UCLA researchers report that women on combination hormone therapy tend to have somewhat denser breast tissue, but they do not necessarily link that to a greater risk of breast cancer.

The researchers, reporting in the Journal of the National Cancer Institute, obtained baseline and 12-month mammograms of 571 women, aged 45 to 64, and reported that women taking a combination of estrogen and progestin appeared to have 3 to 5 percent denser tissue than women taking estrogen alone or no hormone.

However, despite some studies suggesting that mammographic density is a risk factor for breast cancer, lead researchers Dr. Gail Greendale emphased that "there are no data that prove that an increase in mammographic density equates to an increase in breast cancer risk."

In an editorial in the same journal, Dr. Rowan Chlebowski of the Harbor-UCLA Research and Education Institute and Dr. Anne McTiernan of the Fred Hutchinson Cancer Research Center in Seattle note that the hormones appear to increase the density of the tissue by a relatively small amount.

"The authors themselves raise the most critical question -- what is the link between such changes in breast density in women receiving postmenopausal hormone therapy and subsequent changes in breast cancer risk?" Chlebowski and McTiernan ask.

Other sources: Journal of the National Cancer Institute