Effect of screening mammography on breast-cancer mortality in Norway

January 01, 0001

Effect of screening mammography on breast-cancer mortality in Norway

A challenge in quantifying the effect of screening mammography on breast-cancer mortality is to provide valid comparison groups. The use of historical control subjects does not take into account chronologic trends associated with advances in breast-cancer awareness and treatment. The Norwegian breast-cancer screening program was started in 1996 and expanded geographically during the subsequent 9 years. Women between the ages of 50 and 69 years were offered screening mammography every 2 years. The authors compared the incidence-based rates of death from breast cancer in four groups: two groups of women who from 1996 through 2005 were living in counties with screening (screening group) or without screening (nonscreening group); and two historical-comparison groups that from 1986 through 1995 mirrored the current groups.

They found: "We analyzed data from 40,075 women with breast cancer. The rate of death was reduced by 7.2 deaths per 100,000 person-years in the screening group as compared with the historical screening group (rate ratio, 0.72) and by 4.8 deaths per 100,000 person-years in the nonscreening group as compared with the historical nonscreening group (rate ratio, 0.82), for a relative reduction in mortality of 10% in the screening group (P=0.13, not significant). Thus, the difference in the reduction in mortality between the current and historical groups that could be attributed to screening alone was 2.4 deaths per 100,000 person-years, or a third of the total reduction of 7.2 deaths."

The authors concluded: "The availability of screening mammography was associated with a reduction in the rate of death from breast cancer, but the screening itself accounted for only about a third of the total reduction."

Less benefit that many would like to believe.

For the full abstract, click here.

N Engl J Med 363:1203-1210, 23 September 2010 © 2010 to the Massachusetts Medical Society
Effect of Screening Mammography on Breast-Cancer Mortality in Norway. Mette Kalager, Marvin Zelen, Froydis Langmark, and Hans-Olov Adami. Correspondence to Dr. Kalager: [email protected]

Category: X. Female Genital System, Breast. Keywords: screening, mammography, mortality, breast cancer, cohort study, journal watch.
Synopsis edited by Dr Linda French, Toledo, Ohio. Posted on Global Family Doctor 12 October 2010

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