Ignore call to abandon prostate cancer tests

William Aiken, Contributor

The United States Preventive Services Task Force (USPSTF) ignited a fierce firestorm of debate in the US and around the world when it released its latest recommendations regarding prostate-specific antigen (PSA)-based prostate cancer screening last Friday. In its release, it recommended against PSA-based prostate cancer screening in all men!

The USPSTF is an American organisation consisting of an independent panel of non-federal experts in preventive and evidence-based medicine. It makes recommendations regarding various preventive health services based on an assessment of the currently available evidence and disseminates these recommendations which serve as guidelines for clinical practice in the US. The recommendations are meant for the US population, but interests outside the US, rightly or wrongly, depend on these recommendations for guidance on clinical practice in their respective countries.

The aim of cancer screening is to detect disease at a pre-symptomatic stage in its evolution with the belief that earlier treatment is more likely to result in cure than later treatment, which is typically administered when symptoms arise. For a cancer-screening programme to be considered effective, it must not only unequivocally demonstrate that it reduces cancer-specific mortality, but there must not be an excess of harmful effects generated in achieving this end.

Prostate cancer has a wide spectrum of behaviour, with some cancers causing death in 10 to 15 years from the time of discovery if left alone, while other cancers never cause a problem in the man's lifetime. As even the more aggressive prostate cancers tend to be relatively slow-growing, it is generally agreed that a man should have at least a 10-15 year life expectancy to benefit from screening tests.

The USPSTF, citing evidence from several clinical trials which examined PSA-based prostate cancer screening, found that there was no appreciable decrease in prostate-cancer mortality among screened men.

Harm outweighs benefit

The USPSTF also found that more harm than good is done by screening men for prostate cancer, mostly because of the significant likelihood of detecting and treating indolent cancers that would never have caused a problem.

Can the USPSTF recommendations be applied locally?

While the USPSTF presents a cogent argument for its recommendation against PSA-based screening, the evidence on which this recommendation is based was obtained from studies with participants who were overwhelmingly Caucasian.

Prostate cancer disproportionately affects men of African descent and is also known to run a more aggressive course and to have a poorer prognosis in men of African heritage. African Americans have the highest prostate cancer incidence in the world, while the Caribbean has the highest prostate cancer mortality rate. Men of African descent, therefore, have a higher prostate cancer risk profile and, therefore, stand to benefit more from PSA-based screening, notwithstanding the potential harms involved. The risk-benefit ratio is, therefore, skewed towards benefit in black men. The USPSTF recommendation cannot be generalised to the Caribbean and should, therefore, not be blindly followed.

Preventing prostate cancer

Despite all the research done on prostate cancer to date, the only established risk factors for the disease remain race, age and family history. No modifiable risk factors have been unequivocally identified which can be manipulated to decrease the risk of the disease. Therefore, screening is currently the mainstay of prevention and should not be thrown out wholesale as the USPSTF is attempting to do, without first determining if it might be of particular benefit to specific high-risk groups, such as men of African descent and men with a strong family history.

Ultimately, what is required is a test that will distinguish those prostate cancers that are destined to behave badly from those that are relatively innocuous. Until this is available, urologists continue to recommend that men 40 years and older of African descent, as well as men with a positive family history who, based on their health, have at least a 10-15-year life expectancy continue yearly screening tests for the disease.

Dr William Aiken is consultant urologist and head of urology, UHWI. Email feedback to columns@gleanerjm.com.