Screening with a PSA test has a small impact on prostate cancer deaths but leads to overdiagnosis

The largest study to date investigating a single invitation to a PSA blood test* to screen for prostate cancer has found it had a small impact on reducing deaths, but also led to overdiagnosis and missed early detection of some aggressive cancers. 

The CAP trial, published in the Journal of the American Medical Association (JAMA) and carried out by researchers from the universities of Bristol, Oxford and Cambridge, involved over 400,000 men aged 50-69. Just under half received a single invitation for a PSA test as part of the trial. 

After following up for 15 years, there was a small difference in the number of men who died from prostate cancer between the two groups – nearly 7 men out of every 1,000 in the group invited for screening had died from prostate cancer, compared to nearly 8 men out of every 1,000 in the group who hadn’t been invited for screening. 

The results of the trial show that an estimated 1 in 6 cancers found by the single PSA screening were overdiagnosed. 

Cancer Research UK warns that overdiagnosis** of prostate cancer is the main worry with PSA testing for early detection. This can result in the unnecessary treatment of cancers that would not have caused any harm in someone’s lifetime. Overdiagnosis can have a negative psychological impact, and treatment of prostate cancer may cause physical side effects including the possibility of infection following a biopsy, erectile dysfunction, and bladder and bowel problems.  

Cancer Research UK also raises awareness of the importance of listening to your body and getting to know what's normal for you. If you notice a change that doesn’t go away or is new, then speak to your doctor. 

If a man has urinary symptoms*** – most of which are caused by a non-cancerous enlargement of the prostate – he can contact his GP for advice, and this may include a PSA test.  

Professor Richard Martin, lead author and Cancer Research UK scientist at the University of Bristol, said: 

“Our studies have been measuring the effectiveness of the PSA test with hundreds of thousands of men for 15 years. The key takeaway is that the small reduction in prostate cancer deaths by using the test to screen healthy men does not outweigh the potential harms. 

“This results in some men going on to have invasive treatment that they don’t need, many years earlier than without screening, and the test is also failing to spot some cancers that do need to be treated. We need to find better ways to spot aggressive prostate cancers, so we can treat them early.” 

Prostate cancer is the 2nd biggest cancer killer of men in the UK, causing 12,000 deaths a year. There is currently no national screening programme for the disease. The UK National Screening Committee (NSC)****, which reviews the evidence for screening programmes, doesn’t currently recommend screening for prostate cancer because it is unclear that the benefits outweigh the harms. 

Despite being widely used to decide when to send men with urinary symptoms for further checks, when used to screen for prostate cancer, research has shown that the PSA test is inaccurate - it increases detection of low-risk prostate cancers and misses some high-risk ones. 

There have been improvements in diagnosing and treating the disease in the years since this trial began, including the introduction of MRI before biopsy. These changes may help to prevent some harms associated with PSA testing, but more research is needed into ways to find aggressive cancers that need to be treated. 

Naser Turabi, director of evidence and implementation at Cancer Research UK, said: 

“Prostate cancer remains the second most common cause of cancer death in men in the UK. Despite breakthroughs in treating the disease, there’s more we can do. 

“The evidence shows that using a single invitation for a PSA test for a prostate cancer screening programme is likely to do more harm than good for men. 

“We are funding research to help us find ways of diagnosing the disease early to reduce mortality, and we have trials taking place to find the best treatment for men with prostate cancer.  Our search is not over – we're determined to find ways to accurately detect aggressive prostate cancer early and identify those at highest risk.” 

Early prostate cancer usually has no symptoms so early detection is challenging. To try and save more lives from the disease, Cancer Research UK is funding more trials and research into prostate cancer. This includes speeding up diagnosis for men with aggressive disease with new blood, urine or genetic tests so they can start treatment sooner. 

Other research, such as the STAMPEDE trial, is aiming to find the best treatment for men with advanced prostate cancer to further improve survival and quality of life. The charity has spent £21 million on prostate cancer research over the last two years to improve outcomes for patients. 

Dr Neil Smith, GP for Cancer Research UK and GP Lead for Lancashire and South Cumbria Cancer Alliance, said: 

“With prostate cancer causing 12,000 deaths in the UK every year, we completely understand why men want to know if they have the disease, even when they don’t have symptoms. However, this research highlights that a PSA test for early detection can do more harm than good – it's simply not accurate enough and can lead to some men having tests and treatment that they don’t need.  

“You know your body best – so if you do notice any unusual changes, contact your GP. It probably won’t be cancer, but if it is, then spotting it earlier means that treatment is more likely to be successful.” 

ENDS 

For media enquiries, contact Anna Cawdron in the Cancer Research UK press office on anna.cawdron@cancer.org.uk / 020 3469 8928, or out of hours, on 020 3469 8301.   

Notes to editor 

The new 15-year CAP study paper can be viewed in full here. The study can be found on JAMA here once the embargo lifts. 

The 10-year findings of the study, which found no mortality benefits from a single invitation for PSA screening, can be viewed here. 

The study spanned around 570 GP practices across the UK. Cancer Research UK is funding work to follow the men in this study for another three years, to see any longer-term effects, and try and identify if specific groups of men do benefit from the test. 

*The PSA test is a blood test that measures the amount of prostate specific antigen (PSA) in someone’s blood. Both normal and cancerous prostate cells produce PSA, so it's normal for all men to have some PSA in their blood. A high level of PSA can be a sign of cancer, but it can also be raised after recent ejaculation, vigorous exercise or because of a urine infection. 

If someone has a high level of PSA, they may be referred by their GP to a specialist, to have further checks to see if they have prostate cancer. 

Prostate cancer - UK National Screening Committee (UK NSC) - GOV.UK (view-health-screening-recommendations.service.gov.uk) 

** Overdiagnosis is the diagnosis of a cancer that wouldn’t have gone on to cause harm in a person’s lifetime. It means that in some cases, if someone hadn’t been tested for cancer through screening or another type of test like PSA, the person might never have known they had cancer, and would not have died from the disease. In these scenarios, it means someone will go through treatment, distress and potential side effects when they didn’t need to. Different studies are investigating how we can better identify which cancers need treating, and which ones don’t. More information can be found here. 

*** Urinary symptoms such as difficulty peeing or needing to pee more often are usually caused by a condition called benign prostatic hyperplasia (BPH).  People with bothersome urinary symptoms should see their GP.  

****The UK National Screening Committee (NSC) advises ministers and the NHS about aspects of screening. They review the evidence around whether or not to support the introduction of a new screening programme, which includes ensuring the benefits of a screening programme outweigh the harms. The NSC does not currently recommend screening for prostate cancer, because the PSA test is not accurate enough to detect prostate cancer that needs treatment.  The new results from this study will be factored into future NSC’s reviews on the evidence around prostate screening.