Mammographic density and histopathologic markers: An example of using tissue microarrays in breast cancer research

Background: Mammographic density is a strong predictor of breast cancer risk, yet the underlying cellular basis is not clear. This study examined the association of mammographic density with the expression of hormonal and proliferation markers in epithelium and of matrix metalloproteinases (MMPs) and their inhibitors (TIMP) in stromal tissue of breast cancer cases using tissue microarrays (TMAs). Methods: We recruited breast cancer cases from a nested case-control study within the Multiethnic Cohort in Hawaii and obtained paraffin-embedded pathologic blocks through the tumor registry. For 279 participants, TMAs with up to 4 malignant and 4 benign cores were prepared and immunostained for estrogen receptor alpha (ERα) and beta (ERβ), progesterone receptor (PR), HER2/neu, Ki-67, PCNA, MMPs 1, 3, 9, and 12, and TIMP3 using standard methods and evaluated by qualitative and quantitative techniques. Mammographic density was assessed on digitized prediagnostic mammograms using a computer-assisted method. General linear models adjusted for known confounders were applied to estimate mean densities by staining category. Results: For 277 breast cancer cases, at least one core could be evaluated, but benign cores were only available for 159 women. Expression of most markers was more frequent in malignant than in benign tissue, while TIMP3 expression was higher in benign stromal than malignant tissue. None of the markers showed a statistically significant association with breast density in the entire study population. However, women with positive PR, ERß, Ki-67, and PCNA staining had 2–4% higher percent density than those with no staining and mean density was consistently lower with more extensive TIMP3 expression. Conclusions: Given the suggestive findings, future studies examining hormonal effects, cell proliferation, proteases and their inhibitors, and additional pathways, e.g., inflammation, are needed to elucidate histopathologic correlates of breast density. This study suggests several important points on how to optimize the use of TMAs in epidemiologic research.