Dear Doctors: I heard there will be a saliva test to see who has a high risk of getting prostate cancer. I don’t see how saliva would have anything to do with your prostate gland. How does the test work, and how can I get access to it?
Dear Reader: A test that analyzes bodily fluids is known as a liquid biopsy. The most common are the blood and urine tests many of us are familiar with. Recently, though, thanks to advances in genetic research and medical technology, saliva is being explored as a diagnostic tool. The fluid that we produce by the pint each day and rarely think about is 98% water. However, that remaining 2% turns out to be a trove of valuable information.
Saliva contains proteins, electrolytes, hormones, peptides, free fatty acids, mucus, antibacterial compounds, RNA fragments and nucleic acids that come from throughout the body. Researchers are exploring how these can be used as biomarkers to pinpoint the presence of a disease or condition. Existing saliva tests screen for HIV, Cushing’s disease, hepatitis C and even pregnancy. Salivary analysis can also help diagnose certain oral diseases. Researchers are now exploring saliva as a tool in identifying Huntington’s disease, Parkinson’s disease, Alzheimer’s disease, COVID-19 and a range of cancers.
You are correct that a saliva test that flags a high risk of prostate cancer is under development. Unlike a blood test, a saliva test can be completed at home. The person spits into a specially prepared tube, then mails the sample to a lab for analysis. The prostate cancer test you asked about works by identifying genetic variants that are known to signal a significant risk of developing the disease.
Initial research suggests this saliva test can be more accurate at identifying men who are at high risk of cancer than the prostate-specific antigen blood test. Also known as the PSA test, it measures blood levels of a protein that is produced by cancer cells. However, that protein is also produced by noncancerous cells. Several factors unrelated to cancer can lead to elevated PSA levels. This includes having an enlarged prostate, vigorous exercise, having a urinary tract infection, recent ejaculation, certain medications and being older. As a result, PSA tests can yield false positives, which can lead to unnecessary medical interventions and procedures.
In the most recent clinical trial of the saliva test, researchers analyzed samples from 6,000 men between 55 and 69 years old -- the age at which prostate cancer risk begins to rise. Those who tested positive for the genetic variants repeated the saliva test, and also underwent a PSA blood test. When the results were compared, the saliva test identified a higher proportion of aggressive cancers than the PSA test. It also yielded fewer false positives.
At this time, the test you are asking about is still in the research stage and is not yet in use. However, clinical trial results have been promising, and the hope is the test will become available soon.
(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
