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April 4, 2009 2:13 am
The New England Journal of Medicine recently published research findings on prostate cancer screening. The results, from my reading at least, showed that screening was not terribly useful. So I was bewildered by subsequent media coverage that urged men to exercise “their right” to a prostate specific antigen blood test or PSA. A number of people called for the UK urgently to review its PSA screening policy.
The problem is that many prostate cancers are “benign” in their behaviour – men die with, rather than from, them – and the treatment is worse than the disease. The difficulty is in distinguishing these more placid tumours from aggressive ones.
The NEJM reported on two randomised controlled trials, one from Europe and the other from the US, where the PSA test is already widely used. The US study, involving almost 77,000 men, assigned half to PSA screening for six years and rectal examination for four years. The other group had “usual care”. After seven to 10 years’ follow-up, there was no significant difference in the mortality rate between the two groups.
The European study assigned 182,000 men to either PSA screening approximately once every four years, or to none. The conclusion was that screening “reduced the rate of death from prostate cancer by 20 per cent” but “was associated with a high risk of overdiagnosis”. In other words, over a period of nine years, in order to prevent one death from prostate cancer, 1,410 men have to be screened, and 48 men would have to be treated for prostate cancer despite the fact that they would not be harmed by the condition. However, both are interim, not final, results. Other large studies are ongoing.
It seems to me that PSA screening is either an ineffective or marginally effective intervention with significant side-effects. Men do have a right to the test. But the doctor has a duty to ensure that the pros and cons are explained adequately and fairly. However, doctors are also ethically bound to “do no harm”, so should they perform PSA screening at all? Once I would have argued for the patient to be autonomous, and for the doctor to support and facilitate. Now I’m not so sure.
Cervical cancer screening is also in the news because of a young and famous victim. As a result, there have been calls to start screening women under 25, the current age at which testing starts in England. However, when this was recently tried on the NHS, it was stopped because it produced numerous false positives and offered only a minute chance of preventing a death. If we respond more to hysteria than fact, it is unlikely that we are going make better health decisions any time soon.
Margaret McCartney is a GP in Glasgow.
For lively discussion of the latest medical issues go to Margaret McCartney’s blog
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