A simple saliva test could one day detect stomach cancer earlier avoiding the need for invasive tests and potentially saving thousands of lives, promising new research has suggested.
Also known as gastric cancer, the disease is thought to often be caused by bacteria like Helicobacter pylori that live in the stomach.
However, until now, scientists were unsure which bacteria specifically trigger the cancer – or how these organisms end up in the stomach.
Every year, around 6,700 people in the UK are diagnosed with the disease and roughly 3,600 die as a result over the same period.
Now, Chinese researchers have identified 20 species of bacteria that they say are reliably found in the stomachs of stomach cancer patients.
The scientists, from Shanghai Jiao Tony University School of Medicine, argue these bacteria cause a build-up of acid in the stomach, leading to cancerous changes.
Crucially, they conclude that the majority of these bacteria begin life in the mouth, before making their way down into the stomach.
Helicobacter pylori (H. pylori) is a type of bacteria that infects the lining of the stomach
The study, published in the journal Cell Reports Medicine, argues that, in the future, patients could regularly undergo a saliva test to look for signs of these bacteria in the mouth, catching the disease in its earliest and easiest-to-treat stage.
‘This study is newsworthy because it strengthens the idea that gastric cancer may involve a broader oral-gut microbiome axis, not just H. pylori,’ Professor Stuart McDonald, an experts in gastrointestinal biology at Queen Mary University, said.
‘It also suggests that saliva or stool samples could eventually help doctors spot stomach cancer without invasive tests.
‘Whilst there are important limitations, it is an important clue in the search for easier ways to detach stomach cancer earlier and should this be successful, easier to treat.’
According to previous studies, stomach cancer is most often caused by a bacteria called Helicobacter pylori, which is responsible for around 40 per cent of cases in the UK.
The bug spreads through contaminated food and water, and can often trigger uncomfortable symptoms like indigestion and stomach ulcers. However, many experience no symptoms.
In some cases, Helicobacter pylori remains in the stomach for months while for others, it can stay there for years, even decades.
Other causes of stomach cancer include smoking, heavy alcohol consumption and poor diet.
The disease is twice as common in men as it is in women, according to research.
At present, the disease is usually diagnosed via an endoscopy – where a small camera is threaded down through the mouth and into the stomach to look for signs of cancer.
However, the team at Shanghai Jiao Tony University School of Medicine believe they have found an alternative.
They analysed over 400 saliva and stool samples from gastric cancer patients, in order to look for bacteria present in their stomachs.
They identified 23 species of bacteria were found in the stomachs of these patients.
Significantly, the scientists, led by Dr Fang Jingyuan, a stomach cancer expert, found that 20 of these bacteria were also found in the mouths of patients.
They concluded that this suggested the bugs begin life in the mouth before spreading to the gut.
Dr Jingyuan and his team argue that the most likely explanation is that these patients were first infected with Helicobacter pylori, which inflames the lining of the stomach, and hampers the immune system’s ability to clear other infections.
So, when these species of oral bacteria make their way to the stomach, they lead to persistent infections, and eventually trigger cancerous changes in the lining.
The researchers say their findings suggest that a nationwide stomach cancer screening programme could be rolled out using a cheap and easy-to-use saliva test.
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They claim that early research, based on computer modelling, suggests such a programme could correctly identify the early stages of stomach cancer in nearly nine in ten cases.
Writing in the journal Cell Reports Medicine, they concluded: ‘Our microbial signatures are robust predictors, with oral models outperforming gut ones – suggesting earlier or more pronounced oral alterations.
‘By framing non-Hp opportunists, our findings advance mechanistic understanding and nominate biomarkers for diagnostics and microbiome-targeted therapies in gastric cancer.’
Other experts said the findings were promising but further research was needed before a saliva test could be developed.
‘The saliva of the cancer patients could predict the presence of gastric cancer,’ says Prof Gary Moran, an oral health expert at Dublin Dental University Hospital.
‘This could be useful but requires validation in other cohorts.’
Loss of appetite, difficulty swallowing, indigestion that doesn’t go away and unexplained fatigue are all symptoms of stomach cancer, according to Cancer Research UK.
However, the cancer is diagnosed late because these symptoms are often dismissed by patients.
The survival rates for stage 4 stomach cancer – the most advanced stage – are bleak with around only 20 per cent of patients surviving for one year or more after their diagnosis in the UK.
