MEDICATIONS: BREAST DENSITY CHANGES AS HORMONE REPLACEMENT THERAPY STARTS AND STOPS

Increases in breast density associated with HRT are potentially reversible when therapy ends

January 10, 2001 —: Changes in breast density associated with hormone replacement therapy are dynamic, increasing with initiation and decreasing when therapy is discontinued, according to an article in the January 10, 2001, issue of The Journal of the American Medical Association. Carolyn M. Rutter, Ph.D., and colleagues with Group Health Cooperative of Puget Sound and the University of Washington in Seattle, examined the effects of initiation, discontinuation, and continued use of hormone replacement therapy (HRT) on breast density in postmenopausal women. They studied 5,212 naturally postmenopausal women between the ages 40 to 96 who were enrolled in a large health maintenance organization in western Washington State. Each of the women had two screening mammograms between 1996 and 1998. According to background information cited in the study, initiation of HRT has been shown to increase breast density. Increased density reduces the accuracy of screening mammography. HRT has been directly associated with decreases in both sensitivity and specificity of mammography, which is likely a result of corresponding increases in density. Studies also have associated increased density with increased risk of breast cancer. Although the effect of initiating HRT on breast density has been well studied, the effects of continuing and discontinuing HRT have not been systematically examined.

The authors defined HRT to include estrogens alone and estrogens in combination with a progestin, delivered orally or by a patch. They compared breast density among women who were divided into groups based on patterns of HRT use:

· Nonusers were those who did not use HRT before either mammogram.

· Discontinuers were those who used HRT before their first mammogram, but not before their second mammogram.

· Initiators were those who did not use HRT before their first mammogram, but began using HRT before their second mammogram.

· Continuing users were those who used HRT prior to both mammograms.

"Our findings suggest that in some women, HRT increases breast density but these increases are potentially reversible with cessation of HRT," the authors report.

"Relative to nonusers, women who initiated HRT were more likely to show increases in breast density [2.57 times more likely] while women who discontinued HRT use were more likely to show decreases in density [1.81 times more likely] and women who continued to use HRT were more likely to show both increases in density [1.33 times more likely] and sustained high density [1.45 times more likely]," they write. The authors point out that their analyses provide important new information about women who discontinue HRT use and women who are continuing users. "Discontinuation of HRT was associated with subsequent decreases in density, and increases in breast density were sustained by continued HRT use," they write. The authors report their findings also suggest the probability of experiencing an increase in density following HRT initiation, or sustained high density following continued HRT use, may be affected by age. The authors believe the study results have important implications for breast cancer screening. "Increased density adversely affects the accuracy of screening mammography and is a strong, if not the strongest, risk factor for cancer missed at screening," they write. "Hormone replacement therapy is associated with decreases in both the sensitivity and specificity of mammography. Observed decreases in mammographic accuracy among women using HRT are a likely result of corresponding increases in density."