Saliva: The next frontier in cancer detection

Scientists are finding tumour signals in spit that could be key to developing diagnostic tests for various types of cancer

In the late 1950s, dentist and US Navy Capt. Kirk C. Hoerman, then a young man in his 30s, attempted to answer a bold question: Might the saliva of prostate cancer patients have different characteristics from that of healthy people? Could it contain traces of a disease that’s so far away from the mouth?

Without wasting more of their own saliva on elaborate discussion, Hoerman and his colleagues from the department of dental research at the Naval Training Center in Great Lakes, Illinois, got down to work. They analyzed samples from more than 200 patients and healthy controls, and found that the saliva of patients with untreated prostate cancer showed a significant increase in the levels of enzymes called acid phosphatases.

Writing in 1959 in the journal  Cancer, the researchers then made a prescient reflection: that it may be valuable to observe discrete biochemical changes in tissues distant from the site of tumor origin.

More than 60 years later, the idea that saliva analysis can be used to detect different types of cancer is gaining traction in the scientific community. In the specialized literature, papers containing the keywords “diagnosis,” “cancer” and “saliva” grew more than tenfold over the past two decades, from 26 in 2001 to 117 in 2011, 183 in 2016 and 319 in 2021, according to the PubMed database, a search engine for biomedical research articles.

The appeal of this approach is obvious. Although cancer can be diagnosed through tissue biopsy, that requires trained physicians wielding long needles, scalpels, endoscopes or other tools to pry into the body to take samples. Liquid biopsy, which looks for traces of tumor components in fluids such as blood, urine, cerebrospinal fluid, semen or saliva, is a less invasive alternative. Of these, the simplest sample to collect is undoubtedly saliva.

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The approach has already paid off: In 2021, the US Food and Drug Administration gave an innovative device designation to a saliva-based oral and throat cancer prediagnostic tool developed by the US company Viome. (Such designations are granted to novel medical devices that have the potential to provide more effective treatment or diagnosis of life-threatening diseases.) Based on artificial intelligence and machine learning, the tool analyzes a saliva sample for the activity of genes (in particular, messenger RNA) belonging to the bacterial community housed in the mouth. For unknown reasons, this community is modified when a tumor develops on the lips, tongue, throat or surrounding areas.