A trial looking at a PSA blood test for prostate cancer (CAP trial)

Cancer type:

Prostate cancer

Status:

Results

Phase:

Other

This trial was done to see if an invitation to have a PSA blood test Open a glossary item would reduce the number of men dying from prostate cancer.

The trial was supported by Cancer Research UK. It was open for people to join between 2002 and 2009.

The team published their initial results in 2018, having followed up the men for an average of 10 years. They published the longer term results in 2024, having followed them up for an average of 15 years.

More about this trial

Prostate specific antigen (PSA) is a protein that is often raised in men who have prostate cancer. But it can be raised for other reasons. Some men with a raised PSA don’t have prostate cancer. And some men with prostate cancer don’t have a raised PSA.

Men whose prostate cancer is diagnosed after a routine PSA test often have lower risk cancers. This means they are likely to grow slowly and may never cause any problems or need treatment during a man’s lifetime. It is important that screening tests do not overdiagnose Open a glossary item these lower risk cancers. The treatment people have may cause unpleasant side effects.

Some prostate cancers grow more quickly and need treatment straight away. Screening aims to identify these cancers early. And to reduce the number of men who die because of their prostate cancer.

Researchers wanted to find out if the PSA test can be used as a screening test for men aged 50 to 69. Screening means testing people for early stages of an illness before they have any symptoms. There is no screening programme for prostate cancer in the UK.

As part of this trial, some men were offered a PSA test and some men weren’t, although they could have the test if they asked their GP for it.

The main aim of the trial was to see if an invitation to have a PSA test would reduce the number of men dying from prostate cancer.

Summary of results

This trial showed that only a few less men who were invited for a PSA test died because of prostate cancer.

There was a small difference between the group of men who were invited to have a PSA test, and those who weren’t.

Results
This trial recruited over 400,000 men who had not been diagnosed with prostate cancer at the start of the trial. The men taking part were placed into 1 of 2 groups at random, and:

about half were offered a PSA blood test
about half were not offered a PSA test (the control group)

Just under 200,000 men were invited to see a nurse to discuss having a PSA test to begin with. Of these:

more than 70,000 saw a nurse
more than 60,000 had a PSA blood test
just under 7,000 had a raised PSA level
just under 6,000 had a biopsy of their prostate
just under 3,000 were diagnosed with prostate cancer

The team looked at the long term results in 2021. The men taking part had been in the trial between 12 and 19 years by then. The median Open a glossary item time they’d been in the trial was 15 years.

Prostate cancer risk
The team looked at the risk of being diagnosed with prostate cancer 15 years after joining the trial.

They found that out of every 1,000 men it was:

71 men in the group who had been offered a PSA test
69 men in the control group who were not offered a PSA test

They then looked at the risk of dying because of prostate cancer. Out of every 1,000 men this was:

7 men in the group who had been offered a PSA test
8 men in the control group who were not offered a PSA test

They also looked at the total number of men that had died of any cause. This could have been because of prostate cancer. But it could have been for any other reason. It was just over 230 out of every 1,000 men in each group.

The results showed that the men who were diagnosed with prostate cancer after having the PSA test as part of the trial, were more likely to:

be younger when they were diagnosed
have cancers that were low risk
have cancer that had not spread

So it was more likely that they had prostate cancer diagnosed that wouldn’t need treatment or cause problems during their lifetime.

Conclusion
The trial team concluded that a few less men in the PSA test group died because of prostate cancer. But the difference between the two groups was very small.

Out of every 1,000 men who were invited for a PSA test, one less man died of prostate cancer. There was no difference in the number who died overall.

The team point out that it is important to balance the potential benefits of screening with the risks of being overdiagnosed Open a glossary item with prostate cancer that would never cause harm in someone’s lifetime. The team say this overdiagnosis can affect quality of life and having unnecessary treatment can cause side effects. These possible side effects include infection after a prostate biopsy , bladder and bowel problems and problems getting an erection.

The team say this trial provides men aged 50 to 69 years with information about the potential benefits and risks of having a PSA test. They point out that this information can now be used to support decision making about whether or not to have a PSA test.

More detailed information
There is more information about this research in the references below.

Please note, the information we link to here is not in plain English. It has been written for healthcare professionals and researchers.

PSA Screening and 15-year Prostate Cancer Mortality: A secondary analysis of the CAP randomized clinical trial.
Richard M. Martin and others
Journal of the American Medical Association (JAMA), published online 6th April, 2024.

Effect of a Low-Intensity PSA-Based Screening Intervention on Prostate Cancer Mortality: The CAP Randomized Clinical Trial.
Richard M Martin and others
Journal of the American Medical Association (JAMA), 2018. Volume 319, issue 9, pages 883-895.

Where this information comes from
We have based this summary on the information in the articles above. These have been reviewed by independent specialists (peer reviewed Open a glossary item ) and published in medical journals. We have not analysed the data ourselves.