An experimental cancer-detection method
that uses bodily fluids, such as urine and saliva, may one day help patients
avoid an invasive biopsy, researchers report.
The test may be particularly useful in diagnosing lung cancer, according to
Dr. David Sidransky, of the Johns Hopkins University School of Medicine in
Baltimore, Maryland.
Sidransky and colleagues found that urine, saliva, or lung fluids can reveal
specific genetic mutations that signal cancer of the bladder, head and neck, or
lungs, according to a report in the March 17th issue of Science.
These findings are particularly important to lung cancer diagnoses since
most cases are caught only at an advanced stage, Sidransky told Reuters Health.
"We're very excited because it's been impossible to get an early test for
lung cancer," he said, adding that trials with larger groups of patients are 6
to 12 months away.
While most cancer-related mutations have been found in the DNA that exists
in the nucleus, a structure found inside cells, Sidransky's team took a
different approach to hunting for genetic damage.
The investigators examined DNA in mitochondria, which are specialized
energy-producing compartments found outside of the nucleus of a cell. Because
every cell contains numerous copies of mitochondrial DNA but only two copies of
DNA in the nucleus, the researchers guessed that mitochondrial mutations would
be easier to spot in body fluids.
In a new study, Sidransky's group examined matched samples of tumors and
body fluids from more than 20 patients with lung, head and neck, or bladder
cancer. First, they looked for mitochondrial DNA mutations in the tumors. Most
of those they found were normal genetic variations, but some mutations were
exclusive to the type of cancer the patient had.
Next, the researchers examined lung fluid from the lung cancer patients,
urine samples from bladder cancer patients, and saliva from those with head and
neck cancer. Eighty percent of the lung-fluid samples and both urine samples
showed the same mitochondrial mutations found in patients' tumors, as did six of
nine saliva samples.
Not all of the tumor samples showed cancer-specific mutations in
mitochondria -- a sign that some cancer cases will slip by fluid testing.
"These mutations might not be in all tumors," Sidransky said. Based on this
study, he estimates that about two-thirds of tumors probably have such markers.
Even if testing for these mutations doesn't catch all tumors, Sidransky added,
what matters is that the tests are highly specific. That is, they don't
incorrectly identify a tumor-free patient as having cancer. The researchers are
in the process of identifying all of the mutations that go with a particular
cancer.
Sidransky said fluid screening would likely find its first use in monitoring
people at risk for lung cancer. A smoker, for example, might provide a mucus
sample to determine how their mitochondrial DNA looks when they are healthy.
Over time, more samples would be studied to detect cancerous mutations.
