There have been renewed calls for the introduction of a national screening programme for prostate cancer in the UK. Former British prime minister Rishi Sunak, actors and sportspeople have joined a campaign by Prostate Cancer Research seeking the introduction of a screening programme.
Prostate cancer is the most common cancer in men if skin cancer is excluded. Each year, more than 3,000 men are diagnosed with prostate cancer in Ireland. One in eight men will get prostate cancer at some point in their lives. And the chances of getting prostate cancer increase as you get older.
The prostate is a gland about the size of a walnut and is located around the urethra – the tube that runs from the bladder to the penis. However, late last year, the UK national screening committee announced a draft decision to advise the government there against routine population screening for all men.
We have a blood test to detect the disease, so why the reluctance to start screening here and in the UK?
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The evidence shows that the standard blood test used for early detection, the prostate specific antigen (PSA) test, is not accurate enough when used as a general screening tool. The PSA test isn’t nearly as reliable as the tests used for breast and cervical cancer screening programmes. While breast cancer tests have a “sensitivity” (ability to accurately detect cancer) of between 50 and 91 per cent, the PSA test has a sensitivity of just 20 per cent.
Conditions such as a benignly enlarged prostate, infections or even recent exercise can give false results and make it look like someone has cancer when they don’t. (And PSA testing can also trigger false negatives so that men with prostate cancer are told they don’t have the disease.)
This means that if we had a national screening programme, many men with an elevated PSA would have to undergo a whole chain of unnecessary tests and investigations into the prostate, some of which can be invasive and painful. The uncertainty surrounding prostate cancer screening is illustrated by the 23-year follow-up results of the European Randomized Study of Screening for Prostate Cancer (ERSPC) trial.
ERSPC is a multicentre, randomised study conducted across eight European countries in more than 160,000 men aged 55-69 years. One group of participants was offered repeat PSA testing while the other was not invited to screening. The results showed the absolute risk reduction of prostate cancer screening was 0.2 per cent. This means that the number needed to screen to prevent one prostate cancer death is approximately 500. Or to put it another way, some 499 out of 500 men get no benefit from being invited to be screened.
A supplemental figure was also revealing: it showed that screening is twice as likely to find low-risk cancer but 44 per cent less likely to find high-risk prostate cancer. Most prostate cancers are slow-growing, with postmortem studies showing that a high percentage of older men who died from other causes had prostate cancer they never knew about.
The problems of PSA screening highlighted by the ERSPC research are that prostate cancer is rarely deadly and is often slow-growing. The research also shows that screening is most likely to pick up low-risk tumours. However, once a PSA test is positive it is hard not to act, and the interventions can result in complications, such as incontinence and impotence. And PSA tests cannot distinguish between slow-growing and more aggressive prostate cancers.
The real dilemma around PSA screening is the need to develop a test that will accurately diagnose aggressive prostate cancer in younger men. Until such a test emerges, it will be difficult to justify a national prostate cancer screening programme.
Where does that leave men aged 50 or over who are wondering whether to have a PSA test? They need to make an informed choice having discussed the pros and cons with their GP.
