Hormone therapy reduces mammography’s effectiveness

Treating the hot flashes, mood swings, and other symptoms of menopause with hormone therapy combining estrogen and progesterone compromises the diagnostic performance of mammography, according to a report from the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center. Women receiving both hormones had a higher chance of abnormal mammograms and breast biopsies.

Oncologist Dr. Rowan Chlebowski and colleagues reviewed the cases of 16,608 postmenopausal women, 8506 of whom received a combination of estrogen and progesterone and 8102 who were given a placebo. All had participated in the Women's Health Initiative clinical trial from 1993 to 1998. They had received a mammogram and breast examination annually, with biopsies performed according to a physician's judgment.

The number of women who developed breast cancer over the 5.6 years in either group was relatively small: 199 patients in the combined hormone group and 150 in the placebo group. But 35% of the women taking hormones had abnormal mammograms compared with 23% who were not on a hormone regime.

Women taking hormones were 4% more likely to have a mammogram with abnormalities after one year and 11% more likely after five years. The hormone group also had more breast biopsies: 10% compared with 6.1% in the placebo group.

Chlebowski noted that the negative effects of the hormones (conjugated equine estrogens plus medroxyprogesterone acetate) on mammograms linger up to a year and a half for women who discontinued taking them. (see figure)

The study was published Feb. 25 in the Archives of Internal Medicine (2008;168[4]:370-381).

Although the researchers have not pinpointed why the hormones interfered with the breast imaging accuracy, they suspect that the hormones' effect on breast density may be a factor. Density was not measured in this study, however.

The results suggested to Chlebowski that a better diagnostic tool is needed to screen women receiving the combined hormone treatment.

"From these new findings, women will have to consider that, if they take estrogen plus progesterone for menopausal symptoms for five years, they'll have one in 10 chance of having an otherwise avoidable mammogram with some abnormality, and a one in 25 chance of having an otherwise avoidable breast biopsy," he said. "If a woman says that's a small price to pay for having to relieve my menopausal symptoms, then she should go ahead [with hormone treatment]."

Because women who have had a hysterectomy can get treated with estrogen alone, Chlebowski is also examining mammograms from estrogen-alone files. He expects to complete the new study by year's end.

For more information from the Diagnostic Imaging archives:

Breast MR shows promise for population at high risk

Confounding factors make mammography less accurate

Premenopausal women with dense breast reap benefits of digital mammography