Effect of screening mammography on breast-cancer mortality

In the United States, breast cancer is the second leading cause of cancer-related death among women. For women between 50 and 70 years old, screening mammography has long been recommended has as a means to detect cancers as early as possible and thus begin treatment sooner.

As treatments have improved, however, there has been continued disagreement among experts over the relative value of mammograms. A 2010 study by Harvard School of Public Health researchers, “Effect of Screening Mammography on Breast-Cancer Mortality in Norway,” finds that mammography can help to reduce mortality rate from breast cancer, but the magnitude of reduction is more modest than previously predicted.

The data was based on more than 40,000 women diagnosed with breast cancer who took part in a screening program that began in 1996. The women were divided among four groups: The first lived in areas where mammograms were provided every two years and the second in areas where screening wasn’t available. The remainder of the study group consisted of two historical-comparison groups similar to first two groups.

The study’s findings include:

• In the screening group, the death rate was reduced by 7.2 deaths per 100,000 person-years.
• In the nonscreening group, the death rate declined by 4.8 deaths per 100,000 person-years.
• The reduction in mortality that could be attributed to screening alone was 2.4 deaths per 100,000 person-years, or about a third of the total reduction of 7.2 deaths.

Because mammography screening was only associated with a third of the reduction in mortality from breast cancer, the remaining two-thirds must come from factors other than the mammograms themselves. The researchers suggest that improved treatment and increased awareness of the disease as possible reasons for the reduction in mortality.

Tags: cancer, technology