Mammograms’ value studied, again

September 23, 2010

Studies done decades ago found that mammograms reduced the breast cancer death rate by 15 to 25%. But that was when treatment was much less effective. A new study looks at an aging question: Should mammograms still be the “gold standard?”

Studies done decades ago found that mammograms reduced the breast cancer death rate by 15 to 25%. But that was when treatment was much less effective. A new study looks at an aging question: Should mammograms still be the “gold standard?”

In the new study reported in the New England Journal of Medicine, mammograms, combined with modern treatment, reduced the death rate by 10%, but the study data indicated that the effect of mammograms alone could be as low as 2% or even zero.

The study looked at what happened in Norway before and after 1996, when the country began rolling out mammograms for women ages 50 to 69 along with special breast cancer teams to treat all women with breast cancer.

Below is a synopsis, for full article see theNEJM

Effect of Screening Mammography on Breast-Cancer Mortality in Norway
Mette Kalager, M.D., Marvin Zelen, Ph.D., Frydis Langmark, M.D., and Hans-Olov Adami, M.D., Ph.D.
N Engl J Med 2010; 363:1203-1210

Background
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.

Methods
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. We 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.

Results
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; 95% confidence interval [CI], 0.63 to 0.81) 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; 95% CI, 0.71 to 0.93; P<0.001 for both comparisons), for a relative reduction in mortality of 10% in the screening group (P=0.13). 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.

Conclusions
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.