Sex steroids, growth factors and mammographic density: a cross-sectional study of UK postmenopausal Caucasian and Afro-Caribbean women

Lipidome of mammographic breast density in premenopausal women

BACKGROUND

High mammographic breast density (MBD) is a strong risk factor for breast cancer development, but the biological mechanisms underlying MBD are unclear. Lipids play important roles in cell differentiation, and perturbations in lipid metabolism are implicated in cancer development. Nevertheless, no study has applied untargeted lipidomics to profile the lipidome of MBD. Through this study, our goal is to characterize the lipidome of MBD in premenopausal women.

METHODS

Premenopausal women were recruited during their annual screening mammogram at the Washington University School of Medicine in St. Louis, MO. Untargeted lipidomic profiling for 982 lipid species was performed at Metabolon (Durham, NC®), and volumetric measures of MBD (volumetric percent density (VPD), dense volume (DV), and non-dense volume (NDV)) was assessed using Volpara 1.5 (Volpara Health®). We performed multivariable linear regression models to investigate the associations of lipid species with MBD and calculated the covariate-adjusted least square mean of MBD by quartiles of lipid species. MBD measures were log10 transformed, and lipid species were standardized. Linear coefficients of MBD were back-transformed and considered significant if the Bonferroni corrected p-value was < 0.05.

RESULTS

Of the 705 premenopausal women, 72% were non-Hispanic white, and 23% were non-Hispanic black. Mean age, and BMI were 46 years and 30 kg/m2, respectively. Fifty-six lipid species were significantly associated with VPD (52 inversely and 4 positively). The lipid species with positive associations were phosphatidylcholine (PC)(18:1/18:1), lysophosphatidylcholine (LPC)(18:1), lactosylceramide (LCER)(14:0), and phosphatidylinositol (PI)(18:1/18:1). VPD increased across quartiles of PI(18:1/18:1): (Q1 = 7.5%, Q2 = 7.7%, Q3 = 8.4%, Q4 = 9.4%, Bonferroni p-trend = 0.02). The lipid species that were inversely associated with VPD were mostly from the triacylglycerol (N = 43) and diacylglycerol (N = 7) sub-pathways. Lipid species explained some of the variation in VPD. The inclusion of lipid species increased the adjusted R2 from 0.45, for a model that includes known determinants of VPD, to 0.59.

CONCLUSIONS

We report novel lipid species that are associated with MBD in premenopausal women. Studies are needed to validate our results and the translational potential.

Pubertal mammary gland development is a key determinant of adult mammographic density

Mammographic density refers to the radiological appearance of fibroglandular and adipose tissue on a mammogram of the breast. Women with relatively high mammographic density for their age and body mass index are at significantly higher risk for breast cancer. The association between mammographic density and breast cancer risk is well-established, however the molecular and cellular events that lead to the development of high mammographic density are yet to be elucidated. Puberty is a critical time for breast development, where endocrine and paracrine signalling drive development of the mammary gland epithelium, stroma, and adipose tissue. As the relative abundance of these cell types determines the radiological appearance of the adult breast, puberty should be considered as a key developmental stage in the establishment of mammographic density. Epidemiological studies have pointed to the significance of pubertal adipose tissue deposition, as well as timing of menarche and thelarche, on adult mammographic density and breast cancer risk. Activation of hypothalamic-pituitary axes during puberty combined with genetic and epigenetic molecular determinants, together with stromal fibroblasts, extracellular matrix, and immune signalling factors in the mammary gland, act in concert to drive breast development and the relative abundance of different cell types in the adult breast. Here, we discuss the key cellular and molecular mechanisms through which pubertal mammary gland development may affect adult mammographic density and cancer risk.

Mammographic breast density and its association with urinary estrogens and the fecal microbiota in postmenopausal women

BACKGROUND

Breast density, as estimated by mammography, is a strong risk factor for breast cancer in pre- and postmenopausal women, but the determinants of breast density have not yet been established. The aim of this study was to assess if urinary estrogens or gut microbiota alterations are associated with mammographic density in postmenopausal women.

METHODS

Among 54 cancer-free, postmenopausal controls in the Breast and Colon Health study, we classified low- versus high-density women with Breast Imaging Reporting and Data System (BI-RADS, 5th edition) mammographic screening data, then assessed associations with urinary estrogens and estrogen metabolites (determined by liquid chromatography/tandem mass spectrometry), and fecal microbiota alpha and beta diversity (using Illumina sequencing of 16S rRNA amplicons).

RESULTS

Multiple logistic regression revealed no significant association between breast density and fecal microbiota metrics (PD_tree P-value = 0.82; un-weighted and weighted UniFrac P = 0.92 and 0.83, respectively, both by MiRKAT). In contrast, total urinary estrogens (and all 15 estrogens/estrogen metabolites) were strongly and inversely associated with breast density (P = 0.01) after adjustment for age and body mass index.

CONCLUSION

Mammographic density was not associated with the gut microbiota, but it was inversely associated with urinary estrogen levels.

IMPACT

The finding of an inverse association between urinary estrogens and breast density in cancer-free women adds to the growing breast cancer literature on understanding the relationship between endogenous estrogens and mammographic density.

Association between mammographic density and tumor marker-defined breast cancer subtypes: a case-control study

High mammographic density (MD) is the most important risk factor for breast cancer. This study aimed to clarify the relationship between MD and breast cancer subtypes defined by tumor markers. We enrolled 642 women with breast cancer (69% premenopausal) and 1241 controls matched for age and menopausal status. Absolute mammographic dense area (ADA), percent mammographic dense area (PDA), and nondense area were assessed using a computer-assisted thresholding technique. We classified breast cancer cases into four subtypes using information on tumor marker expression such as estrogen receptor (ER), progesterone receptor (PR), and Cerb2 receptor (HER2); luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+, HER2+), HER2-overexpressing (ER-, PR-, and HER2+), and triple-negative (ER-, PR-, and HER2-). Analysis was carried out using a conditional logistic regression model with adjustment for covariates. ADA and PDA were associated positively with the risk of breast cancer overall. Both ADA and PDA tended to have a positive association with breast cancer with any ER, any PR, or HER2-, but not for HER2+. The risk of luminal A breast cancer increased significantly 1.11 times (95% confidence interval: 1.01-1.23) for ADA and 1.12 times (95% confidence interval: 1.01-1.24) for PDA, estimated per 1 SD of the age and BMI-adjusted MD. However, the risk of breast cancer with luminal B, HER2-overexpressing, and triple-negative subtypes did not differ (P>0.10). Differential associations between MD measures and breast cancer by tumor marker status or tumor marker-defined subtypes were not detected. These findings suggested that the association between MD and breast cancer subtype may be because of other causal pathways.

Mammographic Density and Circulating Sex Hormones: a Cross-Sectional Study in Postmenopausal Korean Women

Mammographic density (MD) is a strong independent risk factor for breast cancer. It has been suggested that breast cancer is related to the exposure to circulating sex hormones. However, relations between MD and hormones have been inconsistent. In addition, such relations are mainly evaluated in Western populations. Therefore, we conducted a cross-sectional study in 396 cancer-free postmenopausal Korean women who had never used hormone replacement therapy. We assayed estradiol, testosterone, and sex hormone-binding globulin (SHBG) levels. We then calculated free testosterone (cFT) levels. Total and dense areas of digital mammogram were measured using a computer-assisted thresholding method, and non-dense area and percent dense area were calculated. Linear mixed model was used for analyses. Estradiol and testosterone levels were not associated with any MD measures after adjusting for reproductive factors and body mass index. However, cFT was persistently associated with non-dense area even after adjusting for covariates, with non-dense area increased by 3.5% per 1 standard deviation increase of cFT. SHBG showed an inverse association with non-dense area, although it showed a positive association with dense area and percent dense area regardless of adjustment for covariates. Non-dense area was decreased by 5.6% while percent dense area was increased by 13.4% per 1 standard deviation increase of SHBG. These findings suggest that SHBG might be related with breast cancer risk, probably through its association with breast density.

Association between expression of inflammatory markers in normal breast tissue and mammographic density among premenopausal and postmenopausal women

OBJECTIVE

Inflammatory markers may be associated with breast cancer risk. We assessed the association between expression levels of proinflammatory (interleukin 6, tumor necrosis factor-α, C-reactive protein, cyclooxygenase 2, leptin, serum amyloid A1, interleukin 8, and signal transducer and activator of transcription 3) and anti-inflammatory markers (transforming growth factor-β, interleukin 10, and lactoferrin) in normal breast tissue with mammographic density, a strong breast cancer risk indicator, among 163 breast cancer patients.

METHODS

The expression of inflammatory markers was visually evaluated on immunohistochemistry stained slides. The percent mammographic density (PMD) was estimated by a computer-assisted method in the contralateral cancer-free breast. We used generalized linear models to estimate means of PMD by median expression levels of the inflammatory markers while adjusting for age and waist circumference.

RESULTS

Higher expression levels (above median) of the proinflammatory marker interleukin 6 were associated with higher PMD among all women (24.1% vs 18.5%, P = 0.007). Similarly, higher expression levels (above median) of the proinflammatory markers (interleukin 6, tumor necrosis factor-α, C-reactive protein, and interleukin 8) were associated with higher PMD among premenopausal women (absolute difference in the PMD of 8.8% [P = 0.006], 7.7% [P = 0.022], 6.7% [P = 0.037], and 16.5% [P = 0.032], respectively). Higher expression levels (above median) of the anti-inflammatory marker transforming growth factor-β were associated with lower PMD among all (18.8% vs 24.3%, P = 0.005) and postmenopausal women (14.5% vs 20.7%, P = 0.013).

CONCLUSIONS

Our results provide support for the hypothesized role of inflammatory markers in breast carcinogenesis through their effects on mammographic density. Inflammatory markers could be targeted in future breast cancer prevention interventions.

Stromal characteristics may hold the key to mammographic density: the evidence to date

There is strong epidemiological data indicating a role for increased mammographic density (MD) in predisposing to breast cancer, however, the biological mechanisms underlying this phenomenon are less well understood. Recently, studies of human breast tissues have started to characterise the features of mammographically dense breasts, and a number of in-vitro and in-vivo studies have explored the potential mechanisms through which dense breast tissue may exert this tumourigenic risk. This article aims to review both the pathological and biological evidence implicating a key role for the breast stromal compartment in MD, how this may be modified and the clinical significance of these findings. The epidemiological context will be briefly discussed but will not be covered in detail.

Prolactin receptor in breast cancer: marker for metastatic risk

Prolactin and prolactin receptor signaling and function are complex in nature and intricate in function. Basic, pre-clinical and translational research has opened up our eyes to the understanding that prolactin and prolactin receptor signaling function differently within different cellular contexts and microenvironmental conditions. Its multiple roles in normal physiology are subverted in cancer initiation and progression, and gradually we are teasing out the intricacies of function and therapeutic value. Recently, we observed that prolactin has a role in accelerating the time to bone metastasis in breast cancer patients and identified the mechanism by which prolactin stimulated breast cancer cell-mediated lytic osteoclast formation. The possibility that the prolactin receptor is a marker for metastasis, and specifically bone metastasis, is one that may have to be put into the context of the different variants of prolactin, different prolactin receptor isoforms and intricate signaling pathways that are regulated by the microenvironment. The more complete the picture, the better one can test biomarker identity and design clinical trials to test therapeutic intervention. This review will cover the recent advances and highlight the complexity of prolactin receptor biology.

Racial Differences in Quantitative Measures of Area and Volumetric Breast Density

BACKGROUND

Increased breast density is a strong risk factor for breast cancer and also decreases the sensitivity of mammographic screening. The purpose of our study was to compare breast density for black and white women using quantitative measures.

METHODS

Breast density was assessed among 5282 black and 4216 white women screened using digital mammography. Breast Imaging-Reporting and Data System (BI-RADS) density was obtained from radiologists' reports. Quantitative measures for dense area, area percent density (PD), dense volume, and volume percent density were estimated using validated, automated software. Breast density was categorized as dense or nondense based on BI-RADS categories or based on values above and below the median for quantitative measures. Logistic regression was used to estimate the odds of having dense breasts by race, adjusted for age, body mass index (BMI), age at menarche, menopause status, family history of breast or ovarian cancer, parity and age at first birth, and current hormone replacement therapy (HRT) use. All statistical tests were two-sided.

RESULTS

There was a statistically significant interaction of race and BMI on breast density. After accounting for age, BMI, and breast cancer risk factors, black women had statistically significantly greater odds of high breast density across all quantitative measures (eg, PD nonobese odds ratio [OR] = 1.18, 95% confidence interval [CI] = 1.02 to 1.37, P = .03, PD obese OR = 1.26, 95% CI = 1.04 to 1.53, P = .02). There was no statistically significant difference in BI-RADS density by race.

CONCLUSIONS

After accounting for age, BMI, and other risk factors, black women had higher breast density than white women across all quantitative measures previously associated with breast cancer risk. These results may have implications for risk assessment and screening.

Circulating insulin-like growth factor-I, insulin-like growth factor binding protein-3 and terminal duct lobular unit involution of the breast: a cross-sectional study of women with benign breast disease

Background

Terminal duct lobular units (TDLUs) are the primary structures from which breast cancers and their precursors arise. Decreased age-related TDLU involution and elevated mammographic density are both correlated and independently associated with increased breast cancer risk, suggesting that these characteristics of breast parenchyma might be linked to a common factor. Given data suggesting that increased circulating levels of insulin-like growth factors (IGFs) factors are related to reduced TDLU involution and increased mammographic density, we assessed these relationships using validated quantitative methods in a cross-sectional study of women with benign breast disease.

Methods

Serum IGF-I, IGFBP-3 and IGF-I:IGFBP-3 molar ratios were measured in 228 women, ages 40-64, who underwent diagnostic breast biopsies yielding benign diagnoses at University of Vermont affiliated centers. Biopsies were assessed for three separate measures inversely related to TDLU involution: numbers of TDLUs per unit of tissue area (“TDLU count”), median TDLU diameter (“TDLU span”), and number of acini per TDLU (“acini count”). Regression models, stratified by menopausal status and adjusted for potential confounders, were used to assess the associations of TDLU count, median TDLU span and median acini count per TDLU with tertiles of circulating IGFs. Given that mammographic density is associated with both IGF levels and breast cancer risk, we also stratified these associations by mammographic density.

Results

Higher IGF-I levels among postmenopausal women and an elevated IGF-I:IGFBP-3 ratio among all women were associated with higher TDLU counts, a marker of decreased lobular involution (P-trend = 0.009 and <0.0001, respectively); these associations were strongest among women with elevated mammographic density (P-interaction <0.01). Circulating IGF levels were not significantly associated with TDLU span or acini count per TDLU.

Conclusions

These results suggest that elevated IGF levels may define a sub-group of women with high mammographic density and limited TDLU involution, two markers that have been related to increased breast cancer risk. If confirmed in prospective studies with cancer endpoints, these data may suggest that evaluation of IGF signaling and its downstream effects may have value for risk prediction and suggest strategies for breast cancer chemoprevention through inhibition of the IGF system.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0678-4) contains supplementary material, which is available to authorized users.

Adolescent endogenous sex hormones and breast density in early adulthood

INTRODUCTION

During adolescence the breasts undergo rapid growth and development under the influence of sex hormones. Although the hormonal etiology of breast cancer is hypothesized, it remains unknown whether adolescent sex hormones are associated with adult breast density, which is a strong risk factor for breast cancer.

METHODS

Percentage of dense breast volume (%DBV) was measured in 2006 by magnetic resonance imaging in 177 women aged 25-29 years who had participated in the Dietary Intervention Study in Children from 1988 to 1997. They had sex hormones and sex hormone-binding globulin (SHBG) measured in serum collected on one to five occasions between 8 and 17 years of age. Multivariable linear mixed-effect regression models were used to evaluate the associations of adolescent sex hormones and SHBG with %DBV.

RESULTS

Dehydroepiandrosterone sulfate (DHEAS) and SHBG measured in premenarche serum samples were significantly positively associated with %DBV (all P trend ≤0.03) but not when measured in postmenarche samples (all P trend ≥0.42). The multivariable geometric mean of %DBV across quartiles of premenarcheal DHEAS and SHBG increased from 16.7 to 22.1 % and from 14.1 to 24.3 %, respectively. Estrogens, progesterone, androstenedione, and testosterone in pre- or postmenarche serum samples were not associated with %DBV (all P trend ≥0.16).

CONCLUSIONS

Our results suggest that higher premenarcheal DHEAS and SHBG levels are associated with higher %DBV in young women. Whether this association translates into an increased risk of breast cancer later in life is currently unknown.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov Identifier, NCT00458588 April 9, 2007; NCT00000459 October 27, 1999.

Relationship of serum estrogens and metabolites with area and volume mammographic densities

Elevated mammographic density is a breast cancer risk factor, which has a suggestive, but unproven, relationship with increased exposure to sex steroid hormones. We examined associations of serum estrogens and estrogen metabolites with area and novel volume mammographic density measures among 187 women, ages 40-65, undergoing diagnostic breast biopsies at an academic facility in Vermont. Serum parent estrogens, estrone and estradiol, and their 2-, 4-, and 16-hydroxylated metabolites were measured using liquid chromatography-tandem mass spectrometry. Area mammographic density was measured in the breast contralateral to the biopsy using thresholding software; volume mammographic density was quantified using a density phantom. Linear regression was used to estimate associations of estrogens with mammographic densities, adjusted for age and body mass index, and stratified by menopausal status and menstrual cycle phase. Weak, positive associations between estrogens, estrogen metabolites, and mammographic density were observed, primarily among postmenopausal women. Among premenopausal luteal phase women, the 16-pathway metabolite estriol was associated with percent area (p = 0.04) and volume (p = 0.05) mammographic densities and absolute area (p = 0.02) and volume (p = 0.05) densities. Among postmenopausal women, levels of total estrogens, the sum of parent estrogens, and 2-, 4- and 16-hydroxylation pathway metabolites were positively associated with area density measures (percent: p = 0.03, p = 0.04, p = 0.01, p = 0.02, p = 0.07; absolute: p = 0.02, p = 0.02, p = 0.01, p = 0.02, p = 0.03, respectively) but not volume density measures. Our data suggest that serum estrogen profiles are weak determinants of mammographic density and that analysis of different density metrics may provide complementary information about relationships of estrogen exposure to breast tissue composition.

Immunoassay and Nb2 lymphoma bioassay prolactin levels and mammographic density in premenopausal and postmenopausal women the Nurses' Health Studies

Higher circulating prolactin levels have been associated with higher percent mammographic density among postmenopausal women in some, but not all studies. However, few studies have examined associations with dense area and non-dense breast area breast or considered associations with prolactin Nb2 lymphoma cell bioassay levels. We conducted a cross-sectional study among 1,124 premenopausal and 890 postmenopausal women who were controls in breast cancer case-control studies nested in the Nurses' Health Study (NHS) and NHSII. Participants provided blood samples in 1989-1990 (NHS) or 1996-1999 (NHSII) and mammograms were obtained from around the time of blood draw. Multivariable linear models were used to assess the associations between prolactin levels (measured by immunoassay or bioassay) with percent density, dense area, and non-dense area. Among 1,124 premenopausal women, percent density, dense area, and non-dense area were not associated with prolactin immunoassay levels in multivariable models (p trends = 0.10, 0.18, and 0.69, respectively). Among 890 postmenopausal women, those with prolactin immunoassay levels in the highest versus lowest quartile had modestly, though significantly, higher percent density (difference = 3.01 percentage points, 95 % CI 0.22, 5.80) as well as lower non-dense area (p trend = 0.02). Among women with both immunoassay and bioassay levels, there were no consistent differences in the associations with percent density between bioassay and immunoassay levels. Postmenopausal women with prolactin immunoassay levels in the highest quartile had significantly higher percent density as well as lower non-dense area compared to those in the lowest quartile. Future studies should examine the underlying biologic mechanisms, particularly for non-dense area.

Endogenous sex hormones and breast density in young women

BACKGROUND

Breast density is a strong risk factor for breast cancer and reflects epithelial and stromal content. Breast tissue is particularly sensitive to hormonal stimuli before it fully differentiates following the first full-term pregnancy. Few studies have examined associations between sex hormones and breast density among young women.

METHODS

We conducted a cross-sectional study among 180 women ages 25 to 29 years old who participated in the Dietary Intervention Study in Children 2006 Follow-up Study. Eighty-five percent of participants attended a clinic visit during their luteal phase of menstrual cycle. Magnetic resonance imaging measured the percentage of dense breast volume (%DBV), absolute dense breast volume (ADBV), and absolute nondense breast volume (ANDBV). Multiple-linear mixed-effect regression models were used to evaluate the association of sex hormones and sex hormone-binding globulin (SHBG) with %DBV, ADBV, and ANDBV.

RESULTS

Testosterone was significantly positively associated with %DBV and ADBV. The multivariable geometric mean of %DBV and ADBV across testosterone quartiles increased from 16.5% to 20.3% and from 68.6 to 82.3 cm(3), respectively (Ptrend ≤ 0.03). There was no association of %DBV or ADBV with estrogens, progesterone, non-SHBG-bound testosterone, or SHBG (Ptrend ≥ 0.27). Neither sex hormones nor SHBG was associated with ANDBV except progesterone; however, the progesterone result was nonsignificant in analysis restricted to women in the luteal phase.

CONCLUSIONS

These findings suggest a modest positive association between testosterone and breast density in young women.

IMPACT

Hormonal influences at critical periods may contribute to morphologic differences in the breast associated with breast cancer risk later in life.

Exogenous estrogen as mediator of racial differences in bioactive insulin-like growth factor-I levels among postmenopausal women

BACKGROUND

The role of exogenous estrogen use in racial differences in insulin-like growth factor-I (IGF-I) levels which affect cancer risk is unclear. We investigated whether the relationship between race and circulating bioactive IGF-I proteins was mediated by exogenous estrogen and the extent to which exogenous estrogen influenced the race-IGF-I relationship in postmenopausal women.

METHODS

This cross-sectional study included 636 white and 133 African American postmenopausal women enrolled in an ancillary study of the Women's Health Initiative Observational Study. To assess exogenous estrogen use (nonusers [n = 262] vs users [n = 507]) as a mediator of the race-IGF-I relationship, we used the Baron-Kenny method and an estimation of the proportional change in the odd ratios for IGF-I levels on race plus a bootstrapping test for the significance of the mediation effect.

RESULTS

Compared with white women, African American women were more likely to have high IGF-I levels and less likely to use exogenous estrogen. After accounting for race, estrogen nonusers had higher IGF-I levels than estrogen users did. Among oral contraceptive ever users, exogenous estrogen had a strong mediation effect (67%; p = .018) in the race-IGF-I relationship. In the women with a history of hypertension, exogenous estrogen explained racial differences in IGF-I levels to a modest degree (23%; p = .029).

CONCLUSIONS

Exogenous estrogen use has a potentially important role in disparities in IGF-I bioactivity between postmenopausal African American and white women. A history of oral contraceptive use and hypertension may be part of the interconnected hormonal pathways related to racial differences in IGF-I levels.

Sex hormones and breast cancer risk and prognosis

The study of large prospective collections of plasma samples from women prior to the development of breast cancer has firmly established certain sex steroids as being significantly associated with risk. The strongest associations have been found in postmenopausal women in whom the within person variability of most hormones is markedly reduced but some positive associations have also been seen in premenopausal women. Plasma estrogens show the strongest correlations with risk and these are strengthened by measurement or calculation of the proportion of estradiol that circulates free of sex hormone binding globulin (SHBG), consistent with this being the most active fraction. The relationships have been reported to potentially explain virtually all of the association of breast cancer with body mass index in postmenopausal women; this is likely to be due to non-ovarian estrogen synthesis being prominent in subcutaneous fat. These strong relationships have led to plasma and urine estrogen levels being used as intermediate end-points in the search for genes that affect breast cancer risk via their role in steroid disposition. Plasma androgen levels also show a relationship with breast cancer risk that is weakened but not eliminated by 'correction' for estrogen levels. This has been argued to be evidence of the local production of estrogens being important in the etiology of breast cancer. Given that plasma steroid levels do not correlate closely with mammographic density, which is strongly associated with risk, the opportunity exists to combine the two factors in assessing breast cancer risk but the low availability of suitable estrogen assays is a major impediment to this. In established breast cancer, plasma estrogens have been found to correlate with gene expression of estrogen dependent genes and the expression of these varies across the menstrual cycle of premenopausal women. There is infrequently a need for routine measurement of plasma estrogen levels but it has been important in the comparative pharmacology and dose-related effectiveness of aromatase inhibitors. Measurement may be needed to identify residual ovarian function in women who have amenorrhea subsequent to cytotoxic chemotherapy indicating their unsuitability for aromatase inhibitor treatment. Use of highly sensitive assays has also revealed that the association between BMI and plasma estrogen levels persists in patients on 3rd generation aromatase inhibitors and that measurable increments in plasma estrogen levels occur with some vaginal estrogen preparations that are of concern in relation to treatment efficacy.

Mammographic density-a review on the current understanding of its association with breast cancer

There has been considerable recent interest in the genetic, biological and epidemiological basis of mammographic density (MD), and the search for causative links between MD and breast cancer (BC) risk. This report will critically review the current literature on MD and summarize the current evidence for its association with BC. Keywords 'mammographic dens*', 'dense mammary tissue' or 'percent dens*' were used to search the existing literature in English on PubMed and Medline. All reports were critically analyzed. The data were assigned to one of the following aspects of MD: general association with BC, its relationship with the breast hormonal milieu, the cellular basis of MD, the generic variations of MD, and its significance in the clinical setting. MD adjusted for age, and BMI is associated with increased risk of BC diagnosis, advanced tumour stage at diagnosis and increased risk of both local recurrence and second primary cancers. The MD measures that predict BC risk have high heritability, and to date several genetic markers associated with BC risk have been found to also be associated with these MD risk predictors. Change in MD could be a predictor of the extent of chemoprevention with tamoxifen. Although the biological and genetic pathways that determine and perhaps modulate MD remain largely unresolved, significant inroads are being made into the understanding of MD, which may lead to benefits in clinical screening, assessment and treatment strategies. This review provides a timely update on the current understanding of MD's association with BC risk.

Bioavailable insulin-like growth factor-I inversely related to weight gain in postmenopausal women regardless of exogenous estrogen

BACKGROUND

Weight gain, insulin-like growth factor-I (IGF-I) levels, and excess exogenous steroid hormone use are putative cancer risk factors, yet their interconnected pathways have not been fully characterized. This cross-sectional study investigated the relationship between plasma IGF-I levels and weight gain according to body mass index (BMI), leptin levels, and exogenous estrogen use among postmenopausal women.

METHODS

This study included 794 postmenopausal women who enrolled in an ancillary study of the Women's Health Initiative Observational Study between February 1995 and July 1998. The relationship between IGF-I levels and weight gain was analyzed using ordinal logistic regression. We used the molar ratio of IGF-I to IGF binding protein-3 (IGF-I/IGFBP-3) or circulating IGF-I levels adjusting for IGFBP-3 as a proxy of bioavailable IGF-I. The plasma concentrations were expressed as quartiles.

RESULTS

Among the obese group, women in the third quartile (Q3) of IGF-I and highest quartile of IGF-I/IGFBP-3 were less likely to gain weight (>3% from baseline) than were women in the first quartiles (Q1). Among the normal-weight group, women in Q2 and Q3 of IGF-I/IGFBP-3 were 70% less likely than those in Q1 to gain weight. Among current estrogen users, Q3 of IGF-I/IGFBP-3 had 0.5 times the odds of gaining weight than Q1.

CONCLUSIONS

Bioavailable IGF-I levels were inversely related to weight gain overall.

IMPACT

Although weight gain was not consistent with increases in IGF-I levels among postmenopausal women in this report, avoidance of weight gain as a strategy to reduce cancer risk may be recommended.

Combined effects of endogenous sex hormone levels and mammographic density on postmenopausal breast cancer risk: results from the Breakthrough Generations Study

BACKGROUND

Mammographic density and sex hormone levels are strong risk factors for breast cancer, but it is unclear whether they represent the same aetiological entity or are independent risk factors.

METHODS

Within the Breakthrough Generations Study cohort, we conducted a case-control study of 265 postmenopausal breast cancer cases and 343 controls with prediagnostic mammograms and blood samples. Plasma was assayed for oestradiol, testosterone and sex hormone-binding globulin (SHBG) concentrations and mammographic density assessed by Cumulus.

RESULTS

Oestradiol and testosterone were negatively and SHBG positively associated with percentage density and absolute dense area, but after adjusting for body mass index the associations remained significant only for SHBG. Breast cancer risk was independently and significantly positively associated with percentage density (P=0.002), oestradiol (P=0.002) and testosterone (P=0.007) levels. Women in the highest tertile of both density and sex hormone level were at greatest risk, with an odds ratio of 7.81 (95% confidence interval (CI): 2.89-21.1) for oestradiol and 4.57 (95% CI: 1.75-11.9) for testosterone and high density compared with those who were in the lowest tertiles. The cumulative risk of breast cancer in the highest oestradiol and density tertiles, representing 8% of controls, was estimated as 12.8% at ages 50-69 years and 19.4% at ages 20-79 years, and in the lowest tertiles was 1.7% and 4.3%, respectively. Associations of breast cancer risk with tertiles of mammographic dense area were less strong than for percentage density.

CONCLUSIONS

Endogenous sex hormone levels and mammographic density are independent risk factors for postmenopausal breast cancer, which in combination can identify women who might benefit from increased frequency of screening and chemoprophylaxis.

Longitudinal changes in IGF-I and IGFBP-3, and mammographic density among postmenopausal women

A relation between the breast cancer risk factors, insulin-like growth factor-I (IGF-I) and mammographic density, is biologically plausible, but results from cross-sectional epidemiologic studies have been mixed. Our objective was to examine the relation in a longitudinal manner, that is, between the change in circulating IGF-I concentrations and the change in mammographic measures over one year. Data from an exercise intervention trial conducted in 302 postmenopausal women ages 50 to 74 years were used. Blood drawn at baseline and postintervention was assessed for IGF-I and its binding protein (IGFBP-3) by direct chemiluminscent immunoassay. Area and volumetric measurements of mammographic dense fibroglandular and nondense fatty tissue were made. Statistical analyses were based on multiple linear regression. A one SD (20.2 ng/mL) change in IGF-I over one year was associated with small changes in percent dense area [mean: 0.8%; 95% confidence interval (CI), 0.1-1.4] and dense area (mean: 1.2 cm(2); 95% CI, 0.2-2.1). Change in IGFBP-3 was also associated with percent and absolute dense area. Absolute and percent dense volume, and mammographic measures representing fatty tissue (nondense area and volume) were not associated with changes in IGF-I and IGFBP-3. Longitudinal associations may be more detectable than cross-sectional associations due to the absence of confounding by invariant personal factors. Absolute and percent dense area, measures that are related to breast cancer risk, may be affected by IGF-I. Confirmation should be sought in further longitudinal studies in which larger changes in the IGF system are evoked.

Plasma leptin levels, LEPR Q223R polymorphism and mammographic breast density: a cross-sectional study

Obesity is associated with breast cancer in post-menopausal women, and breast density is a marker of breast cancer risk. Leptin is produced by the adipose tissue, acts through receptors that are polymorphic in nature, and is considered a cancer growth factor. The relationship between body mass index, leptin, leptin receptors and breast density is not well studied. A cross-sectional analysis in 392 post-menopausal healthy women was conducted; participants provided permission to obtain copies of their most recent screening mammogram. Non-fasting plasma leptin levels were determined using a commercially available leptin ELISA kit. Analysis of the Q223R genotypes of the LEPR gene were performed by PCR followed by restriction fragment length polymorphism analysis using DNA extracted from buffy coat samples. A statistically significant positive relationship was observed between leptin levels and body mass index (p<0.0001); leptin was significantly positively associated with mammography total breast area and non-dense breast area (p<0.0001), while it was inversely associated with percent breast density (p<0.0001). Leptin levels varied across the LEPR Q223R polymorphism, and were higher in women homozygous for the AA variant. Percent breast density decreased across the LEPR Q223R genotype, with lower percent density in women with the AA genotype. When dense area was considered according to quartiles of leptin and stratified by LEPR Q223R, a significant inverse trend between leptin levels and dense breast area was observed only among women with the G/G genotype (p-trend<0.001). After adjustment for possible confounders, leptin levels were significantly inversely associated with percent breast density (p=0.01). A significant interaction between body mass index and leptin levels on percent breast density was observed (p=0.03). These findings suggest that the association between leptin and breast density may vary by LEPR Q223R genotype, and that body mass index and leptin may act in an interactive way in determining breast density.

Mammographic breast density response to aromatase inhibition

PURPOSE

Mammographic breast density (MBD) is decreased by tamoxifen, but the effect of aromatase inhibitors is less clear.

EXPERIMENTAL DESIGN

We enrolled early-stage postmenopausal patients with breast cancer initiating adjuvant aromatase inhibitor therapy and ascertained mammograms before and at an average 10 months of aromatase inhibitor therapy. We matched cases to healthy postmenopausal women (controls) from a large mammography screening cohort on age, baseline body mass index, baseline MBD, and interval between mammograms. We estimated change in MBD using a computer-assisted thresholding program (Cumulus) and compared differences between cases and matched controls.

RESULTS

In predominantly White women (96%), we found 14% of the 387 eligible cases had a MBD reduction of at least 5% after an average of 10 months of aromatase inhibitor therapy. MBD reductions were associated with higher baseline MBD, aromatase inhibitor use for more than 12 months, and prior postmenopausal hormone use. Comparing each case with her matched control, there was no evidence of an association of change in MBD with aromatase inhibitor therapy [median case-control difference among 369 pairs was -0.1% (10th and 90th percentile: -5.9%, 5.2%) P = 0.51]. Case-control differences were similar by type of aromatase inhibitor (P's 0.41 and 0.56); prior use of postmenopausal hormones (P = 0.85); baseline MBD (P = 0.55); and length of aromatase inhibitor therapy (P = 0.08).

CONCLUSIONS

In postmenopausal women treated with aromatase inhibitors, 14% of cases had a MBD reduction of more than 5%, but these decreases did not differ from matched controls. These data suggest that MBD is not a clinically useful biomarker for predicting the value of aromatase inhibitor therapy in White postmenopausal women.

Is mammographic density differentially associated with breast cancer according to receptor status? A meta-analysis

Mammographic density (MD) is a strong marker of breast cancer risk, but it is debated whether the association holds, and is of a similar magnitude, for different subtypes of breast cancer defined by receptor status or gene expression profiles. A literature search conducted in June 2012 was used to identify all studies that had investigated the association of MD with subtype-specific breast cancer, independent of age. 7 cohort/case-control and 12 case-only studies were included, comprising a total of >24,000 breast cancer cases. Random effects meta-analysis models were used to combine relative risks (RR) of MD with subtype-specific breast cancer for case-control studies, and in case-only studies to combine relative risk ratios (RRR) of receptor positive versus negative breast tumors. In case-control/cohort studies, relative to women in the lowest density category, women in the highest density category had 3.1-fold (95 % confidence interval [CI] 2.2, 4.2) and 3.2-fold (1.7, 5.9) increased risk of estrogen receptor positive (ER+) and ER- breast cancer, respectively. In case-only analyses, RRRs of breast tumors being ER+ versus ER- were 1.13 (95 % CI 0.89, 1.42) for medium versus minimal MD. MD remained associated with screen-detected ER+ tumors, despite the expectation of this association to be attenuated due to masking bias and overdiagnoses of ER+ tumors. In eight contributing studies, the association of MD did not differ by HER2 status. This combined evidence strengthens the importance of MD as a strong marker of overall and of subtype-specific risk, and confirms its value in overall breast cancer risk assessment and monitoring for both research and clinical purposes.

The heritability of mammographic breast density and circulating sex-hormone levels: two independent breast cancer risk factors

BACKGROUND

Mammographic breast density and endogenous sex-hormone levels are both strong risk factors for breast cancer. This study investigated whether there is evidence for a shared genetic basis between these risk factors.

METHODS

Using data on 1,286 women from 617 families, we estimated the heritabilities of serum estradiol, testosterone, and sex-hormone binding globulin (SHBG) levels and of three measures of breast density (dense area, nondense area, and percentage density). We tested for associations between hormone levels and density measures and estimated the genetic and environmental correlations between pairs of traits using variance and covariance components models and pedigree-based maximum likelihood methods.

RESULTS

We found no significant associations between estradiol, testosterone, or SHBG levels and any of the three density measures, after adjusting for body mass index (BMI). The estimated heritabilities were 63%, 66%, and 65% for square root-transformed adjusted percentage density, dense area, and nondense area, respectively, and 40%, 25%, and 58% for log-transformed-adjusted estradiol, testosterone, and SHBG. We found no evidence of a shared genetic basis between any hormone levels and any measure of density, after adjusting for BMI. The negative genetic correlation between dense and nondense areas remained significant even after adjustment for BMI and other covariates (ρ = -0.34; SE = 0.08; P = 0.0005).

CONCLUSIONS

Breast density and sex hormones can be considered as independent sets of traits.

IMPACT

Breast density and sex hormones can be used as intermediate phenotypes in the search for breast cancer susceptibility loci.

Estrogen metabolism and mammographic density in postmenopausal women: a cross-sectional study

BACKGROUND

Prospective studies have consistently found that postmenopausal breast cancer risk increases with circulating estrogens; however, findings from studies of estrogens and mammographic density (MD), an intermediate marker of breast cancer risk, have been inconsistent. We investigated the cross-sectional associations of urinary estrogens, and their 2-, 4-, and 16-hydroxylated metabolites with MD.

METHODS

Postmenopausal women without breast cancer (n = 194), ages 48 to 82 years, and reporting no current menopausal hormone therapy use were enrolled at a clinic in Western NY in 2005. Urinary estrogens and estrogen metabolites were measured using mass spectrometry. Percent MD and dense area (cm(2)) were measured using computer-assisted analyses of digitized films. Linear regression models were used to estimate associations of log-transformed estrogen measures with MD while adjusting for age, body mass index (BMI), parity, and past hormone therapy use.

RESULTS

Urinary concentrations of most individual estrogens and metabolites were not associated with MD; however, across the interdecile range of the ratio of parent estrogens (estrone and estradiol) to their metabolites, MD increased by 6.8 percentage points (P = 0.02) and dense area increased by 10.3 cm(2) (P = 0.03). Across the interdecile ranges of the ratios of 2-, 4-, and 16-hydroxylation pathways to the parent estrogens, MD declined by 6.2 (P = 0.03), 6.4 (P = 0.04), and 5.7 (P = 0.05) percentage points, respectively. All associations remained apparent in models without adjustment for BMI.

CONCLUSION

In this study of postmenopausal women, less extensive hydroxylation of parent estrogens was associated with higher MD.

IMPACT

Hydroxylation of estrogens may modulate postmenopausal breast cancer risk through a pathway involving MD.

Androgen replacement therapy in women

Female androgens are derived from either the adrenal and peripheral conversion of the adrenal sex steroid precursor, dehydroepiandrosterone, or from direct ovarian production. Adrenal insufficiency or bilateral oophorectomy (surgical menopause) result in severe androgen deficiency, which can be clinically associated with impaired libido, drive and energy. Physiological menopause does not necessarily lead to androgen deficiency. The previously suggested definition of female androgen deficiency syndrome, as the concurrent presence of low androgen levels and low libido, is not precise enough and may lead to overdiagnosis. Current replacement options include transdermal testosterone or oral dehydroepiandrosterone treatment, both of which have been shown to result in significant improvements, in particular in libido and mood, while long-term effects on body composition, cardiovascular and cancer risk are less documented. Owing to these concerns, androgen replacement should be reserved for women with severe androgen deficiency due to an established cause and matching clinical symptoms.

Rotating night shift work and mammographic density

BACKGROUND

An increased risk of breast cancer has been observed in night shift workers. Exposure to artificial light at night and disruption of the endogenous circadian rhythm with suppression of the melatonin synthesis have been suggested mechanisms. We investigated the hypothesis that rotating night shift work is associated with mammographic density.

METHODS

We conducted a cross-sectional study on the association between rotating night shift work characteristics, 6-sulfatoxymelatonin (MT6s) creatinine adjusted in a spot morning urine sample, and a computer-assisted measure of mammographic density in 640 nurses and midwives ages 40 to 60 years. The associations were evaluated using regression models adjusted for age, body mass index, menopausal status, age at menopause, age at menarche, smoking, and the calendar season of the year when mammography was conducted.

RESULTS

The adjusted means of percentage of mammographic density and absolute density were slightly higher among women working rotating night shifts but not statistically significant [percentage of mammographic density = 23.6%, 95% confidence interval (CI), 21.9%-25.4% vs. 22.5%, 95% CI, 20.8%-24.3%; absolute density = 23.9 cm(2), 95% CI, 21.4-26.4 cm(2) vs. 21.8 cm(2), 95% CI, 19.4-24.3 cm(2) in rotating night shift and day shift nurses, respectively). There were no significant associations between the current or cumulative rotating night shift work exposure metrics and mammographic density. No association was observed between morning MT6s and mammographic density.

CONCLUSIONS

The hypothesis on the link between rotating night shift work, melatonin synthesis disruption, and mammographic density is not supported by the results of the present study.

IMPACT

It is unlikely that the development of breast cancer in nurses working rotating night shifts is mediated by an increase in mammographic density.

Racial variation in umbilical cord blood sex steroid hormones and the insulin-like growth factor axis in African-American and white female neonates

PURPOSE

To evaluate whether there is racial variation in venous umbilical cord blood concentrations of sex steroid hormones and the insulin-like growth factor (IGF) axis between female African-American and white neonates.

METHODS

Maternal and birth characteristics and venous umbilical cord blood samples were collected from 77 African-American and 41 white full-term uncomplicated births at two urban hospitals in 2004 and 2005. Cord blood was measured for testosterone, dehydroespiandrosterone-sulfate, estradiol, and sex steroid hormone-binding globulin (SHBG) by immunoassay. IGF-1, IGF-2, and IGF-binding protein-3 (IGFBP-3) were measured by ELISA. Crude and multivariable-adjusted geometric mean concentrations were computed for the hormones.

RESULTS

African-American neonates weighed less at birth (3,228 g vs. 3,424 g, p < 0.004) than whites. Birth weight was positively correlated with IGF-1, IGFBP-3, and the molar ratio of IGF-1 to IGFBP-3, but inversely correlated with the molar ratio of IGF-2 to IGFBP-3. Adjusted models showed higher testosterone (1.82 ng/ml vs. 1.47 ng/ml, p = 0.006) and the molar ratio of testosterone to SHBG (0.42 vs. 0.30, p = 0.03) in African-American compared to white female neonates. IGF-1, IGF-2, and IGFBP-3 were lower in African-American compared to white female neonates, but only the difference for IGF-2 remained significant (496.5 ng/ml vs. 539.2 ng/ml, p = 0.04).

CONCLUSION

We provide evidence of racial variation in cord blood testosterone and testosterone to SHBG in African-American compared to white female neonates, and higher IGF-2 in white compared to African-American female neonates. Findings suggest plausible explanations for a prenatal influence on subsequent breast cancer risk and mortality. Further work is needed to confirm these observations.

Genetic variation in PRL and PRLR, and relationships with serum prolactin levels and breast cancer risk: results from a population-based case-control study in Poland

Introduction

Studies suggest that high circulating levels of prolactin increase breast cancer risk. It is unclear if genetic variations in prolactin (PRL) or prolactin receptor (PRLR) genes also play a role. Thus, we examined the relationship between single nucleotide polymorphisms (SNPs) in PRL and PRLR, serum prolactin levels and breast cancer risk in a population-based case-control study.

Methods

We genotyped 8 PRL and 20 PRLR tag SNPs in 1965 breast cancer cases and 2229 matched controls, aged 20-74, and living in Warsaw or Łódź, Poland. Serum prolactin levels were measured by immunoassay in a subset of 773 controls. Odds ratios (ORs) and 95% confidence intervals (CIs) for genotype associations with breast cancer risk were estimated using unconditional logistic regression, adjusted for age and study site. Geometric mean prolactin levels were estimated using linear regression models adjusted for age, study site, blood collection time, and menstrual cycle day (premenopausal women).

Results

Three SNPs were associated with breast cancer risk: in premenopausal women, PRLR rs249537 (T vs. C per-allele OR 1.39, 95% CI 1.07 - 1.80, P = 0.01); and in postmenopausal women, PRLR rs7718468 (C vs. T per-allele OR 1.16, 95% CI 1.03 - 1.30, P = 0.01) and PRLR rs13436213 (A vs. G per-allele OR 1.13 95% CI 1.01 - 1.26, P = 0.04). However, mean serum prolactin levels for these SNPs did not vary by genotype (P-trend > 0.05). Other SNPs were associated with serum prolactin levels: PRLR rs62355518 (P-trend = 0.01), PRLR rs10941235 (P-trend = 0.01), PRLR rs1610218 (P-trend = 0.01), PRLR rs34024951 (P-trend = 0.02), and PRLR rs9292575 (P-trend = 0.03) in premenopausal controls and PRL rs849872 (P-trend = 0.01) in postmenopausal controls.

Conclusions

Our data provide limited support for an association between common variations in PRLR and breast cancer risk. Altered serum prolactin levels were not associated with breast cancer risk-associated variants, suggesting that common genetic variation is not a strong predictor of prolactin-associated breast cancer risk in this population.

Estrogens in the breast tissue: a systematic review

The role of estrogens in breast carcinogenesis has been investigated at the level of whole body (plasma) and cell (molecular, receptors, etc.). Growing attention focused on the breast tissue being an intracrine organ, with potentially important local estrogen production in the breast. However, very little is known about the local breast tissue estrogen levels. Understanding the role of the tissue estrogens in breast carcinogenesis might open new avenues in breast cancer prevention. This systematic review summarizes published studies that measured local estrogen levels in the breast and offers suggestions for strategies to fill gaps in our existing scientific knowledge.

Testosterone and risk of breast cancer: appraisal of existing evidence

The objective of this review was to examine data from preclinical, clinical and epidemiological studies to evaluate if testosterone (T) poses increased risk of breast cancer in women. Appraisal of the existing literature produced several lines of evidence arguing against increased breast cancer risk with T. These include: (i) Data from breast tumor cell lines treated with androgens did not corroborate the notion that T increases breast cancer risk. On the contrary, androgens appear to be protective, as they inhibit tumor cell growth. (ii) Many of the epidemiological studies claiming an association between T and breast cancer did not adjust for estrogen levels. Studies adjusted for estrogen levels reported no association between T and breast cancer. (iii) Data from clinical studies with exogenous androgen treatment of women with endocrine and sexual disorders did not show any increase in incidence of breast cancer. (iv) Women afflicted with polycystic ovary disease, who exhibit high levels of androgens do not show increased risk of breast cancer compared to the general population. (v) Female to male transsexuals, who receive supraphysiological doses of T for long time periods prior to surgical procedures, do not report increased risk of breast cancer. (vi) Finally, women with hormone responsive primary breast cancer are treated with aromatase inhibitors, which block conversion of androgens to estrogens, thus elevating androgen levels. These women do not experience increased incidence of contralateral breast cancer nor do they experience increased tumor growth. In conclusion, the evidence available strongly suggests that T does not increase breast cancer risk in women.

American Society of Clinical Oncology/College of American Pathologists guideline recommendations for immunohistochemical testing of estrogen and progesterone receptors in breast cancer (unabridged version)

PURPOSE

To develop a guideline to improve the accuracy of immunohistochemical (IHC) estrogen receptor (ER) and progesterone receptor (PgR) testing in breast cancer and the utility of these receptors as predictive markers.

METHODS

The American Society of Clinical Oncology and the College of American Pathologists convened an international Expert Panel that conducted a systematic review and evaluation of the literature in partnership with Cancer Care Ontario and developed recommendations for optimal IHC ER/PgR testing performance.

RESULTS

Up to 20% of current IHC determinations of ER and PgR testing worldwide may be inaccurate (false negative or false positive). Most of the issues with testing have occurred because of variation in pre-analytic variables, thresholds for positivity, and interpretation criteria.

RECOMMENDATIONS

The Panel recommends that ER and PgR status be determined on all invasive breast cancers and breast cancer recurrences. A testing algorithm that relies on accurate, reproducible assay performance is proposed. Elements to reliably reduce assay variation are specified. It is recommended that ER and PgR assays be considered positive if there are at least 1% positive tumor nuclei in the sample on testing in the presence of expected reactivity of internal (normal epithelial elements) and external controls. The absence of benefit from endocrine therapy for women with ER-negative invasive breast cancers has been confirmed in large overviews of randomized clinical trials.

Aromatase immunoreactivity is increased in mammographically dense regions of the breast

Mammographic breast density (MBD) is one of the strongest risk factors for breast cancer. Unfortunately, the biologic basis underlying this association is unknown. This study compared aromatase expression or immunoreactivity (IR) in core biopsies from mammographically dense versus non-dense regions of the breast to examine whether estrogen synthesis in the breast is associated with MBD and one possible mechanism through which MBD may influence breast cancer. Eligible participants were 40+ years, had a screening mammogram with visible MBD and no prior cancer or current endocrine therapy. Mammograms were used to identify dense and non-dense regions and ultrasound-guided core biopsies were performed to obtain tissue from these regions. Immunostaining for aromatase employed the streptavidin-biotin amplification method and #677 mouse monoclonal antibody. Aromatase IR was scored in terms of extent and intensity of staining for each cell type (stroma, epithelium, adipocytes) on histologic sections. A modified histological H-score provided quantitation of aromatase IR in each cell type and overall. Repeated measure analyses evaluated average differences (β(H)) in H-score in dense versus non-dense tissue within and across cell types. Forty-nine women with mean age 50 years (range: 40-82), participated. Aromatase IR was increased in dense (vs. non-dense) tissue in both the stroma (β(H) = 0.58) and epithelium (β(H) = 0.12) (P < 0.01). Adipocytes from non-dense tissue, however, had a greater IR compared to those from dense tissue (β(H) = -0.24, P < 0.01). An overall H-score which integrated results from all cell types demonstrated that aromatase IR was twice as great for dense (mean H-score = 0.90, SD = 0.53) versus non-dense (mean H-score = 0.45, SD = 0.39) breast tissue (β(H) = 0.45; P < 0.001). Overall, aromatase IR was greater for mammographically dense versus non-dense tissue and may partly explain how MBD influences breast cancer.