ScienceDaily (Feb. 27, 2008) — Combined hormone therapy appears to increase the risk that women will have abnormal mammograms and breast biopsies and may decrease the effectiveness of both methods for detecting breast cancer, according to a new report.

Hormone therapy use remains common among women beginning menopause, according to background information in the article. "For women with a uterus considering combined estrogen plus progestin use, identified breast cancer issues represent a concern," the authors write.

Rowan T. Chlebowski, M.D., Ph.D., of the Los Angeles Biomedical Research Institute at Harbor--UCLA Medical Center, and colleagues studied 16,608 post-menopausal women who participated in the Women's Health Initiative (WHI) clinical trial, beginning in 1993 through 1998. A total of 8,506 women were randomly assigned to receive a combination of estrogen (0.625 milligrams of conjugated equine estrogens per day) plus progesterone (2.5 milligrams of medroxyprogesterone acetate per day), while 8,102 took a placebo. Each woman received a mammogram and breast examination yearly, with biopsies performed based on physicians' clinical judgment.

During the 5.6 years of the study, 199 women in the combined hormone group and 150 women in the placebo group developed breast cancer. Mammograms with abnormal results were more common among women taking hormones than among women taking placebo (35 percent vs. 23 percent); women taking hormones had a 4 percent greater risk of having a mammogram with abnormalities after one year and an 11 percent greater risk after five years.

Breast biopsies also were more common among women taking hormones than among those assigned to placebo (10 percent vs. 6.1 percent). "Although breast cancers were significantly increased and were diagnosed at higher stages in the combined hormone group, biopsies in that group less frequently diagnosed cancer (14.8 percent vs. 19.6 percent)," the authors write.

"After discontinuation of combined hormone therapy, its adverse effect on mammograms modulated but remained significantly different from that of placebo for at least 12 months," they continue.

Use of combined hormones increases breast density, which increases the risk of breast cancer and may also delay diagnosis, the authors note. However, breast density was not measured in the current study.

"Use of conjugated equine estrogens plus medroxyprogesterone acetate for approximately five years resulted in more than one in 10 and one in 25 women having otherwise avoidable mammogram abnormalities and breast biopsies, respectively, and compromised the diagnostic performance of both," the authors conclude. "This adverse effect on breast cancer detection should be incorporated into risk-benefit discussions with women considering even short-term combined hormone therapy."

Journal reference: Arch Intern Med. 2008;168[4]:370-377.

The WHI program is funded by the National Heart, Lung, and Blood Institute, U.S. Department of Health and Human Services.

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Adapted from materials provided by JAMA and Archives Journals.

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