Prostate cancer overdiagnosis risk increases substantially in older men

Researchers at Queen Mary University of London have found that the likelihood of prostate cancer overdiagnosis – the detection of a cancer that would never have been diagnosed during a patient's lifetime but for PSA screening – is low in younger men but rises substantially with old age.

In a new study, published on 21 April in the International Journal of Cancer, researchers from Queen Mary University of London found that overdiagnosis of prostate cancer through prostate-specific antigen (PSA) screening is low in younger men, but it rises sharply with age. 

The study, which aimed to estimate the impact of age on overdiagnosis of prostate cancer 15 years after screening stops, analysed long-term follow-up data from the UK CAP (Cluster Randomised Trial of PSA Testing for Prostate cancer) trial, alongside English male mortality rates.

Analyzing data from more than 400,000 men randomised as part of the CAP trial, the team compared the prostate cancer detection rate at screening (1.17%) with the difference in incidence 15 years post-screening (0.14%). They found that 11.7% of prostate cancers diagnosed at the one-off PSA screen would have remained undiagnosed for 15 years if they had been randomised to the control arm (not invited for screening), and importantly, if they would not die from other causes. 

However, when competing mortality (ie, the risk of dying from something other than prostate cancer) was factored in, the team found that the picture changed markedly by age:

• Men diagnosed at age 50 had a 16% chance that their cancer would never have been detected within 15 years 
• This rose to 32% for men diagnosed aged 70

And rose further to 58% for men diagnosed at age 80.

The findings suggest that prostate cancer screening and PSA testing is more appropriate for men in their 50s and early 60s, as there are likely to be low levels of overdiagnosis in this group.

These findings suggest the need for more targeted, age-informed PSA testing or prostate cancer screening policies, including reexamining PSA testing policies in settings where they have led to high rates of opportunistic screening in older men, like the UK.

This is because the current `PSA tests on demand' healthcare policy has led to high rates of opportunistic PSA testing in older men, who are at high risk of harms from overdiagnosis. These harms include unnecessary treatment – including surgery and radiotherapy – which carries significant side effects and can have a negative impact on the quality of life of men whose cancers would never have harmed them. In addition, screening men older than 70 years is also unlikely to confer benefit in terms of mortality reduction." 

Dr Adam Brentnall, Reader in Biostatistics at Queen Mary's Wolfson Institute of Population Health and lead author of the study

The authors note that there are some limitations to their analysis, including the fact that screening in the CAP trial was done before the use of magnetic resonance imaging targeted biopsy, which is expected to reduce overdiagnosis. Ongoing trials, including TRANSFORM, co-led by Professor Rhian Gabe from Queen Mary and IMProVE co-led by Queen Mary's Professor Peter Sasieni in the UK, will help to provide additional evidence on overdiagnosis using contemporary screening protocols.