Reducing the harm caused by screening mammography

By Charles Wright

Women have a right to be confused about whether they should have screening mammography or not. They have been told for two generations that it is life-saving.

They have been bombarded by messages from healthcare professionals and public health programs urging them to comply: “If you don’t go for regular mammograms you need more than your breasts examined”; “Give your mother the gift of life for mother’s day — give her a mammogram”; “Mammograms can detect breast cancer when it is still curable.” Health agencies and ministries have enthusiastically supported breast screening as a demonstration of their commitment to women’s health.

When first introduced in the 1970s there was good reason for the hope that mammography would be a major tool in dealing with the scourge of breast cancer and that early diagnosis and treatment would translate into many lives saved.

A huge industry to support the demand was built involving doctors, radiologists, technicians and equipment manufacturers. The many adverse consequences of breast screening have been well known since the beginning but they were generally deemed acceptable at first with the prospect of saving women’s lives. With hindsight this was a mistake.

What has only more recently been recognized, quantified and publicized, is just how serious the negative effects are in relation to how very small the potential benefits.

The facts have now been clearly presented by many independent expert groups, including the Canadian Task Force on Preventive Health Care, the U.S. Agency for Health Care and Quality and the Cochrane International Collaboration. Public understanding is not helped by debates about relative and absolute death rate results. But the easy way to grasp the results is to consider what happens to a large group of women, say 2,000, who are screened regularly for 10 years.

One woman will have her life prolonged while 700 will have at least one false-positive mammogram with all the resultant anxiety and further investigations, 70-80 will have unnecessary biopsies and at least 10 women will be diagnosed and treated for a ‘cancer’ that would never have developed in any case.

In addition, several women will have a false-negative mammogram that failed to show a real cancer that shows up soon after.

Cancer of the breast can be a devastating disease and almost every woman knows of a friend or relative who had breast cancer successfully treated after a screening mammogram.  The cruel reality is that the screening so rarely brings any change to the eventual result.

For the one in 2,000 who benefits, more than 800 are harmed.

What can be done about the current confusion and conflicting advice on the subject? Concerning the support of screening programs we have to decide whether to heed the consistent findings of independent experts, or the advice of those with a large vested interest in the screening industry. John Maynard Keynes, the famous economist, famously responded to a challenge that he had changed his opinion on a disputed topic, saying, “When the facts change, I change my mind.  What do you do, sir?”

It may take a long time to dispel the false hope that has been given to women, but public education dealing with the current evidence will have to be planned and presented. There is a more immediate need to replace current advocacy with honesty and balance in how the facts are presented.

In every medical test or procedure the potential benefit and harm must be considered, and it is now clear that in the case of screening mammography the harms tip the scale heavily.

At the very least a consent form summarizing the facts clearly and in plain language should have to be signed by women presenting for screening while plans for gradual re-allocation of resources are developed.

Some women may wish to continue with regular screening in spite of this information but unfortunately we now know that mammography does not pass the test for any acceptable screening program designed for the general population: namely, that it must cause significant benefit with insignificant harm.

Dr. Charles Wright is an expert advisor with He is also councillor with the Health Council of Canada.


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