According to the results of a study conducted in Canada, the sharp drop in use of combined (estrogen plus progestin) hormone therapy that occurred between 2002 and 2004 was accompanied by an almost 10% decrease in breast cancer incidence. These results were published in the Journal of the National Cancer Institute.
As women reach menopause and beyond, more than 80% will experience symptoms such as hot flashes, night sweats, sleep disturbance, and vaginal dryness. Estrogen, with or without progestin, is an effective treatment for many of these symptoms. Over the last several years, however, studies have raised important concerns about the health effects of menopausal hormone therapy.
In 2002, a report from the Women’s Health Initiative indicated that combined hormone therapy increased the risk of breast cancer, heart disease, stroke, and blood clots. Use of combined hormone therapy decreased the risk of fractures and colorectal cancer, but these benefits were thought to be outweighed by the risks for most women.
After this report, use of combined hormone therapy declined markedly. Studies from several countries—including the United States—suggest that this decline in hormone use was followed by a decline in breast cancer incidence rates.
To evaluate trends in hormone use and breast cancer in Canada, researchers collected information about women between the ages of 50 and 69 who participated in the National Population Health Survey between 1996 and 2006.
- Between 2002 and 2004, the percent of women who used combined hormone therapy decreased from 12.7% to 4.9%. During this same period, the rate of breast cancer declined 9.6%.
- Since 2005 there has been some rebound in breast cancer rates. This suggests that avoidance of hormone therapy may act primarily by slowing the growth of breast cancer (rather than preventing breast cancer).
- Mammography rates remained stable throughout the study period.
- The study did not have information about the hormone receptor status of the breast cancers that were diagnosed, nor was information available about duration of hormone use.
The researchers conclude that between 2002 and 2004, a decline in hormone therapy use in Canada was accompanied by a decline in breast cancer incidence.
Additional research is warranted to determine the biologic link between hormone therapy and breast cancer. The results of the current study suggest that combined hormone therapy may speed the growth of breast cancers.
Reference: De P, Neutel I, Olivotto I, Morrison H. Breast cancer incidence and hormone replacement therapy in Canada. Journal of the National Cancer Institute [early online publication]. September 23, 2010.