Based on results recently presented at the 2006 San Antonio Breast Cancer Symposium, researchers speculate that a sudden decrease in the incidence of breast cancer in 2003 may be due to a reduction in the use of postmenopausal hormone therapy.
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 the most effective treatment for many of these symptoms. Recent studies, however, have raised concerns about the health effects of postmenopausal hormone therapy.
Use of estrogen plus progestin has been linked with an increased risk of heart disease, breast cancer, stroke, and blood clots and a decreased risk of fractures and colorectal cancer. Use of estrogen alone, which is generally reserved for women who have had a hysterectomy, has been linked with an increased risk of strokes and a decreased risk of fractures.
This recent information about the potential health risks of postmenopausal hormone therapy came from large clinical trials conducted as part of the Women?s Health Initiative (WHI). After the first WHI results were released in 2002, there was a rapid decline in the use of postmenopausal hormone therapy.
A possible link between this decline in use of postmenopausal hormone therapy and a drop in breast cancer incidence was suggested by evaluation of a large U.S. cancer registry. Between 1990 and 1998, the rate of breast cancer increased by 1.7% each year. After 1998 breast cancer rates began to decline by 1% each year. In 2003, however, there was a sharp 7% drop in the rate of breast cancer.
Overall in 2003 there was an 8% decline in the rates of estrogen receptor (ER)-positive breast cancer, and a 4% decline in the incidence of ER-negative breast cancer. Among women aged 50 to 69 years, the incidence of ER-positive breast cancers decreased by 12% and the incidence of ER-negative breast cancer decreased by 4%.
Researchers can only indirectly infer the cause of the dramatic decline in ER-positive breast cancers in 2003. The authors of the current study note, however, that it makes sense that a sudden decline in use of postmenopausal hormone therapy could cause a drop in breast cancer incidence within a short time period.