MEDICAL MATTERS:When testing for prostate cancer is ill-advised
TEN YEARS ago, if a (male) patient came for a consultation and said: “Doc, I wonder would you do the blood test for prostate cancer?” the likely reply was, “Sure”. Now, however, following the publication of a recent raft of research, the likelihood of me advising against regular screening using the PSA test has increased significantly.
PSA stands for prostate specific antigen, a substance whose levels in the body increase when prostate cancer develops. But it also becomes elevated for other reasons, with the result that what experts originally thought would make an ideal screening test (along with a rectal examination of the prostate gland), has been found to be increasingly fallible.
The Swedish authors of the most recent research into prostate cancer screening have said it may give rise to both over-detection and over-treatment.
In a particularly well-designed trial just published in the British Medical Journalinvolving more than 9,000 men who were followed up over a 20-year period, researchers found that screening for prostate cancer using a combination of a rectal examination and a blood test did not prolong the survival of those men who developed the disease.
There were 85 cases (5.7 per cent) of prostate cancer diagnosed in the screened group and 292 (3.9 per cent) in the group who were not screened at regular intervals. This difference was not statistically significant. However, the tumours found in the men who were screened were smaller and more localised within the gland
than those diagnosed opportunistically, suggesting that screening is detecting cancers that are low-risk because of their slow rate of growth. If left alone, many of these cancers would cause no harm.
Understandably, some men when they hear the word cancer cannot rest easy until they undergo treatment.
And if they opt for aggressive surgical intervention, some end up being impotent and incontinent, with far more damage to their health than the cancer ever posed.
The main risk factor for prostate cancer is advanced age, with 80 per cent of cases occurring in men over 65. In many instances, the cancer is non-aggressive, so that the lifetime risk of dying from prostate cancer is 3 per cent.
So what is a man supposed to do? For those aged over 60, there is relatively simple advice. It follows research published last year, again in the British Medical Journal,which showed that a man's PSA score at 60 can strongly predict his lifetime risk of dying from prostate cancer.
If your PSA is 2.0 or higher at age 60, then your risk of developing prostate cancer within the next 25 years is elevated. About one in four men will have a score of 2.0 or higher and, while most of them will not develop prostate cancer, the risk is such that they will benefit from regular screening.
It’s best to look at absolute risks in dilemmas such as this. A 60 year old with a PSA just above 2.0 has a 6 per cent chance of dying from prostate cancer in the next 25 years; with a score of 5.0, the risk rises to 17 per cent. For those with a PSA of 1.0 or lower at age 60, the chance of developing the cancer is just 0.2 per cent. Further screening beyond age 60 is unlikely to benefit this group.
The advice for men aged 75 or older is also pretty straightforward. PSA testing has been found to be unhelpful for men with a life expectancy of 10 years or less; again the slow growing nature of most prostate cancers means that men of this age are more likely to die from something other than prostate cancer.
For men aged between 50 and 59, it is harder to give definitive advice. What we can say is that if you are labelled as low-risk when tested at 50, then it’s probably okay to have your next PSA when you reach 60.
And if you are unlucky enough to be diagnosed with prostate cancer, be sure to ask about the downsides of treatment as well as the benefits.