Dense breast tissue displays elevated aromatase expression

MedWire News: Researchers have found that dense breast tissue in healthy women contains more stromal cells and displays greater aromatase enzyme expression, but reduced lobular involution compared with non-dense tissue.

The findings may provide a clue as to why increased breast density is such a major risk factor for the development of breast cancer, suggest the researchers who note that this is the first study to examine both dense and non-dense tissue taken from the same breast in healthy volunteers.

Karthik Ghosh (Mayo Clinic, Rochester, Minnesota) and colleagues recruited 60 women, aged between 40 and 85 years, with no personal history of breast cancer and took eight core-needle biopsies from various parts of their breasts.

They examined the biopsies to determine the percentage of epithelium tissue, stroma, and fat content in each. Ghosh and team explain that the epithelium is primarily composed of milk glands and ductal cells, and stroma is the connective tissue that supports epithelial cells.

They found that areas of density contained much more epithelium (6%) and stroma (64%) and much less fat (30%), compared with non-dense tissue, which contained less than 1% epithelium, about 20% stroma, and almost 80% fat.

"This shows us that both the epithelium and stroma contribute to density, and suggests that the large difference in stroma content in dense breast tissue may play a significant role in breast cancer risk," Ghosh said.

In addition the researchers also looked for the presence of lobular involution – a decrease in the size and number of milk ducts that has been associated with decreased breast cancer risk. They found that 35% of dense tissue had complete involution compared with 85% of non-dense tissue.

Lastly, Ghosh and team performed molecular analysis on the samples, which revealed that dense breast tissue had significantly greater intensity of aromatase expression than non-dense tissue.

Noting that aromatase helps convert androgen hormones into estrogen, which is key to driving breast cancer development, study co-author Celine Vachon (Mayo Clinic) commented: “If aromatase is differentially expressed in dense and non-dense breast tissue, this could provide one mechanism by which density may increase breast cancer risk.”