British study reports lack of benefit for mammography
SOUTHAMPTON, ENGLAND––A new study, published online on December 8 in the British Medical Journal, questioned the benefits of mammography to screen for breast cancer. The suggested that a screening mammogram could be doing more harm than good; furthermore, the researchers noted that it backs up the findings of a previous Cochrane review. The study was conducted by James Raftery, PhD, professor of health technology assessment, and Maria Chorozoglou, a research fellow, at the Wessex Institute, University of Southampton, United Kingdom.
The investigators noted that the Forrest report, which was first published in 1986, suggested that screening would reduce the death rate from breast cancer by almost one third, with minimal harmful effects and at a low cost. However, a Cochrane review published in 2009 reported that the benefits were not so apparent because of the risk for overtreatment.
The authors of the Cochrane report wrote, "[F]or every 2000 women invited for screening throughout 10 years, one will have her life prolonged, and 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily.” The new study updates the previous Forrest report by including recent estimates for mortality, as well as the effects of false-positives and overdiagnosis.
In order to evaluate benefits of mammography to screen for breast cancer, the outcomes of 100,000 women aged 50 years or older were modeled in two cohorts from the United Kingdom. (A cohort is a group of subjects have shared a particular time together during a particular time span.) One cohort underwent screening, and the other did not. Outcomes measured were death from breast cancer or any cause, as well as a false-positive diagnosis and surgery. These outcomes made up the main outcome of quality-adjusted life years (QALYs). A total of 5 scenarios were modeled; they included data similar to the initial Forrest report and updated with more accurate breast cancer mortality data as well as losses of quality of life from surgery and false-positive diagnoses.
The researchers found that including the harm from false-positive results and unnecessary surgery reduced the benefits of a screening mammogram by about 50%, with negative net QALYs occurring in years soon after the introduction of screening. The authors noted: "When we updated the estimate for reduction in breast cancer mortality for all ages, with the meta-analysis of the eight trials [included in the Cochrane review]...the net cumulative QALY gain at 20 years fell to around 3,100 QALYs or by about 6%... When we added harms in scenario 3[, which included losses of quality of life from surgery and false-positive diagnoses], this was reduced to just over 1,500 QALYs or by half." They concluded, "From a public perspective, the meaning and implications of overdiagnosis and overtreatment need to be much better explained and communicated to any woman considering screening.”
The study authors noted, "Ways of reducing the harms from screening might include less frequent screens, particularly for younger women. While further modeling might explore the clinical and cost effectiveness of various options, conclusions will inevitably be limited without better estimates of the level and impact of overtreatment." At present, the UK’s National Health Service currently offers mammography every three years to women aged 47 to 73 years. The national breast screening program in the UK has been officially under review because of ongoing questions about the benefits on mammography.
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