Expression of wild-type estrogen receptor beta protein in human breast cancer: specific correlation with HER2/neu overexpression

The Prognostic Value of Estrogen Receptor β Isoform With Correlation of Estrogen Receptor α Among Sudanese Breast Cancer Patients

Two estrogen receptor isoforms (ERα and ERβ) have been characterized with variable and sometimes contrasting responses to estrogens, partially explained by different receptor signaling pathways in estrogen-sensitive tissues. This is a retrospective, descriptive, cross-sectional study, aiming to evaluate the expression pattern of ERβ, employing immunohistochemical techniques using specific monoclonal antibody for ERβ, to correlate its expression with that of ERα in a Sudanese population. Two-hundred and fifty formalin-fixed paraffin-wax-embedded breast tissue blocks were used in this study. Of these, 200 were taken from breast cancer patients ascertained as study cases, and the remaining 50 were noninvolved surgical margin considered as normal breast tissue. Receptor expression was demonstrated using immunohistochemical techniques. The immune expression of ERβ was detected in 57.5% of breast cancers. It was differentially expressed in breast tissues encompassing normal, noninvasive, as well as invasive carcinoma (P = .02). There was no evidence of a significant relationship between ERβ and ERα expression. Among the ERα-negative tumor, 60.4% expressed ERβ. The expression of ERβ among this subgroup was significantly associated with good clinicopathological parameters such as negative Her2/neu, lower grade, and negative lymph node metastasis (P = .002). This study concludes that ERβ was commonly expressed among Sudanese patients with breast cancer, either co-expressed with ERα or expressed alone. In the ERα-negative subgroup, it was associated with better tumor outcomes suggesting ERβ should be included in the diagnostic protocol as an independent marker for favorable prognosis.

Optimized immunohistochemical detection of estrogen receptor beta using two validated monoclonal antibodies confirms its expression in normal and malignant breast tissues

PURPOSE

Significant controversy exists regarding the expression patterns of estrogen receptor beta (ERβ) in normal and diseased breast tissue. To address this issue, we have validated two ERβ antibodies, optimized the IHC protocols for both antibodies and now report the expression patterns of ERβ in normal and malignant breast tissues.

METHODS

ERβ antibody specificity was determined using western blot and IHC analysis. ERβ protein expression patterns were assessed via IHC in normal breast tissue and invasive breast carcinoma. Further, we report the detailed protocol of the ERβ IHC assay developed in our CAP/CLIA certified laboratory to provide a standardized method for future studies.

RESULTS

We have confirmed the specificity of two independent ERβ monoclonal antibodies, one that detects total (i.e., full length plus splice variants 2-5, which do not include the ligand binding domain) ERβ protein (PPZ0506) and one that detects only the full-length form, which includes the ligand binding domain, of ERβ (PPG5/10). Using these two antibodies, we demonstrate that ERβ is highly expressed in normal human breast tissue as well as in 20-30% of invasive breast cancers. Further, these two antibodies exhibited similar staining patterns across multiple different tissues and were highly concordant with regard to determining ERβ positivity in breast cancers.

CONCLUSIONS

ERβ protein was shown to be abundant in the majority of normal breast epithelial cells and is present in 20-30% of breast cancers. Use of these two antibodies, along with their standardized IHC protocols, provide a reference for future studies aimed at determining the utility of ERβ as a prognostic and/or predictive biomarker in various tissues of benign or malignant states.

Comprehensive assessment of estrogen receptor beta antibodies in cancer cell line models and tissue reveals critical limitations in reagent specificity

Estrogen Receptor-β (ERβ) has been implicated in many cancers. In prostate and breast cancer its function is controversial, but genetic studies implicate a role in cancer progression. Much of the confusion around ERβ stems from antibodies that are inadequately validated, yet have become standard tools for deciphering its role. Using an ERβ-inducible cell system we assessed commonly utilized ERβ antibodies and show that one of the most commonly used antibodies, NCL-ER-BETA, is non-specific for ERβ. Other antibodies have limited ERβ specificity or are only specific in one experimental modality. ERβ is commonly studied in MCF-7 (breast) and LNCaP (prostate) cancer cell lines, but we found no ERβ expression in either, using validated antibodies and independent mass spectrometry-based approaches. Our findings question conclusions made about ERβ using the NCL-ER-BETA antibody, or LNCaP and MCF-7 cell lines. We describe robust reagents, which detect ERβ across multiple experimental approaches and in clinical samples.

ERβ1: characterization, prognosis, and evaluation of treatment strategies in ERα-positive and -negative breast cancer

BACKGROUND

The role and clinical value of ERβ1 expression is controversial and recent data demonstrates that many ERβ antibodies are insensitive and/or non-specific. Therefore, we sought to comprehensively characterize ERβ1 expression across all sub-types of breast cancer using a validated antibody and determine the roles of this receptor in mediating response to multiple forms of endocrine therapy both in the presence and absence of ERα expression.

METHODS

Nuclear and cytoplasmic expression patterns of ERβ1 were analyzed in three patient cohorts, including a retrospective analysis of a prospective adjuvant tamoxifen study and a triple negative breast cancer cohort. To investigate the utility of therapeutically targeting ERβ1, we generated multiple ERβ1 expressing cell model systems and determined their proliferative responses following anti-estrogenic or ERβ-specific agonist exposure.

RESULTS

Nuclear ERβ1 was shown to be expressed across all major sub-types of breast cancer, including 25% of triple negative breast cancers and 33% of ER-positive tumors, and was associated with significantly improved outcomes in ERα-positive tamoxifen-treated patients. In agreement with these observations, ERβ1 expression sensitized ERα-positive breast cancer cells to the anti-cancer effects of selective estrogen receptor modulators (SERMs). However, in the absence of ERα expression, ERβ-specific agonists potently inhibited cell proliferation rates while anti-estrogenic therapies were ineffective.

CONCLUSIONS

Using a validated antibody, we have confirmed that nuclear ERβ1 expression is commonly present in breast cancer and is prognostic in tamoxifen-treated patients. Using multiple breast cancer cell lines, ERβ appears to be a novel therapeutic target. However, the efficacy of SERMs and ERβ-specific agonists differ as a function of ERα expression.

The pattern of proline, glutamic acid, and leucine-rich protein 1 expression in Chinese women with primary breast cancer

BACKGROUND

Disparities of biomarkers' expression in breast cancer across different races and ethnicities have been well documented. Proline, glutamic acid, and leucine-rich protein 1 (PELP1), a novel ER coregulator, has been considered as a promising biomarker of breast cancer prognosis; however, the pattern of PELP1 expression in Chinese women with breast cancer has never been investigated. This study aims to provide useful reference on possible racial or ethnic differences of PELP1 expression in breast cancer by exploring the pattern of PELP1 expression in Chinese women with primary breast cancer.

METHODS

The expression of PELP1 in primary breast cancer samples from 130 Chinese female patients was detected by immunohistochemistry and correlated to other clinicopathological parameters; for comparison, the expression of PELP1 in 26 benign breast fibroadenomas was also examined.

RESULTS

The overall value of the PELP1 H-score in breast cancer was significantly higher than that in breast fibroadenoma (p<0.001). In our breast cancer patients, the ER/HER-2-positive group had significantly higher PELP1 H-scores than their negative counterparts (p=0.003 for ER and p=0.022 for HER-2); the Ki-67-high group also showed significantly higher PELP1 H-scores than the Ki-67-low group (p=0.008). No significant association between PELP1 H-scores and other clinicopathological parameters was found. Finally, the PELP1 H-score in breast cancers of the luminal B subtype was significantly higher than that in the triple negative subtype (p=0.002).

CONCLUSION

Overexpression of PELP1 in Chinese women with primary breast cancer appears to be associated with biomarkers of poor outcome; these results are similar to other reports based on Western populations.

Biomarkers for the clinical management of breast cancer: international perspective

The higher incidence of breast cancer in developed countries has been tempered by reductions in mortality, largely attributable to mammographic screening programmes and advances in adjuvant therapy. Optimal systemic management requires consideration of clinical, pathological and biological parameters. Oestrogen receptor alpha (ERα), progesterone receptor (PgR) and human epidermal growth factor receptor 2 (HER2) are established biomarkers evaluated at diagnosis, which identify cardinal subtypes of breast cancer. Their prognostic and predictive utility effectively guides systemic treatment with endocrine, anti-HER2 and chemotherapy. Hence, accurate and reliable determination remains of paramount importance. However, the goals of personalized medicine and targeted therapies demand further information regarding residual risk and potential benefit of additional treatments in specific circumstances. The need for biomarkers which are fit for purpose, and the demands placed upon them, is therefore expected to increase. Technological advances, in particular high-throughput global gene expression profiling, have generated multi-gene signatures providing further prognostic and predictive information. The rational integration of routinely evaluated clinico-pathological parameters with key indicators of biological activity, such as proliferation markers, also provides a ready opportunity to improve the information available to guide systemic therapy decisions. The additional value of such information and its proper place in patient management is currently under evaluation in prospective clinical trials. Expanding the utility of biomarkers to lower resource settings requires an emphasis on cost effectiveness, quality assurance and possible international variations in tumor biology; the potential for improved clinical outcomes should be justified against logistical and economic considerations.

Development, characterization, and applications of a novel estrogen receptor beta monoclonal antibody

The role of estrogen receptor alpha (ERα) in breast cancer has been studied extensively, and its protein expression is prognostic and a primary determinant of endocrine sensitivity. However, much less is known about the role of ERβ and its relevance remains unclear due to the publication of conflicting reports. Here, we provide evidence that much of this controversy may be explained by variability in antibody sensitivity and specificity and describe the development, characterization, and potential applications of a novel monoclonal antibody targeting full-length human ERβ and its splice variant forms. Specifically, we demonstrate that a number of commercially available ERβ antibodies are insensitive for ERβ and exhibit significant cross-reaction with ERα. However, our newly developed MC10 ERβ antibody is shown to be highly specific and sensitive for detection of full-length ERβ and its variant forms. Strong and variable staining patterns for endogenous levels of ERβ protein were detected in normal human tissues and breast tumors using the MC10 antibody. Importantly, ERβ was shown to be expressed in a limited cohort of both ERα positive and ERα negative breast tumors. Taken together, these data demonstrate that the use of poorly validated ERβ antibodies is likely to explain much of the controversy in the field with regard to the biological relevance of ERβ in breast cancer. The use of the MC10 antibody, in combination with highly specific antibodies targeting only full-length ERβ, is likely to provide additional discriminatory features in breast cancers that may be useful in predicting response to therapy.

PKCα and ERβ Are Associated with Triple-Negative Breast Cancers in African American and Caucasian Patients

Although the incidence of breast cancer in the United States is higher in Caucasian women compared with African American women, African-American patients have more aggressive disease as characterized by a higher percentage of triple-negative breast cancers (TNBCs), high-grade tumors, and a higher mortality rate. PKCα is a biomarker associated with endocrine resistance and poor prognosis and ERβ is emerging as a protective biomarker. Immunohistochemical analysis of ERβ and PKCα expression was performed on 198 formalin-fixed paraffin-embedded primary infiltrating ductal carcinomas from 105 African-American and 93 Caucasian patients. PKCα is positively correlated with TNBC in patients of both races and with high tumor grade in African-American patients. Patients with TNBC express less nuclear ERβ compared with all other subtypes. We find no difference in frequency or intensity of PKCα or ERβ expression between African-American and Caucasian patients. PKCα and ERβ are discussed as potential therapeutic targets for the treatment of patients with TNBC.

A positive cross-regulation of HER2 and ER-α36 controls ALDH1 positive breast cancer cells

Accumulating evidence supports the theory that breast cancer arises from a subpopulation of mammary stem/progenitor cell which posses the ability to self-renew. However, the involvement of estrogen signaling in regulation of breast cancer stem/progenitor cells has not been fully established, mainly because expression and function of ER-α in breast cancer stem cells remains controversial. Previously, our laboratory cloned a variant of ER-α, ER-α36, and found that ER-α36-mediated non-genomic estrogen signaling plays an important role in malignant growth of triple-negative breast cancer cells. In this study, we found that ER-α36 was highly expressed in ER-negative breast cancer SK-BR-3 cells and mediated non-genomic estrogen signaling such as activation of the MAPK/ERK signaling in these cells. Knock-down of ER-α36 expression in these cells using the shRNA method diminished their responsiveness to estrogen and significantly down-regulated HER2 expression. HER2 signaling activated ER-α36 transcription through an AP1 site in the ER-α36 promoter and ER-α36 physically interacted with HER2. We also found that ER-α36 is highly expressed in a subset of SK-BR-3 cells that was positive for ALDH1, a breast cancer stem cell marker, and knock-down of ER-α36 expression reduced the population of ALDH1 positive cells. Our results thus demonstrated that ER-α36 positively regulates HER2 expression and the population of ALDH1 positive breast cancer cells, and suggested that non-genomic estrogen signaling mediated by ER-α36 is involved in maintenance and regulation of breast cancer stem cells.

Maspin expression is frequent and correlates with basal markers in triple-negative breast cancer

Background

Maspin is a unique member of the serine protease inhibitor superfamily and its expression is found in myoepithelial cells of normal mammary glands; therefore, it has been considered to be a myoepithelial marker. We previously reported that maspin was frequently expressed in biologically aggressive breast cancers. In turn, triple-negative (TN) breast cancer is a subtype of tumor with aggressive clinical behavior and shows frequent expression of basal markers. We hypothesized that maspin expression may be frequent and correlate with basal rather than myoepithelial markers in TN breast cancer.

Methods

Paraffin-embedded 135 TN invasive ductal carcinoma tissue samples were immunohistochemically investigated using the Dako Envision+ kit and primary antibodies for maspin, basal (CK5/6, EGFR, CK14) and myoepithelial markers (p63, CD10). The correlation between maspin expression and relapse-free survival (RFS) was investigated by the log-rank test.

Results

The positive rate for maspin was 85.9% and significantly correlated with younger age (P = 0.0015), higher histological grade (P = 0.0013), CK5/6 positivity (P < 0.0001), CK14 positivity (P = 0.0034) and the basal-like subtype defined by CK5/6, EGFR and CK14 positivity (P = 0.013). The positive rates for CK5/6, EGFR, CK14, CD10 and p63 were 59.2%, 48.9%, 34.1%, 17.8% and 12.6%, respectively. There was no significant correlation between maspin expression and RFS.

Conclusions

The positive rate for maspin is the highest among known basal and myoepithelial markers, and strongly correlates with basal markers in TN breast cancer. These results suggested that maspin could be a candidate for a therapeutic target for TN breast cancer.

Aldehyde dehydrogenase 1 expression is a predictor of poor prognosis in node-positive breast cancers: a long-term follow-up study

AIMS

Aldehyde dehydrogenase 1 (ALDH1) has been identified as a reliable marker of breast cancer stem cells. The aim was to determine the prognostic significance of ALDH1 expression in a long-term follow-up study.

METHODS AND RESULTS

Immunohistochemical analyses were performed on 257 invasive ductal carcinomas (IDCs), 109 matched lymph node metastases and 190 ductal carcinomas in situ (DCISs), using paraffin-embedded sections. ALDH1 expression was found in 26% of IDCs, and correlated with larger tumour size (P=0.007), high histological grade (P<0.001), HER2 overexpression (P<0.001) and negative hormone receptor status (P<0.001). ALDH1 expression was observed in 14% of DCISs but was not correlated with any clinicopathological parameter. The IDC patients were followed up for 7-190 months (median: 120 months), and groups with ALDH1 expression had shorter relapse-free survival (P=0.0013) and overall survival (OS) (P=0.0005) by log-rank test. By Cox's multivariate analysis, it had a weak effect on OS (P=0.047), and its most significant effect on OS was observed in node-positive groups (P=0.013). No significant differences in OS stratified by ALDH1 expression status in lymph node metastases were noted.

CONCLUSIONS

ALDH1 expression in primary cancer is an independent prognostic factor in node-positive breast cancer patients.

Estrogen receptor beta in breast cancer--diagnostic and therapeutic implications

More than 10 years have passed since the discovery of the second estrogen receptor, estrogen receptor beta (ERbeta). It is now evident that ERalpha is not the only ER in breast cancer cells; in fact, ERbeta is expressed in the majority of breast cancers although at lower levels than in the normal breast. In addition, ERbeta is expressed in breast cancer infiltrating lymphocytes, fibroblasts and endothelial cells, all known to influence tumor growth. By overexpressing or knocking-out ERbeta in breast cancer cell lines, several researchers have investigated its function with respect to proliferation and tumor growth. It appears that ERbeta is anti-proliferative, in many ways antagonising the function of ERalpha. Furthermore, phytoestrogens have a binding-preference for ERbeta and several epidemiological studies indicate a breast cancer preventing effect of this class of compounds. Tamoxifen is one of the standard, adjuvant treatments for ERalpha positive breast cancer, classically thought to mediate its effect through ERalpha. However, in several recent studies, ERbeta has been described as a potential marker for tamoxifen response. In summary, experimental, epidemiological as well as diagnostic studies point towards ERbeta as an important factor in breast cancer, opening up the possibility for novel ERbeta-selective therapies in the treatment of breast cancer.

A comparison of the effects of soya isoflavonoids and fish oil on cell proliferation, apoptosis and the expression of oestrogen receptors alpha and beta in the mammary gland and colon of the rat

Isoflavonoids and fish oil may be protective against colorectal cancer, but the evidence in relation to breast cancer risk is ambiguous. In the present study, we have investigated the impact of soya-derived isoflavonoids and n-3 fatty acids from fish oil, both individually and in combination, on apoptosis, cell proliferation and oestrogen receptor (ER) expression in the colon and mammary gland of the rat. Female rats were fed diets high in n-3 fatty acids (80 g/kg diet) or soya protein (765 mg/kg diet isoflavones) for 2 weeks, and then killed before the removal of the colon and mammary glands. Cell proliferation and apoptosis were quantified morphologically in whole crypts and terminal end buds. The expressions of ERalpha and ERbeta were measured in colon tissue scrapes and the mammary gland. Fish oil significantly increased apoptosis and decreased mitosis in both tissues, an effect associated with a decrease in the expressions of ERalpha and ERbeta. Soya had no effect on apoptosis in either tissue, but reduced mitosis in the colon (P < 0.001) while increasing it in the mammary gland (P = 0.001). The changes in proliferation were associated with contrasting changes in the ER expression such that fish oil significantly decreased both ERbeta and ERalpha, while soya increased ERalpha and decreased ERbeta. The results may provide a novel mechanism by which n-3 fatty acids could reduce cancer risk, but the interpretation of the results in relation to soya consumption and breast cancer risk requires further investigation.

ERbeta in breast cancer--onlooker, passive player, or active protector?

The role of estrogen exposure in breast cancer risk is well-documented, and both estrogen synthesis and actions through the estrogen receptor (ER) have been targeted by therapies to control hormone-dependent breast cancer. The discovery of a second ER form and its therapeutic implications sparked great interest. Both the original ERalpha and the more recently identified ERbeta subtypes bind and respond similarly to many physiological and pharmacological ligands. However, differences in phytoestrogen binding have been noted, and subtype-specific ligands have been developed. Cell-based assays show that ERbeta and its variants are generally less active on gene transcription than ERalpha, and may influence ERalpha activity; however, both gene- and cell-specific responses occur, and nongenomic activities are less well explored. Specific ligands, and methods to disrupt or eliminate receptor subtype expression in animal and cell models, demonstrate that the ERs have both overlapping and distinct biological functions. Overall, in cell-based studies, ERalpha appears to play a predominant role in cell proliferation, and ERbeta is suggested to be antiproliferative. The potential for distinct populations of breast tumors to be identified based on ER subtype expression, and to exhibit distinct clinical behaviors, is of greatest interest. Several studies suggest that the majority of ER-positive tumors contain both subtypes, but that some tumors contain only ERbeta and may have distinct clinical behaviors and responses. Expression of ERbeta together with ERalpha favors positive responses to endocrine therapy in most studies, and additional studies to determine if the addition of ERbeta to ERalpha as a tumor marker is of clinical benefit are warranted. In contrast, the positive association between ERbeta and HER2 expression in high-grade ERalpha-negative breast cancer does not favor positive responses to endocrine therapy. Expression of ERbeta in specific clinical subpopulations, and the potential for therapies targeting ERbeta specifically, is discussed.

A divergent role for estrogen receptor-beta in node-positive and node-negative breast cancer classified according to molecular subtypes: an observational prospective study

Introduction

Estrogen receptor-alpha (ER-α) and progesterone receptor (PgR) are consolidated predictors of response to hormonal therapy (HT). In contrast, little information regarding the role of estrogen receptor-beta (ER-β) in various breast cancer risk groups treated with different therapeutic regimens is available. In particular, there are no data concerning ER-β distribution within the novel molecular breast cancer subtypes luminal A (LA) and luminal B (LB), HER2 (HS), and triple-negative (TN).

Methods

We conducted an observational prospective study using immunohistochemistry to evaluate ER-β expression in 936 breast carcinomas. Associations with conventional biopathological factors and with molecular subtypes were analyzed by multiple correspondence analysis (MCA), while univariate and multivariate Cox regression analysis and classification and regression tree analysis were applied to determine the impact of ER-β on disease-free survival in the 728 patients with complete follow-up data.

Results

ER-β evenly distributes (55.5%) across the four molecular breast cancer subtypes, confirming the lack of correlation between ER-β and classical prognosticators. However, the relationships among the biopathological factors, analyzed by MCA, showed that ER-β positivity is located in the quadrant containing more aggressive phenotypes such as HER2 and TN or ER-α/PgR/Bcl2^- tumors. Kaplan-Meier curves and Cox regression analysis identified ER-β as a significant discriminating factor for disease-free survival both in the node-negative LA (P = 0.02) subgroup, where it is predictive of response to HT, and in the node-positive LB (P = 0.04) group, where, in association with PgR negativity, it conveys a higher risk of relapse.

Conclusion

Our data indicated that, in contrast to node-negative patients, in node-positive breast cancer patients, ER-β positivity appears to be a biomarker related to a more aggressive clinical course. In this context, further investigations are necessary to better assess the role of the different ER-β isophorms.

Estrogen receptor alpha negative breast cancer patients: estrogen receptor beta as a therapeutic target

Clinical management of breast cancer is increasingly guided by assessment of tumor phenotypic parameters. One of these is estrogen receptor (ER) status, currently defined by ERalpha expression. However with the discovery of a second ER, ERbeta and its variant isoforms, the definition of ER status is potentially more complex. In breast tumors there are two ERbeta expression cohorts. One where ERbeta is co-expressed with ERalpha and the other expressing ERbeta alone. In the latter subgroup of currently defined ER negative patients ERbeta has the potential to be a therapeutic target. Characterization of the nature and role of ERbeta in ERalpha negative tumors is essentially unexplored but available data suggest that the role of ERbeta may be different when co-expressed with ERalpha and when expressed alone. This review summarizes available data and explores the possibility that ERbeta signaling may be a therapeutic target in these tumors. Evidence so far supports the idea that the role of ERbeta in breast cancer is different in ERalpha negative compared to ERalpha positive tumors. However, cohort size and numbers of independent studies are small to date, and more studies are needed with better standardization of antibodies and protocols. Also, the ability to determine the role of ERbeta in ERalpha negative breast cancer and therefore assess ERbeta signaling pathways as therapeutic targets would be greatly facilitated by identification of specific downstream markers of ERbeta activity in breast cancer.

Hormonal markers in breast cancer: coexpression, relationship with pathologic characteristics, and risk factor associations in a population-based study

The objective of this study was to evaluate the coexpression patterns of hormonal markers in breast cancer tissue and their relationship with pathologic characteristics and epidemiologic risk factors. We evaluated the expression of 17 markers by immunohistochemistry in 842 invasive breast carcinomas collected in a population-based case-control study conducted in Poland. Based on marker correlations, factor analysis identified four major coexpression patterns (factors): "nuclear receptor factor" [estrogen receptor (ER)-alpha, progesterone receptor, androgen receptor, cyclin D1, and aromatase], "estrogen metabolism/ER-beta factor" (ER-beta, peroxisome proliferator-activated receptor-gamma, steroid sulfatase, estrogen sulfonotransferase, and cytochrome P450 1B1), "HER2 factor" (human epidermal growth factor receptor 2, E-cadherin, cyclooxygenase-2, aromatase, steroid sulfatase), and "proliferation factor" (cytokeratin 5, cytokeratin 5/6, epidermal growth factor receptor, P53). Three of these factors corresponded to molecular subtypes previously defined by expression profiling; however, the estrogen metabolism/ER-beta factor seemed to be distinctive. High scores for this factor were associated with high tumor grade (P heterogeneity = 0.02), younger age at menarche (P heterogeneity = 0.04), lower current body mass index among premenopausal women (P heterogeneity = 0.01), and older age at menopause (P heterogeneity = 0.04). High scores for the proliferation factor were also associated with early menarche (P heterogeneity < 0.0001), and in contrast to the estrogen metabolism/ER-beta factor, higher current body mass index among premenopausal women (P heterogeneity = 0.03). Our analysis of hormonal pathway markers independently confirmed several previously defined molecular subtypes identified by gene expression profiling and augmented these findings by suggesting the existence of additional relationships related to ER-beta and enzymes involved in hormone metabolism.

Estrogen receptor-beta: why may it influence clinical outcome in estrogen receptor-alpha positive breast cancer?

In the previous issue of the journal, Lin and coworkers present data demonstrate that increased expression of estrogen receptor (ER)-β in ER-α-positive breast cancer cells antagonizes a defined group of ER-α/estrogen stimulated genes that are involved in cell cycle regulation and DNA replication. Similar expression patterns for these genes were found human ER-α positive breast tumors expressing higher levels or ER-β, and this correlated with better clinical outcome. The implications for these data, which suggest that ER-β is a positive actor and diagnostic marker for therapeutic outcome, are discussed.