The Forrest report, published in 1986, led to the introduction of breast cancer screening in the UK and estimated the number of screened and unscreened women surviving each year over a 15-year period. Costs and benefits were measured in quality adjusted life years or QALYs (a combined measure of quantity and quality of life) but it omitted harms.
The report suggested that screening would reduce the death rate from breast cancer by almost one third with few harms and at low cost.
But since then, the harms of breast cancer screening have been identified. Now, James Raftery, Professor of health technology assessment at the University of Southampton, and his colleague Maria Chorozoglou, research fellow, have conducted a study to update the report’s survival estimates.
By combining the benefits and harms of screening in one single measure the study shows that the harms of screening largely offset the benefits up to 10 years, after which the benefits accumulate, but by much less than predicted when screening was first started.
Harms included false positives (abnormal results that turn out to be normal) and overtreatment (treatment of harmless cancers that would never have caused symptoms or death during a patient’s lifetime). The results are based on 100,000 women aged 50 and over surviving by year up to 20 years after entry to the screening programme.
Inclusion of false positives and unnecessary surgery reduced the benefits of screening by about half. The best estimates generated negative net QALYs for up to eight years after screening and minimal gains after 10 years.
After 20 years, net QALYs accumulate, but by much less than predicted by the Forrest report.
It is hoped that the study will lead to patients being more informed of the risks of breast screening and the potential reduction in the number of harms.
Professor Raftery says: “Being screened for breast cancer can be an understandably difficult time for women and can cause anxiety and stress, not only for the patient, but for the family too. If we can ensure that women have a better understanding of the risks of unnecessary treatment before they are screened, it will be better for the patient.”
He adds: “More research is needed to assess the extent of unnecessary treatment and its impact on quality of life. There also needs to be better ways of identifying those most likely to benefit from surgery and for measuring the levels and duration of the harms from surgery.”
Notes for editors
The study will be available on the British Medical Journal website: http://www.bmj.com/