Monday January 30 2017
Stomach cancer is often diagnosed late
“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 which 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.