Prostate cancer: Behind the push to perfect screening
Ireland’s National Screening Service already tests for breast, cervical, and colon cancer. Large-scale trials are under way in Europe and Britain to assess the viability of a test for prostate cancer.
Prostate is the cancer most commonly diagnosed in men. It affects one in six and the risk escalates with age.
“If they live long enough, all men develop areas of cancer in their prostate,” says Mr David Galvin, head of research at the Irish Society of Urology and consultant at the Mater and St Vincent’s University Hospitals.
Because prostate cancer is slowgrowing, not all of these cancer cases “will impact on a man’s health or life expectancy”, Galvin says. However, some will and it’s crucial that those cases are detected and treated promptly. This is where a national screening programme could help.
Ireland’s National Screening Service already tests for breast, cervical, and colon cancer. Large-scale trials are under way in Europe and Britain to assess the viability of a test for prostate cancer.
Ireland is one of five EU countries taking part in Praise-U (Prostate Cancer Awareness and Initiative for Screening in the European Union). It’s a three-year project involving a pilot study led by Galvin and his team at University College Dublin.
“Screening for prostate cancer could be relatively simple, but we haven’t worked out the best way to screen yet,” he says. “That’s why we’re running these trials.”
“There, they will be evaluated by urologists, who will decide whether they are high or low risk,” says Galvin. “High-risk cases will be offered an MRI scan of their prostate, which is up to 90% accurate in detecting possible cancer.”
The prostate is a small gland that runs underneath a man’s bladder. In the 1980s, researchers discovered it secreted a protein, called prostate-specific antigen (PSA), and that PSA levels rose when men have urinary infections, an enlarged prostate, or prostate cancer.
Since then, men presenting to their doctors with symptoms like difficulty peeing have been routinely given a PSA blood test. “We then rule out infection and measure the size of the prostate with a digital rectal exam to decide if there is a risk of cancer,” says Galvin.
This is an effective method of detection, Galvin says, but the problem is that it requires men to present to their GP and not all men do. The Praise-U study will assess if a finger-prick PSA test that can be done at home would catch more prostate cancer cases early.
Some 8,000 men aged between 50 and 69 will be invited to participate in the trial. They will be sent a simple finger-prick test in the post — which can be done in a matter of minutes at home — and then be asked to return their sample in a pre-paid envelope.
Once their sample has been analysed, they will be informed of their results. Most will have normal PSA levels, which means no further testing is required. But some will be referred to rapid access clinics for further investigation.
Galvin believes this home-based test could work better than the current model, which relies on GPs. “GP services are stretched and not resourced to do large-volume testing,” he says. “In addition, making appointments and taking time off work for testing is challenging for many men. A home test fits people’s lives better, as it can be done any time.”
Dr Alan Smith, a consultant in public health medicine with the National Screening Service, outlines other barriers that may prevent men from presenting to their GP with prostate problems.
“Research published in European Urology this year found five categories of barriers,” Smith says. “There’s a lack of knowledge about prostate cancer, it’s symptoms, screening procedures, and risks. There are masculinity constructs, including concerns about bodily invasion from screening procedures. There’s also fear of getting the disease and the screening procedure itself.”
Galvin hopes that “a non-invasive, home-based test that makes screening easier and more accessible could help more men overcome these barriers”.
Yet there are potential problems with PSA tests and the Praise-U pilot.
One is that asking men to prick their fingers and fill a vial with blood is easier said than done. “Not all men successfully fill the container and a third don’t return the kit,” says Galvin. “So we are working to improve the offering.”
Another is the risk of false positives. An enlarged prostate, inflammation, or infection can all cause elevated PSA levels, leading to what Smith calls “a high rate of false alarms, which can lead men down a path of anxiety and invasive follow-up procedures, even when no cancer is present”.
PSA screening isn’t “accurate enough to distinguish between cancers that will cause harm and those that won’t”, Galvin says. This can lead to over-diagnosis and over-treatment of “slow-growing cancers that would never have caused symptoms or shortened a man’s life”.
There can be false negatives, too. Galvin says, “PSA levels don’t go up in 1% to 2% of men with prostate cancer, which means some cancers will be missed in PSA-based screening programmes.”
While Praise-U is being rolled out in Ireland, a large-scale trial, called Transform, is under way in Britain. Simon Grieveson, the assistant director of research at Prostate Cancer UK, explains that it “aims to provide the definitive evidence needed to show the best way to screen men and save thousands of lives a year”.
The trial will have two stages. The first involves 13,500 men, aged 50 to 74, and takes place over two years. Researchers will compare the impact of MRI scans, genetic testing, and PSA blood testing on these men’s health outcomes.
The most effective methods will then be taken forward in to the second stage of the trial, which will involve up to 300,000 men being followed for a decade or more.
“At the end, we hope to have identified the safest, most accurate and cost-effective way of screening men for prostate cancer, so that, one day, all men will get regularly tested and aggressive cancers will be found in time for a cure,” says Grieveson.
The test that is finally determined as the safest and most accurate might not be a PSA. New screening tests are currently being developed, including one that Galvin refers to as “a promising new urine test men can do at home” and a saliva test that can be analysed for genetic variants in a man’s DNA that make them more susceptible to prostate cancer.
The researchers working on the Praise-U and Transform trials are likely to have been bolstered by the findings of a major study that was just published in the New England Journal of Medicine.
This study followed 162,000 men from eight European countries over a 23-year period and concluded that one death from prostate cancer was prevented for every 456 men invited for screening and one death was averted for every 12 men diagnosed.
Smith acknowledges that these are positive findings and strengthen the case for organised screening.
But he points to an equally prominent line in the study, the one that says, ‘the harms associated with PSA-based screening — including unnecessary testing, biopsies, and subsequent over-treatment — remain a critical concern.’
Whether it’s the finger-prick blood test that is being appraised by the Praise-U pilot, or urine or saliva tests that might be considered in future, Smith explains that for any to be approved as part of a screening programme they have to meet 20 criteria set by the national screening advisory committee. The tests, for example, have to be simple, safe, precise, reliable, and validated.
“It’s natural to think that more screening is better and catching cancer early is always the right thing to do,” he says. “But the reality is more complex. A population screening programme can cause more harm than good, if it leads to unnecessary treatment for cancers that would never have threatened somebody’s health. That’s why we need rigorous research, like Praise-U and Transform, to guide our decisions by showing us where the balance truly lies between benefit and harm.”
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