PSA based screening has been described as an expensive public health disaster. But new approaches offer more accurate diagnoses and better outcomes.
Prostate cancer kills over 300,000 men a year world-wide. As it mainly affects older males (only about 10 per cent of those who die of it are aged under 65) these figures, together with those for the disability and distress caused by prostate cancer and its emasculating treatments, are set to rise as populations across the globe become both older and wealthier – sex hormone linked cancer rates are higher in well fed people than in poorer ones.
Given this, and the long established relationship between finding cancers early and being able to cure them, it might well be assumed that any form of testing that can find the disease before it becomes symptomatic and spreads is worth using. That is what many men have been told PSA (Prostate Specific Antigen) blood tests have to offer. But Dr Richard Ablin, who discovered PSA in 1970, has condemned PSA screening as ‘an expensive public health disaster’.
This year a major European evaluation showed that 10 years after PSA testing and subsequent treatment death rates from prostate carcinomas were 20 per cent below those in controls. Yet its authors said that PSA based screening should not be undertaken. This view has been supported by many other experts and groups, including the US Preventive Services Task Force.
So what is going on? Several things. First, some past research was flawed, because it did not adequately account for the fact that most American men have for decades received PSA testing. Hence the benefits of prostate surgery were under-estimated. Even the European figures quoted above are almost certainly too cautious, because the full benefits of operations like prostatectomies are likely to take at least 15 years to become apparent. At that point mortality in treated men could well be 30 per cent down, despite sub-optimal circumstances surrounding the use of PSA tests in past decades.
Second, PSA tests alone are not a good guide to whether or not a cancer is present or how dangerous it is. The fear is that if they are used uncritically too many relatively young men will suffer the unwanted consequences of surgery, including incontinence and impotence, for no real benefit. However, this does not mean that PSA testing is useless. The correct interpretation is that it should be conducted as part of a carefully managed and wider personal care programme.
Population screening is by contrast often taken by medical purists as something capable of generating instant yes or no answers. The problem with this essentially semantic distinction is that it has left a lot of men and many of their doctors uncertain about what they should do about checking for prostate cancer. Less advantaged men, such as proportion of American black males, are particularly likely to lose out as a result.
But recent advances mean that it is time for new approaches and clearer communication. For example, it is now apparent that measurements made in early mid-life to find the 10 per cent of men with the highest PSA levels can with good reliability identify those who are at the highest risk of developing metastatic prostate cancer later in life. If these individuals (along with men who have close relatives with prostate cancer) are followed with special care this will improve outcomes with much less risk of causing harm.
At the same time research in centres like the University College London Hospital (UCLH) has highlighted the fact that past problems with interpreting PSA data have often been associated with the biopsy techniques employed. Better use of MRI scanning before physically intrusive investigations are undertaken, coupled in appropriate instances with novel interventions such as the targeted use of ultra-sound to eliminate cancer cells, promises to deliver radically improved results.
Tests aimed at finding ‘new’ biomarkers like the PCA3 protein (the product of prostate cancer gene 3) urine analysis will also raise the viability of mass screening approaches, as well as contributing to the care of people able to access such technologies on a more individualised basis. This is because they can help to clarify the meaning of the more general PSA warning signal.
For those whose cancers are not detected at a curable stage, innovative vaccines and medicines such as sipuleucel-T and abiraterone are also improving survival, as and when access to them is afforded. The reality about prostate and increasingly other cancers is that after 2,000 years plus of conscious medical and patient struggle we are genuinely close to winning the war.
Some may say that it is economically not worth the investment needed to save older men and women, and add to population ageing. But for me this is sadly mistaken. I think we owe it to ourselves and our common future to push hard for better care now, and refuse a second best world.
David Taylor - Emeritus Professor of Pharmaceutical and Public Health Policy, University College London