Breast screening 'may do more harm than good'

Fresh evidence that benefits have been over-stated

Breast screening may do more harm than good, suggests a new study which estimates that the benefits may be half those stated in the research behind the NHS Breast Screening Programme (NBSP).

Researchers from the University of Southampton found that the harms of screening – false positive results and unnecessary surgery – cancel out the benefits in the first ten years after it is carried out.

This finding will lend weight to critics of the NBSP who argue that its benefits have been over-stated and its risks not communicated to women invited to participate in it.

Although the benefits outweigh the risks after 20 years, it is much less than suggested by the 1986 Forrest report, which led to the introduction of the NBSP and suggested that screening would reduce the death rate from breast cancer by almost one third, with few harms and at low cost. The study authors, led by Professor James Raftery, estimate that after 20 years of screening, 1,536 quality adjusted life years (QALYs) are gained. This is half the 3,301 QALYs estimated by the Forrest report.

The reduction in benefit is the result of including the harms of screening in the calculations – false positives (women with an "abnormal" mammogram who under further assessment are found not to have breast cancer) and unnecessary surgery as a result of overdiagnosis (the overdiagnosis and treatment of cancer which would have never caused symptoms).

In recent years the Cochrane Centre, a Nordic research centre, has fiercely criticised the NBSP for failing to adequately communicate these risks to women. This new study supports the Centre’s argument that the benefits have been overstated.

The study followed 100,000 women aged 50 over 20 years. The authors are calling for more research on the extent of unnecessary treatment and its impact on women’s lives and for the risk of over-diagnosis and over-treatment to be communicated to women.

The Department of Health has commissioned an independent review of the NBSP, which screens 1.8 million women every year. It is being led by national cancer director Professor Mike Richards and the chief executive of Cancer Research UK. A new leaflet for women invited to undergo screening is also being developed, following claims that the current one is unbalanced and fails to convey the downsides to attending.

Around half of all breast cancers diagnosed in women aged 50-70 are diagnosed through the Programme. It has led to a significant increase in the diagnosis of ductal carcinoma in situ (DCIS), an early form of breast cancer which accounts for approximately 20% of screen-detected cancers. This has implications for critical illness insurance providers, because policies typically do not cover DCIS, although some will pay out a small benefit to those women undergoing surgery as a result.

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