Influence of menstrual cycle, parity and oral contraceptive use on steroid hormone receptors in normal breast

Baseline breast tissue characteristics determine the effect of tamoxifen on mammographic density change

Tamoxifen prevents recurrence of breast cancer and is also approved for preventive, risk-reducing, therapy. Tamoxifen alters the breast tissue composition and decreases the mammographic density. We aimed to test if baseline breast tissue composition influences tamoxifen-associated density change. This biopsy-based study included 83 participants randomised to 6 months daily intake of placebo, 20, 10, 5, 2.5, or 1 mg tamoxifen. The study is nested within the double-blinded tamoxifen dose-determination trial Karolinska Mammography Project for Risk Prediction of Breast Cancer Intervention (KARISMA) Study. Ultrasound-guided core-needle breast biopsies were collected at baseline before starting treatment. Biopsies were quantified for epithelial, stromal, and adipose distributions, and epithelial and stromal expression of proliferation marker Ki67, oestrogen receptor (ER) and progesterone receptor (PR). Mammographic density was measured using STRATUS. We found that greater mammographic density at baseline was positively associated with stromal area and inversely associated with adipose area and stromal expression of ER. Premenopausal women had greater mammographic density and epithelial tissue, and expressed more epithelial Ki67, PR, and stromal PR, compared to postmenopausal women. In women treated with tamoxifen (1-20 mg), greater density decrease was associated with higher baseline density, epithelial Ki67, and stromal PR. Women who responded to tamoxifen with a density decrease had on average 17% higher baseline density and a 2.2-fold higher PR expression compared to non-responders. Our results indicate that features in the normal breast tissue before tamoxifen exposure influences the tamoxifen-associated density decrease, and that the age-associated difference in density change may be related to age-dependant differences in expression of Ki67 and PR.

Mapping hormone-regulated cell-cell interaction networks in the human breast at single-cell resolution

The rise and fall of estrogen and progesterone across menstrual cycles and during pregnancy regulates breast development and modifies cancer risk. How these hormones impact each cell type in the breast remains poorly understood because they act indirectly through paracrine networks. Using single-cell analysis of premenopausal breast tissue, we reveal a network of coordinated transcriptional programs representing the tissue-level response to changing hormone levels. Our computational approach, DECIPHER-seq, leverages person-to-person variability in breast composition and cell state to uncover programs that co-vary across individuals. We use differences in cell-type proportions to infer a subset of programs that arise from direct cell-cell interactions regulated by hormones. Further, we demonstrate that prior pregnancy and obesity modify hormone responsiveness through distinct mechanisms: obesity reduces the proportion of hormone-responsive cells, whereas pregnancy dampens the direct response of these cells to hormones. Together, these results provide a comprehensive map of the cycling human breast.

Are the estrogen receptor and SIRT3 axes of the mitochondrial UPR key regulators of breast cancer sub-type determination according to age?

Aging is a major risk factor of developing breast cancer. Despite the fact that post-menopausal women have lower levels of estrogen, older women have a higher rate of estrogen receptor alpha (ERα) positive breast cancer. Conversely, young women who have elevated levels of estrogen tend to develop ERα negative disease that is associated with higher rate of metastasis. This perspective proposes a unifying model centered around the importance of mitochondrial biology in cancer and aging to explain these observations. Mitochondria are essential for the survival of cancer cells and therefore pathways that maintain the functionality of the mitochondrial network in cancer cells fulfill a critical role in the survival of cancer cells. The ERα and the mitochondrial sirtuin-3 (SIRT3) have been reported to be key players of the mitochondrial unfolded protein response (UPR^mt) ^1-5. The UPR^mt is a complex retrograde signaling cascade that regulates the communication between the mitochondria and the nucleus to restore mitochondrial fitness in response to oxidative stress ^5-7. SIRT3 is a major regulator of aging ⁸. Its level decreases with age and single nucleotide polymorphisms (SNPs) that preserve its expression at higher levels are observed in centenarians ^9,10. We propose a model whereby the ERα axis of the UPR^mt acts to compensate for the loss of SIRT3 observed with age, and becomes the dominant axis of the UPR^mt to maintain the integrity of the mitochondria during transformation, thus explaining the selective advantage of ERα positive luminal cells in breast cancer arising from older women.

Hormone Receptor Expression Variations in Normal Breast Tissue: Preliminary Results of a Prospective Observational Study

Normal breast tissue undergoes great variations during a woman’s life as a consequence of the different hormonal stimulation. The purpose of the present study was to examine the hormonal receptor expression variations according to age, menstrual cycle, menopausal state and body mass index. To this purpose, 49 tissue samples of normal breast tissue, obtained during surgery performed for benign and malignant conditions, were immunostained with Estrogen (ER), Progesterone (PR) and Androgen receptors (AR). In addition, Ki67 and Gross Cystic Disease Fluid Protein were studied. The data obtained revealed a great variability of hormone receptor expression. ER and AR generally increased in older and post-menopausal women, while young women presented a higher proliferative rate, evaluated with Ki67. PR increase was observed in women with BMI higher than 25. The different hormonal receptor expression could favor the development of breast cancer.

Investigation of the adolescent female breast transcriptome and the impact of obesity

Background

Early life environmental exposures affect breast development and breast cancer risk in adulthood. The breast is particularly vulnerable during puberty when mammary epithelial cells proliferate exponentially. In overweight/obese (OB) women, inflammation increases breast aromatase expression and estrogen synthesis and promotes estrogen-receptor (ER)-positive breast cancer. In contrast, recent epidemiological studies suggest that obesity during childhood decreases future breast cancer risk. Studies on environmental exposures and breast cancer risk have thus far been limited to animal models. Here, we present the first interrogation of the human adolescent breast at the molecular level and investigate how obesity affects the immature breast.

Methods

We performed RNA-seq in 62 breast tissue samples from adolescent girls/young women (ADOL; mean age 17.8 years) who underwent reduction mammoplasty. Thirty-one subjects were non-overweight/obese (NOB; mean BMI 23.4 kg/m²) and 31 were overweight/obese (OB; BMI 32.1 kg/m²). We also compared our data to published mammary transcriptome datasets from women (mean age 39 years) and young adult mice, rats, and macaques.

Results

The ADOL breast transcriptome showed limited (30%) overlap with other species, but 88% overlap with adult women for the 500 most highly expressed genes in each dataset; only 43 genes were shared by all groups. In ADOL, there were 120 differentially expressed genes (DEG) in OB compared with NOB samples (p_adj < 0.05). Based on these DEG, Ingenuity Pathway Analysis (IPA) identified the cytokines CSF1 and IL-10 and the chemokine receptor CCR2 as among the most highly activated upstream regulators, suggesting increased inflammation in the OB breast. Classical ER targets (e.g., PR, AREG) were not differentially expressed, yet IPA identified the ER and PR and growth factors/receptors (VEGF, HGF, HER3) and kinases (AKT1) involved in hormone-independent ER activation as activated upstream regulators in OB breast tissue.

Conclusions

These studies represent the first investigation of the human breast transcriptome during late puberty/young adulthood and demonstrate that obesity is associated with a transcriptional signature of inflammation which may augment estrogen action in the immature breast microenvironment. We anticipate that these studies will prompt more comprehensive cellular and molecular investigations of obesity and its effect on the breast during this critical developmental window.

Inter-Individual Variation in Response to Estrogen in Human Breast Explants

Exposure to estrogen is strongly associated with increased breast cancer risk. While all women are exposed to estrogen, only 12% are expected to develop breast cancer during their lifetime. These women may be more sensitive to estrogen, as rodent models have demonstrated variability in estrogen sensitivity. Our objective was to determine individual variation in expression of estrogen receptor (ER) and estrogen-induced responses in the normal human breast. Human breast tissue from female donors undergoing reduction mammoplasty surgery were collected for microarray analysis of ER expression. To examine estrogen-induced responses, breast tissue from 23 female donors were cultured ex- vivo in basal or 10 nM 17β-estradiol (E2) media for 4 days. Expression of ER genes (ESR1 and ESR2) increased significantly with age. E2 induced consistent increases in global gene transcription, but expression of target genes AREG, PGR, and TGFβ2 increased significantly only in explants from nulliparous women. E2-treatment did not induce consistent changes in proliferation or radiation induced apoptosis. Responses to estrogen are highly variable among women and not associated with levels of ER expression, suggesting differences in intracellular signaling among individuals. The differences in sensitivity to E2-stimulated responses may contribute to variation in risk of breast cancer.

Exogenous ERα Expression in the Mammary Epithelium Decreases Over Time and Does Not Contribute to p53-Deficient Mammary Tumor Formation in Mice

Approximately 75% of all breast cancers express the nuclear hormone receptor estrogen receptor α (ERα). However, the majority of mammary tumors from genetically engineered mouse models (GEMMs) are ERα-negative. To model ERα-positive breast cancer in mice, we exogenously introduced expression of mouse and human ERα in an existing GEMM of p53-deficient breast cancer. After initial ERα expression during mammary gland development, expression was reduced or lost in adult glands and p53-deficient mammary tumors. Chromatin immunoprecipitation (ChIP)-sequencing analysis of primary mouse mammary epithelial cells (MMECs) derived from these models, in which expression of the ERα constructs was induced in vitro, confirmed interaction of ERα with the DNA. In human breast and endometrial cancer, and also in healthy breast tissue, DNA binding of ERα is facilitated by the pioneer factor FOXA1. Surprisingly, the ERα binding sites identified in primary MMECs, but also in mouse mammary gland and uterus, showed an high enrichment of ERE motifs, but were devoid of Forkhead motifs. Furthermore, exogenous introduction of FOXA1 and GATA3 in ERα-expressing MMECs was not sufficient to promote ERα-responsiveness of these cells. Together, this suggests that species-specific differences in pioneer factor usage between mouse and human are dictated by the DNA sequence, resulting in ERα-dependencies in mice that are not FOXA1 driven. These species-specific differences in ERα-biology may limit the utility of mice for in vivo modeling of ERα-positive breast cancer.

The effect of sex hormones on normal breast tissue metabolism: Evaluation by FDG PET/CT

This study investigated the effect of sex hormones on F-fluorodeoxyglucose (FDG) uptake in normal breast tissue.The retrospective study included 249 premenopausal women (median age, 45 years) who were diagnosed with unilateral breast cancer and underwent FDG positron emission tomography/computed tomography and hormone tests. The volume of interest was within the contralateral normal breast and the standardized uptake values (SUVs) were measured. The correlations of sex hormones (including estrogen, progesterone, testosterone, follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) with the SUVs of the normal breast were analyzed.There was a weak negative correlation between age and breast FDG uptake (P = .012, Spearman coefficient = -.16 for the maximum standardized uptake values [SUVmax]), especially in the luteal phase group (P = .005, Spearman coefficient = -.27 for SUVmax). The SUVs of normal breast tissue were increased when progesterone levels were higher (P = .043, Spearman coefficient = .13 for SUVmax). In the irregular menstrual cycle group, FDG uptake in the breast decreased as FSH (P = .027, Spearman coefficient = -.42 for SUVmax) and LH (P = .048, Spearman coefficient = -.44 for SUVmax) increased.Glucose metabolism of normal breast tissue decreases with age, and progesterone weakly affects breast FDG uptake. Gonadotropins may affect breast FDG uptake in premenopausal women with irregular menstrual cycles.

Estrogen and progesterone signalling in the normal breast and its implications for cancer development

The ovarian hormones estrogen and progesterone are master regulators of the development and function of a broad spectrum of human tissues, including the breast, reproductive and cardiovascular systems, brain and bone. Acting through the nuclear estrogen (ER) and progesterone receptors (PR), both play complex and essential coordinated roles in the extensive development of the lobular alveolar epithelial structures of the normal breast during puberty, the normal menstrual cycle and pregnancy. The past decade has seen major advances in understanding the mechanisms of action of estrogen and progesterone in the normal breast and in the delineation of the complex hierarchy of cell types regulated by ovarian hormones in this tissue. There is evidence for a role for both ER and PR in driving breast cancer, and both are favourable prognostic markers with respect to outcome. In this review, we summarize current knowledge of the mechanisms of action of ER and PR in the normal breast, and implications for the development and management of breast cancer.

Association of reproductive history with breast tissue characteristics and receptor status in the normal breast

Introduction

Reproductive history has been associated with breast cancer risk, but more knowledge of the underlying biological mechanisms is needed. Because of limited data on normal breast tissue from healthy women, we examined associations of reproductive history and established breast cancer risk factors with breast tissue composition and markers of hormone receptors and proliferation in a nested study within the Karolinska Mammography project for risk prediction for breast cancer (Karma).

Materials and methods

Tissues from 153 women were obtained by ultrasound-guided core needle biopsy as part of the Karma project. Immunohistochemical staining was used to assessed histological composition of epithelial, stromal and adipose tissue, epithelial and stromal oestrogen receptor (ER) and progesterone receptor (PR) status, and Ki-67 proliferation status. An individualised reproductive score including parity, number of pregnancies without birth, number of births, age at first birth, and duration of breastfeeding, was calculated based on self-reported reproductive history at the time of the Karma study entry. All analyses were adjusted for age and BMI.

Results

Cumulated reproductive score was associated with increased total epithelial content and greater expression of epithelial ER. Parity was associated with greater epithelial area, increased epithelial–stromal ratio, greater epithelial ER expression and a lower extent of stromal proliferation. Increasing numbers of pregnancies and births were associated with a greater epithelial area in the entire study set, which remained significant among postmenopausal women. Increasing numbers of pregnancies and births were also associated with a greater expression of epithelial ER among postmenopausal women. Longer duration of breastfeeding was associated with greater epithelial area and greater expression of epithelial PR both in the entire study set and among postmenopausal women. Breastfeeding was also positively associated with greater epithelial ER expression among postmenopausal women. Prior use of oral contraceptives was associated with lower epithelial–stromal ratio amongst all participants and among pre- and postmenopausal women separately.

Conclusion

Reproductive risk factors significantly influence the epithelial tissue compartment and expression of hormone receptors in later life. These changes remain after menopause. This study provides deeper insights of the biological mechanisms by which reproductive history influences epithelial area and expression of hormone receptors, and as a consequence the risk of breast cancer.

Electronic supplementary material

The online version of this article (10.1007/s10549-018-4768-0) contains supplementary material, which is available to authorized users.

Obesity reversibly depletes the basal cell population and enhances mammary epithelial cell estrogen receptor alpha expression and progenitor activity

Background

Obesity is correlated with an increased risk for developing postmenopausal breast cancer. Since obesity rates continue to rise worldwide, it is important to understand how the obese microenvironment influences normal mammary tissue to increase breast cancer risk. We hypothesized that obesity increases the proportion of luminal progenitor cells, which are thought to be the cells of origin for the most common types of breast cancer, potentially leading to an increased risk for breast cancer.

Methods

To study the obese microenvironment within the mammary gland, we used a high-fat diet mouse model of obesity and human breast tissue from reduction mammoplasty surgery. We identified changes in breast epithelial cell populations using flow cytometry for cell surface markers, in vitro functional assays and expression of markers on breast tissue sections.

Results

In both obese female mice and women, mammary epithelial cell populations demonstrated significant decreases in basal/myoepithelial cells, using either flow cytometry or cell-type-specific markers (SMA and p63). Estrogen receptor alpha (ERα) expression was significantly increased in luminal cells in obese mammary tissue, compared with control mice or breast tissue from lean women. Functional assays demonstrated significantly enhanced mammary epithelial progenitor activity in obese mammary epithelial cells and elevated numbers of ERα-positive epithelial cells that were co-labeled with markers of proliferation. Weight loss in a group of obese mice reversed increases in progenitor activity and ERα expression observed in obese mammary tissue.

Conclusions

Obesity enhances ERα-positive epithelial cells, reduces the number of basal/myoepithelial cells, and increases stem/progenitor activity within normal mammary tissue in both women and female mice. These changes in epithelial cell populations induced by obesity are reversible with weight loss. Our findings support further studies to examine how obesity-induced changes in stem/progenitor cells impact breast tumor incidence and histologic tumor types.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0921-7) contains supplementary material, which is available to authorized users.

Breast cancer risk factors in relation to estrogen receptor, progesterone receptor, insulin-like growth factor-1 receptor, and Ki67 expression in normal breast tissue

Studies have suggested that hormone receptor and Ki67 expression in normal breast tissue are associated with subsequent breast cancer risk. We examined the associations of breast cancer risk factors with estrogen receptor (ER), progesterone receptor (PR), insulin-like growth factor-1 receptor (IGF-1R), and Ki67 expression in normal breast tissue. This analysis included 388 women with benign breast disease (ages 17–67 years) in the Nurses’ Health Studies. Immunohistochemical staining was performed on tissue microarrays constructed from benign biopsies containing normal breast epithelium and scored as the percentage of epithelial cells that were positively stained. Ordinal logistic regression (outcomes in tertiles), adjusting for age and potential confounders, was performed to estimate odds ratios (OR) and 95% confidence intervals (CI) for the associations with risk factors. Alcohol consumption was positively associated (≥2.5 vs.<0.4 drink/wk: OR = 2.69, 95% CI = 1.26–5.75, p-trend = 0.008) and breastfeeding was inversely associated (≥6 months vs. never: OR = 0.11, 95% CI = 0.04–0.35, p-trend = 0.0003) with ER expression. Height (≥66 vs.<64 inches: OR = 2.50, 95% CI = 1.34–4.67, p-trend = 0.005) and BMI at age 18 (≥22 vs.<20 kg/m²: OR = 2.33, 95% CI = 1.18–4.62, p-trend = 0.01) were positively associated with PR expression. Body size at age 5–10 years was inversely associated with Ki67 (Level ≥ 2.5 vs. 1: OR = 0.55, 95% CI = 0.30–1.01, p-trend = 0.03). Premenopausal BMI (≥25 vs.<20 kg/m²) was positively associated with cytoplasmic IGF-1R (OR = 5.06, 95% CI = 1.17–21.8, p-trend = 0.04). Our data suggest that anthropometrics, breastfeeding, and alcohol intake may influence the molecular characteristics of normal breast tissue, elucidating the mechanisms by which these risk factors operate. However, larger studies are required to confirm these results.

Body size, alcohol intake and breastfeeding may affect the molecular features of normal breast tissue to influence cancer risk. A team led by Hannah Oh from the Harvard T. H. Chan School of Public Health in Boston, USA, examined the link between behavioral and physiological risk factors for breast cancer and the expression levels of certain proteins (such as hormone receptors) that also promote cancer formation. By examining healthy breast tissue biopsied from 388 women diagnosed with benign breast diseases, the researchers showed that alcohol consumption, height and body mass index were all positively associated with the expression of various breast tissue markers, while breastfeeding and early-life body size were inversely associated. The findings point to a connection between lifestyle and breast tissue-specific molecular characteristics that underpin cancer risk.

Genomic Changes in Normal Breast Tissue in Women at Normal Risk or at High Risk for Breast Cancer

Sporadic breast cancer develops through the accumulation of molecular abnormalities in normal breast tissue, resulting from exposure to estrogens and other carcinogens beginning at adolescence and continuing throughout life. These molecular changes may take a variety of forms, including numerical and structural chromosomal abnormalities, epigenetic changes, and gene expression alterations. To characterize these abnormalities, a review of the literature has been conducted to define the molecular changes in each of the above major genomic categories in normal breast tissue considered to be either at normal risk or at high risk for sporadic breast cancer. This review indicates that normal risk breast tissues (such as reduction mammoplasty) contain evidence of early breast carcinogenesis including loss of heterozygosity, DNA methylation of tumor suppressor and other genes, and telomere shortening. In normal tissues at high risk for breast cancer (such as normal breast tissue adjacent to breast cancer or the contralateral breast), these changes persist, and are increased and accompanied by aneuploidy, increased genomic instability, a wide range of gene expression differences, development of large cancerized fields, and increased proliferation. These changes are consistent with early and long-standing exposure to carcinogens, especially estrogens. A model for the breast carcinogenic pathway in normal risk and high-risk breast tissues is proposed. These findings should clarify our understanding of breast carcinogenesis in normal breast tissue and promote development of improved methods for risk assessment and breast cancer prevention in women.

Minireview: Progesterone Regulation of Proliferation in the Normal Human Breast and in Breast Cancer: A Tale of Two Scenarios?

Progesterone (P), which signals through the P receptor (PR), is critical in normal development of the breast, but its signaling axis is also a major driver of breast cancer risk. Here we review recent advances in the understanding of P signaling in the normal human breast, with a focus on the importance of the balance between autocrine and paracrine signaling. To date, most data (which derive largely from mouse models or human breast cancer cell line studies) have demonstrated that the vast majority of PR+ cells appear to act as "sensor" cells, which respond to P stimulation by translating these hormonal cues into paracrine signals. However, growing evidence suggests that, dependent on the cellular context, P may also signal in an autocrine manner in a subset of cells in the normal mouse mammary gland and human breast. It has been suggested that it may be dysregulation of this autocrine signaling, resulting in a "switch" from a predominance of paracrine signaling to autocrine signaling in PR+ cells, which is an early event during breast tumorigenesis. This review summarizes current evidence in the literature that demonstrates the mechanisms through which P acts in the normal human breast, as well as highlighting the important questions that remain unanswered.

Parity and expression of epithelial histopathologic markers in breast tissue

It is well established that pregnancies protect against breast cancer; however, the mechanism involved is not completely understood. We investigated the influence of parity on hormonal and proliferation markers in benign tissue from tumor blocks of breast cancer cases. Women with breast cancer were recruited from a case-control study nested within the Multiethnic Cohort study. Tissue microarrays of benign tissue cores were available for 159 participants. Immunostaining for estrogen receptor α (ERα) and ERβ, progesterone receptor, human epidermal growth factor receptor 2 (Her2/neu), Ki-67, and proliferating cell nuclear antigen (PCNA) in epithelial tissue was evaluated by a pathologic expert. We applied logistic regression models to examine marker expression by parity (0, 1-2, and ≥3 live births with adjustment for age at diagnosis and BMI). Of the 159 women, 24 were nulliparous, 63 had one or two live births, and 72 had three or more live births. Inverse associations were observed between parity and expression of ERα (Ptrend=0.02) and PCNA (Ptrend=0.04). Among nulliparous women, 45.5% were ERα positive in contrast to 18.0 and 18.9% of women with one or two and at least three live births, respectively. The respective values for PCNA were 56.5, 44.3, and 31.1%. No associations were detected for ERβ, progesterone receptor, Her2/neu, and Ki-67. The current findings suggest that pregnancies may protect against breast cancer by reducing susceptibility to estrogenic stimuli and proliferative activity as assessed by the expression of ERα and PCNA in breast tissue.

Estrogen receptor and progesterone receptor expression in normal terminal duct lobular units surrounding invasive breast cancer

Molecular and morphological alterations related to carcinogenesis have been found in terminal duct lobular units (TDLUs), the microscopic structures from which most breast cancer precursors and cancers develop, and therefore, analysis of these structures may reveal early changes in breast carcinogenesis and etiologic heterogeneity. Accordingly, we evaluated relationships of breast cancer risk factors and tumor pathology to estrogen receptor (ER) and progesterone receptor (PR) expression in TDLUs surrounding breast cancers. We analyzed 270 breast cancer cases included in a population-based breast cancer case-control study conducted in Poland. TDLUs were mapped in relation to breast cancer: within the same block as the tumor (TDLU-T), proximal to tumor (TDLU-PT), or distant from (TDLU-DT). ER/PR was quantitated using image analysis of immunohistochemically stained TDLUs prepared as tissue microarrays. In surgical specimens containing ER-positive breast cancers, ER and PR levels were significantly higher in breast cancer cells than in normal TDLUs, and higher in TDLU-T than in TDLU-DT or TDLU-PT, which showed similar results. Analyses combining DT-/PT TDLUs within subjects demonstrated that ER levels were significantly lower in premenopausal women versus postmenopausal women (odds ratio [OR] = 0.38, 95 % confidence interval [CI] = 0.19, 0.76, P = 0.0064) and among recent or current menopausal hormone therapy users compared with never users (OR = 0.14, 95 % CI = 0.046-0.43, P (trend) = 0.0006). Compared with premenopausal women, TDLUs of postmenopausal women showed lower levels of PR (OR = 0.90, 95 % CI = 0.83-0.97, P (trend) = 0.007). ER and PR expression in TDLUs was associated with epidermal growth factor receptor (EGFR) expression in invasive tumors (P = 0.019 for ER and P = 0.03 for PR), but not with other tumor features. Our data suggest that TDLUs near breast cancers reflect field effects, whereas those at a distance demonstrate influences of breast cancer risk factors on at-risk breast tissue. Analyses of mapped TDLUs may provide information about the sequence of molecular changes occurring in breast carcinogenesis.

Progesterone and estrogen receptors segregate into different cell subpopulations in the normal human breast

Progesterone is critical in normal breast development and its synthetic derivatives are emerging as major drivers of breast cancer risk. The recent demonstration that progesterone regulates the stem cell compartment in the murine mammary gland, despite the absence of progesterone receptor (PR) in mammary stem cells, highlights the fact that PR distribution in progenitor cell subsets in the human breast remains to be conclusively shown. By utilising two independent cell sorting strategies to fractionate cells into distinct subpopulations enriched for different cell lineage characteristics, we have demonstrated a consistent enrichment of PR transcripts, relative to estrogen receptor transcripts, in the bipotent progenitor subfraction in the normal human breast. We have also shown co-expression of both steroid hormone receptors with basal markers in a subset of human breast cells, and finally we have demonstrated that PR+ bipotent progenitor cells are estrogen-insensitive, and that estrogen regulates PR in mature luminal cells only.

Lowering oral contraceptive norethindrone dose increases estrogen and progesterone receptor levels with no reduction in proliferation of breast epithelium: a randomized trial

BACKGROUND

This study was conducted to compare breast epithelial-cell proliferation and estrogen and progesterone receptor levels in women taking one of two oral contraceptives (OCs) containing the same dose of estrogen but different doses of the progestin norethindrone (NET).

STUDY DESIGN

Thirty-three women were randomly assigned 1:1 to one of two OCs with 35-mcg ethinylestradiol (EE2) but different doses of NET - 1 or 0.4 mg. At the end of the active pill phase of the third OC cycle, a breast biopsy was performed and the percentages of epithelial cells of the terminal duct lobular units were measured for Ki67 (MIB1), progesterone receptors A and B (PRA and PRB, respectively), and estrogen receptor α (ERα).

RESULTS

The biopsies from 27 women had sufficient epithelium for analysis. The percentages of cells positive for PRA, PRB and ERα were approximately double with the lower progestin dose (PRA: p=.041; PRB: p=.030; ERα: p=.056). The Ki67 percentage was not reduced with the lower progestin dose (12.5% for 0.4-mg NET vs. 7.8% for 1.0-mg NET).

CONCLUSIONS

The increase in PRA-, PRB- and ERα-positive cells with the 60% lower progestin dose OC appears likely to account for its failure to decrease breast-cell proliferation. This breast-cell proliferation result is contrary to that predicted from the results of lowering the medroxyprogesterone acetate dose in menopausal hormone therapy.

Breaking the cycle: An insight into the role of ERα in eukaryotic cell cycles

There have been numerous reviews written to date on estrogen receptor (ER), focusing on topics such as its role in the etiology of breast cancer, its mode of regulation, its role as a transcriptional activator and how to target it therapeutically, just to name a few. One reason for so much attention on this nuclear receptor is that it acts not only as a prognostic marker, but also as a target for therapy. However, a relatively undiscovered area in the literature regarding ER is how its activity in the presence and absence of ligand affects its role in proliferation and cell cycle transition. In this review, we provide a brief overview of ER signaling, ligand dependent and independent, genomic and non-genomic, and how these signaling events affect the role of ER in the mammalian cell cycle.

Human breast cell proliferation and its relationship to steroid receptor expression

The steroidal regulation of proliferation and differentiation in the rodent mammary gland is well described, but how ovarian hormones regulate these processes in the human remains poorly understood. To investigate this, we developed the athymic nude mouse model in which intact normal human breast tissue is grafted subcutaneously and treated with estrogen and/or progesterone at human physiological serum levels. We demonstrated, first, that estrogen and not progesterone is the major epithelial cell mitogen in the adult non-pregnant, non-lactating breast, second, that estrogen induces progesterone receptor (PR) expression and, third, that PR expression is maximally induced at low estrogen concentrations while a higher amount of estrogen was required to induce proliferation. These data raised the question of whether one cell type possessed differential responses to high and low estrogen concentrations or whether PR expression and proliferation occurred in two cell populations. Using double-label immunofluorescence, we demonstrated that steroid receptor expression and cell proliferation (Ki67 antigen) occurred in separate cell populations in normal human breast epithelium, and that cells expressing the estrogen receptor-alpha (ERalpha) invariably contained the PR. We also found that this dissociation between steroid receptor expression and cell proliferation in normal epithelium was disrupted at an early stage in breast tumor formation. Recent findings presented herein support the proposal that some ERalpha/PR-positive epithelial cells are quiescent breast stem cells that act as 'steroid hormone sensors'. Such hormone sensor cells are likely to secrete positive or negative paracrine/juxtacrine factors dependent on the prevailing estrogen or progesterone concentration to influence the proliferative activity of adjacent ERalpha/PR-negative epithelial cells.

Progesterone receptors A and B and estrogen receptor alpha expression in normal breast tissue and fibroadenomas

Fibroadenomas are the most common benign breast tumors, occurring mainly in young women. Their responses to the hormonal environment are similar to those of normal breast tissue, which suggests that steroid receptors may play a role in tumor development. We evaluated the gene and protein expression of progesterone receptors A and B (PRA and PRB) and the protein expression of estrogen receptor alpha (ER-alpha) in fibroadenoma samples, comparing with adjacent normal breast tissue, from 11 premenopausal women. Progesterone and estradiol levels were determined. No alterations in the PRs gene and protein expression and the ER-alpha protein expression were observed between the follicular and luteal phases, in normal breast versus fibroadenomas. Protein levels of PRA and PRB were higher in fibroadenomas compared to normal breast tissue (P = 0.038 and P = 0.031), while the PRs mRNA levels were similar in both tissues (P = 0.721 and P = 0.139). There were no differences in ER-alpha protein expression between normal breast tissue and fibroadenomas (P = 0.508). The PRA:PRB ratio was similar in the tissues, and also showed a strong correlation in both (r = 0.964, P = 0.0001). Our data suggest a role of PRs in the growth and development of fibroadenomas, although without alterations of the PRA:PRB ratio in these tumors. The absence of alterations in ER-alpha protein levels could be a characteristic behavior of fibroadenomas, unlike breast cancer.

Ductal lavage is an inefficient method of biomarker measurement in high-risk women

Effective methods of serial epithelial sampling to measure breast-specific biomarkers will aid the rapid evaluation of new preventive interventions. We report here a proof-of-principle phase 2 study to assess the utility of ductal lavage (DL) to measure biomarkers of tamoxifen action. We enrolled women with a 5-year breast cancer risk estimate >1.6% or the unaffected breast of women with T1a or T1b breast cancer. After entry DL, participants chose tamoxifen or observation and underwent repeat DL 6 months later. Samples were processed for cytology and immunohistochemistry for estrogen receptor alpha, Ki-67, and cyclooxygenase-2. Of 182 women recruited, 115 (63%) underwent entry and repeat DL; 85 (47%) had sufficient cells for analysis from > or =1 duct at both time points; in 78 (43%), cells were sufficient from > or =1 matched ducts. Forty-six women chose observation and 39 chose tamoxifen. We observed greater reductions in the tamoxifen group than in the observation group for Ki-67 (adjusted P = 0.03) and estrogen receptor alpha (adjusted P = 0.07), but not in cyclooxygenase-2 (adjusted P = 0.4) labeling. Cytologic findings showed a trend toward improvement in the tamoxifen group compared with the observation group. Interobserver variability for cytologic diagnosis between two observers showed good agreement (kappa = 0.44). Using DL, we observed the expected changes in tamoxifen-related biomarkers; however, poor reproducibility of biomarkers in the observation group, the 53% attrition rate of subjects from recruitment to biomarker analyses, and the expense of DL are significant barriers to the use of this procedure for biomarker assessment over time.

Progesterone and estrogen receptors in pregnant and premenopausal non-pregnant normal human breast

We report here our studies of nuclear staining for the progesterone and estrogen receptors (PRA, PRB, ERalpha) and cell proliferation (MIB1) in the breast terminal duct lobular unit epithelium of 26 naturally cycling premenopausal women and 30 pregnant women (median 8.1 weeks gestation). Square root transformations of the PRA, PRB and ERalpha values, and a logarithmic transformation of the MIB1 values, were made to achieve more normal distributions of the values. PRA expression decreased from a mean of 17.8% of epithelial cells in cycling subjects to 6.2% in pregnant subjects (P = 0.013). MIB1 expression increased from 1.7% in cycling subjects to 16.0% in pregnant subjects (P < 0.001). PRB and ERalpha expression was slightly lower in pregnant subjects but the differences were not statistically significant. Sixteen of the non-pregnant subjects were nulliparous and ten were parous so that we had limited power to detect changes associated with parity. PRA was statistically significantly lower in parous women than in nulliparous women (32.2% in nulliparous women vs. 10.2%; P = 0.014). PRB (23.5 vs. 12.9%), ERalpha (14.4 vs. 8.6%) and MIB1 (2.2 vs. 1.2%) were also lower in parous women, but the differences were not statistically significant. The marked decreases in PRA in pregnancy and in parous women has also been found in the rat. A reduction in PRA expression may be a useful marker of the reduction in risk with pregnancy and may be of use in evaluating the effect of any chemoprevention regimen aimed at mimicking pregnancy. Short-term changes in PRA expression while the chemoprevention is being administered may be a more useful marker.

Effects of pre- and postmenopausal use of exogenous hormones on receptor content in normal human breast tissue: a randomized study

OBJECTIVE

To examine the effects of exposure to endogenous and exogenous hormones on estrogen receptor-alpha (ERalpha) and progesterone receptor (PR) levels in normal human breast tissue.

METHODS

In a randomized study of women scheduled for mammary reduction plasty (n = 81), ERalpha and PR content in breast parenchyma was analyzed in premenopausal (n = 49) and postmenopausal (n = 16) women. Premenopausal women were randomized to surgery in the follicular or luteal phase of the menstrual cycle or after oral contraceptive treatment for 2 months. Postmenopausal women were randomized to sequential or estrogen-only therapy for 2 months prior to surgery.

RESULTS

ERalpha content was higher in parous than in nulliparous (p = 0.009) premenopausal women and displayed a positive association with age (r(s) = 0.51, p = 0.0002). Compared with premenopausal women in the follicular phase, postmenopausal women had higher ERalpha content (p = 0.040) whereas premenopausal women on oral contraception had lower ERalpha (p = 0.048) and PR (p = 0.007) content. Smokers had lower PR content than non-smokers (p = 0.02).

CONCLUSION

In the present study ERalpha content was higher in parous than in non-parous women and associated with premenopausal age. Short-term oral contraceptives yielded lower ERalpha and PR contents. Postmenopausal estrogen/progestogen combined therapy yielded lower PR content than estrogen-only therapy.

Associations between serum testosterone levels, cell proliferation and progesterone receptor content in normal and malignant breast tissue in postmenopausal women

Progestogens and progesterone receptors (PR) may play an important role in increased breast proliferation following combined estrogen/progestogen hormone therapy, while androgens may counteract this effect. In 50 untreated healthy postmenopausal women and 48 untreated postmenopausal breast cancer patients, we measured serum levels of testosterone (T), sex hormone-binding globulin (SHBG), estrone (E(1)) and adrenal androgens; and additionally, in the breast cancer patients, cortisol and corticosteroid-binding globulin and endocrine data related to breast proliferation (assessed using the Ki-67/MIB-1 monoclonal antibody) and PR levels (determined by enzyme immunoassay) in the breast cancer tissue. In the healthy women the percentage of MIB-1(+) cells showed significant negative correlations with serum levels of total T, calculated free T (fT) and the fT/E(1) ratio; while in the breast cancer patients PR content showed significant negative correlations with fT level, the fT/E(1) ratio and the T/SHBG ratio. No other correlations were found in any of the groups. Our findings in healthy women confirm previous reports of an antiproliferative effect of androgens in breast tissue and our finding in breast cancer patients suggests that this antiproliferative effect may be mediated via downregulation of PR.

New perspectives into the biological and clinical relevance of oestrogen receptors in the human breast

Oestrogen receptor (ER) is arguably the single most important biological predictive factor that exists today. In the last 10 years or so, however, our understanding of ER biology has undergone a paradigm shift following the identification of a second ER, ERbeta, with the original ER being renamed ERalpha. A number of isoforms have additionally been described, especially for ERbeta. Our knowledge of ER signalling has also increased with the recognition of accessory co-regulatory proteins, which help direct the transcriptional cascade. Here we outline these changes and discuss what biological and clinical implications these could have in the mammary gland.

Breast response to menopausal hormone therapy--aspects on proliferation, apoptosis and mammographic density

Breast cancer is the major malignancy among women in the Western world. The breast is clearly a target organ for sex steroid hormones and hormonal treatments have been associated with an increased risk of breast cancer. The balance between proliferation and apoptosis is important for breast cell homeostasis. Mammographic breast density has been identified as a strong and independent risk factor for breast cancer. It seems clear that there is a difference between various hormonal treatments with regard to their effects on breast density and cell proliferation. Also, not all women respond similarly to the same treatment. Combined estrogen and progestogen therapy generally will enhance density and proliferation more than treatment with estrogen alone. Certain constitutional and hormonal factors appear to be predictive of breast reactivity. Older women with a low body mass index respond more strongly to treatment. Estrogen levels have a positive and androgens a negative association to increase in density and proliferation. A combination of increased proliferation and decreased apoptosis could be one mechanism to explain the excess risk of breast cancer during combined estrogen/progestogen treatment. Tibolone seems to have less impact on breast response than conventional hormone therapy. Efforts should be made to identify those women with an adverse response to treatment as well as therapeutic principles with the least possible influence on the breast.

The aged breast

There is a clear association between the development of breast cancer and increasing age, with 80% of cancers occurring in women more than 50 years of age and one-third in women over 70 years. Following the menopause the breast undergoes involution, with the main changes affecting the terminal ductal lobular unit. There is an increase in oestrogen receptor alpha (ERalpha)-positive cells, a decrease in proliferation but, in comparison to premenopausal breasts, a greater number of ERalpha-proliferating cells. The breast cancers that occur in women >/= 75 years are more likely to be ER-positive, with a low growth rate and limited expression of HER-2 and p53. It is proposed that uneven involution of the breast, the persistence of at-risk lesions, the presence of ERalpha-proliferating cells and local oestrogen metabolism in breast adipose tissue are factors in the development of breast cancers with a well-differentiated phenotype.

Endogenous Steroid Hormone Concentrations and Risk of Breast Cancer Among Premenopausal Women

BACKGROUND

Higher levels of endogenous sex steroid hormones are associated with increased risks of breast cancer in postmenopausal women. Data for premenopausal women are sparse, in part because of the complexity of measuring hormone levels that vary cyclically. We prospectively evaluated associations between plasma sex hormone levels and breast cancer risk among premenopausal women in a case-control study nested within the Nurses' Health Study II.

METHODS

From 1996 to 1999, blood samples were collected from 18,521 premenopausal women during the early follicular and midluteal phases of their menstrual cycles. A total of 197 cases of breast cancer were diagnosed among these women after blood collection and before June 1, 2003; these case subjects were matched to 394 control subjects. Logistic regression models, controlling for breast cancer risk factors, were used to calculate relative risks (RRs) and 95% confidence intervals (CIs). All statistical tests were two-sided.

RESULTS

Women in the highest (versus the lowest) quartiles of follicular total and free estradiol levels had statistically significantly increased risks of breast cancer (RR = 2.1 [95% CI = 1.1 to 4.1], P(trend) = .08, and RR = 2.4 [95% CI = 1.3 to 4.5], P(trend) = .01, respectively); the associations were stronger for invasive breast cancer and for estrogen and progesterone receptor-positive (ER+/PR+) tumors. Luteal estradiol levels were not associated with breast cancer risk. Higher levels of total and free testosterone and androstenedione in both menstrual cycle phases were associated with modest, non-statistically significant increases in overall risk of breast cancer and with stronger, statistically significant increases in risks of invasive and ER+/PR+ cancers (e.g., RR of invasive cancers for the top [versus bottom] quartile of luteal total testosterone levels = 2.0 [95% CI = 1.1 to 3.6], P(trend) = .05, and RR of ER+/PR+ cancers = 2.9 [95% CI = 1.4 to 6.0], P(trend) = .02). Levels of estrone, estrone sulfate, progesterone, and sex hormone-binding globulin were not associated with breast cancer risk. The absolute number of cases observed over 3 years were 30 among women in the lowest 25% of follicular total estradiol levels and 50 among women in the highest 25%.

CONCLUSIONS

Levels of circulating estrogens and androgens may be important in the etiology of premenopausal breast cancer.

Ovarian steroids and the human breast: regulation of stem cells and cell proliferation

Ovarian steroidal control of mammary gland proliferation and differentiation is not well defined in the human. We therefore developed the athymic nude mouse model in which intact normal human breast tissue is xenografted subcutaneously and treated with human physiological serum levels of oestrogen (E) and/or progesterone (P). We showed that: (i) E, and not P, is the major steroid hormone inducing proliferation of epithelial cells in the adult non-pregnant, non-lactating breast; (ii) E induces progesterone receptor (PR) expression; and (iii) PR expression is maximally induced at low E concentrations while a higher amount of E was required to induce proliferation. Using double label immuno-fluorescence, we demonstrated that cells expressing the oestrogen receptor-alpha (ER alpha) invariably contained the PR but that steroid receptor expression and cell proliferation (Ki67 antigen) were dissociated. Recently, we have demonstrated that some ER alpha/PR-positive epithelial cells are quiescent breast stem cells suggesting that they act as "steroid hormone sensors" that secrete paracrine factors to regulate the proliferative activity of adjacent ER alpha/PR-negative epithelial cells. The dissociation between steroid receptor expression and cell proliferation in normal epithelium was lost at an early stage in ER alpha/PR-positive breast tumour formation perhaps indicating that they arise from deregulation of the normally quiescent breast stem cells.

Estrogen Receptor Expression in Benign Breast Ductal Cells Obtained from Random Periareolar Fine Needle Aspiration Correlates with Menopausal Status and Cytomorphology Index Score

INTRODUCTION

Estrogen receptor (ER) expression in breast epithelial cells has potential as a risk marker for development of breast cancer and as a response marker for preventive interventions.

AIM

The purpose of this study was to determine if ER expression in benign cytologic specimens acquired by random periareolar fine needle aspiration (RPFNA) increases with morphologic abnormality as has been reported for histologic preparations.

METHODS

ER expression was assessed in 122 women at high risk for development of breast cancer who had RPFNA hyperplasia +/- atypia and were being screened for entry into one of two chemoprevention trials. ER was assessed using antigen retrieval at 90 degrees C for 2 min and the DAKO ER monoclonal antibody (Clone number 1D5). The proportion of cells with definitive staining at each intensity level (0-4) was recorded as a percentage of the total cells counted, to give a weighted intensity score (IS).

RESULTS

Of 122 women, 65% exhibited hyperplasia and 35% exhibited hyperplasia with atypia in their RPFNA specimens. A majority (66%) of subjects had at least 10% of ductal cells exhibiting nuclear staining for ER. Median percent of cells with > or =1+ staining was 20% and the median ER IS was 0.23. There was a strong correlation between ER IS and percentage of ER positive cells (R(2) = 0.88). By univariate analysis ER IS was statistically significantly higher in women older than median age of 48 years (P = 0.025), in postmenopausal women on HRT (P < 0.017), and in women with a Masood cytomorphology index score of > or =14 (P = 0.005). On multivariable analysis, ER IS was significantly associated with postmenopausal status (P = 0.038) and cytomorphology as measured by Masood score (P = 0.043).

CONCLUSION

ER can be readily measured in cytologic specimens obtained by RPFNA with the use of antigen retrieval method. Further, ER expression in cytologic specimens is influenced by postmenopausal status and morphologic abnormality.

Estrogen receptor analysis for breast cancer: current issues and keys to increasing testing accuracy

The estrogen receptor (ER) is a regulator of cellular growth, proliferation, and differentiation. In addition to having prognostic value, ER is the most important biologic marker of therapeutic response in breast cancer. Some level of measurable ER protein is expressed in 70-80% of human breast. Immunohistochemistry is the current method of choice for ER assessment, and its predictive value has been shown to be superior to that of biochemically based assays. Although accurate ER protein assessment is critical for optimal treatment of patients with breast cancer, studies have demonstrated inter-laboratory variability in ER detection. False-negative results for tumors with low ER protein levels have been a subject of recent concern. Lack of standardization for immunohistochemistry between laboratories is thought to be the major reason for testing errors, although variability in scoring methods and reporting practices, which can affect results, also plays a role. In this article, we review studies addressing interlaboratory variability and recommend optimal testing techniques and reporting procedures for ER testing, with the goal of increasing interlaboratory standardization for ER analysis by immunohistochemistry. We additionally highlight recent biologic, molecular, and gene expression profiling data related to ER in breast cancer.

Normal breast lobular architecture in breast biopsy samples from breast cancer cases and benign disease controls

Rodent studies suggest a relationship between lobular maturation and breast cancer risk. Human data are sparse, and were developed using whole mounts of mastectomy or mammoplasty samples, without consideration of menstrual phase in premenopausal women. We studied normal breast lobules in relation to cancer risk in 284 women, using surgical biopsy material (mean two sections and 43.2 lobular structures per subject): 167 were premenopausal; 89 with breast cancer (cases) and 78 undergoing benign breast biopsy (controls). Of 117 postmenopausal women, 67 were cases and 50 were controls. Normal lobular type was classified based on size, and was designated predominant if it constituted 60% or more of the total lobules classified. The control group showed 66% type I, 34% type II and 1% type III lobules while cases showed 69% type I, 31% type II and 7% type III structures. Predominant lobule type showed no association with cancer (p = 0.9). Postmenopausal women had a substantially higher proportion of type I lobules compared to premenopausal women, irrespective of the parity or cancer status (p < 0.001). Lobule type was not associated with menstrual phase classified by dates; however, when menstrual phase was classified using breast morphological characteristics, type I lobules were more abundant in follicular phase and type II in the luteal phase (p < 0.001). In conclusion, we did not observe a relationship between lobular architecture and breast cancer susceptibility when using smaller breast samples usually available in epidemiological studies, but these data highlight the need for menstrual phase stratification in future investigations.

Estrogen receptor mutations in human disease

As early as the 1800s, the actions of estrogen have been implicated in the development and progression of breast cancer. The estrogen receptor (ER) was identified in the late 1950s and purified a few years later. However, it was not until the 1980s that the first ER was molecularly cloned, and in the mid 1990s, a second ER was cloned. These two related receptors are now called ERalpha and ERbeta, respectively. Since their discovery, much research has focused on identifying alterations within the coding sequence of these receptors in clinical samples. As a result, a large number of naturally occurring splice variants of both ERalpha and ERbeta have been identified in normal epithelium and diseased or cancerous tissues. In contrast, only a few point mutations have been identified in human patient samples from a variety of disease states, including breast cancer, endometrial cancer, and psychiatric diseases. To elucidate the mechanism of action for these variant isoforms or mutant receptors, experimental mutagenesis has been used to analyze the function of distinct amino acid residues in the ERs. This review will focus on ERalpha and ERbeta alterations in breast cancer.

Cyclic changes in the mammary gland of cynomolgus macaques

OBJECTIVE

To evaluate the influence of hormonal changes during the menstrual cycle on the mammary gland of female cynomolgus monkeys.

DESIGN

Paired breast biopsy samples were obtained during the follicular and luteal phases of the cycle. Cycle characteristics were assessed by vaginal bleeding, serum hormones, vaginal cytology, and uterine ultrasound. The mammary gland was assessed by histology and immunohistochemistry for Ki67, estrogen receptors (ER) alpha and beta, progesterone receptors (PR), and cleaved caspase 3 (CPP32).

SETTING

Nonhuman primate study in an academic research environment.

ANIMAL(S)

Fifty-two adult, female, feral cynomolgus macaques (Macaca fascicularis), aged 8 to 20 years, obtained from the breeding colony of the Institut Pertanian Bogor (Bogor, Indonesia).

INTERVENTION(S)

None

MAIN OUTCOME MEASURE(S)

Breast histomorphometry, immunohistochemical detection of Ki67, ERs, PR, and CPP32 in breast epithelial cells, and correlation with serum estradiol and progesterone.

RESULT(S)

Serum hormones, vaginal cytology and bleeding patterns were indicative of cycle stage. For lobules, Ki67 expression was higher in the follicular than in the luteal phase. In ducts, Ki67 expression was higher in the luteal than in the follicular phase. Estrogen receptors did not change across the cycle, but ER beta was more abundant. Ductal PR decreased in the luteal phase. Lobular CPP32 was higher during the luteal phase. Correlations of serum estradiol to outcomes varied by cycle stage.

CONCLUSION(S)

These data indicate important regulatory differences in the balance of proliferation and apoptosis in epithelial subpopulations within the breast across the menstrual cycle, indicating different regulatory roles for ER alpha and beta.

Lessons to be learned from clinical studies on hormones and the breast

Estrogen is a well-known mitogen in human breast epithelium but the action of progestogen is complex and incompletely understood. During the last years, accumulating data from animal, clinical and observational studies suggest a proliferative effect in breast tissue when progestogen is added to estrogen. Findings in surrogate markers like breast density add to clinical and epidemiological reports indicating that continuous combined HRT may carry a higher risk of breast cancer than treatment with estrogen alone. Whether the results are valid for all progestogens remains to elucidated. It is also clear that not all women respond in the same way to the same treatment and the biological basis for the marked individual variation in breast response has to be clarified. Further knowledge about the role of androgens and of the impact of different treatment regimens is important and prospective randomized clinical studies are needed.

Steroid receptors and proliferation in the human breast

Despite recent gains in our knowledge of the hormonal control of proliferation and differentiation in the rodent mammary gland, the factors regulating these processes in the human are poorly understood. We have developed a model in which intact normal human breast tissue is grafted subcutaneously into adult female athymic nude mice and treated with oestrogen (E) and/or progesterone (P) at human physiological serum levels. We have shown that (i) E and not P is the major epithelial cell mitogen in the adult non-pregnant, non-lactating breast, (ii) E induces progesterone receptor (PR) expression and (iii) PR expression is maximally induced at low E concentrations while a higher amount of E is required to stimulate proliferation. These data raised the question of whether one cell type demonstrated two different responses to the two different E concentrations or whether PR expression and proliferation occurred in separate cell populations. Using dual label immunofluorescence, we showed that steroid receptor expression and proliferation (Ki67 antigen) are detected in separate cell populations in normal human breast epithelium, and that cells expressing the oestrogen receptor-alpha (ERalpha) invariably contained the PR. We also reported that this separation between steroid receptor expression and proliferation observed in the normal human epithelium is disrupted at an early stage in breast tumourigenesis. One interpretation supported by our recent findings is that some ERalpha/PR-positive epithelial cells are quiescent breast stem cells that act as "steroid hormone sensors". Such hormone sensor cells might secrete positive or negative paracrine/juxtacrine factors dependent on the prevailing E or P concentration to influence the proliferative activity of adjacent ERalpha/PR-negative epithelial cells.

Increase of free insulin-like growth factor-1 in normal human breast in vivo late in the menstrual cycle

Prolonged exposure to endogenous and exogenous sex steroids increases the risk of breast cancer but the mechanisms are poorly understood. Increased levels of circulating insulin-like growth factor-1 (IGF-1) and low levels of IGF binding protein are associated with increased risk of breast cancer suggesting that IGF-1 has to be in its free form to be biologically active. Little is known about sex steroid regulation of IGF-1 locally in the breast. In this study microdialysis was used to determine the local levels of free IGF-1 in normal human breast tissue in healthy female volunteers during the menstrual cycle. The results showed that the extracellular levels of free IGF-1 locally in the breast were doubled in the luteal phase, when estradiol and progesterone levels were elevated, compared with the follicular phase. In plasma, free IGF-1 levels also exhibited a cyclic variation but to a less extent. The increased local levels of the free form of IGF-1 may promote proliferation in the breast epithelium. This could be important in sex steroid dependent breast cancer development.

Effects of low dose tamoxifen on normal breast tissue from premenopausal women

The aim of this study was to determine the effects of low doses of tamoxifen (5 and 10mg/day) for 50 days compared with the standard dose (20 mg/day) on breast biomarkers measured in normal breast tissue from premenopausal patients. A randomised double-blind study was performed using tissue from 56 premenopausal women with a diagnosis of fibroadenoma of the breast. Excisional biopsy was performed on the 50th day of therapy. Normal breast tissue samples were collected during surgery. The patients were divided in groups: A (placebo, n=11); group B (5 mg, n=16), group C (10 mg, n=14) and group D (20 mg, n=15). In this cross-sectional study, differences in the expression of Oestrogen Receptor alpha (ERalpha), Progesterone Receptor (PR), Ki-67, apoptotic bodies and mitotic index between the different groups after treatment can be seen on the normal breast tissue. We believe that a lower dose of tamoxifen could reduce the side-effects associated with treatment without affecting its chemopreventive activity in the breast.

Effects of long-term HRT and tamoxifen on the expression of progesterone receptors A and B in breast tissue from surgically postmenopausal cynomolgus macaques

Estrogen is a well-known mitogen in breast epithelium but the role of progesterone is complex and incompletely understood. In contrast to what is seen in the endometrium, combined estrogen/progestogen treatment for postmenopausal replacement (HRT) may carry a risk for breast cancer beyond that of estrogen alone. The ratio of the two progesterone receptor (PR) isoforms, PRA/PRB may define the response to progesterone in reproductive tissues. In a primate model for long-term HRT, surgically, postmenopausal cynomolgus macaques were treated for 35 months with conjugated equine estrogens (CEE), medroxyprogesterone acetate (MPA), CEE + MPA and tamoxifen (n = 5 in all groups). The immunohistochemical expression of PRA, PRB and the androgen receptor (AR) in breast tissue was quantified by image analysis. Over all, the total PR immunostaining in glandular epithelium was more abundant during CEE (mean 12%) and tamoxifen ( 1%) treatment as compared to CEE/MPA (5%), MPA (4%) and untreated controls (6%). Differences in PRB expression were observed between treatment groups (p < 0.05). In the CEE group levels of PRA were unchanged while there was a decline in the CEE/MPA group. The mean PRA/PRB ratio in the CEE group was 2.7 and in the CEE/MPA group 0.2. Treatment with tamoxifen had effects similar to those of estrogen. There was in all groups a weak positive nuclear AR immunostaining. This is the first in vivo study on the effects on long-term hormonal treatment on the expression of PR isoforms in normal primate breast tissue. The results suggest that hormonal treatments have a different influence on the PRA/PRB balance in the breast.

Estrogen receptor alpha expression in normal human breast epithelium is consistent over time

If increased expression of estrogen receptor alpha (ER) in benign breast epithelium increases susceptibility to breast cancer, such overexpression should be stable over time. There are no published data regarding this important aspect of ER expression in breast epithelium. We examined the temporal consistency of ER expression in the normal breast tissue of 28 women who had 2 separate breast surgical procedures, at least 6 months apart (mean interval, 2.8 years). Paraffin embedded breast tissue blocks containing an adequate sample of normal breast epithelium and no cancer, were sectioned and processed using the 6F11 antibody and standard immunohistochemical techniques. The ER labelling index (ER LI) was calculated by counting a mean of 2,000 epithelial cells. The median ER LI at first sampling was 13.6 and at second sample 15.5, with R(2) = 0.34 and p = 0.001. The ER LI was categorized into high and low values, using a threshold of 10. Twenty-four women (85.7%) showed concordance of high and low expression between the 2 samples (p = 0.002). There were 11 women who were premenopausal at both time points. Among them, much of the variation in ER LI was explained by differences in the menstrual cycle day at the time of sampling and adding the day of cycle to the regression model substantially improved the correlation between first and second labeling indices. These data suggest that ER expression of normal breast tissue is fairly consistent over time and support the notion that overexpression of ER in normal epithelium is a constant feature of the high risk breast.

Oestrogen receptors alpha and beta differ in normal human breast and breast carcinomas

The identification of a second oestrogen receptor, oestrogen receptor (ER) beta, has led to a need to assess the relative importance of the classical ERalpha and ERbeta in human breast and breast carcinomas. ERalpha and ERbeta mRNA was assessed in 61 carcinomas, 8 benign breast lesions, and 30 samples of normal breast using reverse transcriptase (RT)-nested polymerase chain reaction (PCR). Immunohistochemical analysis of ERalpha and ERbeta was performed in 62 carcinomas, the 38 non-malignant breast tissues, and 32 normal breast samples with menstrual cycle data. ERalpha mRNA was detected in 92% of breast cancers, with ERbeta mRNA (wild-type and/or variant form) in 85%; 72% had ERalpha protein, 62% progesterone receptor (PgR), and 32% ERbeta. ERalpha protein had a strong correlation with grade; ERbeta did not, although it was present in three of four grade I carcinomas and in special types. There was no correlation between the presence of ERalpha and ERbeta protein. In non-malignant breast, similar expression of ERalpha and beta was observed, apart from expression of ERbeta in stromal cells and myoepithelium, the latter being confirmed by RT-PCR and western blotting. There were differences in ERalpha in relation to the menstrual cycle but not PgR or ERbeta. The findings indicate a need to understand the role and regulation of ERbeta in normal breast and the reason for its down-regulation in mammary carcinogenesis.

Chemoprevention of breast cancer: implications for postmenopausal women

Estrogen administration is associated with reduction in perimenopausal symptoms and the risk for several conditions affecting postmenopausal women. As estrogen administration also increases the risk for breast cancer, a common dilemma facing many women and their physicians is whether to use estrogen replacement therapy (ERT), a selective estrogen receptor modulator (SERM) that antagonises estrogenic effects in breast tissue but retains some estrogen agonist properties in other organs, or neither. For women with average to moderate risk of breast cancer and with perimenopausal symptoms, ERT may be the best short-term choice. For very high-risk women (>1% per year) with menopausal symptoms, alternatives to ERT might be offered and tried first. A diagnosis of ductal carcinoma in situ or invasive breast cancer within the last 2 to 5 years should be considered a relative contraindication for ERT unless the tumour was estrogen receptor negative. High-risk women without menopausal symptoms are the best candidates for the only currently approved drug for breast cancer risk reduction, tamoxifen. Although the drug is approved for women with a 5-year risk of breast cancer > or = 1.7% (0.34% per year), postmenopausal women most likely to experience a favourable benefit/risk ratio are those with a Gail estimated risk of >0.5% per year without a uterus or >1% per year if they retain their uterus. Tamoxifen should not be used in women with prior history of thromboembolic or precancerous uterine conditions. Tamoxifen is often used in Europe in conjunction with transdermal ERT in hysterectomised women without obvious loss of efficacy or increased risk of thromboembolism. Raloxifene is a second generation SERM with estrogen-like agonist effects on bone but with less uterine estrogen agonist activity than tamoxifen. Raloxifene may have less potent breast antiestrogenic effects than tamoxifen, particularly in a moderate- to high-estrogen environment. Raloxifene is approved for use in reducing risk of osteoporosis, but not breast cancer. Whether it is as effective as tamoxifen in reducing breast cancer risk in postmenopausal women is the subject of a current trial. All women regardless of breast cancer risk are advised to employ nonpharmacological risk reduction measures, including normalisation of bodyweight, exercise, adequate calcium and vitamin D intake, and avoidance of smoking and alcohol. The preventive options are best weighed during an individualised consultation where a woman's menopausal symptoms and risk for breast cancer and other diseases can be examined, and the options for improving postmenopausal health can be discussed.

Molecular and genetic abnormalities in radial scar

Hyperplasia of usual type (HUT) may be an early precursor of breast carcinoma and has been shown to contain molecular and genetic abnormalities previously seen in more advanced breast lesions, such as allelic imbalance (AI) and coexpression of estrogen receptor-alpha (ER) and the proliferation marker Ki67. We have examined hyperplastic and other areas from within radial scar (RS) for such abnormalities, to explore whether such regions of RS are similar at the molecular and genetic level to histologically similar lesions found independent of RS. Abnormal expression of ER and Ki67 in hyperplastic foci and other histologically distinct areas within RS was detected by dual-label immunofluorescence. Subtle differences in expression patterns were seen compared to similar lesions outside RS, with a lower overall level of ER overexpression in HUT within RS (P = 0.0012) and less evidence of the abnormal ER association with Ki67 (P = 0.004). AI of chromosome 16q and 8p was detected in RS, indicating that at least some areas of RS are clonal and neoplastic, but no clear relationship to ER dysregulation was found. Different genetic losses seen in microdissected areas of the same RS indicated clonal differences between these areas. The role of RS as a marker of malignancy and relative risk of breast cancer remains uncertain. Nonetheless, here we provide evidence that some molecular and genetic changes that occur to a greater degree in breast cancer and some premalignant breast lesions are present in a minority of RS.

Breast cancer incidence and estrogen receptor alpha in normal mammary tissue--an epidemiologic study among Japanese women in Japan and Hawaii

We have undertaken a study to examine whether the difference in breast cancer incidence between 2 populations of similar genetic background is reflected in a similar pattern of estrogen receptor alpha expression in normal mammary gland. Study participants were 92 Japanese women from Sapporo, Japan (mean age 48.2 years) and 49 Japanese women from Honolulu, Hawaii (mean age 45.4 years), who underwent biopsy indicating normal breast tissue or benign, nonproliferative breast disease in hospitals in Sapporo, Japan and Honolulu, Hawaii. The breast tissue samples were formalin-fixed and paraffin-embedded. The estrogen receptor immunohistochemistry assays were conducted using Dako kits. Japanese women in Hawaii, who have a higher incidence of breast cancer compared with Japanese women in Sapporo, also had, as predicted, higher mean percentage of estrogen receptor alpha-positive normal mammary cells (2-tailed test, p approximately 0.09). The results of our study are compatible with the hypothesis that estrogen receptor alpha expression in normal mammary tissue increases breast cancer risk and they also indicate that the expression of these receptors is dependent, at least in part, on nongenetic factors.