Mammographic density is related to stroma and stromal proteoglycan expression

Breast cancer risk in the WHI study: The problem of obesity

In the climacteric, about 40% of the women have occult breast tumors the growth of which may be stimulated by hormones. Many genetic, reproductive and lifestyle factors may influence the incidence of breast cancer. Epidemiological data suggest that the increase in the relative risk (RR) of breast cancer induced by hormone replacement therapy (HRT) is comparable with that associated with early menarche, late menopause, late first birth, alcohol consumption, etc. One of the most important risk factors is obesity which exceeds the effect of HRT by far, and in overweight postmenopausal women the elevated risk of breast cancer is not further increased by HRT. As in the WHI study the majority of women was overweight or obese, this trial was unsuitable for the investigation of breast cancer risk. In the women treated with an estrogen/progestin combination, the RR of breast cancer rose only in those women who have been treated with hormones prior to the study, suggesting a selection bias. In the women not pretreated with hormones, it was not elevated. In the estrogen-only arm of the WHI study, there was no increase but a steady decrease in the RR of breast cancer during 6.8 years of estrogen therapy. This result was unexpected, as estrogens are known to facilitate the development and growth of breast tumors, and the effect is enhanced by the addition of progestins. Obese women are at high risk to develop a metabolic syndrome including insulin resistance and hyperinsulinemia. In postmenopausal women, elevated insulin levels are not only associated with an increased risk for cardiovascular disease, but also for breast cancer. This might explain the effects observed in both arms of the WHI study: HRT with relative low doses of estrogens may improve insulin resistance and, hence, reduce the elevated breast cancer risk in obese patients, whereas this beneficial estrogen effect may be antagonized by progestins. The principal options for the reduction of breast cancer risk in postmenopausal women are the prevention of overweight and obesity to avoid the development of hyperinsulinemia, the medical treatment of insulin resistance, the use of low doses of estrogens and the reduction of exposure to progestins. The latter might include long-cycles with the sequential use of appropriate progestins every 3 months for 14 days. There are large inter-individual variations in the proliferative response to estrogens of the endometrium. Control by vaginalsonography and progestin challenge tests may help to identify those women who may be candidates for low-dose estrogen-only therapy.

Association between mammographic breast density and breast cancer tumor characteristics

OBJECTIVE

Few studies have examined the association between breast density and breast cancer tumor characteristics. We examined the association between hormonal, proliferative, and histologic tumor characteristics and mammographic breast density in women with breast cancer.

METHODS

We conducted a cross-sectional analysis in 546 women diagnosed with invasive breast cancer to evaluate the associations between breast density and tumor size, lymph node status, lymphatic or vascular invasion, histologic grade, nuclear grade, tumor differentiation, mitotic index, tumor necrosis, Ki-67 proliferation, estrogen receptor, progesterone receptor, p53, p27, cyclin E, Bcl-2, and C-erb-B2 invasion. Breast density was classified as fatty (Breast Imaging Reporting and Data System code 1 or 2; n = 373) or dense (Breast Imaging Reporting and Data System code 3 or 4; n = 173) for the cancer-free breast. A single pathologist measured all tumor markers. We examined whether the relationships were modified by interval cancer or screen-detected cancer.

RESULTS

Women with a tumor size >1.0 cm were more likely to have dense breasts compared with women with a tumor size < or =1.0 cm after adjusting for confounders (odds ratio, 2.0; 95% confidence interval, 1.2-3.4 for tumor sizes 1.1-2.0 cm; odds ratio, 2.3; 95% confidence interval, 1.3-4.4 for tumor sizes 2.1-10 cm). Tumor size, lymph node status, and lymphatic or vascular invasion were positively associated with breast density among screen-detected cancers. Histologic grade and mitotic index were negatively associated with breast density in women diagnosed with an interval cancer.

CONCLUSIONS

These results suggest that breast density is related to tumor size, lymph node status, and lymphatic or vascular invasion in screen-detected cancers. Additional studies are needed to address whether these associations are due to density masking the detection of some tumors, a biological relationship, or both.

A visual-quantitative analysis of fibroblastic stromagenesis in breast cancer progression

One fundamental difference between normal and transformed cells is the way they interact with their immediate environment. Exploring this difference is crucial for understanding the pathobiology of cancer progression. Benign epithelial tumors are constrained by a surrounding stroma consisting, among other cells, of fibroblasts embedded within fibrillar three-dimensional matrices. However, at a critical point in tumor progression, tumor cells become altered and overcome the barrier, inducing changes in the stroma, which promote, rather than impede, tumor progression. Inherited or acquired genetic aberrations affecting mammary gland epithelia are usually blamed for promoting neoplasia in individuals at "high risk" for breast cancer. However, in addition to these epithelial aberrations certain individuals possess permissive breast stroma. The occurrence of this permissive stroma results in a predisposition for cancer initiation or progression. Here we review stromagenic stages, experimental 3D systems, and discuss digital imaging analyses suitable for uncovering the mechanisms behind fibroblastic breast stromagenesis.

The tension mounts: mechanics meets morphogenesis and malignancy

The tissue microenvironment regulates mammary gland development and tissue homeostasis through soluble, insoluble and cellular cues that operate within the three dimensional architecture of the gland. Disruption of these critical cues and loss of tissue architecture characterize breast tumors. The developing and lactating mammary gland are also subject to a plethora of tensional forces that shape the morphology of the gland and orchestrate its functionally differentiated state. Moreover, malignant transformation of the breast is associated with dramatic changes in gland tension that include elevated compression forces, high tensional resistance stresses and increased extracellular matrix stiffness. Chronically increased mammary gland tension may influence tumor growth, perturb tissue morphogenesis, facilitate tumor invasion, and alter tumor survival and treatment responsiveness. Because mammary tissue differentiation is compromised by high mechanical force and transformed cells exhibit altered mechanoresponsiveness, malignant transformation of the breast may be functionally linked to perturbed tensional-homeostasis. Accordingly, it will be important to define the role of tensional force in mammary gland development and tumorigenesis. Additionally, it will be critical to identify the key molecular elements regulating tensional-homeostasis of the mammary gland and thereafter to characterize their associated mechanotransduction pathways.

Experimental manipulation of radiographic density in mouse mammary gland

INTRODUCTION

Extensive mammographic density in women is associated with increased risk for breast cancer. Mouse models provide a powerful approach to the study of human diseases, but there is currently no model that is suited to the study of mammographic density.

METHODS

We performed individual manipulations of the stromal, epithelial and matrix components of the mouse mammary gland and examined the alterations using in vivo and ex vivo radiology, whole mount staining and histology.

RESULTS

Areas of density were generated that resembled densities in mammographic images of the human breast, and the nature of the imposed changes was confirmed at the cellular level. Furthermore, two genetic models, one deficient in epithelial structure (Pten conditional tissue specific knockout) and one with hyperplastic epithelium and mammary tumors (MMTV-PyMT), were used to examine radiographic density.

CONCLUSION

Our data show the feasibility of altering and imaging mouse mammary gland radiographic density by experimental and genetic means, providing the first step toward modelling the biological processes that are responsible for mammographic density in the mouse.

Can the stroma provide the clue to the cellular basis for mammographic density?

Mammographic density is recognised as a useful phenotypic biomarker of breast cancer risk. Deeper understanding is needed of the cellular basis, but evidence is limited because of difficulty in designing studies to validate hypotheses. The ductal epithelial components do not adequately explain the physical and dynamic features observed. The stroma is thought to interact with ductal structures in cancer initiation. Stromal tissues might account for the mammographic features, and this interplay can be hypothesised to relate risk to density. In a paper in this issue of Breast Cancer Research, Alowami has shown a relationship between density and stromal proteins, which might provide useful insight into mammographic density.