Proponents of screening mammography have been quick to criticize a study published this week by Norwegian and Danish scientists that claims there's no evidence that mammography screening for breast cancer has any effect on death rates.
In a study published online March 24 in the British Medical Journal, researchers from the Nordic Cochrane Centre in Copenhagen and the Norwegian Institute of Public Health in Oslo said reductions in breast cancer death rates in regions with screening were the same or actually smaller than in areas where no women were screened.
The BMJ published a response from Professor Elsebeth Lynge in the Institute of Public Health at the University of Copenhagen March 25.
"Jørgensen et al claim that mammography screening in Denmark had no impact on breast cancer mortality," she wrote. "This claim is unsubstantiated, firstly because the authors used very crude data, and secondly because the analysis was not geared to answer the question."
Breast cancer screening can only have an effect on women not already diagnosed with breast cancer prior to screening, Lynge wrote. Therefore, "refined mortality" should be used to evaluate the benefit of mammography screening, and Jørgensen's team did not do so.
"They merge data from three screening areas starting screening at different points in time, and used age groups instead of cohorts. Together this gave quite 'polluted' data," she wrote.
The measured impact of mammography screening on breast cancer mortality is highly dependent on the dataset used for the analysis, according to Lynge.
"Using cohort-based refined mortality, we found a 25% decrease in breast cancer mortality in the municipality of Copenhagen during the first 10 years following the introduction of mammography screening," Lynge wrote.
Jørgensen's study data are inconsistent, according to Dr. Peter Dean, professor of radiology at the University of Turku in Finland.
"[Jørgensen's team] did not determine whether or not the breast cancer deaths were from cancers diagnosed before or after screening was offered, and whether or not the women had actually attended screening," Dean wrote AuntMinnie.com in an e-mail. "Their inability to find a difference in breast cancer mortality is most likely a result of the dilution of the effect caused by including so many breast cancer deaths from women who had not attended screening."
By Kate Madden Yee
AuntMinnie.com staff writer
March 26, 2010
Related Reading
Breast cancer screens don't save lives: Nordic study, March 25, 2010
Study: Less breast screening leads to more palpable cancers, March 16, 2010
USPSTF guidelines influencing doctors, poll finds, February 16, 2010
Editorial: Research flaws make USPSTF guidelines obsolete, February 8, 2010
ACR, SBI: Breast cancer screening should begin at 40, January 4, 2010
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