Controversy on evidence on PSA tests for prostate cancer
On 19 March, The New York Times (NYT) reported on two large studies, “the first based on rigorous randomized trials”, published on the Prostate Specific Antigen (PSA) test.
In summarising the results, the NYT quotes Dr Peter B Bach, a physician and epidemiologist at Memorial Sloan-Kettering Cancer Center said, “One way to think of the data is to suppose he has a PSA test today”.
“It leads to a biopsy that reveals he has prostate cancer and he is treated for it.
“There is a one in 50 chance that in 2019 or later he will be spared death from a cancer that would otherwise have killed him. And there is a 49 in 50 chance that he will have been treated unnecessarily for a cancer that was never a threat to his life.”
However the study has been challenged by Australia’s and New Zealand’s peak body for urological surgeons.
Having carefully reviewed the study into Prostate Specific Antigen (PSA) blood tests undertaken in the United States, the Urological Society of Australia and New Zealand believes that there were design flaws in the US study which invalidate the results.
“We are concerned that Australian men may be persuaded against having a potentially life-saving PSA blood test following media reports of this US study,” said USANZ president, Dr David Malouf.
Dr Malouf said two studies about the PSA test recently published in the New England Journal of Medicine, one from the US and the other from Europe, had shown very different results and that the conflicting research findings must now be clarified.
“The PLCO study in the US involved 76,000 men and did not demonstrate a benefit from screening. USANZ believes there are fundamental flaws in the study design which make the results of this trial less valid.
“The follow up of patients enrolled in the study was not of adequate duration and in the non-screened or ‘usual care’ arm of the study more than half of the men underwent PSA testing, thus contaminating the unscreened population” Dr Malouf said.
“By contrast, the ERSPC study in Europe, commencing in the 1990s and involving 162,000 men in eight European countries, demonstrated that routine prostate cancer screening could cut death rates from the disease by 20%.
“The study of men aged between 55 and 69 who underwent screening for prostate cancer had a 20% reduction in the risk of dying from prostate cancer compared with men who were not screened. The trial authors estimated that 1,400 men would need to be screened to save one life from prostate cancer.
“These numbers required to save one life are similar to the numbers in breast and colorectal cancer screening programs. While some commentators have argued that many indolent cancers are unnecessarily detected as part of a screening process, in practice many of these men can be reassured and simply monitored without active treatment in the medium and long term”, Dr Malouf said.
Routine population based prostate cancer screening with the PSA blood test is not performed in Australia or New Zealand and is, at present, not advocated by USANZ.
“The position of this professional body remains that patients should have access to PSA based testing if they wish, after discussion with their family doctors and/or specialists about the risks and benefits of such testing.
There is firm data that testing reduces the risk of being diagnosed with advanced disease, and that treating prostate cancers following diagnosis can lead to a reduced risk of dying from the disease compared to no treatment.
The findings of the ERSPC study demonstrates the importance of developing new tests to identify aggressive forms of prostate cancer and differentiate them from more slowly growing tumours.
Such a test will enable clinicians to focus treatment on men whose cancers pose a threat to their health and avoid over-treatment of men with the more indolent forms of the disease”, he said.
