One of the things doctors worry about the most is missing a diagnosis. Treatment starts with diagnosis and to miss a cancer or other serious illness risks exposing people to considerable harm. This driving force has led to the concept of screening for illness in an attempt to find disease, cancer in particular at an early stage. Indeed the aim is to find it before it becomes apparent to the individual.

On the surface it seems impossible to find any fault with this. But if we delve slightly below the surface a different picture emerges. The first critical point is that the assumption behind early cancer diagnosis being beneficial is that cancers will all grow and eventually kill the person with it. The second assumption is that the tests we have are useful in finding cancers. The third point is that we assume that starting treatment earlier will make a difference to the outcome for the individual. And lastly it is assumed that there is no downside or harms, which come from screening. After all it is just a “simple test, which could save your life”.

Over the last few decades our understanding of cancer has changed. Not all cancers grow and become fatal. The analogy is like planting a series of seeds in the garden. Some do not “take” and never grow. Those that sit quietly and never grow are not a threat to health or longevity. Screening tests are not able to differentiate which cancers will be a problem (burst through the surface of the ground and grow) from those that will not.

We also know that the outcome from treating a large number of cancers is not altered by treating them at the earliest stage. In other words, if they get a little bit bigger the end result for the person is the same. To return to our analogy this would be like starting treatment when shoots appear above the ground. It is not about waiting till the cancer gets large (plant is fully grown) to try and remove it.

What we also have now is evidence of the impact of screening programs. Already routine PSA screening for prostate cancer has ceased to be recommended due to the large number of men suffering harm and the small number getting benefit.

Cancers were found which would never have caused symptoms or impacted life expectancy. Yet because they were found they were treated.

It is estimated that between 50 and 90% of thyroid cancers, which are treated, are over diagnosed. This is a staggering number. Even if it is only 50% it is still massive. Once more these cancers are treated because they are found. And they are found because of screening tests. In South Korea there has been a 15-fold increase in diagnosis since screening was introduced but not a change in outcomes.

The biggest issue is screening mammography. This continues to have a saintly aura around it and any questioning of its value will see the questioner accused of being sexist or being against women’s health. Yet new work has shown that up to 50% of cancers found and treated due to screening mammography in the USA are over diagnosed. In Australia the figure is between 30 and 40%.

To the defenders of mammography, women having needless medical treatment, supports women’s health. This does not even take account of the anxiety from false positive tests and biopsies, which are negative. Improvements in breast cancer survival have been due to better treatment. Finding and treating lesions which, (to return to the analogy, would never break the ground surface) would never grow or cause symptoms or reduce life expectancy is not useful.

This ten minute video explains the mammography situation well and I would urge those keen to learn more to watch it. Choosing to have a mammogram or other screening test is up to the individual. The issue I have is with the pushing of these tests by those with vested interest whilst not explaining the risks.

It may be easier to promote a “life saving test” than to explain the risks and downside. This is no longer an excuse not to do so. Individuals need to inform themselves before being railroaded by public health messages, which are guilty of deception, by omission.