The mouth may be sending more than breath into the body. New research links oral bacteria to gastric cancer by comparing microbes in saliva, tongue and stool, showing similar bacterial fingerprints and raising the possibility that mouth microbes travel to the gut and influence tumor risk. Scientists say saliva and stool testing could reveal patterns tied to stomach cancer, though the findings do not yet prove cause and effect and more work is needed.
Researchers from BGI Genomics in China analyzed 404 samples comparing people with gastric cancer to those with chronic gastritis, using data published in Cell Reports Medicine. They scanned the gut microbiome in stool alongside the oral microbiome from saliva and the tongue to see which species turned up where. The comparison aimed to map overlaps and test whether oral organisms appear deeper in the digestive tract.
The analysis revealed 28 gut species that differed between the two groups, and many of those were species normally associated with the mouth. Most notable were oral bacteria including Streptococcus, lactobacillus and other lactic acid bacteria, which showed up more frequently in stool from the gastric cancer group. Twenty oral-gut species were detected in both saliva and stool and were enriched in patients with gastric cancer.
Genetic comparisons suggested a close match between an individual’s oral bacteria and the bacteria found later in that same person’s gut, hinting at transmission from mouth to stomach. That oral-gut overlap is what drives the study’s central idea that the oral microbiome might influence conditions down the digestive tract. Still, the authors emphasize that this is an association study and cannot prove these microbes caused the cancers observed.
“Collectively, these findings underscore the critical role of the oral-gut microbiome axis in [gastric cancer],” the researchers concluded in the study publication. They propose that profiling saliva and stool could eventually help identify risk patterns or earlier stages of disease, but they stop short of recommending clinical use until further validation. For now, the work is a foundation for follow-up studies that can test timing, mechanism and causality.
Dr. Brian Slomovitz, director of gynecologic oncology and co-chair of the Cancer Research Committee at Mount Sinai Medical Center in Miami Beach, explained the logic of how microbes might act in a two-step process. “[The study] demonstrates how the microbiome of one area of the body can migrate and affect the ability of cancers to develop in another part of the body,” he said, describing a potential initiator-promoter model. “The initiator in gastric cancers is usually inflammatory, such as H.pylori infection,” he added, tying well-understood inflammation to later microbial shifts.
“This inflammation leads to damaged mucosal cells where the lactic acid-producing bacteria can colonize. This helps to explain why cancers still develop even after treating H. pylori infection,” Slomovitz continued, outlining how initial injury could open ecological niches for other bacteria to take hold. If lactic acid producers move in and alter the local environment, they could theoretically support progression from damaged tissue to malignancy. That idea frames future interventions aimed at prevention or combined therapies.
“Perhaps we will learn that by altering the microbiome, we can help better treat cancers (in combination with immunotherapy or chemotherapy) or even prevent cancer,” Slomovitz said, suggesting practical next steps if the link proves causal. He cautioned, “These results will build a foundation for future research. However, we are not ready to incorporate this into clinical practice.” The cautious optimism reflects the gap between a promising association and actionable medical screening or therapy.
Fox News senior medical analyst Dr. Marc Siegel also weighed in on broader implications for health, noting established links between gut microbes and systemic disease. “There is a correlation between the bacteria found in the gut and neurogenerative disease and increased cancer risk,” he told Fox News Digital, stressing the rising awareness of microbiome influence. “It is very important that we work toward a healthy microbiome in the gut to decrease the risk of inflammation and cancer,” he added, pointing to lifestyle and medical strategies that might support microbial balance.
