Jane McCredie: Double standards

WHEN a new pharmaceutical product hits the market, we expect regulators and professional bodies to be rigorous in assessing its safety and efficacy before any recommendation is made to patients.

But screening tests? Not so much.

Perhaps it’s natural that people are instinctively more worried about substances they put into their bodies than they are about tests that, after all, are simply going to give them information.

Except it really isn’t that simple, especially when it comes to a deeply flawed tool like the prostate-specific antigen (PSA) test used to predict men’s risk of developing prostate cancer.

The PSA test has been dividing medical opinion for more than a decade, as witnessed by reader comments on a recent MJA InSight column by Dr Michael Gliksman.

And who can forget the uproar when Professor Alan Coates, then president of the Cancer Council, went public with his decision not to have the test in 2003 based on his belief that the risks outweighed the benefits.

Advocates of screening — including medical professionals — often point to cases where the test could reasonably be said to have saved an individual man’s life by leading to early diagnosis of an aggressive cancer.

Yet, on a population level it’s not hard to mount an argument that the test does more harm than good.

New guidelines released this month by the American College of Physicians (ACP) recommend against the test unless the patient expresses a clear preference for it after discussion with his doctor — a discussion that would include being informed about “the limited potential benefits and substantial potential harms of prostate cancer screening”.

This issue has been bedevilled for years by conflicting guidelines that have failed to provide clear advice to either patients or clinicians, something the ACP set out to address.

In Australia, the NHMRC is conducting an independent evaluation of the evidence to help GPs and other health practitioners provide consistent, evidence-based advice to patients.

That’s all good, but it leaves the question of how this test came to be widely used, given the lack of evidence that the benefits outweigh the harms.

It’s hard to imagine a cancer drug being as widely prescribed if large trials had found no evidence it reduced mortality, while associating it with calamitous side effects such as incontinence and erectile dysfunction in a substantial minority of those treated.

Yet that seems to be pretty much the situation with the PSA test, at least in relation to asymptomatic men with no familial risk factors.

Dr Mitchell Katz, a primary care physician and director of the Los Angeles County Department of Health Services, wrote in JAMA Internal Medicine last week, asking why services such as his continue to offer the test.

Dr Katz is sceptical even about suggestions the decision should be left to the patient after discussion with his physician.

“Should we be offering our patients a menu of ineffective interventions on the idea that they are better able than we are to determine effectiveness”, he asks.

In his search for an understanding of the persistence of the PSA test, Dr Katz suggests most doctors want to “make their own decision on the basis of available evidence, even in fields in which they are not necessarily expert”.

“Is this a particularly noble aspect of our profession (doing what we believe even if the experts disagree)”, he wonders. “Or a kind of arrogance (yes, the … experts recommended against this test, but I know better? Or is it both?”

Provocative questions. But I think there is another question worth asking: should screening tests have to meet the same standard of evidence as any other medical intervention?

Jane McCredie is a Sydney-based science and medicine writer.

Posted 22 April 2013