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PSA testing

In the first of two articles this week focusing on prostate cancer, GP expert Dr Graham Easton examines the pros and cons of testing for prostate specific antigen and explores the fallout from this clinical controversy for GPs

In the first of two articles this week focusing on prostate cancer, GP expert Dr Graham Easton examines the pros and cons of testing for prostate specific antigen and explores the fallout from this clinical controversy for GPs

Many men present to their GPs requesting a test for prostate cancer. They have no symptoms, but their argument is that it is better to be safe than sorry.

The controversy

The logic behind the request is that a simple test will catch the disease early while still treatable. But the snag is that there is no robust evidence that screening healthy men for prostate cancer improves mortality, and it may do more harm than good.

This friction between intuitive logic and a lack of high-quality evidence to back it up has created an enduring and often vicious controversy. Experts are still divided on the issue, official recommendations have been conflicting, and powerful and vocal lobby groups have sprung up to press for widespread population screening.

Nowhere has the debate been more prickly than in the US where the American Urological Association recommends that all men with at least a 10-year life expectancy should be offered regular prostate cancer testing after the age of 50. For example, in 2001 two editors of the Western Journal of Medicine argued in the San Francisco Chronicle that there was no good evidence to screen healthy men for prostate cancer. Their article provoked a strong backlash; they were accused of promoting geriatricide and many advocates of prostate screening called for them to be sacked. The hope is that the debate about the value of prostate cancer screening will be settled once and for all when we see the results from two ongoing large, high-quality trials.

• The European ERSPC trial started in 1991 and is looking at the effects of prostate cancer screening in 183,000 men aged 50-75.

• The American PLCO trial, which started in 1993, is a 23-year trial across 10 screening centres in the US.

The fall-out

Until these key trials come to their conclusions, what evidence do GPs have to go on?

Digital rectal examination (DRE) has not been proved to improve morbidity or mortality and the accuracy of the examination depends on who is doing it. Even among trained clinicians, it has poor reproducibility. The other problem with DRE as a screening test is that when it is used on its own, more than half of men with prostate cancer detected will have disease that has spread outside the gland at diagnosis. The prostate specific antigen (PSA) test picks up more cancers at earlier stages and smaller sizes than DRE, but it is not a specific test for prostate cancer. For example, it can also be raised if the prostate is:

• enlarged (benign prostatic hyperplasia – BPH)

• inflamed (prostatitis)

• infected.

Roughly two out of three men with a raised PSA will not have prostate cancer. Unfortunately it is a test with high false positive and false negative rates. The imperfect nature of these two GP-friendly screening tests leads to other potential problems. Abnormal results can lead to anxiety, diagnostic biopsies are painful and can cause bleeding and infection, and some men will have unnecessary treatments, all of which have significant side-effects.

Of course, for some men, a true negative test will provide welcome reassurance that all is well. And for those men who have a true positive, they may benefit from having an aggressive cancer picked up early and treated. A recent report found that in early prostate cancer, radical prostatectomy reduces mortality and the risk of spread compared with watchful waiting. But it is hard to predict the natural history of early prostate cancer – whether it will behave like a pussy cat or a tiger – and from post-mortem examination studies it is still true that men tend to die with the disease rather than from it.

A recent Cochrane review found two randomised controlled trials of prostate screening which looked at more than 50,000 men. The available evidence was flawed but found that men randomised to screening had prostate cancer more frequently detected but did not have a reduction in prostate cancer specific mortality. Case control studies have generally not found reduced mortality with testing.

Reflecting on the evidence

Weighing up the evidence for and against a national screening programme, the UK National Screening Committee's position is that until there is clear evidence to show that a national screening programme will bring more benefit than harm, the NHS will not be inviting men who have no symptoms for prostate cancer screening.

However, in recognising the considerable demand for the PSA test among men worried about the disease, the Government has introduced a PSA Informed Choice Programme. The key elements are the provision of high-quality information for men requesting the test, to help them decide whether to have the test according to the available evidence about risks and benefits.

Practical implications for GPs

NHS prostate cancer risk management programme

This suggests GPs should provide men with balanced information on the benefits and limitations of the PSA test for prostate cancer. There is an excellent information pack designed to help the primary care team counsel men who request the test, with algorithms and diagrams to explain the possible outcomes.

There is also a patient leaflet which aims to give balanced information in a clear way to help men make their own decisions. You can download both from the NHS cancer screening website (see 'further information', right). In my experience men will still ask: 'But what would you do, doctor?' I always bounce their question back to them; without any robust evidence either way, it really has to be a personal decision.

You can be clear, though, that men with a life expectancy of less than 10 to 15 years (because of advanced age or a serious co-existing condition) are unlikely to benefit from routine testing. I sometimes summarise the pros and cons by saying to the patient: 'On the one hand it may pick up cancer early when it can still be treated; and a normal result could put your mind at rest. On the other hand, it is not a very accurate test for prostate cancer, and could lead to unnecessary worry or medical tests and even surgery that you don't need.'

Online cancer risk calculator

When it comes to discussing what to do after a DRE or PSA test you could try the Online cancer risk calculator developed by the National Cancer Institute (search under prostate). It is designed to estimate the risk of biopsy detectable prostate cancer; all patients have to do is type in their age, race, PSA level, family history of prostate cancer, DRE result, and any previous biopsy result. It then gives a risk in percentage terms.

It is very easy to use and I can imagine it being a helpful tool to use in a discussion with a patient about whether to refer for a biopsy.

Dr Graham Easton is a GP in Ealing, west London

Competing interests: Dr Easton has helped prepare the patient leaflets for the Informed Choice Programme, and has worked with the Prostate Cancer Charity on an audio programme of men's experiences of prostate cancer

key points

• Early detection and treatment may improve morbidity and mortality, and provide reassurance.

• Prostate cancer testing by DRE and PSA testing can have false positive and false negative results, and detects many cancers that may never cause any symptoms or shorten lifespan.

• There is no robust evidence for or against a screening programme for prostate cancer; the results of the ERSPC and PLCO trials should help fill the evidence vacuum.

• There is no population screening programme for prostate cancer in the UK, but men interested in a PSA test should be given balanced information so they can make an informed decision.

• Asymptomatic men with life expectancy of less than 10 to 15 years are unlikely to benefit from routine testing.

• An online prostate cancer risk calculator could help with decisions about when to refer after PSA testing.

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