UK Study Finds Lack of Net Benefit for Mammography

Emma Hitt, PhD

December 09, 2011

December 9, 2011 — Mammographic breast cancer screening could be doing more harm than good, according to a new analysis conducted in the United Kingdom that backs up the findings of a previous Cochrane review.

James Raftery, PhD, professor of health technology assessment, and Maria Chorozoglou, a research fellow at the Wessex Institute, University of Southampton, United Kingdom, reported their findings in an article published online December 8 in the British Medical Journal.

According to the researchers, the Forrest report, 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 found that the benefits were not so apparent because of the risk for overtreatment.

"[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 authors of the 2009 Cochrane report write.

The current analysis updates the previous Forrest report by including recent estimates for mortality, as well as the effects of false-positives and overdiagnosis.

The outcomes of 100,000 women aged 50 years or older were modeled in 2 cohorts from the United Kingdom. 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 that included data similar to the initial Forrest report, updated with more accurate breast cancer mortality data and with losses of quality of life from surgery and false-positive diagnoses.

The study found that including the harms from false-positive results and unnecessary surgery reduced the benefits of screening by about half, with negative net QALYs occurring in years soon after the introduction of screening.

"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 3100 QALYs or by about 6%," the authors write. "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 1500 QALYs or by half."

"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," they conclude.

According to the researchers, "[w]ays of reducing the harms from screening might include less frequent screens, particularly for younger women. While further modelling 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."

The United Kingdom's National Health Service currently offers mammography every 3 years to women aged 47 to 73 years. The national breast screening program in the United Kingdom has been officially under review because of ongoing questions about the benefits on mammography, as reported by Medscape Medical News on October 25, 2011.

The study was not commercially funded. The authors have disclosed no relevant financial relationships.

BMJ. Published online December 8, 2011. Full text

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