The introduction of routine breast screening may have resulted in more harm than benefits, researchers from the University of Southampton, England, reported in BMJ (British Medical Journal). They explain that examples of harms include abnormal results that eventually prove to be normal ones (false positives), and treating patients for cancers that are harmless and would not threaten the woman’s lifespan (overtreatment).
Authors James Raftery and Maria Chorozoglou found that the harms caused by routine mammographies generally offset the benefits by nearly ten years, after which the benefits start building up. However, they never accumulate by as much as experts had predicted when screening started.
A 1986 report – the Forrest Report – estimated how many screened and unscreened females would survive over a 15-year period; the estimate was for each year, up to 15 years. The results of the estimate persuaded health authorities in the UK to start routine breast screening.
They worked out costs and benefits in QALYs (quality adjusted life years) – this is a combination of quantity and quality of life measurement. They did not account for harms. They estimated that by introducing routine breast cancer screening, which they thought had few harms and are not costly, would lower breast cancer mortality rates by nearly one third.
Since 1986, experts have accepted that there are harms associated with routine breast cancer screening. The Southampton researchers set out to update the survival estimates of the report by turning the combined benefits and harms of mammographies into a single measure.
They gathered data on 100,000 females, all aged 50+ years who survived up to two decades after initially entering the mammography program. The researchers established that the benefits of screening were approximately halved when false positives and unnecessary surgery were included.
According to their best estimates, the results were negative net QALYs for up to 8 years following screening with no significant gains after one decade, whilst net QALYs accumulate after 20 years, yet by significantly less than previously predicted by the Forrest report.
The authors of the study state that the extent of unnecessary treatments and their impact on women’s quality of life requires more research, calling to improve methods that identify those women who would potentially benefit most from surgery, and to calculate the levels and duration of the harms from surgery.
They also comment that the meaning and implications of over-diagnosis and over-treatment have to be explained much better from a public point of view, so that women who consider screening gain a better understanding.
According to a study on French women published last month in bmj.com, the ongoing uncertainty regarding the extent of over-treatment is apparent with 1% of women being over-diagnosed with invasive breast cancer because of screening.
Written by Petra Rattue