Hormone Therapy Associated With Increased Breast Density

A new study suggests that the use of combination hormone therapy is associated with a modest increase in breast density, which is a known risk factor for breast cancer. The findings appear in the Jan. 1 issue of the Journal of the National Cancer Institute.

The degree of breast-cancer risk that is associated with breast density is greater than that associated with almost all other known breast-cancer risk factors. A previous analysis of data from the Postmenopausal Estrogen/Progestin Interventions (PEPI) Trial, a randomized trial looking at the effects of postmenopausal hormone therapy (estrogen alone or estrogen plus three different progestin regimens) on breast density, showed that some women who used combination estrogen/progestin therapy experienced an increase in breast density. However, the analysis did not look at the magnitude of that increase. Past studies suggest that the greater the breast density, the greater the risk for breast cancer.

Researchers from UCLA, the University of Southern California and Wake Forest University examined digitized mammograms at baseline and after one year of therapy from 571 postmenopausal women enrolled in the PEPI trial who were randomly assigned to receive daily doses of estrogen alone, estrogen plus cyclic medroxyprogesterone acetate, estrogen plus continuous medroxyprogesterone acetate, estrogen plus micronized progesterone, or a placebo.

“We found that the use of estrogen/progestin combination therapy, regardless of how the progestin was given, was associated with a 3 percent to 5 percent increase in breast density,” said Dr. Gail A. Greendale, professor of medicine and obstetrics and gynecology at the David Geffen School of Medicine at UCLA, research director for the Iris Cantor-UCLA Women’s Health Center, and a researcher at UCLA’s Jonsson Cancer Center. “The use of estrogen alone was not associated with significant increases in breast density” she said.

The authors conclude that the use of combination hormone therapy, but not the use of estrogen alone, is associated with increases in breast density. “However, the link between change in breast density resulting from hormone use and change in breast-cancer risk remains uncertain,” they say.

In addition to Greendale, lead author of “Postmenopausal Hormone Therapy and Change in Mammographic Density,” other participating researchers included Dr. Beth Reboussin, Carol Wailauskas and Stacey Slone from the Department of Public Health Services at Wake Forest University School of Medicine; and Dr. Malcolm C. Pike and Dr. Giske Ursin in the Department of Preventive Medicine/Norris Comprehensive Cancer Center at the University of Southern California.