In the past, physicians routinely prescribed hormone replacement therapy to women to decrease their risk of osteoporosis and help relieve menopausal symptoms. But in 2002, results from the Women’s Health Initiative (WHI) indicated that estrogen plus progesterone hormone therapy was associated with increased risks of breast cancer , coronary artery disease , stroke , and blood clots. And in 2004, the estrogen-alone arm of the WHI was stopped early because estrogen alone was linked with an increased risk of stroke. But it was not clear how estrogen alone affected breast cancer risk.

A new WHI report in the April 12, 2006 issue of the Journal of the American Medical Association found that estrogen alone did not increase of breast cancer in postmenopausal women who had a hysterectomy , but it was associated with a higher incidence of abnormal mammogram results.

About the Study

This study included 10,739 postmenopausal women who had a prior hysterectomy. They were randomly assigned to receive 0.625 milligrams of estrogen (Premarin) or a placebo daily. The women underwent annual mammograms and clinical breast exams to screen for breast cancer. The researchers followed the women for an average of seven years (when the study was stopped) and tracked which women developed breast cancer.

During the study, 237 women developed invasive breast cancer. Estrogen therapy did not significantly affect the risk of developing breast cancer overall. But upon further analysis, the researchers found that estrogen was associated with 29% reduction in the risk of ductal cancers (those occurring in the milk ducts). Furthermore, estrogen was associated with a reduced risk of breast cancer in women who had no history of benign (non-cancerous) breast disease and no first-degree relatives (e.g., mother, sister) with breast cancer. Women taking estrogen were more likely to have abnormal mammograms than those taking the placebo, with 36% of those in the estrogen group having an abnormal mammogram, compared with 28% in the placebo group.

This study was limited because the researchers only followed the women until they stopped taking estrogen. It is possible that some cancers may have been too small to be detected during this time.

How Does This Affect You?

These findings suggest that estrogen alone is not associated with an increased risk of breast cancer in postmenopausal women who have had a hysterectomy. In fact, it appears that estrogen alone may actually decrease the risk of breast cancer in certain groups of women.

Does this mean that estrogen-alone hormone therapy is a safe option for managing menopausal symptoms? Not necessarily. Estrogen alone is not prescribed to women who still have a uterus because it increases the risk of endometrial cancer (cancer of the uterine lining). And estrogen alone has been associated with an increased risk of stroke. But whether you and your doctor decide hormone therapy is for you depends on your individual risks. Short-term use to treat menopausal symptoms for a year or two appears to be relatively safe, but hormone therapy has a complex set of risks and benefits that must be carefully weighed for each individual.