Decreased TGFβ signaling and increased COX2 expression in high risk women with increased mammographic breast density

Abstract

High mammographic density is associated with a increased risk of breast cancer. We hypothesized that specific pathways exist that are associated with increased mammographic density, and may therefore be used to identify potential targets for chemoprevention. Histologically confirmed normal breast tissue was collected from women undergoing breast surgery who had available demographic data and mammograms for review. Women with low versus high mammographic breast density were compared. Differentially expressed genes using Affymetrix HG U133Plus2 chips were identified in dense versus non-dense tissue. Immunohistochemical analysis (IHC) of estrogen receptor, progesterone receptor, Ki67, and COX2 expression was performed. About 66 women were identified, 28 (42%) had high, and 38 (58%) had low mammographic density. About 73 genes had differential expression between normal breast tissue with high and low mammographic density (P < 0.001, fold change ≥1.5with a low false discovery rate (<10%). Network and canonical pathway analysis indicated decreased TGFβ signaling (TGFBR2, SOS, SMAD3, CD44 and TNFRSF11B) in dense breast tissue relative to non-dense breast. By IHC, only COX2 expression in the stroma was statistically significant on multivariate analysis. TGFβ ligands are currently the only growth factors known to prevent mammary epithelial cell proliferation. TGFβ signaling has been reported to be inhibited by COX-2, and these molecules are highly differentially expressed in individuals at high risk of developing breast cancer. These results strongly suggest that COX2 inhibition should be investigated for breast cancer prevention despite possible increase in cardiovascular risk.

Amount of stroma is associated with mammographic density and stromal expression of oestrogen receptor in normal breast tissues

“…In accordance with our results, Yang and colleagues found no significant association between stromal ER and PR and dense versus nondense breast tissues after univariate analysis of 66 patients undergoing mastectomy for breast cancer [16]. Pang and colleagues in contrast found a positive association between stromal PR expression and mammographic density in breast biopsies from 18 women at high risk of breast cancer, but not for any other stromal markers investigated [10].…”

“…Surprisingly, only two studies, with conflicting results, have investigated the expression of hormone receptors and proliferation in stromal cells in relation to mammographic density. Yang and colleagues found no association between stromal hormone receptors ER and PR and mammographic density [16], whereas Pang and colleagues found higher expression of stromal PR in mammographically dense breasts [10]. To the best of our knowledge, no study has investigated the expression of stromal hormone receptors in relation to distribution of breast tissue compartments.…”

Relationship of Mammographic Density and Gene Expression: Analysis of Normal Breast Tissue Surrounding Breast Cancer

“…This null result for epithelium may be attributed to lower variation in epithelial percentage across patients (interquartile range for percent composition was 4.4-13.2%) and random measurement error in our estimation of epithelial percentage, but our molecular data and the published literature underscore the importance of stroma in mammographic density (30-32). Few gene expression studies have emphasized stromal biology in mammographic density, but one study by Yang et al used canonical pathway analysis of MD-associated gene expression to identify decreased TGF-β signaling in dense breast tissue (33). Our findings confirmed this association by showing the strong association between TGF-β signature and adipose and stromal composition.…”

“…While a limited number (27, 33) of studies previously addressed genomic signatures of mammographic density, these studies identified very few density-associated genes (<100 genes), limiting their value in defining the biology of mammographic density. Weak associations with individual gene expression changes in previous studies may reflect low statistical power to detect a small differentially expressed signature (51, 52), but it is striking that such a strong breast cancer risk factor should produce such weak genomic expression, when other factors such as age and BMI have broad effects on normal tissue gene expression (20, 21).…”

Genetic Variation in Transforming Growth Factor Beta 1 and Mammographic Density in Singapore Chinese Women

“…TGF-β also plays a critical role in normal mammary development and morphogenesis with growth inhibitory properties (10, 11). Consistent with the anti-proliferative role of TGF-β in normal mammary tissue, decreased TGF-β signaling was shown to be associated with increased breast density in a microarray-based analysis of normal breast tissue of breast cancer patients (12). …”