Mammography study contradicts previous reports

LOS ANGELES – As if the mammography debate was not already thoroughly confusing, a Swedish study released Wednesday suggests that screening of women in their 40s could reduce the death rate by as much as 29 percent, a much higher rate than has previously been observed.

Proponents of screening argued that the study is the largest ever conducted and provides strong support for guidelines of the American Cancer Society and other groups calling for regular screening of women in this age group. But critics charged that the study was poorly designed and potentially vastly misleading. A major criticism of the study was that it made no attempt to weigh the risks of mammography against the benefits.

Last November, the U.S. Preventive Services Task Force, which was established in 1986 to assess the value of preventive medical techniques, concluded that mammography for women in their 40s was probably not a good idea. The panel concluded that screening could reduce the risk of dying by about 15 percent among women in their 40s. But the risks of false positives and invasive procedures associated with them largely outweighed the potential benefits of the procedure.

Earlier this month, a study from Norway concluded that the routine mammography may not even be all that beneficial for women older than 50. Those researchers found that improvements in breast cancer awareness and new treatments for the disease were the prime drivers in reducing the death rate from breast cancer and that routine mammography may contribute as little as 2 percent to the reduction.

The new study was published online in the journal Cancer on Wednesday.

Epidemiologist Hakan Jonsson of Umea University in Sweden and his colleagues took advantage of the fact that, since 1986, about half of Sweden’s counties have offered routine mammography to women in their 40s and half have not. Using a cancer registry, the team examined records for more than 1 million women in the two groups of counties. They found 619 breast cancer deaths among women in the counties that offered screening, compared with 1,205 deaths in a similar group that were not screened. That amounted to a 26 percent reduction in deaths among women who were offered screening and a 29 percent reduction among those who actually received mammograms.