Oral Microbes Linked to Gastric and Colorectal Cancer Detection in New Research

Researchers analysing the composition of oral microbes have identified signals associated with gastric and colorectal cancer, according to a study published in the Cell Press journal Cell Host & Microbe on 20th August. The findings raise the possibility of developing new, less invasive screening tests for gastrointestinal cancers.

It is widely understood that the microbiome, especially microbes found in the mouth and gut, can have a profound effect on health. Co-corresponding and lead author Jihyun F. Kim of Yonsei University in Seoul said: “Many species of microbes associated with the mouth are also present in the gut and may flourish there. These observations made us wonder whether oral microbes reach and persist in the gastrointestinal tract differently in people with cancer.”

To conduct the study, the researchers recruited 507 volunteers to donate both oral and faecal samples using a highly standardised collection process. The cohort included 129 healthy individuals, 215 people with metabolic disorders such as metabolic syndrome, hypertension, hyperlipidaemia, and type 2 diabetes, 77 people with gastric cancer, and 86 people with colorectal cancer. For the volunteers with cancer, samples were collected before the start of any treatment.

The team used gene sequencing to create what they called a Mouth-to-Faeces (MF) index, which measures the extent to which identical microbial sequence variants are found in oral and faecal samples from the same person.

The MF index was significantly elevated in patients with gastric or colorectal cancer but not in people with metabolic disorders, and the association remained robust for both cancers even after accounting for alcohol consumption, regular exercise, and BMI.

Co-corresponding author Sun Ha Jee, also of Yonsei, said: “The presence of oral-associated bacteria in the gut of patients with cancer was not entirely unexpected. What we had not fully anticipated was how the signal varied across disease groups, how much of it could be detected in oral samples alone, and how strongly it depended on the way microbial features were represented.”

Although only a small fraction of oral bacterial variants were also detected in the gut, models built using only these oral features could distinguish patients with cancer from healthy individuals across several independent cohorts.

The team also compared the signatures found in the cancer patients with results from faecal occult blood tests, a standard colorectal cancer screening tool that analyses stool samples. They found higher sensitivity with the oral samples, which were collected using a simple mouth rinse. Independent reporting on the study noted sensitivity of 92.9% for the oral approach, compared with 61.0% for the standard test.

Co-corresponding author Yong Chan Lee of Yonsei said: “It was notable that cancer-related information could be recovered from oral samples alone.”

The researchers are planning a study to prospectively validate the findings in people who do not already have a cancer diagnosis, and they plan to incorporate higher-resolution metagenome sequencing. Additional research will examine causality: whether increased mouth-gut microbial sharing contributes to cancer development, whether cancer creates conditions that allow oral bacteria to remain in the gastrointestinal tract, or both.

Co-corresponding author Tae Il Kim, also of Yonsei, said: “Before any of this could be used in practice, it would need to go through clinical studies in real screening populations.”