Harvard Women's Health Watch

In Brief: Drop in breast cancer may reflect decline in hormone use

In Brief

Drop in breast cancer may reflect decline in hormone use

The sharpest decline in the number of new breast cancer cases ever observed in a single year occurred between 2002 and 2003. That same year, hormone therapy prescriptions took a nosedive following the abrupt termination — for safety reasons — of the Women's Health Initiative (WHI) trial of combined estrogen and progestin (Prempro) in postmenopausal women. Coincidence? Probably not, according to research led by scientists at M.D. Anderson Cancer Center in Houston. The researchers first speculated about a link between decreased breast cancer incidence and falling hormone therapy use at the San Antonio Breast Cancer Symposium in December 2006. They published a more complete set of findings in the April 19, 2007, issue of the New England Journal of Medicine, showing that the rate of new breast cancers remained low in 2004, an indication that the earlier decline was more than just a statistical fluke. Hormone therapy use followed a similar pattern (see graphs).

Breast cancer incidence in women age 50 and over in the United States, 2000–2004

Number of hormone therapy prescriptions* in the United States, 2000–2004

Sources: Adapted from SEER Cancer Statistics Review, 1975–2004, available online at seer.cancer.gov/csr, and Ravdin PM, et al. New England Journal of Medicine, April 19, 2007, pp. 1670–74.

*For Premarin and Prempro, the two most commonly prescribed forms of hormone therapy.

Analyzing data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) registries, the Texas researchers found that breast cancer incidence fell by nearly 7% in 2003, compared with 2002. Using additional calculations, they determined that the decline actually began in mid-2002, after the WHI found that the women in the trial who were taking Prempro had an increased risk of heart disease, breast cancer, stroke, and blood clots, compared with those taking a placebo. The researchers also found that by the end of 2002, prescriptions for HRT had dropped by nearly 40% from the previous year; they fell 50% between the end of 2002 and the end of 2003. Use has continued to decline since then, albeit at a slower pace.

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