Prostate cancer – to screen or not to screen

A trial called the CAP trial started in the early part of this century. It was a trial based in England and Wales and it recruited a few hundred thousand men between 2002 and 2009. The aim of the trial was to see if inviting men for one prostate cancer test (called a PSA test) made a difference to deaths from prostate cancer at 10 years of follow-up. There were secondary aims, which included looking at all cause deaths and over diagnoses of prostate cancer and looking at these after different time periods - 5 years, 10 years and 15 years etc.

The 10-year results were published in 2018. These found that the invitation to one PSA test made no difference to deaths from prostate cancer. A recent paper has just been published looking at the 15-year deaths. This found a small difference with the group invited to screening having a very small lower incidence of death from prostate cancer. However, there was no difference in deaths from any cause (which is the only measure of deaths that matters). And, the 18 year results were also available and these showed no difference in deaths from any cause or deaths from prostate cancer. Hence the difference in prostate cancer deaths at 15 years looked like an anomaly.

The diagnoses of prostate cancer were higher in the intervention group – multiples higher at 18-months and 10-year follow-up. That would be expected. But the recent paper reported that approximately one in six cancers were over diagnoses. These would have been treated and treatment for prostate cancer can harm – incontinence and impotency being common outcomes.

If being invited for prostate cancer screening makes no difference to overall mortality and can unnecessarily harm, the question to screen or not to screen does not seem difficult to answer.

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