The American actor and director Ben Stiller said last week that a simple blood test saved his life from prostate cancer. The test, known as a prostate specific antigen (PSA) test, is widely available and found that he was suffering from a ‘mid-range aggressive’ prostate cancer at the age of 48 for which he has now received treatment.
It seems an obvious assumption to make that if he had not had a PSA test then his cancer would never have come to light and he would have died from it. With prostate cancer killing over 10,000 men a year in the UK, any early, accurate screening test which reliably identified all men with this cancer, and in doing so saved their lives without having unnecessary treatment, would be a huge medical tool.
Unfortunately, the PSA test isn’t that test. Not only are there strong reasons why it is not offered as a routine screening test here in the UK but, somewhat counter-intuitively, early diagnosis may not even affect the longevity of that patient.
Starting at first principles, then, the benefit of PSA testing as a screening tool remains uncertain. It may have value for screening first-degree relatives of men with prostate cancer who are consequently at an increased risk of developing the disease — about 10 to 15 per cent of British men — but this approach still needs to be fully tested.
There are many unknowns about the PSA test. It can often detect problems in the prostate at an early stage, but a positive result does not always mean cancer. In fact, two thirds of men with a raised PSA level don’t have prostate cancer — so-called ‘false positive’ tests — and one review of PSA screening suggested that for every life saved, 27 men would have to be diagnosed with it.
On the flipside, up to 15 per cent of men with prostate cancer have a normal PSA level — the ‘false negative’ test. The PSA test is also not reliable at finding out which prostate cancers will then go on to become invasive. So, many men with a raised PSA can be given damaging treatments such as surgery and chemotherapy for a cancer that they often would die with and not because of, and which in large numbers of cases would never have done them any harm at all. (Just 25 per cent of men who have a prostate biopsy due to an elevated PSA level are found to actually have prostate cancer.)
Thus, getting the result of a PSA test — or even having it in the first place — can be a confusing situation that requires clear information and advice from a health professional. The NHS currently recommends detailed information that should be supplied to men who have requested a PSA test so they can make an informed choice.
But the simple fact remains that no one really knows how best to use this test. It is useful for diagnosing and monitoring men who already have symptoms associated with prostate cancer, and there is an argument for thinking it could also be useful for screening men at a higher relative risk of the disease, such as close relatives of prostate cancer patients.
I recently chaired a meeting of a dozen or so key urologists in the UK and asked them if they would have a routine PSA test. Not one said yes. This leaves us in something of a fudge – the test is out there, it can sometimes pick up prostate cancer, but has significant errors and implications for treating men unnecessarily.
My current view is in line with the general NHS advice, which is that if you are a man over 50 and want to have your PSA level tested, your GP should talk through the pros and cons of the test and, if agreed, arrange this for you on the NHS. If your PSA is raised, then other tests may be required but a change in a PSA level by itself is not a reason for starting treatment.
Better testing is key here, and on the horizon is a new test called the IsoPSA test. It is hoped that this test will be able to differentiate between high-risk and low-risk disease, as well as benign conditions, by identifying structural changes in protein biomarkers as opposed to the current PSA test that simply measures the protein’s concentration in a patient’s blood.
In the meantime though, the medical balancing act of having a PSA test against the overdiagnosis of a cancer that will never kill and the overtreatment of someone who does not need it continues.
Ben Stiller will disagree – and I can understand why – but the UK will not be recommending routine PSA testing for all men any time soon.