Spit Test More Accurate at Identifying Future Prostate Cancer Risk

Currently, blood tests that measure the level of a protein called prostate-specific antigen (PSA) are commonly used to identify men at higher risk for prostate cancer. This test is typically used based on a man's age, ethnicity, or if they are exhibiting symptoms. Since elevated PSA levels can indicate prostate cancer, men with high PSA results are referred for additional testing to detect the disease. However, PSA tests are known to falsely suggest prostate cancer in three out of four cases, and it can also identify slow-growing cancers that are unlikely to ever be life-threatening. This leads to unnecessary procedures, including MRI scans, biopsies, and treatments. Now, a new study has introduced a spit test, where a sample can be easily collected at home, that has been found to be more accurate in identifying the risk of future prostate cancer in some men compared to the standard PSA blood tests.

Researchers from The Institute of Cancer Research (ICR, London, UK) and The Royal Marsden NHS Foundation Trust (London, UK) conducted trials using a new DNA test designed to detect genetic variants associated with prostate cancer. The results of the BARCODE 1 study, published in the New England Journal of Medicine, presented a polygenic risk score based on DNA extracted from saliva. The study showed that for men with the highest risk scores, this DNA test outperformed the traditional PSA blood test. The saliva test not only reduced the number of false positives compared to the PSA test, but it also detected cancers that the PSA test would have missed, and it identified a higher proportion of aggressive cancers. The test was also able to identify prostate cancers that had been missed by MRI scans.

The study involved calculating the polygenic risk score (PRS) for 6,142 European men, aged 55-69, a group at increased risk for prostate cancer. The PRS was based on 130 genetic variations linked to prostate cancer and was developed through research on the DNA of hundreds of thousands of men. The men in the top 10% of risk scores were considered to be at the highest risk and invited for further screening. After undergoing MRI and prostate biopsy, 187 of the 468 men in this high-risk group were diagnosed with prostate cancer, which is a much higher rate than the 25% of men with elevated PSA levels who are diagnosed with the disease. Notably, 63.1% of these 187 men had a PSA level below 3.0 µg/L, which is typically considered a normal level, meaning no further screening would normally be recommended. Previous studies have indicated that the PSA test often detects cancers that are not clinically significant and do not require treatment.

The PRS saliva test, in contrast, identified a higher proportion of aggressive cancers—those that grow quickly and are more likely to spread—compared to the PSA test. Of the 187 cancers identified, 55.1% were aggressive, compared to just 35.5% detected by the PSA test in a similar study. Moreover, the PRS test was more accurate than MRI scans in detecting cancer in these men with high genetic risk, as 125 men (66.8%) had prostate cancer confirmed by biopsy that MRI failed to detect. Given that the PSA test is often inaccurate, the PRS saliva test offers a valuable additional screening tool, especially for men at higher risk of prostate cancer or those presenting with symptoms. Future research will continue to follow men with high PRS scores to track if they develop prostate cancer. Since the start of the BARCODE 1 study, an international team of researchers has identified additional risk variants for men of Asian and African ancestry, and the ICR team has developed an updated version of the test, called PRODICT, that can be used for these populations. A new study using PRODICT has been launched, incorporating more genetic variants that are indicative of cancer than the original test.

“With this test, it could be possible to turn the tide on prostate cancer. We have shown that a relatively simple, inexpensive spit test to identify men of European heritage at higher risk due to their genetic makeup is an effective tool to catch prostate cancer early,” said ICR Professor Ros Eeles. “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.”