Screening reduces breast cancer deaths at the cost of over-diagnosis

The review estimated that in the UK screening prevents about 1,300 breast cancer deaths per year. At the same time it can lead to about 4,000 women each year aged 50-70 having treatment for a condition that would never have troubled them.

The expert panel’s report, commissioned by Cancer Research UK and the Department of Health, has studied all the available evidence. It concluded that for each prevented breast cancer death about three over-diagnosed cases will be identified and treated. Over-diagnosis means that a cancer was detected through screening but would not have caused a problem in the woman’s lifetime.

It is not possible, however, for either the woman or her doctor to know which screen-detected cancers are potentially fatal and which represent over-diagnosis. All the cases, therefore, will usually be treated with the accompanying impact on quality of life and psychological well-being.

The panel, chaired by Sir Michael Marmot, professor of epidemiology and public health and Director of the Institute of Health Equity at University College London, concluded that breast cancer screening extends lives through early detection and treatment. It also acknowledged that screening results in over-diagnosis.

Just over 1% of the 307,000 women aged 50-52 who are invited to begin screening each year would have an over-diagnosed cancer in the next twenty years. Less than 0.5% of those women will have their life extended in the next twenty years.

“It was extremely important to look at all the available evidence surrounding both the achievements and shortcomings of the UK Breast Screening Programmes in the wake of increasing debate over their effectiveness,” said Professor Marmot.

“It is now vital to give women information that is clear and accessible before they go for a mammogram so they can understand both the potential harms and benefits of the process,” he added.