A potentially groundbreaking development in medical research suggests that a straightforward saliva test might soon be able to identify stomach cancer at an earlier stage. This non-invasive method could eliminate the need for more intrusive procedures and has the potential to save thousands of lives.

Stomach cancer, also referred to as gastric cancer, is frequently linked to the presence of bacteria like Helicobacter pylori in the stomach. Despite this association, it has been unclear which specific bacteria are responsible for triggering the disease and how they find their way into the stomach.

In the United Kingdom alone, approximately 6,700 individuals receive a stomach cancer diagnosis annually, and around 3,600 succumb to the disease each year. These statistics underscore the urgent need for earlier detection methods.

Recently, researchers from Shanghai Jiao Tong University School of Medicine have made a significant breakthrough. They have pinpointed 20 species of bacteria consistently found in the stomachs of patients with this form of cancer.

The team proposes that these identified bacteria contribute to an acid accumulation in the stomach, which may lead to cancerous transformations. This discovery could pave the way for early diagnosis and improved survival rates through a simple saliva test.

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.

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 patients 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.

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.