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CHICAGO - An ambitious study by 10 of the world's top breast cancer statisticians has confirmed that screening mammograms can help prevent deaths from the disease. But the benefit may be smaller than women have been led to believe.
The percentage of American women who die of breast cancer has been declining steadily since 1990, prompting advocates of screening to proclaim that earlier detection through special X-rays called mammograms is saving lives. But skeptics have argued that the credit belongs to improved post-surgical treatments that have come into widespread use - mainly combination chemotherapy and tamoxifen, a hormonal medication.
The statisticians were convened by the National Cancer Institute to try to determine how much of the improvement is due to mammography and how much to treatment.
In today's issue of the New England Journal of Medicine, the researchers who make up the Cancer Intervention and Surveillance Modeling Network, or Cisnet, reported that both screening and treatment have helped reduce the death rate from breast cancer in the United States. On average, they estimated that screening is responsible for nearly half of the decline.
"This provides one piece of additional evidence that mammography saves lives," said Eric Feuer, chief of statistical research at the National Cancer Institute.
Using seven different mathematical models, the researchers estimated that screening, by itself, reduced deaths by an average of 15 percent. The average benefit from post-operative drug treatment was 19 percent, the researchers estimated.
Those benefits may be lower than experts had expected, said Cisnet member Donald Berry, of M.D. Anderson Cancer Center in Houston. Clinical trials have found mammography can reduce breast cancer deaths by more than 20 percent, and some estimates top 60 percent. Likewise, studies on chemotherapy and tamoxifen have indicated that together they can reduce deaths by about one-third.
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