NCPA - National Center for Policy Analysis


October 28, 2005

Mammograms contributed to between 28-65 percent of the sharp decrease in breast cancer deaths that occurred among U.S. women from 1990-2000, according to a study published in the New England Journal of Medicine.

The breast cancer death rate decreased 24 percent from 1990-2000, but it was unknown whether the decline was due to increased mammography -- which can detect cancers in earlier stages -- or improved treatment or a combination of both. The researchers found that both contributed to the decline and quantified the contribution of each factor.

For the study, statisticians assembled by the National Cancer Institute used seven statistical models to analyze data on breast cancer screening and treatment from 1975 to 2000. The death rate was steady from 1975 until 1990. It then dropped from 49.7 deaths per 100,000 women ages 40 to 75 in 1990 to 38 per 100,000 women for that age group in 2000. According to researchers:

  • Mammography alone reduced the death rate by an average of 15 percent.
  • Post-operative treatments, including chemotherapy and hormone therapy with drugs such as tamoxifen, reduced the death rate by an average of 19 percent.
  • The combination of mammography and adjuvant treatments decreased the death rate by 12-21 percent.

Although both mammograms and new treatments had been tested in clinical trials, researchers did not know what occurred in the real world, where women did not always follow medical advice and doctors did not always use the tests and drugs as carefully in the studies.

There has been a general consensus among scientists that the drug therapies were effective but a sharp divide over whether the benefits of mammograms outweighed the risks of false positives and unnecessary treatments, according to the researchers.

Source: Donald A. Berry et al., "Effect of Screening and Adjuvant Therapy on Mortality from Breast Cancer," New England Journal of Medicine, Vol. 353:1784-1792, No. 17, October 27, 2005.

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