‘Introducing breast cancer screening in the UK may have caused more harm than good’, says a new study published on bmj.com that supports the claim.

The authors explain that harms include false positives, such as abnormal results that actually prove to be normal, and over-treatment, such as treating patients for harmless cancers, which if left untreated, would have never have caused the patient to experience any symptoms or threaten his/her life, either because the cancer is so slow to advance that the patient dies of other causes before, if any symptoms develop, or because the cancer stays dormant or regresses.

According to the study, the harms of screening mostly offset benefits by up to 10 years. After that, benefits accumulate, yet not nearly by as much as researchers predicted at the start of screening.

Britain’s introduction to breast screening was initiated through the Forrest report in 1986, in which the number of screened and unscreened women who survive each year over a 15-year period was estimated. The researchers calculated costs and benefits in quality adjusted life years or QALYs, a combined measure of quantity and quality of life, but did not account for harms. The study indicated that breast cancer mortality rates would be reduced by almost a third through the introduction of breast cancer screening, and that screenings presented few harms and were low-cost.

Scientist have acknowledged the harms of breast cancer screening since the Forrest report and researchers at the University of Southampton decided to update the report’s survival estimates by combining both benefits and harms of screening in one single measure.

Their results are based on 100,000 women aged 50 years and above, who survived up to 20 years after initially entering the screening 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: Grace Rattue