Hormone therapy increases frequency of abnormal mammograms, breast biopsies

Combined hormone therapy appears to increase the risk that women will have abnormal mammograms and breast biopsies, and it may decrease the effectiveness of both methods for detecting breast cancer, according to a report in the Feb. 25 issue of Archives of Internal Medicine.

Rowan T. Chlebowski, M.D., Ph.D., a lead investigator at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center (LA BioMed), was the lead author of the report. He and his colleagues studied 16,608 post-menopausal women who participated in the Women's Health Initiative (WHI) clinical trial, a 15-year study that began in 1993.

The research team examined the effect of combined hormone therapy on breast cancer detection over five years and found it resulted in more than one in 10 women having otherwise avoidable mammogram abnormalities and one in 25 women having breast biopsies. Combined hormone therapy also compromised the diagnostic performance of mammograms and breast biopsies.

“These findings represent a concern for post-menopausal women who are considering hormone therapy,” said Dr. Chlebowski. “They should take the results of this study into consideration and consult with their physicians before undergoing even short-term hormone therapy.”

The study examined the use of conjugated equine estrogens plus medroxyprogesterone acetate for approximately five years. 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 placebos: 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 combined hormone therapy than among those taking placebos: 10 percent vs. 6.1 percent.

“After discontinuation of combined hormone therapy, the adverse effects on mammogram and breast biopsy performance were seen even in younger women in the fifth decade of life, so the finding may impact women just entering menopause as well,” said Dr. Chlebowski.

The study found the adverse effect of combined hormone therapy on mammograms “modulated but remained significantly different from that of placebo for at least 12 months,” according to the study's authors.