June 7, 2007 -- The incidence of breast cancer in American women continued to fall in 2003, accelerating a trend of dropping rates researchers have observed since 1999, a government study concluded Thursday.
The study showed that rates of invasive breast cancer, or cancer that spreads deep into breast tissue or into other parts of the body, dropped 6.1% between 2002 and 2003, from 127 to 119 diagnoses per 100,000 women. It was the biggest year-to-year drop since 1999, when invasive breast cancer rates began falling.
The study, published by the CDC, analyzed just over 1 million breast cancer diagnoses.
The study is the one of several this year to document falling rates of breast cancer, one of the four most common causes of cancer death for American women. The disease killed 41,000 women in 2004, though that figure represented just more than 7% of all cancer deaths among women.
Still, researchers warned that the figures represent a mix of good and bad news about cancer in U.S. women.
Experts attribute a portion of declining breast cancer rates to a drastic decline in the use of hormone replacement therapy (HRT), which several large studies blamed for spurring cancers. But part of the decline also appears to stem from the fact that fewer American women are getting mammographies to screen for breast cancer.
In 2002, findings from the Women's Health Initiative seemed to show increased risk of breast cancer, heart attacks, strokes, and blood clots linked to use of HRT. Also, a report by the U.S. Preventive Services Task Force recommended against using HRT for prevention of chronic conditions, such as heart disease, in postmenopausal women. Many women quit taking HRT with a nearly 70% drop in HRT use.
“Part of this appears to be a really good thing: the HRT decline,” Sherri Stewart, PhD, the CDC epidemiologist who wrote the report, tells WebMD.
Look Less, Find Less
Mammography rates in women over 40 have dropped by up to 2.4%, according to a pair of recent studies.
Lower screening rates likely means that fewer cancers are identified in U.S. women. The effect appears to be contributing to part of the lower incidence nationwide, though it does not mean the actual rate of breast cancers has gone down, says Peter Ravdin, MD, PhD, an oncologist and breast cancer researcher at the University of Texas M.D. Anderson Cancer Center in Houston.
“The idea that you look less hard, you find less breast cancer, and you don’t see it until later -- that is problematic,” says Ravdin, who authored a study earlier this year that found similar declines in breast cancer rates.
“Hopefully everyone doesn’t get so reassured about cancer that they stop their mammograms,” he tells WebMD.
The report shows that breast cancer rates dropped significantly between 2002 and 2003 in 24 of 41 states analyzed by researchers. The largest decline was in Indiana, which saw a 12.1% reduction.