New study assesses risk-reduction of mammography

The Buzz: A novel study from Norway suggests that risk reduction from mammography may be much lower than previously thought.
Citation: M Kalager et. al. Effect of Screening Mammography on Breast-Cancer Mortality in Norway.  N Engl J Med 2010; 363:1203-1210

Summary: Previous observational attempts to quantify the benefit of mammography have relied on historical data for control groups, making it difficult to control for the effect that time (increased breast cancer awareness, better treatment methods, e.g.) may have on improvement in breast cancer survival. Norway has a national public health system which rolled out a program for breast cancer screening (mammography every 2 years for women aged 50-69) and treatment (multidisciplinary treatment teams offered to all women with a new diagnosis of breast cancer) staggered region by region from 1996 to 2005. Using data from 40,075 women, this study compared similar groups in counties where the new program simultaneously was and was not available, thus eliminating possible confounding effects of time.  The study also looked at geographically matched groups from 1986-1995 when the new program was not available. Absolute risk reduction from the combined screening and treatment program in women 50-69 years old was found to be 10%, though it was not possible to say how much of the benefit was from mammography itself.

To address this question, the study included analysis of women aged 70-84 who did not undergo mammography but who were treated by the new teams. In this group, the benefit of the new treatment teams was an 8% reduction in risk.

According to an accompanying editorial, these data suggest that "2500 women would need to be screened over a 10-year period for 1 to avoid death from breast cancer." Moreover, of those 2500, 1000 would be expected to have a false positive on mammography, and 5 to 15 would be wrongly diagnosed and treated. The editor suggests that the decision to initiate or continue screening mammography might be best decided by an informed patient, and that its use should not be a measure of quality in our current health care system.
By: Spencer Blackman MD