The introduction of breast cancer screening in the UK have caused more harm than
good, claims a new study published on bmj.com.
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). This may be because the cancer
grows so slowly that the patient dies of other causes before it produces
symptoms, or the cancer remains dormant or regresses.
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.
Forrest report in 1986, which led to the introduction of breast cancer
screening in the UK,
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.
suggested that screening would reduce the death rate from breast cancer by
almost one third with few harms and at low cost.
the Forrest report, the harms of breast cancer screening have been
acknowledged. So, researchers at the University
of Southampton set out to
update the report's survival estimates by combining the benefits and harms of
screening in one single measure.
results are based on 100,000 women aged 50 and over surviving by year up to 20
years after entry to the screening programme.
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.
20 years, net QALYs accumulate, but by much less than predicted by the Forrest
authors say more research is needed on the extent of unnecessary treatment and
its impact on quality of life. They also call for improved ways of identifying
those most likely to benefit from surgery and for measuring the levels and
duration of the harms from surgery. 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 add.
the continuing uncertainty surrounding the extent of overtreatment is apparent
in a study of French women published on bmj.com last month, which put
overdiagnosis of invasive breast cancer due to screening at around 1%.