Breast adipose tissue estrogen metabolism in postmenopausal women with or without breast cancer.

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Breast Adipose Tissue Estrogen Metabolism in Postmenopausal Women With or Without Breast Cancer Hanna Savolainen-Peltonen, Veera Vihma, Marjut Leidenius, Feng Wang, Ursula Turpeinen, Esa Hämäläinen, Matti J. Tikkanen, and Tomi S. Mikkola Department of Obstetrics and Gynecology (H.S.-P., T.S.M.) and Heart and Lung Center (V.V., F.W., M.J.T.), Helsinki University Central Hospital and University of Helsinki, Folkhälsan Research Center (H.S.-P., V.V., F.W., M.J.T., T.S.M.), Biomedicum, and Breast Surgery Unit (M.L.) and HUSLAB (U.T., E.H.), Helsinki University Central Hospital, 00029 Helsinki, Finland

Context: It has been shown that breast tumor actively produces and metabolizes steroid hormones. However, little is known about the possible mechanisms through which the nonmalignant adipose tissue contributes to steroid hormone metabolism. Objective: We compared the metabolic pathways producing active estradiol in breast sc adipose tissue of postmenopausal women with or without breast cancer. Design and Setting: Serum and adipose tissue samples were obtained during elective surgery. Patients: We studied postmenopausal women undergoing mastectomy due to an estrogen receptor-positive breast tumor (n ⫽ 14) and women undergoing breast reduction mammoplasty (n ⫽ 14). Interventions: Estrone, estradiol, and estradiol fatty acyl ester concentrations were determined by liquid chromatography-tandem mass spectrometry. mRNA expression levels of estrogen-converting enzymes were analyzed by quantitative RT-PCR. Results: Estradiol concentration in breast sc adipose tissue was lower in women with cancer than in controls (median 33 vs 62 pmol/kg; P ⫽ .002), whereas the serum concentrations did not differ. Also, the mRNA expression for 17␤-hydroxysteroid dehydrogenase type 12 was lower in the adipose tissue of women with cancer compared with controls (0.19 ⫾ 0.10 vs 0.37 ⫾ 0.21, P ⫽ .018). Conclusions: Estrogen metabolism is differentially regulated in the adipose tissue of women with or without cancer. In the sc adipose tissue proximal to breast tumor 17␤-hydroxysteroid dehydrogenase type 12 expression is lower than in controls, which could indicate that the conversion of estrone to estradiol is decreased. Further studies are needed to establish the clinical significance of our findings in the development and growth of breast cancer in postmenopausal women. (J Clin Endocrinol Metab 99: E2661–E2667, 2014)

T

here is increasing evidence of the active role of adipose tissue in tumor initiation and growth. Obese individuals have an increased risk of developing breast cancer, particularly at the postmenopausal age when adipose tissue becomes the principal site of estrogen biosynthesis (1). The exact mechanisms behind this increased risk are not

fully understood, but they may be related to hyperinsulinemia, inflammation, altered growth factor, or adipokine secretion or to altered steroid hormone metabolism (2). Although the circulating postmenopausal estrogen levels are low, they have been positively associated with an increased breast cancer risk in postmenopausal women (3–5).

ISSN Print 0021-972X ISSN Online 1945-7197 Printed in U.S.A. Copyright © 2014 by the Endocrine Society Received June 3, 2014. Accepted September 8, 2014. First Published Online September 12, 2014

Abbreviations: ANCOVA, analysis of covariance; BMI, body mass index; CI, confidence interval; CYP19A1, aromatase; E1, estrone; E2, estradiol; E2-FAE, E2 fatty acyl esters; FEI, free estradiol index; 17␤-HSD, 17␤-hydroxysteroid dehydrogenase; LC-MS/MS, liquid chromatography-tandem mass spectrometry; LIPE, hormone-sensitive lipase; STS, steroid sulfatase; WHR, waist to hip ratio.

doi: 10.1210/jc.2014-2550

J Clin Endocrinol Metab, December 2014, 99(12):E2661–E2667

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Savolainen-Peltonen et al

Estrogen Metabolism in Breast Adipose Tissue

In postmenopausal women, estrogens are formed in peripheral tissues from circulating androgen precursors. In adipose tissue, aromatase converts androstenedione and testosterone to estrone (E1) and estradiol (E2), respectively (6, 7). Estrone is also formed from estrone sulfate by steroid sulfatase (STS) and is further converted to E2 by 17␤-hydroxysteroid dehydrogenase (17␤-HSD) types 1, 7, and 12 (8, 9). Estradiol may be esterified with longchain fatty acids to an inactive form in adipose tissue in which it may be stored and possibly released later (10, 11). The esterifying enzyme in adipose tissue is not known, but hormone-sensitive lipase is, at least partly, responsible for the hydrolysis of E2 fatty acyl esters (E2-FAE) (11). Most of these metabolic pathways have been intensively studied in breast tumors (12–14). Less is known about the sex steroid levels and metabolism in nonneoplastic sc breast adipose tissue. Women with hormone receptor-positive tumors have been shown to have higher circulating sex steroid levels than women with hormone receptor-negative tumors (15). It has also been suggested that E2 levels in breast adipose tissue from women with breast cancer are lower than in sc abdominal adipose tissue from healthy postmenopausal women (16, 17). With the increasing knowledge of the active paracrine interactions between the adipocytes and the tumor cells (18), studying the sex steroid metabolism in breast adipose tissue becomes of interest. To study estrogen metabolism in breast adipose tissue, we assessed E2 and E2-FAE concentrations in the breast sc adipose tissue in postmenopausal women with or without breast cancer. Furthermore, we studied the most important metabolic pathways that drive toward the formation of biologically active E2 by analyzing the expression of aromatase (CYP19A1), STS, 17␤-HSD types 1, 7, and 12, and hormone-sensitive lipase (LIPE). Because the hormone receptor status defines clinically and etiologically


different forms of breast cancer (19), we chose women with an estrogen receptor-positive tumor.

Materials and Methods Subjects and study design We studied postmenopausal women operated for estrogen receptor-positive breast cancer (mastectomy; n ⫽ 14) or undergoing breast surgery for nonmalignant reasons (reduction mammoplasty; n ⫽ 14). Women in our study did not use systemic postmenopausal hormone therapy for at least 4 weeks before the operation. Detailed clinical information, including medical history, medication use, weight, and height as well as waist and hip circumference were gathered at the preoperative visit. Information related to tumor pathology was obtained from medical records. Blood samples were obtained before the operation. Serum was separated by centrifugation within 1 hour and stored at ⫺20°C until analysis. Two sc adipose tissue samples (1 g each) were taken perioperatively from the reduction mammoplasty or mastectomy specimens. From the mastectomy specimens, one sample was taken as close to the breast tumor as possible (N1) and the other one more than 5 cm from the tumor (N2). The samples were snap frozen in liquid nitrogen, and stored at ⫺80°C until further processing. The study was approved by the Ethics Committee of Helsinki University Central Hospital, and study subjects gave their written informed consent.

Quantification of estrogens in breast adipose tissue and serum Serum and adipose tissue E2 and E2-FAE concentrations were determined as described (20). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used as the analytical method and performed as previously reported (11). Concentration of E2-FAE was expressed as picomoles per liter of E2. Serum E1 concentration was determined by LC-MS/MS as described (21). Serum SHBG was measured with an Immulite 2000 Xpi analyzer using a chemiluminescent enzyme immunoassay (Siemens Healthcare Diagnostics). The free estradiol index (FEI), calculated by dividing the serum E2 level by the serum SHBG

Table 1. Clinical Characteristics of the Women With Breast Cancer and Control Women

Age, ya Age at menarche, ya Age at menopause, ya Years from menopausea Number of laborsa History of estrogen use, ya BMI, kg/m2a WHRa Hypertension, %b Hypercholesterolemia, %b Diabetes type 2, %b

Breast Cancer (n ⴝ 14)

Control (n ⴝ 14)

P Value

63 (54 –70) 13 (11–16) 52 (42–56) 11 (4 –28) 2 (0 –3) 6 (0 –23) 24 (20 –34) 0.85 (0.76 –1.0) 36 (n ⫽ 5) 14 (n ⫽ 2) 7 (n ⫽ 1)

59 (49 –75) 14 (11–16) 52 (44 –55) 8 (0.5–23) 2 (0 – 4) 8 (0 –12) 28 (22–38) 0.92 (0.82– 0.99) 43 (n ⫽ 6) 29 (n ⫽ 4) 7 (n ⫽ 1)

.072 .18 1.00 .19 .25 .67 .085 .008 .70 .36 1.00

Statistically significant P values are in bold. a

The data are expressed as median (range).

b

The data are expressed as percentages (number of women).


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level and multiplying by 100, was used as a measure of bioavailable E2.

Preparation and quantification of mRNA Frozen adipose tissue (200 mg) was homogenized in 1 mL Trizol, and total RNA was isolated and purified as described previously (20). A total of 1.0 ␮g of RNA was reverse transcribed into cDNA. mRNA expression levels of LIPE, CYP19A1, 17␤HSD types 1, 7, and 12, and STS were quantified by real-time PCR as described previously (20). Data were normalized to the geometric mean of two reference genes, importin 8 (IPO8) and lysine-specific demethylase 2B (KDM2B) (20).

Statistical analysis Data are expressed as median (range) or median [95% confidence interval (CI)] unless otherwise stated. The statistical tests were performed using SPSS Statistics version 19.0 software. The normality of variables was assessed with the Shapiro-Wilk test. Differences in baseline characteristics between women with cancer and control women were compared using the Student’s t test for parametric variables, the Mann-Whitney U test for nonparametric variables, and the ␹2 test for categorical variables. Between-group differences were evaluated by analysis of covariance (ANCOVA) with adjustment for age at specimen collection and waist to hip ratio (WHR). Pairwise comparisons were done with the Wilcoxon signed ranks test. Correlation analyses were performed using Spearman’s nonparametric correlation or partial correlation with adjustment for age at specimen collection and WHR. The level of significance was P ⬍ .05.

Results Patient characteristics Women with or without breast cancer were comparable in the primary clinical characteristics, except for WHR, being slightly higher in the control women (Table 1). The WHR correlated significantly with body mass index (BMI; r ⫽ 0.78, P ⬍ .0001). A total of 64% (n ⫽ 9) of the breast tumors were of ductal and the remaining of lobular histology. Estrogen receptor expression was detected in 100% (n ⫽ 14) and progesterone receptor expression in 79% (n ⫽ 11) of the breast tumors. Serum and adipose tissue estrogen concentrations E2 concentration in nonmalignant sc adipose tissue was lower in the women with breast cancer than in the control women (Figure 1A). Furthermore, adipose tissue E2 level was inversely related with tumor size, but the correlation reached statistical significance (r ⫽ ⫺0.59, P ⫽ .034) only after the removal of one outlier (Figure 1B). Although adipose tissue E2-FAE concentration was lower in the women with cancer, the difference did not reach statistical significance (P ⫽ .078) (Figure 1A). The adipose tissue E2-FAE level did not correlate with tumor size (r ⫽ ⫺0.03, P ⫽ .922). Adipose tissue E2 or E2-FAE concentrations

Figure 1. A, Serum and breast adipose tissue E2 and E2-FAE levels (picomoles per liter in serum and picomoles per kilogram in adipose tissue) in postmenopausal women with or without breast cancer. The data are expressed as adjusted mean and 95% CI. #, P ⫽ .002, breast cancer compared with control (ANCOVA, adjusted for age and WHR); *, P ⬍ .01, adipose tissue compared with the respective serum concentration (Wilcoxon’s signed ranks test). When the results were adjusted for age and BMI, #, P ⫽ .012, breast cancer compared with control. B, Correlation of breast adipose tissue E2 level (picomoles per kilogram) with tumor size in women with breast cancer. Correlation coefficient was ⫺0.40 (P ⫽ .16); however, when the one outlier (marked with x) was excluded from the analysis, the correlation coefficient was ⫺0.59 (P ⫽ .034) (Spearman’s nonparametric correlation).

measured proximal to the tumor (N1) did not differ from those measured distal to the tumor (N2) (data not shown). In contrast to adipose tissue, circulating E2 and E2-FAE were in the same range in the women with cancer and the control women (Figure 1A). Serum E1 levels were similar in both groups [adjusted mean 83 pmol/L (95% CI 59 – 111) vs 96 pmol/L (95% CI 68 –125), P ⫽ .54 cancer vs control]. In addition, FEI, a measure of bioavailable E2, did not differ between the women with or without cancer [35 (95% CI 19 –51) vs 34 (95% CI 15–53), P ⫽ .95]. Finally, E2 and E2-FAE concentrations in the adipose tissue were higher than those in serum, both in the women with or without cancer (Figure 1A). Serum E2 (P ⫽ .002


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Table 2. Correlations Between Circulating and Breast Adipose Tissue Estrogens in Women With Breast Cancer (n ⫽ 14) and Control Women (n ⫽ 14) Breast Cancer Serum

Adipose tissue E2 E2-FAE

Control Serum

E1

E2

FEI

E2-FAE

E1

E2

FEI

E2-FAE

0.35 0.64a

0.29 0.46

0.58 0.023

⫺0.19 0.076

0.72a 0.69a

0.36 0.55

0.73a 0.43

⫺0.014 0.46

Correlation coefficients between the corresponding variables are expressed in the table; partial correlation, controlled for age and WHR. a

P ⬍ .05; statistically significant correlation coefficients are in bold.

and P ⫽ .005 for cancer and control, respectively) and adipose tissue E2 (P ⫽ .041 and P ⫽ .008) levels were higher than the respective E2-FAE levels. In women with breast cancer, adipose tissue E2 correlated with age (r ⫽ 0.57, P ⫽ .034). Moreover, serum E1 (r ⫽ 0.58, P ⫽ .039) and serum E2-FAE (r ⫽ 0.58, P ⫽ .030) correlated with WHR. Serum E2-FAE correlated negatively with age (r ⫽ ⫺0.62, P ⫽ .019). In control women, no such correlations were found. When controlling for age and WHR, serum E1 correlated positively with adipose tissue E2-FAE level both in women with or without cancer (Table 2). In contrast, serum E1 and FEI were associated with adipose tissue E2 concentration only in control women (Table 2). Estrogen-related gene expression in adipose tissue In women with breast cancer, the relative expression of 17␤-HSD type 12 was significantly lower in the sc adipose tissue proximal to the breast tumor (N1) than in the control women (Figure 2). Furthermore, the mRNA expression of 17␤-HSD type 12 and type 7 were significantly lower in the N1 sample compared with the N2 sample.

Slight but not significant reduction was also observed in the mRNA expression of 17␤-HSD type 1. The relative mRNA expression of CYP19A1 in adipose tissue correlated positively with WHR (r ⫽ 0.55, P ⫽ .041) in the women with cancer. In the control women, the expression of CYP19A1 correlated positively with age (r ⫽ 0.76, P ⫽ .003). When controlling for age and WHR, 17␤-HSD type 7 mRNA expression correlated significantly with the adipose tissue E2-FAE level in the women with cancer (Table 3). The correlation of 17␤-HSD type 12 mRNA tended to correlate with adipose tissue E2 in the control women (r ⫽ 0.52, P ⫽ .081) but not in the women with cancer. We found no significant correlations between circulating estrogens and the mRNA levels of estrogenrelated genes (data not shown).

Discussion

We show that nonmalignant breast sc adipose tissue comprises a potential storage and source site of estrogens in postmenopausal women. Adipose tissue E2 levels were lower in women with breast cancer compared with controls, whereas the serum concentrations of E1, E2, E2-FAE, and FEI did not differ. Furthermore, the relative mRNA expression of 17␤-HSD type 12, converting E1 to E2, was significantly lower in the adipose tissue of women with breast cancer compared with controls. Thus, our findings indicate that in women with breast cancer, estrogen metabolism is altered in the breast subcutaneous adipose tissue. Sex steroid metabolism in breast tumor tissue has been extensively studied. Several reports show higher Figure 2. The relative mRNA expression of estrogen-related genes in breast adipose tissue of postmenopausal women with breast cancer and in controls. The N1 sample was taken close to concentrations of E2 in the tumor tisthe breast tumor and the N2 sample more than 5 cm from the tumor. The data are expressed as sue compared with the nonneoplasmedian ⫾ 95% CI. *, P ⫽ .018, compared with control (ANCOVA, adjusted for age and WHR); tic tissue of the same breast, and #, P ⫽ .03, compared with N1 (Wilcoxon’s signed ranks test). If the results were adjusted for age higher E2 concentrations in the and BMI, *, P ⫽ .049, N1 compared with control.


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Table 3. Correlations Between Estrogen-Related Gene mRNA Expression and Steroid Hormone Levels in the Breast Adipose Tissue of Women With Breast Cancer (n ⫽ 14) and Control Women (n ⫽ 14) Breast Cancer

Adipose tissue E2 E2-FAE

Control

CYP19A1

LIPE

STS

17␤HSD 1

17␤HSD 7

17␤HSD 12

CYP19A1

LIPE

STS

17␤HSD 1

17␤HSD 7

17␤HSD 12

0.44 0.37

⫺0.35 0.096

⫺0.16 0.24

⫺0.18 0.16

0.094 0.60a

⫺0.28 0.18

⫺0.29 ⫺0.18

0.34 0.35

0.22 0.087

⫺0.36 ⫺0.31

⫺0.019 0.075

0.52 0.37

Correlation coefficients between the corresponding variables are expressed in the table; partial correlation, controlled for age and WHR. a

P ⬍ .05; statistically significant correlation coefficients are in bold.

breast cancer tissue compared with serum (13, 14, 22). This local estrogen production in the tumor is thought to stimulate the growth of hormone-dependent breast cancer. However, in these studies, breast tissue samples containing glandular or both glandular and adipose tissue were examined, whereas less is known about the estrogen levels exclusively in breast adipose tissue (15, 17, 23). In our study, adipose tissue estrogen levels proximal to or more distal from the tumor were similar, in line with a previous study (23). Our finding that estrogen levels are higher in breast sc adipose tissue than in serum is in line with previous data (15, 17). However, we emphasize that in the current and previous (17, 22) studies, the comparison of estrogen levels between adipose tissue and serum are based on the assumption that 1 g of adipose tissue corresponds to 1 mL of serum, which is only an approximation. Furthermore, it has been suggested that circulating estrogens would contribute to the breast tissue steroid hormone levels (24). In our study, the interchange between plasma and adipose tissue is possible based on the positive correlation between bioavailable E2, as detected by FEI, in serum and E2 in adipose tissue. However, the difference in E2 concentrations in adipose tissue, but not in serum, between the breast cancer and control women indicates that local mechanisms in the adipose tissue may regulate estrogen metabolism. In addition to 17␤-HSD type 12, the 17␤-HSD types 1 and 7 also tended to be lower in the sc adipose tissue proximal to the breast tumor. It has been suggested that 17␤-HSD type 12 is the most abundant 17␤-HSD type in the adipose tissue in general (8) and is also important in the mammary gland (25), whereas in the breast tumor tissue,17␤-HSD types 1 and 7 may be more important (26, 27). We do not know the reason for the reduced mRNA expression for 17␤-HSD type 12, but it might result in diminished formation of E2 from E1. It has been reported that breast cancer cells and adipocytes interact with each other and that adipocyte functioning may change when exposed to breast cancer cells, possibly due to increased expression of proinflammatory cytokines or other medi-

ators (2, 18). Altogether the changes in the 17␤-HSD metabolic pathways may, at least in part, explain the reduction in the concentration of E2 in breast sc adipose tissue in women with cancer. Another potential explanation may be the high-affinity uptake of E2 from adipose tissue due to binding to the estrogen receptors in breast tumor, as has been suggested (27). If so, one could expect that increasing tumor size may be associated with an increased uptake of E2 from nonmalignant adipose tissue. Although 17␤-HSD gene expressions were different proximal to or more distal from the tumor, we did not find any significant topographical differences in the mRNA expression of aromatase in breast adipose tissue. Previous studies have shown higher expression and activity of aromatase in adipose tissue adjacent to the breast tumor compared with the most distal quadrant (28), although the results are not entirely consistent (29, 30). It has been suggested that malignant cells could release growth factors or adipokines that enhance aromatase expression close to the tumor (7). The variations in aromatase expression in different breast regions have also been shown to associate with the number of stromal cells in adipose tissue (31); thus, the selection of sample site may influence the results. We used breast sc adipose tissue to minimize the possible influence of microscopically small subsets of glandular or malignant tissue. In postmenopausal women, the low serum and adipose tissue sex steroid concentrations are difficult to measure accurately. Previous studies showing associations between circulating sex steroids, BMI, and breast cancer risk have used RIA methodology for the steroid measurements (32, 33) or combined data from different immunological assays (3). Currently the use of mass spectrometry is preferred because it provides greater specificity and sensitivity than immunological methods, which is extremely important when assessing very low E2 concentrations (34, 35). To the best of our knowledge, this is the first study to analyze serum and adipose tissue E2 and E2-FAE concentrations with mass spectrometric methods in women with or without breast cancer. We have previously reported higher E2 and E2-FAE levels in postmenopausal serum and


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breast sc adipose tissue by fluoroimmunoassay compared with LC-MS/MS (11). This may be due to the reduced specificity of the immunoassay when analyzing low estrogen concentrations. In contrast to some previous studies, we used WHR, instead of BMI, as a controlling factor in the statistical analyses. Previous studies show that WHR is as good a, or a better, measure of adiposity and a relevant marker of increased risk for several diseases (36 –38). Although WHR in the control group was higher than in the cancer group, there was a significant positive correlation between the two measures. Also, our main results did not change if BMI was used as a controlling factor. Interestingly, there was a positive correlation between adipose tissue E2 and age in breast cancer patients, suggesting the possibility of increasing accumulation of E2 to the adipose tissue with age. Our study has some limitations. First, we acknowledge the relatively small number of women in our study, which may affect the power in some of our statistical analyses. Second, although the mRNA expression levels of the steroidogenic enzymes were analyzed, the protein levels or the activities of the corresponding enzymes could not be analyzed. Finally, we studied Caucasian women; therefore, our results may not be applicable to women of different ethnic origins. As a strength of our study, we consider the use of a LC-MS/MS method with greater specificity and sensitivity than the previously used methods. In conclusion, concentrations of both free E2 and the esterified form are higher in the adipose tissue overlying breast parenchyma than in serum after menopause. Estrogen metabolism is differently regulated in the breast adipose tissue of women with cancer compared with the controls. The lower levels of E2 in the sc adipose tissue of a breast with cancer may be due to the lower expression of 17␤-HSD enzymes, especially type 12, in the adipose tissue surrounding the tumor. However, the possibility of enhanced uptake of E2 from adipose tissue by the tumor cannot be excluded. Further studies are needed to establish the clinical significance of our findings in the development and growth of breast cancer in postmenopausal women.

Acknowledgments We thank Päivi Ihamuotila and Kirsti Räsänen for their expert technical assistance. Address all correspondence and requests for reprints to: Tomi S. Mikkola, MD, PhD, Department of Obstetrics and Gynecology, Helsinki University Central Hospital, Haartmaninkatu 2,


PO Box 140, FIN-00029 HUS, Helsinki, Finland. E-mail: [email protected]. This work was supported by Folkhälsan, the Sigrid Jusélius Foundation, the Päivikki and Sakari Sohlberg Foundation, the Finnish Foundation for Cardiovascular Research, the Paulo Foundation, the Finnish Menopause Society, State Funding for University-Level Health Research, and Finska Läkaresällskapet. Disclosure Summary: The authors have nothing to disclose.

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Cardiovascular risk in postmenopausal women with and without breast cancer.

Kinetics of testosterone metabolism in normal postmenopausal women and women with breast cancer.

The network of antigen-antibody reactions in adult women with breast cancer or benign breast pathology or without breast pathology.

Inhibition of oestrogen synthesis in postmenopausal women with breast cancer.

On estrogen, cholesterol metabolism, and breast cancer.

Combined conjugated esterified estrogen plus methyltestosterone supplementation and risk of breast cancer in postmenopausal women.

A(nother) scientific strategy to prevent breast cancer in postmenopausal women by enhancing estrogen-induced apoptosis?

Relationship between crown-like structures and sex-steroid hormones in breast adipose tissue and serum among postmenopausal breast cancer patients.

Regional adipose tissue metabolism in postmenopausal women after treatment with exogenous sex steroids.

Serum estrogen receptor bioactivity and breast cancer risk among postmenopausal women.

Aminoglutethimide inhibits extraglandular estrogen production in postmenopausal women with breast carcinoma.

[Estrogen and gonadotropin levels in postmenopausal women with different parenchymal patterns of the breast (proceedings)].

The risk of contralateral breast cancer in daughters of women with and without breast cancer.

Menopausal status, adipose tissue, and breast cancer risk: impact of estrogen replacement therapy.

Oral health after breast cancer treatment in postmenopausal women.

Bisphosphonates do not reduce breast cancer in postmenopausal women.

Wedge resection with or without radiation in early breast cancer.

Economic evaluation of hormonal therapies for postmenopausal women with estrogen receptor-positive early breast cancer in Canada.

Locoregional and Overall Recurrence After Neaodjuvant Endocrine Therapy Versus Chemotherapy in Postmenopausal Women With Estrogen Receptor+ HER2- Breast Cancer.

Gene expression in breast and adipose tissue after 12 months of weight loss and vitamin D supplementation in postmenopausal women.

Normal breast tissue estrogen levels.

Antiestrogenic effects of the fetal estrogen estetrol in women with estrogen-receptor positive early breast cancer.

Adipose tissue, a neglected factor in aetiology of breast cancer?

Differential expression of progesterone receptor, FOXA1, GATA3, and p53 between pre- and postmenopausal women with estrogen receptor-positive breast cancer.