifen-resistant or tamoxifen-stimulated phenotype, resulting in disease recurrence. Several mechanisms have been proposed to account for tamoxifen-resistant breast cancer, in the hope of developing a more effective first-line or perhaps second-line treatment strategy. One popular theory is the occurrence of a mutation in the estrogen receptor, the drug target. A plethora of studies have reported the detection of estrogen receptor mRNA splice variants, and it has been suggested that the accumulation of these variant mRNAs are responsible for the development of tamoxifen-resistant breast cancer. In this review, several questions will be posed to address the suitability of both laboratory and clinical evidence to support this hypothesis. Although there is adequate data generated in the laboratory, there is, as yet, no compelling evidence to suggest that mutation of the estrogen receptor is the molecular mechanism producing tamoxifen-stimulated growth in human breast and endometrial cancer.

In situ hybridization of chromosome 6 on fine-needle aspirates from breast carcinomas: comparison of numerical abnormalities and ER/PgR status and staining pattern

The estrogen receptor (ER) gene is located on chromosome 6. The aim of our study was to investigate whether numerical chromosomal aberrations were reflected in estrogen/progesterone receptor (PgR) status and staining pattern. Fine-needle aspirates from 51 breast carcinomas were investigated immunocytochemically for ER/PgR and by in situ hybridization technique using digoxigenin-labeled alpha-satellite probe for chromosome 6. Cases with > or = 70% two-signal nuclei were regarded as disome; the remaining tumors showed aneusomy with a variable number of signals. Aneusomy was found in 32 tumors (63%), whereas 19 (37%) had a normal number of chromosome 6. Chromosomal gain occurred in all aneusome cases except one. ER- and/or PgR-positive tumors had an equal distribution of disomy and aneusomy. Variable ER staining pattern or ER and/or PgR negativity was associated with numerical aberrations in chromosome 6 in 76% of the tumors. Cancers with uniform ER staining pattern all had normal chromosome number.

Differential expression of estrogen receptor mRNA splice variants in the tamoxifen resistant human breast cancer cell line, MCF-7/TAMR-1 compared to the parental MCF-7 cell line

Breast cancer patients with an estrogen receptor (ER) positive tumor can be treated with the anti-estrogen tamoxifen, but development of anti-estrogen resistance is a serious problem. We have analyzed a tamoxifen resistant human breast cancer cell line MCF-7/TAMR-1 for alterations in ER which might explain the tamoxifen resistance. The MCF-7/TAMR-1 cells expressed both wild-type ER mRNA and protein, and by RT-PCR we were able to clone ER cDNAs corresponding to the following mRNA splice variants: ER delta E2, ER delta E4, ER delta E5, ER delta E7 and a new double splice variant lacking both exon 4 and 7 (ER delta E4,7) The existence of the ER delta E4,7 variant was confirmed by RNase protection assay. Semi-quantitative RT-PCR revealed that ER delta E2 mRNA was expressed at a higher level in MCF-7/TAMR-1 cells, whereas the ER delta E5 mRNA was expressed at a significantly lower level in MCF-7/TAMR-1 cells compared with MCF-7 cells. The differential expression of the two ER mRNA splice variants indicates that they may be involved in anti-estrogen resistance, although the present knowledge of their biological function does not provide us with an explanation.

Role of estrogen receptor variants in the development of hormone resistance in breast cancer

Recent evidence suggests that the progression to hormone resistance in some breast tumors is due to mutations in the estrogen receptor (ER). Various types of ER variants have been found in breast cancer biopsies and breast cancer cell lines. The ER variants include dominant-positive receptors that are transcriptionally active in the absence of estrogen, and dominant-negative receptors that are themselves transcriptionally inactive but prevent the action of the normal receptor. The mechanisms by which these variants cause loss of hormonal control is becoming clear. ER variants may be prognostic factors for breast cancer. By modifying the action of ER variants, it should be possible to develop new strategies for treatment of malignant breast disease.

Abnormal estrogen receptor in clinical breast cancer

We have discovered a number of estrogen receptor variants in clinical breast cancer tissues. We have base-pair insertions, transitions, and deletions of exons 3, 5 and 7. Using a transactivation assay we have discovered receptors with outlaw function consisting of both dominant-positive receptors which are transcriptionally active in the absence of estrogen, and dominant-negative receptors which are transcriptionally inactive themselves but prevent normal estrogen receptor function.

Oestrogen receptor gene structure and function in breast cancer

The mechanisms underlying loss of oestrogen responsiveness in breast cancer are not well-defined. Potential mechanisms include loss of receptor expression, alterations in the oestrogen receptor (ER) gene producing proteins with abnormal function, or changes to receptor-dependent or -independent pathways controlling cell proliferation. Examination by Southern analysis of the ER gene in a series of ER-negative and -positive breast tumour biopsies failed to provide evidence of gross rearrangements and in only one of thirty seven tumour DNA samples was significant gene amplification observed. No restriction fragment length polymorphisms were detected for the restriction enzymes EcoR I, Pst I or Hind III. Methylation of the ER gene as assessed by Hpa II and Msp I restriction enzyme digests varied between tumours but the degree of methylation was not correlated with levels of expression of the receptor protein. Similar findings applied in a series of ER-negative and -positive breast cancer cell lines and clonal lines of MCF-7 cells, which were developed as an in vitro model for the acquisition of oestrogen and antioestrogen resistance. In this model there was no evidence that changes to ER receptor function and/or structure at the level of the ER gene, mRNA, ligand binding, and ability to induce progesterone receptor might account for the development of hormone resistance. However, the ability of ER to interact with a DNA sequence containing the vitellogenin promoter oestrogen response element, as assessed by gel retardation assay, was impaired in the clone showing the greatest degree of oestrogen and antioestrogen resistance.

Chromosomal abnormalities in human breast cancer

This review emphasizes cytogenetic changes and DNA analyses by Southern blot in primary breast tumors, rather than metastases, established cell lines, and pleural effusions. The data suggests that the most frequently altered chromosomes and chromosome regions are 1p, 1q, 2q, 3p, 5, 6q, 8p, 8q, 11p, 11q, 12, 13q, 14q, 16, 17p, and 17q. Changes on 8q, 11p, 11q, 13q, and 17q appear to be associated with either progression of the disease or poor prognosis. Alterations on 1p and 3p may represent early events in the development of breast cancer.