Could a breathalyzer detect cancer? - Julian Burschka
How is it that a breathalyzer can measure
the alcohol content in someone’s blood,
hours after they had their last drink,
based on their breath alone?
Exhaled breath contains trace amounts
of hundreds, even thousands,
of volatile organic compounds:
small molecules lightweight enough
to travel easily as gases.
One of these is ethanol,
which we consume in alcoholic drinks.
It travels through the bloodstream
to tiny air sacs in the lungs,
passing into exhaled air
at a concentration 2,000 times lower,
on average, than in the blood.
When someone breathes
into a breathalyzer,
the ethanol in their breath
passes into a reaction chamber.
There, it’s converted to another molecule,
called acetic acid,
in a special type of reactor that produces
an electric current during the reaction.
The strength of the current
indicates the amount of ethanol
in the sample of air,
and by extension in the blood.
In addition to the volatile
organic compounds like ethanol
we consume in food and drink,
the biochemical processes of our cells
produce many others.
And when something disrupts
those processes, like a disease,
the collection of volatile
organic compounds in the breath
may change, too.
So could we detect disease
by analyzing a person’s breath,
without using more invasive
diagnostic tools
like biopsies, blood draws, and radiation?
In theory, yes,
but testing for disease is a lot more
complicated than testing for alcohol.
To identify diseases,
researchers need to look at a set
of tens of compounds in the breath.
A given disease may cause
some of these compounds
to increase or decrease in concentration,
while others may not change—
the profile is likely to be different
for every disease,
and could even vary for different stages
of the same disease.
For example, cancers are among
the most researched candidates
for diagnosis through breath analysis.
One of the biochemical changes
many tumors cause
is a large increase
in an energy-generating process
called glycolysis.
Known as the Warburg Effect,
this increase in glycolysis results
in an increase of metabolites like lactate
which in turn can affect a whole cascade
of metabolic processes
and ultimately result
in altered breath composition,
possibly including an increased
concentration of volatile compounds
such as dimethyl sulfide.
But the Warburg Effect is just one
potential indicator of cancerous activity,
and doesn’t reveal anything
about the particular type of cancer.
Many more indicators are needed
to make a diagnosis.
To find these subtle differences,
researchers compare the breath
of healthy people
with the breath of people
who suffer from a particular disease
using profiles based on hundreds
of breath samples.
This complex analysis
requires a fundamentally different,
more versatile type of sensor
from the alcohol breathalyzer.
There are a few being developed.
Some discriminate
between individual compounds
by observing how the compounds move
through a set of electric fields.
Others use an array of resistors
made of different materials
that each change their resistance
when exposed to a certain mix
of volatile organic compounds.
There are other challenges too.
These substances are present
at incredibly low concentrations—
typically just parts per billion,
much lower than ethanol concentrations
in the breath.
Compounds’ levels may be affected
by factors other than disease,
including age, gender, nutrition,
and lifestyle.
Finally, there’s the issue
of distinguishing which compounds
in the sample
were produced in the patient’s body
and which were inhaled
from the environment
shortly before the test.
Because of these challenges,
breath analysis isn’t quite ready yet.
But preliminary clinical trials
on lung, colon,
and other cancers
have had encouraging results.
One day, catching cancer early
might be as easy as breathing in and out.
