For many years, breast density - the
ratio of fatty or non-dense cells to connective or dense tissue in the breast - has been known to be a risk factor for breast cancer. Women with greater than 50 percent dense tissue are at a two- to six-fold increased risk compared with women who have low-density breasts.
Karthik Ghosh is a breast cancer researcher and physician at the Mayo Clinic. Ghosh and colleagues wanted to understand why women with denser breasts were at greater risk, so they examined the breast tissue of healthy women.
"That would help us understand what normal dense and non-dense tissue is and thus have some understanding of not only the tissue on the cellular level, but also on the molecular level," she says.
Among the preliminary findings: women with dense breasts have a greater proportion of epithelium, that is, tissue composed of cells that line the milk and duct glands. There is also more stroma or fibrous tissue that serves as a base for the epithelium.
"That is the place where finally cancer arises," Ghosh says, adding that there are also "certain [biological] markers that the stroma produces that ultimately leads to an increased risk down the line, which is why the change occurs."
Ghosh says among the biological markers in the dense tissues is aromatase, an enzyme that converts hormones in the breast to estrogen.
"What this means is that perhaps this change may be contributing to a greater amount of estrogen production itself within dense tissue, and that potentially could be a reason for the increased risk for women with dense breasts."
Estrogen, a primary female sex hormone, has been linked to breast cancer development. Ghosh says while these are preliminary findings, the healthy breast tissue data provides a valuable baseline for further studies.
Ghosh and colleagues presented their work at the recent Breast Cancer Symposium in San Antonio, Texas.