Researchers Report Early Success Using Saliva to Detect Oral Cancer
Scientists funded by the National Institute of Dental and Craniofacial
Research, part of the National Institutes of Health, reported today
taking a major step forward in using saliva to detect oral cancer.
As published in the current issue of Clinical Cancer Research, the
scientists found they could measure for elevated levels of four
distinct cancer-associated molecules in saliva and distinguish with
91 percent accuracy between healthy people and those diagnosed with
oral squamous cell carcinoma.
This so-called "proof-of-principle" study marks the first
report in the scientific literature that distinct patterns of "messenger
RNA" not only are measurable in saliva but can indicate a developing
tumor. Messenger RNA (mRNA) is the molecular intermediate between
gene and protein, serving as a chemical record that an individual
gene has been expressed.
According to David Wong, D.M.D., D.M.Sc., a scientist at the University
of California at Los Angeles (UCLA) School of Dentistry and senior
author on the paper, it may be possible with further refinement
of the test, possibly by including additional cancer-linked mRNAs,
to attain the necessary 99 to 100 percent accuracy of commercial
diagnostic tests for oral squamous cell carcinoma, the sixth most
common cancer in the United States. Wong noted that currently no
biochemical or genetic diagnostic tests are commercially available
for oral cancer.
He also noted that the RNA patterns in saliva may be informative
for other cancers and common diseases. "Saliva is a mirror
of our blood," said Wong. "We're now conducting our initial
studies of saliva as a possible diagnostic fluid for other human
cancers and system diseases, and we should have our preliminary
data in the Spring."
Wong said he and his colleagues never intended to study mRNA patterns
in saliva. They had been searching exclusively in the mouth's soft
tissues, or mucosa, for proteins that might be associated with oral
cancer, when Maie St. John, M.D., Ph.D., a head-and-neck surgery/otolaryngology
resident at UCLA, who was then on a training rotation in Wong's
lab, posed a simple question: If proteins associated with cancer
are present in the oral mucosa, can they also pass from tissue into
While looking for cancer-linked proteins in saliva, St. John happened
to notice mRNA from the gene encoding one of her proteins of interest.
This chance discovery raised two intriguing possibilities that would
alter the course of research in Wong's lab: Does saliva contain
a wide range of different mRNAs that have value in diagnosing disease?
If correct, are there different collective patterns of mRNA in the
saliva of a healthy person compared with someone who has a developing
St. John said pursuing this line of research was potentially important
because previous studies had established that mRNA can be as informative
of health and disease as changes in protein or DNA. In addition,
mRNA has the key advantage over these more traditional analytes
in that it can be readily extracted in bulk from a tissue or bodily
fluid and processed much faster for a comprehensive picture of which
mRNAs are present in a given tissue or bodily fluid and at which
"What really interested us was the idea that mRNA analyses
could be performed in a bodily fluid as easily obtained as saliva,"
said St. John. "If correct, a salivary test in theory would
be quick, painless, and most likely less expensive than current
But would it be as informative as testing blood? Before they could
answer this question, Wong and colleagues first had to define all
of the individual mRNAs naturally present in saliva. As published
this year in the Journal of Dental Research, they found people have
about 3,000 chemically distinct mRNAs in their saliva at any one
time. Of this total, a "core signature" of about 280 mRNAs
are generally present in the saliva of healthy people.
With these baseline data as their scientific anchor, the researchers
could begin to test whether saliva contains distinct mRNA patterns.
"We obtained saliva and blood from 32 people who had been recently
diagnosed with oral squamous cell carcinoma but not treated,"
said Yang Li, D.D.S., Ph.D., lead author on the study and a researcher
in Wong's laboratory. "Because salivary diagnostics with RNA
had yet to be tried, we referenced all of our data through blood.
That is, whatever we found in saliva, we looked to see if it matched
our data in blood."
As presented in their current Clinical Cancer Research paper, the
scientists extracted the mRNA from the saliva of the cancer patients
and soon discovered 1,679 genes were expressed at significantly
different levels in the cancer patients compared to healthy individuals.
Upon further analysis, they noticed seven mRNAs in particular that
were present at a 3.5-fold higher level in the cancer patients.
Interestingly, among them was the mRNA for the gene IL-8, whose
protein St. John had originally searched for in saliva.
The researchers then whittled down their list of signature mRNAs
to four, based on statistical models that indicated the synchronized
rise in expression of these four molecules increased the probability
that the saliva belonged to a cancer patient. These four mRNAs are
from the following genes: Interleukin 1-beta (IL1B), Ornithine decarboxylase
antizyme 1 (OAZ1), spermidine/spermine N1-acetyl transferase (SAT),
and interleukin 8 (IL-8).
To put this idea to the test, they screened the saliva again to
see how often they could correctly identify the samples from the
cancer patients. In all instances, they had no foreknowledge of
whether a healthy person or a cancer patient provided the saliva
Wong said the group could identify the saliva from cancer patients
in nine out of 10 samples. What's more, he said the sensitivity
and specificity of their saliva tests were as good or better than
their reference work in blood. "This was primarily an exploratory
study to validate our initial finding of a unique molecular signature
of mRNAs in people with oral squamous cell carcinoma," said
Wong. "We will follow up with a larger cohort of about 200
patients in the near future, and this study will hopefully allow
us to distinguish in saliva between the various stages of the cancer
and ultimately push our accuracy up to as close to 100 percent as
He also noted that these initial results serve to highlight the
potential clinical value of saliva as a diagnostic biofluid. "Many
have thought of saliva as very difficult to work with in the laboratory,
in part because the molecular information contained within it is
highly degradable," said Wong. "The truth is oral health
researchers have worked on saliva for decades, and they have established
defined ways to work with fluids that are consistent, reproducible,
and which keep these molecules in a stable state. We have a marvelous
way to completely stop the degradation of mRNA in saliva, and it
allowed us to gather these data."