Different types of postmenopausal hormone therapy and mammographic density in Norwegian women

Biological Mechanisms and Therapeutic Opportunities in Mammographic Density and Breast Cancer Risk

Mammographic density is an important risk factor for breast cancer; women with extremely dense breasts have a four to six fold increased risk of breast cancer compared to women with mostly fatty breasts, when matched with age and body mass index. High mammographic density is characterised by high proportions of stroma, containing fibroblasts, collagen and immune cells that suggest a pro-tumour inflammatory microenvironment. However, the biological mechanisms that drive increased mammographic density and the associated increased risk of breast cancer are not yet understood. Inflammatory factors such as monocyte chemotactic protein 1, peroxidase enzymes, transforming growth factor beta, and tumour necrosis factor alpha have been implicated in breast development as well as breast cancer risk, and also influence functions of stromal fibroblasts. Here, the current knowledge and understanding of the underlying biological mechanisms that lead to high mammographic density and the associated increased risk of breast cancer are reviewed, with particular consideration to potential immune factors that may contribute to this process.

Age at Menarche and Late Adolescent Adiposity Associated with Mammographic Density on Processed Digital Mammograms in 24,840 Women

Background: High mammographic density is strongly associated with increased breast cancer risk. Some, but not all, risk factors for breast cancer are also associated with higher mammographic density.Methods: The study cohort (N = 24,840) was drawn from the Research Program in Genes, Environment and Health of Kaiser Permanente Northern California and included non-Hispanic white females ages 40 to 74 years with a full-field digital mammogram (FFDM). Percent density (PD) and dense area (DA) were measured by a radiological technologist using Cumulus. The association of age at menarche and late adolescent body mass index (BMI) with PD and DA were modeled using linear regression adjusted for confounders.Results: Age at menarche and late adolescent BMI were negatively correlated. Age at menarche was positively associated with PD (P value for trend <0.0001) and DA (P value for trend <0.0001) in fully adjusted models. Compared with the reference category of ages 12 to 13 years at menarche, menarche at age >16 years was associated with an increase in PD of 1.47% (95% CI, 0.69-2.25) and an increase in DA of 1.59 cm² (95% CI, 0.48-2.70). Late adolescent BMI was inversely associated with PD (P < 0.0001) and DA (P < 0.0001) in fully adjusted models.Conclusions: Age at menarche and late adolescent BMI are both associated with Cumulus measures of mammographic density on processed FFDM images.Impact: Age at menarche and late adolescent BMI may act through different pathways. The long-term effects of age at menarche on cancer risk may be mediated through factors besides mammographic density. Cancer Epidemiol Biomarkers Prev; 26(9); 1450-8. ©2017 AACR.

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.

Physical activity and mammographic density in a cohort of postmenopausal Norwegian women; a cross-sectional study

Mammographic density (MD) is a strong risk factor for breast cancer and may represent a useful intermediate marker for breast cancer risk. Physical activity (PA) is known to be associated with a reduced risk of breast cancer. If PA is associated with MD then this would be useful for breast cancer prevention studies. MD was assessed on digitized mammograms using a computer assisted method (Madena) in 2218 postmenopausal women. A questionnaire assessed PA, by asking about the duration and intensity of light, moderate, strenuous PA/week. We used multivariate linear regression models to estimate least square means of percent MD by total and intensity of PA with adjustment for confounders. The mean age (± s.d) was 58.4 (±5.3) and mean BMI was 24.6 (±4.6). We observed a statistically significant inverse association between total PA and MD in the over-weight (BMI = 25.0-29.9) women, where mean MD among women with highest activity (>360 mins/week) was 12.6% (95%CI; 11.2%-14.0%), while among women with no activity it was 15.9% (95 CI; 13.6%-18.2%, p for trend = 0.04). There was no association in the other BMI strata. MD was 12.1% (11.2%-13.0%) in the highest group (> 180 mins/week) of moderate/strenuous activity and in the no activity group 14.8% (14.2%-15.5%, p for trend = 0.001) in the over-weight women. There was no association between light PA and MD in all women combined or in any other BMI strata. We found some evidence of an inverse association between PA and MD among overweight women.

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.

Less mammographic density after nasal versus oral administration of postmenopausal hormone therapy

OBJECTIVE

Nasal administration gives a more acute but shorter rise in serum hormone levels than oral administration and may therefore have less effect on the fibroglandular tissue in the breasts. We studied the change in mammographic breast density after nasal vs. oral administration of postmenopausal hormone therapy (PHT).

METHODS

We studied participants in a randomized, controlled trial on the impact of nasal vs. oral administration of PHT (combined 17β-estradiol plus norethisterone) for 1 year. Two radiologists classified mammographic density at baseline and after 1 year into four categories. Also, the percentage density was calculated by a computer-based method. The main outcome measure was the difference in the proportion of women with an increase in mammographic density category after 1 year between the nasal and oral groups. Also, the change in the percentage density was calculated.

RESULTS

The study group comprised 112 healthy postmenopausal women (mean age 56 years), of whom 53 received oral and 59 intranasal PHT. An increase in mammographic density category after 1 year was seen in 20% of the women in the nasal group and in 34% of the oral group. This resulted in a non-significant difference in the proportion of women in whom mammographic breast density had increased by 214% (95% confidence interval (CI) 230% to 2.7%). The mean change in percentage density was 21.2% in the nasal group and + 1.2% in the oral group, yielding a 22.4% differential effect (95% CI 27.3% to 2.5%).

CONCLUSIONS

One year of nasal PHT gave a smaller, although not statistically significant, increase in mammographic density than oral PHT. Remaining issues are the relation between the route of administration of PHT and breast complaints and breast cancer risk.

Breast density changes associated with postmenopausal hormone therapy: post hoc radiologist- and computer-based analyses

OBJECTIVE

The aim of this study was to assess the impact of oral hormone therapy (HT) on breast density in postmenopausal women and to compare the use of computer-based automated approaches for the assessment of breast density with reference to traditional methods.

METHODS

Low-dose oral estrogen (1 mg) continuously combined with drospirenone (2 mg) was administered to postmenopausal women for up to 2 years (26 treatment cycles, 28 d/cycle) in a randomized, placebo-controlled trial. This post hoc analysis assessed the changes in breast density measured from digitized images by two radiologist-based approaches (Breast Imaging Reporting and Data System score and interactive threshold) and one computer-based technique (heterogeneity examination of radiographs). Correlations of temporal changes in breast density with changes in serum estradiol levels, biochemical markers of bone metabolism, and bone mineral density at the spine and femur were also assessed.

RESULTS

Breast density assessed by the radiologist-based approaches increased significantly from baseline in the HT group (P < 0.01), with significant divergence from placebo at 2 years (P < 0.01). Heterogeneity examination of radiograph score by computer-based technique was unchanged in the HT group and decreased significantly with placebo (P < 0.001) to produce a significant group divergence (P < 0.05). Changes in mammographic markers by radiologist- and computer-based approaches correlated with each other in the HT group (P < 0.01) but not in the placebo group.

CONCLUSIONS

HT for 2 years in postmenopausal women significantly increased radiologist-assessed breast density compared with placebo, in addition to significant changes in estrogen levels, markers of bone metabolism, and bone mineral density. Computer-automated techniques may be comparable with and offer advantages over traditional methods.

Decrease in breast density in the contralateral normal breast of patients receiving neoadjuvant chemotherapy: MR imaging evaluation

PURPOSE

To investigate the change of breast density with quantitative magnetic resonance (MR) imaging in the contralateral normal breast of patients receiving neoadjuvant chemotherapy.

MATERIALS AND METHODS

This study was approved by the institutional review board and was HIPAA compliant. Informed consent was obtained. Fifty-four patients with breast cancer (mean age, 47 years; age range, 30-74 years) treated with NAC protocol and enrolled in a breast MR imaging research study were studied. The density in the contralateral normal breast was analyzed by using an MR imaging-based segmentation method. The effect of chemotherapy on the change of density following the doxorubicin and cyclophosphamide (AC) and the AC and taxane regimen was evaluated. The dependence on age was investigated by using a multivariate regression model.

RESULTS

In patients who underwent both AC and taxane follow-up, the mean percentage of change from the individual's baseline density was -10% (95% confidence interval: -12.8%, -7.2%) after AC and -12.7% (95% confidence interval: -16%, -9.4%) after AC and taxane. In patients who underwent both follow-up studies after one to two and four cycles of AC, the mean percentage of change was -9.4% (95% confidence interval: -13.5%, -5.3%) after one to two cycles of AC and -14.7% (95% confidence interval: -20.6%, -8.7%) after four cycles of AC. The percentage reduction of density was significantly dependent on age. Patients younger than 40 years had a greater reduction after chemotherapy than patients older than 55 years (P = .01).

CONCLUSION

By using three-dimensional MR imaging, patients receiving chemotherapy showed reduction of breast density, and the effects were significant after initial treatment with one to two cycles of the AC regimen.

Genotypes and haplotypes in the insulin-like growth factors, their receptors and binding proteins in relation to plasma metabolic levels and mammographic density

BACKGROUND

Increased mammographic density is one of the strongest independent risk factors for breast cancer. It is believed that one third of breast cancers are derived from breasts with more than 50% density. Mammographic density is affected by age, BMI, parity, and genetic predisposition. It is also greatly influenced by hormonal and growth factor changes in a woman's life cycle, spanning from puberty through adult to menopause. Genetic variations in genes coding for hormones and growth factors involved in development of the breast are therefore of great interest. The associations between genetic polymorphisms in genes from the IGF pathway on mammographic density and circulating levels of IGF1, its binding protein IGFBP3, and their ratio in postmenopausal women are reported here.

METHODS

Samples from 964 postmenopausal Norwegian women aged 55-71 years were collected as a part of the Tromsø Mammography and Breast Cancer Study. All samples were genotyped for 25 SNPs in IGF1, IGF2, IGF1R, IGF2R, IGFALS and IGFBP3 using Taqman (ABI). The main statistical analyses were conducted with the PROC HAPLOTYPE procedure within SAS/GENETICS (SAS 9.1.3).

RESULTS

The haplotype analysis revealed six haploblocks within the studied genes. Of those, four had significant associations with circulating levels of IGF1 or IGFBP3 and/or mammographic density. One haplotype variant in the IGF1 gene was found to be associated with mammographic density. Within the IGF2 gene one haplotype variant was associated with levels of both IGF1 and IGFBP3. Two haplotype variants in the IGF2R were associated with the level of IGF1. Both variants of the IGFBP3 haplotype were associated with the IGFBP3 level and indicate regulation in cis.

CONCLUSION

Polymorphisms within the IGF1 gene and related genes were associated with plasma levels of IGF1, IGFBP3 and mammographic density in this study of postmenopausal women.

Exogenous and endogenous hormones, mammographic density and breast cancer risk: can mammographic density be considered an intermediate marker of risk?

Elevated mammographic density measures are a well-established, relatively strong risk factor for breast cancer development. A systematic review of prospective cohort studies and cross-sectional studies strikingly establishes parallels between the associations of combined postmenopausal estrogen and progestin replacement therapy with, on the one hand, mammographic densities and, on the other hand, breast cancer risk. Other parallel observations were the inverse associations of both mammographic density and breast cancer risk with the selective estrogen receptor modulator tamoxifen, and direct associations with prolactin. Paradoxically, however, high mammographic density has been found associated with higher risks of both estrogen- and progesterone-receptor positive (ER+/ PR+) and negative (ER-/PR-) breast cancers, while hormone replacement therapy (HRT) use, but also circulating (blood) levels of androgens, estrogens, and prolactin appear to be associated more specifically to the risk of ER+ tumors. The effects of aromatase inhibitors and gonadotropin-releasing hormone agonists on breast density, as well as on breast cancer risk, still require further investigation. Regarding circulating levels of insulin-like growth factor (IGF)-I or IGFBP-3, studies did not show fully consistent relationships with mammographic density measures and breast cancer risk. In view of these various findings, it is impossible, at present, to propose mammographic density measures as an intermediate risk-related phenotype, integrating the effects of exogenous and/or endogenous hormones on the risk of developing breast cancer.

Breast cancer susceptibility loci and mammographic density

Introduction

Recently, the Breast Cancer Association Consortium (BCAC) conducted a multi-stage genome-wide association study and identified 11 single nucleotide polymorphisms (SNPs) associated with breast cancer risk. Given the high degree of heritability of mammographic density and its strong association with breast cancer, it was hypothesised that breast cancer susceptibility loci may also be associated with breast density and provide insight into the biology of breast density and how it influences breast cancer risk.

Methods

We conducted an analysis in the Nurses' Health Study (n = 1121) to assess the relation between 11 breast cancer susceptibility loci and mammographic density. At the time of their mammogram, 217 women were premenopausal and 904 women were postmenopausal. We used generalised linear models adjusted for covariates to determine the mean percentage of breast density according to genotype.

Results

Overall, no association between the 11 breast cancer susceptibility loci and mammographic density was seen. Among the premenopausal women, three SNPs (rs12443621 [TNRc9/LOC643714], rs3817198 [lymphocyte-specific protein-1] and rs4666451) were marginally associated with mammographic density (p < 0.10). All three of these SNPs showed an association that was consistent with the direction in which these alleles influence breast cancer risk. The difference in mean percentage mammographic density comparing homozygous wildtypes to homozygous variants ranged from 6.3 to 8.0%. None of the 11 breast cancer loci were associated with postmenopausal breast density.

Conclusion

Overall, breast cancer susceptibility loci identified through a genome-wide association study do not appear to be associated with breast cancer risk.

Rationale for low-dose systemic hormone replacement therapy and review of estradiol 0.5 mg/NETA 0.1 mg

The menopausal transition is associated with several symptoms, for which both non-pharmacological and pharmacological measures are available to provide relief. However, present knowledge indicates that the former is not highly effective, and that the latter, in terms of systemic oestrogen and progestogen-based hormone replacement therapy (HRT), although being effective (e.g. on vasomotor symptoms, bleeding control, bone mineral density, vaginal atrophy and quality of life), can be associated with some caveats. Amongst these are an increased risk for coronary heart disease, breast cancer, venous thromboembolism and stroke. In recent years, literature has indicated a dose dependency for HRT on some of the caveats, hence authorities (Food and Drug Administration, and the European Medicines Agency) and menopause societies (International Menopause Society and North American Menopause Society) now recommend that women deemed in need of HRT should receive the lowest possible dose without compromising the effect of symptom relief. Estradiol 0.5 mg/norethisterone acetate (NETA) 0.1 mg, despite being a lower dose than conventional hormones, is a compound, among a few other low-dose options, that can be used in such therapy. As a first-line oral option, it has demonstrated its effectiveness (which seems comparable to other compounds), with high tolerability and, apparently, no safety concerns, in a 6-month study. Further long-term clinical trials and observational studies are mandatory in order to capture any potential harm as well as to elucidate this compound's full potential. Following a thorough literature search using PubMed and MEDLINE from the earliest publication dates through to January 2008, including results from various types of clinical trials and statements on HRT, we review the rationale for these recommendations. We also review the effects and safety of a novel 'ultra-low-dose' oral continuous combined HRT tablet, estradiol 0.5 mg/NETA 0.1 mg.

Different measures of smoking exposure and mammographic density in postmenopausal Norwegian women: a cross-sectional study

Background

Recent cohort studies have suggested an increased risk of breast cancer with long duration of smoking, and with smoking initiation before first birth. Cigarette smoking may have both carcinogenic effects and antiestrogenic effects on the breast tissue. We decided to examine the relationship between different measures of smoking exposure and mammographic density.

Methods

Lifetime smoking history was collected through interview and questionnaires among 907 postmenopausal participants in the Tromsø Mammography and Breast Cancer study. The mammograms were obtained from the governmental Norwegian Breast Cancer Screening Program. Mammograms were classified according to the percentage and absolute mammographic densities using a previously validated computer-assisted method.

Results

Sixty-five percent of the women reported having ever smoked cigarettes, while 34% were current smokers. After adjustment for age, age at first birth, parity, age at menopause, postmenopausal hormone therapy use, and body mass index, smoking was inversely associated with both measures of mammographic density (both trends P < 0.01). Both current smokers and former smokers had significantly lower adjusted mean percentage mammographic density compared with never smokers (P = 0.003 and P = 0.006, respectively). An inverse dose–response relationship with mammographic density was found between both the number of cigarettes and the number of pack-years smoked among current smokers. Current smokers who smoked 11 cigarettes or more daily had a 3.7% absolute (36% relative difference) lower percentage mammographic density compared with current smokers who smoked seven cigarettes or less daily (P = 0.008). When former smokers were stratified according to time since smoking cessation, we found that women who had stopped smoking less than 24 years ago had a significantly lower mean percentage mammographic density compared with never smokers (P < 0.001).

Conclusion

We found modest inverse dose–response associations between numbers of cigarettes and of pack-years smoked and both measures of mammographic density among current smokers. Former smokers who had stopped smoking less than 24 years ago also had a statistically significantly lower mean percentage mammographic density when compared with never smokers. These findings are consistent with an antiestrogenic effect of cigarette smoking on the breast tissue.

Endogenous sex hormones, prolactin and mammographic density in postmenopausal Norwegian women

The associations between endogenous sex hormone levels and breast cancer risk in postmenopausal women are well established. Mammographic density is a strong risk factor for breast cancer, and possibly an intermediate marker. However, the results from studies on the associations between endogenous sex hormones and mammographic density are conflicting. The authors examined the associations between circulating levels of sex hormones, sex hormone binding globulin (SHBG) and prolactin and mammographic densities among postmenopausal women not currently using postmenopausal hormone therapy (HT). The authors also examined if insulin-like growth factor-I (IGF-I) levels influenced the association between estrogen and mammographic density. Altogether, 722 postmenopausal participants in the Norwegian governmental mammographic screening program had endogenous hormone concentrations measured. Mammograms were classified according to percent and absolute mammographic density using a previously validated computer-assisted method. After adjustment for age, number of children, age at menopause, body mass index and HT use, both plasma concentrations of SHBG (p-trend = 0.003) and estrone (p-trend = 0.07) were positively associated with percent mammographic density. When the analyses were stratified according to median IGF-I concentration, the weak association between estrone and mammographic density was strengthened among women with IGF-I levels below median, while the association disappeared among women with over median IGF-I levels (p for interaction = 0.02). In summary, the authors found a positive association between plasma SHBG levels and mammographic densities among 722 postmenopausal Norwegian women not currently using HT. Further, the authors found a positive but weak association between plasma estrone concentration and mammographic density, which appeared to be modified by IGF-I levels.

Insulin-like growth factor and mammographic density in postmenopausal Norwegian women

Insulin-like growth factor-I (IGF-I) is associated with breast cancer risk among premenopausal women but rarely among postmenopausal women. Recent data from two European studies suggested an increased risk of breast cancer with increasing levels of IGF-I among women >50 years old or among postmenopausal hormone therapy users >or=55 years old. Mammographic density is one of the strongest risk factors, and possibly an intermediate marker, for breast cancer. We examined the relationship between IGF and mammographic density among postmenopausal women overall and according to hormone therapy use. Altogether, 977 postmenopausal participants in the Norwegian governmental mammographic screening program had IGF concentrations measured by ELISA. Mammograms were classified according to percent and absolute mammographic densities using a previously validated computer-assisted method. After adjustment for age, number of children, age at menopause, body mass index, and hormone therapy use, both plasma IGF-I concentration (P(trend) = 0.02) and IGF-I/IGF binding protein 3 ratio (P(trend) = 0.02) were positively associated with percent mammographic density. The magnitudes of differences in percent mammographic density between women in the lowest and highest quartiles of IGF-I concentrations were 1.5% absolute difference and 21% relative difference. These associations were similar with absolute mammographic density as the outcome variable. When the analyses were stratified according to hormone therapy use, the associations between IGF-I and mammographic density were significant among noncurrent users (P(trend) = 0.03). In conclusion, we found a positive but weak association between plasma IGF-I concentrations and both percent and absolute mammographic densities among postmenopausal women. These associations were found among noncurrent hormone therapy users but not among current users.