Oral Microbiome Signals Offer New Path to Detecting Gastric Cancer

Oral bacteria can migrate throughout the body and may signal the presence of gastrointestinal cancer.

Image credit:© iStock.com, nopparit

The microbiome—the collection of microbes inhabiting the body—flourishes in its respective niches. Oral microbes face environmental conditions distinct from those in the stomach or intestines, leading different bacterial species to dominate specific body sites. Consequently, each localized microbiome exhibits a unique microbial signature.

When disease disrupts the body, these barriers break down. A recent study demonstrated that oral bacteria can travel through the gastrointestinal tract in certain cancers.1 This breakdown of the body’s compartmentalization may serve as a disease indicator, potentially enabling faster, simpler diagnostics for gastrointestinal cancers.

DNA Analysis Reveals Bacterial Migration in Disease

In prior work, researchers at Yonsei University observed that the oral bacterium Fusobacterium nucleatum, the microbe had also been found in colorectal tumor tissues. Building on that finding, they enrolled 507 participants with various health statuses for the current investigation. Among them, 215 had metabolic disorders—including metabolic syndrome, hypertension, hyperlipidemia, or type 2 diabetes—77 were diagnosed with gastric cancer, 86 with colorectal cancer, and 129 served as healthy controls.

Participants provided oral swabs and stool samples, which the researchers analyzed using amplicon sequencing to characterize the bacterial communities in each specimen.

Initial analyses revealed that oral and fecal microbiomes shared more similarities in patients than in healthy individuals, although this trend varied across conditions. To quantify microbial translocation, the team devised an index reflecting the proportion of gene signatures common to oral and fecal samples. In gastrointestinal cancer patients, this index was about threefold higher than in controls, indicating a substantial increase in oral‑gut bacterial overlap. Although lifestyle factors such as alcohol consumption and physical activity affected the index values, adjusting for these variables did not diminish the association between cancer status and the migration metric.

“The detection of oral‑associated bacteria in the guts of cancer patients was not wholly surprising,” remarked Sun Ha Jee, a public‑health researcher at Yonsei University and co‑author of the study. “However, we did not anticipate the extent to which this signal would differ among disease categories, how much of it could be identified using oral samples alone, or how strongly it would rely on the representation of microbial features.”

Microbial Assessment Outperforms Common Cancer Test

The investigators evaluated whether microbial signatures could distinguish cancer types. They found that the profiles successfully differentiated gastric and colorectal cancers from healthy controls using oral microbiome data alone. When benchmarked against the standard fecal occult blood test (FOBT) for colorectal cancer, models that incorporated oral and fecal microbial data substantially outperformed the FOBT. The authors highlighted that the strength of oral‑based predictions is especially valuable because saliva samples are simple to obtain.

“Although only a modest proportion of oral bacterial taxa were also present in the gut, models constructed exclusively from these oral markers were able to separate cancer patients from healthy subjects in multiple independent cohorts,” explained Yong Chan Lee, a gastroenterologist at Yonsei University College of Medicine and study co‑author.

These findings suggest that a microbial‑based assay could eventually serve as a diagnostic tool for gastrointestinal cancers, although the authors emphasize that additional clinical trials are required before such a test could be adopted in routine hospital practice.

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