msnbc.com news services
updated 12/14/2006 3:10:04 PM ET 2006-12-14T20:10:04

In a startling turnaround, breast cancer rates in the United States dropped dramatically in 2003, and experts said they believe it is because many women stopped taking hormone pills.

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The 7.2 percent decline came a year after a big federal study linked hormone replacement therapy used at menopause to a higher risk of breast cancer, heart disease and other problems. Within months, millions of women stopped taking estrogen and progestin pills.

A new analysis of federal cancer statistics, presented Thursday at a scientific conference called the San Antonio Breast Cancer Symposium, revealed the drop in tumors.

About 200,000 cases of breast cancer had been expected in 2003; the drop means that about 14,000 fewer women actually were diagnosed with the disease in 2003 than in 2002.

“It is the largest single drop in breast cancer incidence within a single year I am aware of,” said Dr. Peter Ravdin, a research professor in the Department of Biostatistics at the University of Texas M. D. Anderson Cancer Center, where the analysis was conducted.

“Something went right in 2003, and it seems that it was the decrease in the use of hormone therapy, but from the data we used we can only indirectly infer that is the case,” he said in a statement.

The researchers stressed that because their analysis is based on population statistics, the reasons for the drop are not completely certain. But evidence showed that the steepest decline in breast cancer diagnosis, at 12 percent, occurred in women between the ages 50 to 69 with estrogen receptor positive breast cancer. These types of tumors are fueled by the hormone estrogen.

Because breast cancer takes years to form, experts think the hormones mostly caused small tumors that had been growing to stop or shrink, making them no longer detectable on mammograms. Whether this is true or will result in fewer cases over the long run will take more time to tell.

Alarm over HRT
A big study in 2002 suggested that the combination of estrogen and progestin raised the risk of breast cancer and brought a premature halt to a Women’s Health Initiative study of more than 16,600 women between 50 and 79 who were taking hormones. The news caused widespread alarm and confusion.

More analysis of the Women’s Health Initiative also showed that hormone replacement therapy (HRT) could raise the risk of heart disease and especially strokes, and HRT was abandoned except as a way to relieve the most debilitating and stressful symptoms of menopause, such as hot flashes and insomnia.

Ravdin said about 30 percent of American women over the age of 50 had been taking HRT in the early years of this decade but about half of the women stopped in the later part of 2002 after the results of this link were made public.

'Source of fuel is cut'
“Research has shown that ER-positive tumors will stop growing if they are deprived of the hormones, so it is possible that a significant decrease in breast cancer can be seen if so many women stopped using HRT,” Ravdin said.

“It takes breast cancer a long time to develop, but here we are primarily talking about existing cancers that are fueled by hormones and that slow or stop their growing when a source of fuel is cut,” added Donald Berry, an M.D. Anderson professor who helped lead the study.

“Incidence of breast cancer had been increasing in the 20 or so years prior to July 2002, and this increase was over and above the known role of screening mammography. HRT had been proposed as a possible factor, although the magnitude of any HRT effect was not known.” 

The next set of cancer statistics is due out in April.

The Associated Press and Reuters contributed to this report.

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