A sharp decline in U.S. breast cancer deaths in 2003 held steady the following year, providing further evidence that the drop is related to the large number of women who stopped hormone replacement therapy, researchers report today.
Between 2001 and 2004, the number of breast cancer cases dropped 8.6% overall -- 11.8% among women older than 50, the primary consumers of the hormones, according to the study in the New England Journal of Medicine.
The continued decline shows that the drop in cases "was not a one-year wonder, a short-lived anomaly," said one of the study's authors, Dr. Peter Ravdin of the University of Texas M.D. Anderson Cancer Center.
Over the two-year study, 30,000 fewer women developed breast cancer than would have been expected from previous trends, and the incidence reached its lowest rate since 1987. An estimated 200,000 cases are diagnosed each year.
"We can't prove" that decreases in hormone therapy caused the decline in breast cancer, "but it is such a substantial reduction that you would need something big to have occurred to explain it," said coauthor Dr. Rowan T. Chlebowski of the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center. "If it is not hormone replacement therapy, we still need to explain it."
Independently, in an online paper in the journal Lancet, British researchers linked hormone replacement therapy to a 20% increase in the risk of ovarian cancer. They calculated that there were an additional 1,300 cases of ovarian cancer and 1,000 deaths in the United Kingdom between 1991 and 2005 resulting from the treatment.
In the 1990s, hormone replacement drugs were among the most prescribed medications for women older than 50, with more than 90 million prescriptions written in the U.S. each year for 15 million women. The therapy controlled symptoms of menopause and was thought to reduce the risk of heart disease.
That changed abruptly in mid-2002, when a large study known as the Women's Health Initiative showed an increased risk of breast cancer associated with the treatment.
Prescriptions for the drugs, generally a combination of estrogen and progestin, plummeted by at least 38% in 2003 and by an additional 20% in 2004.
In December, Ravdin and his colleagues reported at the San Antonio Breast Cancer Symposium that the incidence of breast cancers had dropped nearly 7% in 2003, and argued that the decline was caused by the drop in hormone replacement therapy.
