An MRI scan could improve the accuracy of prostate cancer screening
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There is both good news and bad news about prostate cancer screening. First, the bad news: the blood test involved, which measures a compound called prostate-specific antigen (PSA), is too inaccurate. As a result, some men end up having cancer treatments they didn’t really need, which can result in incontinence and erectile dysfunction.
On the other hand, combining a PSA test with an MRI scan of the prostate would make screening more accurate, especially if the dual test were recommended only for those at high risk of the tumour. A group of experts called the Lancet Commission on Prostate Cancer has made this recommendation in a new report.
A rethink on prostate screening is certainly needed, but will these new proposals succeed in reducing the harms?
Prostate screening has long been controversial. Although PSA is released at high levels by cancerous prostate cells, it is produced at lower levels by healthy ones too.
The blood test was introduced as a way to track the success of cancer treatment. It started being used as a screening test in the 1990s, partly as a result of campaigns by men’s health groups that wanted something equivalent to breast cancer checks.
The problem is that PSA alone is an unreliable screening tool. Levels can become temporarily raised after sex, during a urinary tract infection or even by a bike ride. Even if the rise is persistent, most prostate cancers grow so slowly that, if left alone, they would never have been noticed or caused any problems.
These issues would matter less were it not for the fact that the treatments to remove the cancer – usually surgery or radioactive pellets put into the tumour – can often cause permanent incontinence or erectile dysfunction. Even a biopsy to find out if cancer is present can result in these problems.
Randomised trials show that, for every 1000 men who take up regular PSA screening, there is one fewer death from prostate cancer over 10 years but three men are left with incontinence and 25 with impotence.
These uncomfortable figures have left health services in most high-income countries, including the UK and Australia, with an uneasy compromise. They don’t send invitations for prostate screening – unlike with breast or bowel cancer checks – but people who ask for the test can have one if the risks are explained.
The upshot is that PSA tests are taken up more by men with higher incomes and less by those with lower incomes or who are Black, says the new report. This is unfortunate because men of African heritage are about twice as likely to get prostate cancer as men with European heritage.
The report’s authors say health systems should use a more sophisticated form of screening, involving both a PSA test and an MRI scan. The scan lets doctors assess the prostate’s size and spot any suspicious areas that might indicate a cancer.
In some countries, including the UK, something approaching this dual method is already happening, because the next step for anyone found to have high PSA levels is an MRI scan. This means those whose scan results are reassuring can avoid the more invasive biopsy. “That mitigates hugely the problem of overdiagnosis,” says Nicholas James at the Institute of Cancer Research in London, one of the report authors.
But it could be even better to combine the PSA test with the MRI scan before any results are fed back, to avoid men being mistakenly told they may have cancer, says James.
The commission says health services should begin formal screening campaigns using this combined method, but targeting three groups known to be at higher risk. These are: Black men, anyone with a family history of prostate cancer, and men with mutations in one of the BRCA genes, which are also linked with breast cancer.
This would avoid the current situation where men with lower risk levels are arguably getting too many PSA tests, while those at higher risk get fewer or none at all.
The proposals are certainly thought-provoking, but it remains to be seen whether they will curb people’s appetite for prostate screening. Some US doctors already go further than the current recommendations, carrying out PSA tests on blood taken for men’s annual health checks, without even discussing it with the individuals concerned, says David Ropeik, a US author who has recently written a book called Curing Cancerphobia.
The arrival of PSA testing may be like the opening of Pandora’s box, says James – but with the proposed new approach, at least some of the harms would probably be reduced.
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