Nearly half of prostate cancers in Australia are over-diagnosed

An Australian-first study led by Bond University on the Gold Coast has found that at least 41 per cent of prostate cancers detected by commonly performed screening tests are over-diagnosed.

The new research, which was published in peer-reviewed medical journal, BMJ Open, is the first of its kind to detail the extent of prostate cancer over-diagnosis in Australia.

Lead author of the study and researcher at Bond University’s Centre for Research in Evidence-Based Practice (CREBP), Dr Thanya Pathirana, said over-diagnosis of prostate cancer often led to harmful and unnecessary treatment.

“Over-diagnosis of a cancer occurs when people are diagnosed with a dormant cancer that would not harm them if left undetected and untreated. This is a known adverse effect of prostate cancer screening,” she said.

“What we know about over-diagnosis is it can lead to unnecessary and, in some cases, harmful procedures and treatments such as prostate surgery, radiotherapy and hormone therapy.

“In the case of prostate cancer, this can also include a prostatectomy (removal of the prostate gland), which can cause incontinence or impotence.

“Our estimates of over-diagnosis are comparable with results from randomised control trials done in the United States and Europe, so this is a trend we are seeing around the world.”

Based on lifetime risk of developing prostate cancer, the study compared pre and post-screening eras using data from the Australian Institute of Health and Welfare (AIHW) and statistical software from the United States National Cancer Institute’s Division of Cancer Control and Population Sciences (DevCan).

In cancer research, ‘lifetime risk’ refers to the likelihood a person who is free of a certain type of cancer will develop or die from that type of cancer during their lifetime.

The research found the lifetime risk of being diagnosed with prostate cancer rose from 6.1 per cent in 1982 (1 in 17 Australian men) to 19.6 per cent in 2012 (1 in 5 Australian men), with a rapid increase following the introduction of prostate-specific antigen (PSA) testing in Australia in 1989.

Co-author of the study and director of Bond University’s CREBP - a leading global centre for research into over-diagnosis – Professor Paul Glasziou, said the findings clearly demonstrated Australia had been over-diagnosing cases of prostate cancer for decades.

“These results show a clear increase in Australian men’s lifetime risk of a prostate cancer diagnosis – particularly following the introduction of PSA testing in Australia,” he said.

“The spike strongly suggests we have been over-diagnosing – and by that I mean we are detecting dormant cancers that would never have become symptomatic.

“To address this issue of over-diagnosis, all asymptomatic men should engage in an informed discussion with their general practitioner about the risks and potential benefits of prostate cancer screening.

“Don’t get me wrong - men still need to remain vigilant when it comes to early detection, however they need to be informed and engage in shared decision making with their medical professionals about the harms of prostate cancer screening and other associated procedures.”

Co-author of the study and Senior Lecturer in Clinical Epidemiology at the University of Sydney, Dr Katy Bell, said the estimate of over-diagnosis in the paper meant the effectiveness of measures to prevent over-diagnosis could now be measured.

“Now we have a baseline estimate of prostate cancer over-diagnosis in Australia, we can use this to monitor the effects of interventions that aim to prevent over-diagnosis,” she said.

“For example, using magnetic resonance imaging (MRI) scans to decide whether or not to biopsy a man’s prostate may lead to fewer over-diagnosed cancers.

“Using the method we describe in our paper, we can now assess whether or not this, and other measures aiming to prevent over-diagnosis, actually lead to a measurable reduction in over-diagnosis.”

Information to help patients and general practitioners make an informed decision about PSA screening is provided by the Royal Australasian College of General Practitioners (RACGP).

The Prostate Cancer Foundation of Australia (PCFA) also provides guidelines for men who decide to be screened on its website – https://www.prostate.org.au/media/611493/PSA-Testing-Guidelines-Short-Form.pdf

Read a copy of the research paper at https://bmjopen.bmj.com/content/9/3/e022457

7 April 2019.