Dec. 14, 2006 (San Antonio) -- The number of women diagnosed with fell sharply in the United States in 2003 -- a decline researchers attributed to a parallel drop in the number of women taking hormone replacement therapy.
That means as many as 14,000 fewer women were diagnosed with breast cancer in 2003 than in 2002, a year in which the American Cancer Society estimates there were 203,500 new cases, says researcher Donald Berry, PhD, a biostatistician at The University of Texas M.D. Anderson Cancer Center in Houston.
More importantly, the steepest decline -- about 20% -- occurred in postmenopausal women whose cancers were fueled by estrogen, he says, providing more evidence of a link between breast cancer and hormone replacement therapy (HRT).
Breast Cancer and Hormone Replacement Therapy
For years, doctors routinely prescribed hormone replacement therapy to older women to replace the estrogen that naturally declines after .
By 2000, about 30% of women over age 50 were on HRT, says co-researcher Peter Ravdin, MD, PhD, also a biostatistician at M.D. Anderson.
But in July 2002, a Women's Health Initiative study of 16,608 women aged 50 to 79 who were using HRT was halted when the combination of estrogen and progestin was found to significantly increase a woman's risk of .
That resulted in a 50% drop in HRT use over the next six months, Ravdin says.
"If you stop HRT, your chance of getting breast drops immediately and quite dramatically," Berry says.
"These are very exciting data," says Eric Winer, MD, a breast cancer specialist at the Dana-Farber Cancer Institute and moderator of the session at which the analysis was presented.
"It is very clear that the results of the Women's Health Initiative led to a dramatic change in what women did -- they stopped taking HRT. And HRT withdrawal appears to have had an immediate effect on breast cancer incidence," he tells WebMD.
Breast Cancer Rates May Rebound
In their study, the Texas researchers analyzed government statistics on cancer rates in nine regions of the country from 1990 to 2003, the latest year for which data were available.
Overall, breast cancer rates increased by 1.7% a year from 1990 to 1998. Then they began to slowly creep down, relative to other years, by 1% annually from 1998 to 2002.
But, "If you asked, in 2002, if we saw any change in breast cancer incidence, the basic answer would have been, 'No,'" Ravdin tells WebMD. "But then we saw a major shift."
Berry says he suspects breast cancer rates will eventually start creeping upward again.
"It's like watering a plant," says Berry. "If you stop watering it, it stops growing as much. But eventually it will find water from another source and start growing again."
Though HRT appears the most likely cause for the decline, other factors -- such as lower use of screening mammography -- may also play a role, he adds.