A study conducted in Norway suggests that for women between the ages of 50 and 69, a mammography screening program reduced the risk of death from breast cancer by 10%, and accounted for roughly one-third of the decline in breast cancer mortality during that time period. These results were published in the New England Journal of Medicine.
A mammogram is an X-ray of the breast. A screening mammogram is a mammogram that is performed in a woman without breast symptoms. The goal of screening mammography is to detect breast cancer at an early stage when it is most easily treated.
Although there has been debate about how well screening mammography performs in young women, most studies have reported that screening mammography reduces breast cancer mortality among women over the age of 50. The extent of the benefit, however, may change over time as improvements are made in breast cancer treatment and breast cancer awareness.
To further explore the impact of screening mammography among women between the ages of 50 and 69, researchers in Norway evaluated trends in breast cancer mortality as a screening program was gradually implemented in the country. Between 1986 and 2005, information was available for more than 40,000 women with breast cancer.
- Women in the screening group had a 10% reduction in breast cancer mortality.
- Norway experienced a decline in breast cancer mortality during the period of the study, but a majority of the decline in mortality appears to be due to factors other than screening (such as improvements in treatment). Screening is thought to account for roughly one-third of the reduction in breast cancer deaths.
An editorial that accompanies the article provides perspective by applying these results to the U.S. population. Currently, the 10-year risk of breast cancer death for a 50-year-old woman in the United States is 4 per 1,000 women. Applying the Norwegian results, the risk without screening would be about 4.4 per 1,000 women. To look at it another way, 2,500 women would need to be screened over a 10-year period to avoid one death from breast cancer.
These results suggest that screening mammography may provide less of a benefit than previously reported.
 Kalager M, Zelen M, Langmark F, Adami H-O. Effect of screening mammography on breast-cancer mortality in Norway. New England Journal of Medicine. 2010;363:1203-10.
 Welch HG. Screening mammography—a long run for a short slide? New England Journal of Medicine. 2010;363:1276-78.