Breath test shows potential for detecting cancer

"Breath
test could
save lives
by
diagnosing
deadly
cancers
earlier,"
reports
The Daily
Telegraph.
The story
is based on new research into whether it is
possible to detect cancers of the stomach
and oesophagus (gullet) using a breath test.
A possible "chemical signature" composed
of five substances was tested against the
breath samples of more than 300 people
who previously had an endoscopy to
investigate upper digestive tract symptoms.
The researchers found that four of these
chemicals were expressed differently in the
breath samples from those diagnosed with
cancer, compared to those where no cancer
had been found.
The breath test was able to correctly
indicate cancer in around 80% of patients
who had cancer, and similarly able to
correctly exclude cancer in around 80% who
did not have cancer.
These were early findings from a conference
presentation. While they show promise, it is
not possible to say from the available
information whether the test could have a
future role in practice.
In most of these people with cancer who
took part in the research, the cancer had
spread to the lymph nodes. It is unclear if
the breath test would be able to detect less
advanced cases.
Both oesophageal and stomach cancer tend
to be diagnosed late because in the early
stages they either cause no symptoms – in
the case of oesophageal cancer – or
symptoms that are vague and easy to
mistake for other less serious conditions –
in the case of stomach cancer .
A breath test sensitive enough to identify a
"chemical signature" of cancer and allow
earlier diagnosis would be ideal. However,
the test is not completely reliable and larger
studies are needed to confirm these early
findings.
Where did the story come from?
The study was carried out by researchers
from Imperial College London and the
Karolinska Institutet in Sweden. Funding was
provided by the National Institute for Health
Research. The study has not yet been
published in a journal but was presented at
the European Cancer Congress held in
Amsterdam.
This has been reported widely and mostly
accurately in the UK media with a number of
quotes from the research team.
What kind of research was this?
This was a case-control study that aimed to
see whether a breath test could be used to
detect stomach and oesophageal cancers
(OGC).
The study is currently only available as a
published protocol and poster presentation
with accompanying press release. A full
study publication is not available so we
can't fully critique the methods and
analysis.
Worldwide, OGC cancers account for around
1.4 million diagnoses a year but diagnosis
tends to be late and therefore survival rates
are low.
At the moment these cancers can only be
diagnosed using endoscopy, which involves
a camera attached to a flexible tube being
passed down the throat. The procedure can
be uncomfortable and is costly to the NHS.
A breath test that is able to identify the
"chemical signature" of a cancer could be
an ideal way to indicate a cancer diagnosis
and help decide whether further invasive
investigations are needed. It would hopefully
enable more patients to be diagnosed at an
earlier stage of the disease.
What did the research involve?
The researchers included two groups of
patients, those diagnosed with an OGC and
those found to be cancer-free (the control
group).
All participants were over 18 years of age
and had already had an endoscopy to
investigate upper gastrointestinal
symptoms.
Only people with non-metastatic cancer
(cancer that hadn't spread to other organs)
were included in the OGC group. Potential
participants were excluded if they had an
active infection, known liver failure, and if
they were unable to provide informed
consent or unable to provide a 500ml
breath sample.
Breath samples from both groups were
collected in steel breath bags from three
hospitals. Before sample collection the
participants were instructed to fast for at
least six hours and rest in the same area for
at least 20 minutes. All breath samples were
sent to a central laboratory for analysis.
A previous systematic review carried out by
the research group had identified significant
differences in the volatile organic compound
profiles from exhaled breath of people with
OGC cancer.
Based on these findings, the chemicals of
interest in the breath samples were:
butyric acid
pentanoic acid
hexanoic acid
butanal
decanal
These five substances were considered a
"chemical signature" for OGC cancer.
What were the basic results?
The analysis included 335 patients (163
with OGC, 172 controls). More than two
thirds of the OGC group (69%) had cancer
that had spread to nearby lymph nodes.
Of the five chemicals of interest, four were
expressed differently in the OGC group
compared to the control group. This
association remained after adjustments were
made for possible confounders including
patient age, other medical conditions and
medications.
The test correctly detected 80% of cancer
cases and 81% of non-cancer cases.
How did the researchers interpret the
results?
The researchers conclude: "This study
shows the potential of breath analysis in
non-invasive diagnosis of OGC. The
potential benefits of this technology to
patients may be early diagnosis and
improved chance of survival. If placed as an
endoscopy triage test, the benefits to the
healthcare system may include cost-saving
through reducing the number of negative
endoscopies. However these findings must
be further validated in an un-enriched larger
population of patients undergoing diagnostic
endoscopy and in false negative patients the
value of repeat testing should be
established."
Conclusion
This study aimed to see whether a breath
test could be used to detect stomach and
oesophageal cancers.
The researchers found that the breath test
was fairly accurate in distinguishing between
those with and without cancer.
The lead researcher, Dr Markar, said:
"Because cancer cells are different to
healthy ones, they produce a different
mixture of chemicals. This study suggests
that we may be able detect these differences
and use a breath test to indicate which
patients are likely to have cancer of the
oesophagus and stomach, and which do
not."
However he went on to say that the findings
of this study would need to be validated in a
larger sample of patients before being put
into practice.
These are early findings presented at a
conference. While they show promise, it is
not possible to say from the available
information whether the test could have a
future role in practice. In most of the
patients involved in the research the cancer
had spread to the lymph nodes. It is unclear
if the breath test would be able to detect
cancers at an earlier stage.
As the researchers suggest, this test is
likely to be most useful as a possible
indicator for when endoscopy, a more
invasive test, is needed in people who
present with gastrointestinal symptoms.
A breath test sensitive enough to identify a
"chemical signature" of cancer could be an
ideal way to diagnose more patients at an
earlier stage of the disease. However, at
only around 80% accurate, the test is not
infallible. The consequences of not carrying
out further tests for the 20% with cancer
who would test negative need to be
considered.
It is also not possible to say whether this
test could have an impact on survival
outcomes. We need further larger studies to
validate these findings and weigh up the
risks and benefits before considering using
this test to screen for cancer.
Read more about stomach cancer and
oesophageal cancer , including symptoms
and diagnosis.
Analysis by Bazian . Edited by NHS Choices .
Follow NHS Choices on Twitter . Join the
Healthy Evidence forum