How A Specific Antigen Blood Test Alone Can't Confirm Prostate Cancer

Prostate cancer is the most common cancer in Australia, with about 26,000 men diagnosed per year. The majority (more than 85%) are aged over 60.

Prostate cancer kills around 3,900 Australians a year. Yet most prostate cancers progress very slowly and many men die "with" and not "from" prostate cancer.

Prostate cancer is currently detected with a blood test. This measures the amounts of prostate specific antigen (PSA) in the blood, a protein produced by the prostate gland.

But while an elevated PSA can indicate prostate cancer, other non-cancerous conditions, such as prostate enlargement or inflammation, can also increase PSA levels.

New draft guidelines aim to provide clearer recommendations about the role PSA tests should play in detecting prostate cancer.

Life-saving treatment vs harmful overdiagnosis

Early detection of prostate cancer by PSA testing is important. It allows for timely treatments such as prostate removal surgery, radiation or hormonal therapy.

But despite their effectiveness, these treatments can cause problems such as erectile dysfunction. Urinary incontinence issues occur in up to 14% of patients.

Therefore, if the prostate cancer is considered low-risk and has not spread outside the prostate, the clinician may recommend "active surveillance" to closely monitor the cancer for signs of progression.

If the low-risk prostate cancer doesn't progress, treatment and its associated side effects can be delayed or avoided.

The controversy around PSA testing is it can over-diagnose low-risk prostate cancers that would never become life-threatening.

PSA tests may also give false positive results when someone doesn't have cancer.

Such scenarios cause harm to men who are over-treated for prostate cancer solely based on elevated PSA levels.

In a decades-long clinical study involving 182,000 men, PSA testing reduced prostate cancer deaths by 20% compared to men who didn't undergo testing.

But a trade-off was having to over-treat around 48 men to prevent one prostate cancer death.

We need to find the balance between enabling early life-saving detection and preventing harmful over-treatment of men with low-risk prostate cancer.

What do the draft guidelines say?

The Prostate Cancer Foundation of Australia has released new draft clinical guidelines for the early detection of prostate cancer for public consultation.

The following recommended changes aim to reduce over-treatment and minimise harm.

1. Offer all men a 'baseline' PSA test at 40

All men would be offered an initial PSA test at age 40 to provide a baseline PSA measurement to compare against follow-up tests.

A baseline PSA measurement would enable the calculation of PSA doubling time: the number of months taken for PSA level to double from baseline.

Aggressive fast-growing tumors tend to have shorter PSA doubling times, so this would enable early detection of high-risk prostate cancer for prompt treatment.

Such a change could improve prostate cancer risk classification and spare more men from unnecessary harmful treatment side effects.

2. GPs offer men aged 50-69 PSA tests every two years

The draft guidelines recommend GPs offer PSA testing every two years for all men aged 50-69.

For men over 70, PSA testing would be recommended based on clinical assessment by GPs.

Men are more likely to be diagnosed with prostate cancer at an advanced age. So as they get older and have a shorter life expectancy, the harms of treatment are more likely to outweigh the benefits of early detection.

This recommendation could reduce over-diagnosis by considering individual life expectancy, overall health and potential treatment harms.

3. Target populations at greater risk

As with other cancer types, prostate cancer is a disease caused by gene malfunctioning leading to tumour growth. Men with a family history of prostate cancer are around three times more likely to develop and die from prostate cancer due to their genetic susceptibility.

Aboriginal and Torres Strait Islander men have a higher risk of dying from prostate cancer compared to non-Indigenous men. This may be due to delayed diagnoses and limited access to prostate cancer treatment options in remote areas.

For these men with higher prostate cancer risk, the draft guidelines recommend earlier and more frequent PSA testing, starting at age 40.

This change could prioritise and serve targeted, high-risk populations of men who would benefit most from more regular PSA testing.

No more 'finger up the bum'

Previously, men with high PSA levels were referred for needle prostate biopsies which involve invasive insertion of needles into different areas of the prostate to remove tissue samples for lab analyses.

Needle biopsies are painful and come with risks of bleeding or infection. So, it's helpful to use additional prostate cancer testing approaches to guide who is referred for a biopsy.

The new draft guidelines no longer recommend the use of digital rectal examination, the dreaded "finger up the bum", to screen for signs of prostate cancer together with PSA testing. Men find this unpleasant and embarrassing.

Instead, clinicians can turn to advanced imaging. Medicare rebates have been available for magnetic resonance imaging to diagnose prostate cancer since 2018.

Medical specialists often order a multiparametric MRI (mpMRI) following elevated PSA levels to determine if biopsies are required. This is a specialised MRI that uses strong magnets and radio waves to construct a detailed three-dimensional image of the prostate from different angles and identify suspicious-looking areas.

The draft guidelines recommend mpMRI to supplement PSA testing to better determine if a biopsy is needed. This saves men from unnecessary invasive procedures and reduces health-system costs.

The information gathered from the public consultations will inform the final draft prostate cancer early detection guidelines. The final recommendations will then be sent to the National Health and Medical Research Council for approval, before becoming clinical practice.

(Author: Kevin M. Koo, NHMRC Emerging Leadership Fellow, The University of Queensland)

(Disclaimer Statement: Kevin M. Koo receives funding from the Prostate Cancer Foundation of Australia.)

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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