Behind the headlines: PSA screening reduces prostate cancer deaths but can miss aggressive cancer

Researchers involved in the 15-year-long CAP (Cluster Randomised Trial of PSA Testing for Prostate Cancer) study have released results showing that using PSA blood testing to screen for prostate cancer can slightly reduce the risk of men dying from the disease (meaning 1 in 1000 fewer men die from the disease), but may miss aggressive cancers in some men, and over diagnose the disease in others. 

The trial involved more than 400,000 men aged 50 to 69, and these findings were announced today (Saturday 6 April) at the annual European Association of Urology Conference and published in full in the Journal of the American Medical Association. 

The results are important. They reinforce the evidence from another large, long-term screening trial that came to the same overall conclusion. That trial was the basis for our view that PSA blood testing does reduce deaths from prostate cancer, but also has the potential to cause harm to a large number of men and misses too many significant cancers. 

Below we dive into the results and what they mean for men at risk of prostate cancer and the potential for a screening programme: 

What were the results?

Of the 400,000 men in the trial, around half were invited to have a PSA blood test, while the other half were not. 

Comparing the two groups after 15 years, there was a small difference in the number of men who died from prostate cancer.  

In the group who were invited for a PSA blood test, around 7 out of every 1,000 men died of prostate cancer. In the group who weren't invited, around 8 out of every 1,000 men died from the disease. 

However, over the course of the 15 years, men in the PSA arm were also more likely to experience one of the harms we know can happen when diagnosing prostate cancer (like a diagnosis of a cancer that will never cause harm, or an unnecessary biopsy and potential side effects). For example, in the group that were invited for a PSA blood test, 22 out of every 1,000 men were diagnosed with a harmless prostate cancer compared to 16 out of every 1,000 in the group who weren’t invited.  

It’s also clear that the PSA testing included in this trial didn’t do a good enough job at preventing death from prostate cancer. We can see this in the large number of men who were invited to have a PSA blood test but who still died from the disease (7 out of every 1,000). 

Were these results unexpected?

The results tally with those from the European Randomized Study of Prostate Cancer Screening (ERSPC) trial, but those results have not been accepted as widely or as confidently as we believe they should have been. 

The latest results from the UK CAP trial are really important because they back up those findings and make it impossible to ignore the fact that PSA testing does save lives but also – in both of these trials – leads to a lot of extra biopsies and a lot of extra diagnoses of harmless cancers.  

It’s also important to note that both trials were conducted in the era before MRI scanning was routinely used before sending men with a raised PSA for a biopsy. The modern pathway in the UK, where MRI is widely used, is likely to have reduced harm – although there is not the same level of evidence of that harm reduction as we now have for the results using the old pathway. 

How does this help men at risk of prostate cancer?

The results from both CAP and ERSPC show us where the system of testing and diagnosis can be improved to help men who are at risk of prostate cancer. 

Firstly, they show us what we need to do to help men now.  

The results from the trials show that the evidence is still complicated, with both harms and benefits possible once men choose to have a PSA blood test. 

This means we need to make sure that all men at higher risk (all men over 50, and men over 45 who are Black or have a family history of prostate cancer) understand their risk, as well as the pros and cons of getting a PSA blood test. This is especially important as prostate cancer often shows no symptoms in its early stages. 

Our online risk checker is the best way to do that, as it gives balanced, up-to-date information on the PSA blood test to help men understand their risk and what they can choose to do about it. 

Secondly, the results show us what we need to do now to help men in the future. 

The only way we will improve the path ahead for men is to develop and test new ways to diagnose prostate cancer that can find the aggressive cancers, that can be missed by PSA blood tests, and further reduce the number of men sent for a biopsy or diagnosed with a harmless cancer unnecessarily.  

Our £42m TRANSFORM trial is designed to do exactly that: testing new, modern methods to diagnose prostate cancer, and accelerating and supporting the development of diagnostic tests that are still in their infancy. That trial will find the best way to screen men for prostate cancer, so one day all men get an accurate, early diagnosis and we save more lives while doing less harm. 

Commenting on the release of these results, Dr Matthew Hobbs, Director of Research at Prostate Cancer UK, said: “A previous major European trial showed that screening with PSA blood tests does reduce deaths from prostate cancer but that it also misses important cancers and harms men who are given treatments or biopsies they don’t need. The results from the UK CaP trial are extremely significant because they back up these findings.  

“This balance of benefit and harm, and the fact that men often have no symptoms from early-stage prostate cancer, makes choosing whether or not to have a PSA blood test a complex decision. Prostate Cancer UK’s online Risk Checker helps men understand their risk and gives balanced, up-to-date information on the PSA blood test to help men weigh up all the key considerations before making that decision. If you’re a man over 50, a Black man over 45, or a man over 45 with a strong family history of prostate cancer, you are at higher risk of getting the disease — you can take the Risk Checker now.  

“The way we diagnose prostate cancer has improved a lot since these trials, thanks to the introduction of routine MRI scans which have made the process safer and more accurate. However, we still need better evidence to understand the full impact of MRI and other recent changes. The number of men screened who still died of prostate cancer in both trials makes crystal clear that the imperative now is to develop, test, and prove new ways to diagnose prostate cancer that detect those aggressive cancers missed by PSA tests and reduce potential harm even further.  

“Prostate Cancer UK has launched the landmark £42m TRANSFORM trial to do just that, so that eventually each man with aggressive prostate cancer gets an early, accurate diagnosis. We are proud to be leading the charge to save more lives and do less harm by putting a very significant amount of funding into the next definitive prostate cancer screening trial.”