New WHI Data Show No Increased Risk of Breast Cancer With Conjugated Estrogens Alone

Data published recently in the Journal of the American Medical Association showed that in the estrogen-alone substudy of the Women's Health Initiative (WHI), conjugated estrogens at a dose of 0.625 mg did not increase breast cancer incidence in postmenopausal women. The authors also noted the possibility of a protective effect of conjugated estrogens against breast cancer incidence in three groups—women with a low 5-year estimated risk of developing breast cancer as measured by the Gail risk score, women with no first-degree relatives with breast cancer, and women with no prior history of benign breast disease.

"We know there are many symptomatic menopausal women who are appropriate candidates for estrogen therapy but are afraid to take it due to concerns about breast cancer risk," said Ginger Constantine, MD, vice president, Women's Health Care and Bone Repair, Wyeth Pharmaceuticals. "It's important that women talk to their doctor or health-care professional about these new results because they show that conjugated estrogens did not increase the incidence of breast cancer among the menopausal women studied."

Overall Results

Overall, the study authors concluded that postmenopausal women who have had a hysterectomy and were treated with conjugated estrogens alone for an average of 7.1 years did not have an increased incidence of breast cancer. Further analyses found that women who consistently took conjugated estrogens as prescribed had a statistically significant decrease in breast cancer risk (hazard ratio = 0.67; 95% confidence interval = 0.47-0.97; P = .03) compared to women taking placebo.

Findings about breast cancer risk and hormone use have been mixed. Some studies have reported an increased risk of breast cancer with hormone therapy. Other studies have not shown this increase, such as this WHI estrogen-alone substudy. The WHI estrogen-alone substudy was a prospective, randomized, placebo-controlled trial that enrolled more than 10,700 postmenopausal women age 50 to 79 years with a prior hysterectomy. Preliminary findings from the WHI estrogen-alone substudy were first published April 14, 2004, in JAMA.

All women in the WHI estrogen-alone study underwent routine mammography at the start of the study and then annually. This current study reported that by the end of the first year, the percentage of mammograms requiring short-term follow-up was significantly higher in the conjugated estrogens group compared to the placebo group.

"The findings from this current study may be reassuring because even with the reported increased number of abnormal mammograms and biopsies, there was no reported increase in breast cancer incidence, and there was a significant decrease in the most common type of breast cancer," says Hugh Taylor, MD, director of the Yale Menopause Program, associate professor, Yale University School of Medicine, Department of Obstetrics, Gynecology and Reproductive Sciences.