A study blaming a fall in PSA testing for a rise in aggressive cancers is flawed, experts say
A study linking increasing rates of aggressive prostate cancer to reduced PSA testing has been met with an angry backlash from cancer experts who say the study authors “don’t know what they don’t know”.
Alarming headlines around the world quoted the authors’ claim that aggressive prostate cancer numbers were “skyrocketing”, and new recommendations against routine screening might be to blame.
“The fact that men in 2013 who presented with metastatic disease had much higher PSAs than similar men in 2004 hints that more aggressive disease is on the rise,” said lead author, urologist Dr Edward Schaeffer.
“If I were a patient, I would want to be vigilant. I firmly believe that PSA screening and rectal exams save lives.”
But the American Cancer Society has slammed the study’s methodology, saying it was “far from adequate” to answer the question of whether a reduction in PSA screening led to more advanced cancers.
“The way epidemiologists measure things like incidence and mortality is to study rates, the number of cases per a number of people (usually per 100,000) to look for trends,” said the group’s chief medical officer, Dr Otis W. Brawley.
“But this study, done by a group of urologists, didn’t do that,” he said in a statement. “Rather than measure rates of metastatic disease, they looked at the number of cases. That is far from the same thing.”
The study analysed the records of 767,000 men diagnosed with prostate cancer between 2004 and 2013 according to the National Cancer Data Base.
In 2003, 3% of men had metastatic disease at diagnosis, compared with 5.1% a decade later – a rise from 1685 to 2890 in absolute numbers, a relative increase of 72%.
The biggest relative increase – of 92% – in advanced cancers was found in the 55-69 years’ age group, in which PSA screening was thought to be most beneficial, the authors wrote.
But rising rates of advanced cancer might have been due to a growing population or an ageing one instead, Dr Brawley explained.
The benefits of PSA testing have been long debated, but earlier this year the NHMRC endorsed recommendations from the Prostate Cancer Foundation of Australia and Cancer Council of Australia not to routinely screen.
Prior to that, many guidelines in Australia also held this recommendation, including the RACGP’s red book.
While the same study hasn’t been repeated in Australia, mortality rates from prostate cancer have been falling, according to Cancer Council Australia chief executive Professor Sanchia Aranda.
“We’re not seeing any signals in the Australian data that the reductions in PSA testing are leading to unnecessary deaths,” she said.
There was a growing awareness that there were significant harms associated with a positive PSA test, as well as the limitations of the test itself, she said.
“All the new PSA guidelines are really saying is that men need to understand the significance of overdiagnosis, and that they should undergo PSA testing fully informed of that so that if they do get a diagnosis they don’t rush into treatment,” Professor Aranda said.
The problem with the PSA as a screening test was that it was not accurate, she said.
“It detects an antigen that is present if cancer is present. But it’s also present if you ride a bike, or run or have a lot of sexual activity. There are a lot of false positives, which make it not good for a screening test,” she said.
To be useful, a screening test must also improve mortality rates.
“But we’re at a point where that’s hard to do,” Professor Aranda said. “Survival has risen from 58% in the 80s to 94% in 2010, so we’re talking about a dramatic change for good in the management of prostate cancer.”
Critics of the US study also pointed out that the increase in aggressive cancers actually began before the US Preventive Services Task Force changed their guidelines in 2008 to remove routine PSA screening, and warning healthcare practitioners about the risks of overtreatment.
They also found that low-risk prostate cancer had dropped 34% over the study period.
“There may or may not be a rise in the rates of metastatic disease; but because of a flawed analysis, this study does not answer that important question,” said Dr Brawley, who accused the study of clouding the waters.
Prostate Cancer Prostatic Dis; online 19 July
