Bacteria in mouth that could be triggering growth of colon cancer discovered

Scientists have discovered a new type of bacteria that could be behind the rise in colon or colorectal cancer cases.

The study, published in the journal Nature, found that a particular bacterium, which appears to shield tumour cells from cancer-fighting drugs, was found in 50% of the tumours tested in the study.

Researchers from Fred Hutch Cancer Centre, US, believe this revelation could help improve therapeutic approaches and early screening methods for colorectal cancer, which is among the top ten most common types of cancers in India.

As per the study, this bacterium is commonly found in the mouth and can travel to the gut and grow within colon cancer tumours.

This microbe is also a culprit for driving cancer progression and leads to poorer patient outcomes after cancer treatment.

Examining colorectal cancer tumours removed from 200 patients, the team measured levels of Fusobacterium nucleatum, a bacterium known to infect tumours.

In about 50% of the cases, they found that only a specific subtype of the bacterium was elevated in the tumour tissue compared to healthy tissue.

The researchers also found this microbe in higher numbers within stool samples of colon cancer patients compared with stool samples from healthy people.

"We’ve consistently seen that patients with colorectal tumours containing Fusobacterium nucleatum have poor survival and poorer prognosis compared with patients without the microbe,” explained Susan Bullman, Fred Hutch cancer microbiome researcher and co-corresponding study author.

The researchers wanted to discover how the microbe moves from its typical environment of the mouth to a distant site in the lower gut and how it contributes to cancer growth.

The predominant group of Fusobacterium nucleatum in colorectal cancer tumours, thought to be a single subspecies, is actually composed of two distinct lineages known as “clades.”

By separating the genetic differences between these clades, the researchers found that the tumour-infiltrating Fna C2 type had acquired distinct genetic traits suggesting it could travel from the mouth through the stomach, withstand stomach acid and then grow in the lower gastrointestinal tract (GI).

The analysis revealed 195 genetic differences between the clades.

Then, comparing tumour tissue with healthy tissue from patients with colon cancer, the researchers found that only the subtype Fna C2 is significantly enriched in colorectal tumour tissue and is responsible for cancer growth.