At-home saliva test could help diagnose prostate cancer sooner

A new saliva test for identifying men at high risk of prostate cancer could help find more cases of the disease earlier, when doctors have a better chance of treating it successfully.

The researchers behind the BARCODE 1 study, which we helped fund, say their test could help “turn the tide” on prostate cancer.

Although it is the second biggest cancer killer of men in the UK, taking around 12,000 lives a year, there is no national screening programme for prostate cancer. This is because the only current option, the prostate-specific antigen (PSA) blood test, is too inaccurate.

Instead of measuring the amount of PSA in blood, the new spit test sorts people into groups by looking through the DNA in their saliva samples for a range of small genetic changes linked to prostate cancer. The results of the trial suggest that this approach works better. The men the new test puts in its highest risk group are more likely to have prostate cancer than men with raised PSA levels.

The new test also falsely identified prostate cancer fewer times than the PSA test does, and picked up a higher proportion of aggressive cancers.

“With this test, it could be possible to turn the tide on prostate cancer,” said Ros Eeles, a professor at the Institute of Cancer Research and a consultant at the Royal Marsden NHS Foundation Trust, which jointly led the research. ”We have shown that a simple, cheap spit test to identify men at higher risk due to their genetic makeup is an effective tool to catch the cancer early.”

Eeles is presenting the results of BARCODE 1 at the annual American Society of Clinical Oncology meeting in Chicago. She ties her work to a long legacy of research into the genetic markers of prostate cancer.

“Building on decades of research into the genetic markers of prostate cancer, our study shows that the theory does work in practice – we can identify men at risk of aggressive cancers who need further tests, and spare the men who are at lower risk from unnecessary treatments.”

From PSA testing to polygenic risk scoring

In the study, spit samples were used to calculate prostate cancer polygenic risk scores (PRSs) for more than 6,000 European men. All participants were recruited through their GP surgeries when they were between 55 and 69 – an age at which risk of prostate cancer is increased.

Their PRSs were based on 130 genetic variations – many hereditary – shown to be linked with prostate cancer through studies into the DNA of hundreds of thousands of men.

For BARCODE 1, the men with the highest 10% of risk scores were invited to further screening. Following an MRI and a prostate biopsy, 187 of them (40% of the total) were diagnosed with prostate cancer. That’s a significant jump from the 25% of men identified by PSA tests who actually have prostate cancer. Moreover, 147 (78%) of the men diagnosed thanks to the new saliva test had a ‘normal’ PSA level, which would usually indicate that no further screening is required.

The researchers also took a closer look at how the prostate cancers picked up by their new test behaved (which can be assessed by looking at how abnormal they appear, measured by grade). PSA testing picks up many people who have cancers that grow too slowly to cause any significant health impacts, meaning that men may undergo unnecessary MRI scans, invasive biopsies, and treatments. Importantly, then, the new spit test identified a higher proportion of aggressive cancers – which are fast growing and likely to spread – than the PSA test. Of the 187 cancers detected in BARCODE 1, 55% were aggressive cancers, compared with 36% of those identified by a PSA test in a recent study.

The PRS test is also more accurate than an MRI scan for men who score in the highest 10% for genetic risk.

Naser Turabi, our director of evidence and implementation, put the findings into context.

“Right now, there’s no reliable method to detect aggressive prostate cancer, but this study brings us a step closer to finding the disease sooner in those people who need treatment,” he said. “It’s encouraging to see that genetic testing might help to guide a more targeted approach to screening based on someone’s risk of developing prostate cancer. More research is now needed to confirm if this tool can save lives from the disease so that it can be rolled out to improve diagnosis.”

Since BARCODE 1 started, an international research team has identified more genetic variants associated with prostate cancer risk in men of Asian and African ancestry. The ICR team intend to trial a saliva test for this population to ensure polygenic risk scoring can benefit all men. They are also comparing the saliva test to other potential screening options as part of the ongoing TRANSFORM trial.