A Women’s Health Initiative ancillary study concludes that estrogen-alone hormone therapy causes a sustained and modest increase in mammographic density in postmenopausal women, a risk factor for breast cancer. The results of the study were published online Nov. 10 in the Journal of Clinical Oncology.
"Increased mammographic density increases breast cancer risk and also makes interpreting mammograms more difficult. Therefore, it is important to identify factors that might elevate density levels," said lead author Dr. Anne McTiernan, an internist and epidemiologist in the Public Health Sciences Division’s Epidemiology Program who collaborated with other WHI researchers on the study.
The researchers assessed the impact of estrogen therapy over a two-year period in a random sample of 435 racially and ethnically diverse participants from 15 WHI clinics. They found the hormone use caused a 2.6 percent difference in mammographic density between the treatment and placebo groups. These effects were greatest in women age 70 to 79. They found density increases in both non-Hispanic white and African American women, but not in Hispanic participants.
Previous studies have found that breast cancer risk increases by about 15 percent with each 10 percent increase in density. An earlier WHI study found an even greater difference—6.9 percent—between women using combined hormone therapy (estrogen and progestin) versus placebo.
The Hutchinson Center houses the WHI Clinical Coordinating Center, which oversees the statistical, epidemiologic, nutritional and clinical aspects of the study and is responsible for data collection, management and analysis.
The National Heart, Lung and Blood Institute, the U.S. Department of Health and Human Services and Wyeth-Ayerst Research Laboratories funded the study.
McTiernan recently received the 2009 Roger Moe Award for Translational Research at the Current Concepts and Challenges in Breast Cancer conference sponsored by the Center, the Seattle Cancer Care Alliance and the University of Washington.