Colon Cancer

The Mouth Bacterium Found Inside Bowel Tumours

The evidence here is strong and unusually specific, tracing a named organism from where it belongs to where it shouldn't be. Colon cancer is the third most common cancer worldwide. Diet has long been linked to it, and the assumption was that food acted on the bowel lining directly. Part of the story turns out to involve a bacterium that isn't a normal resident of the gut at all.

An organism in the wrong place

Fusobacterium nucleatum lives in the mouth, where it's an ordinary member of the dental plaque community.

It's found far more often in colorectal tumour tissue than in the healthy lining next to it. It reaches the gut either by being swallowed or by travelling through the bloodstream.

It doesn't arrive passively. It carries surface proteins that let it stick specifically to tumours. One, called Fap2, binds sugar molecules that tumours display. Another, FadA, binds a protein on the surface of gut lining cells.

Those attachments let it colonise, form protective biofilms, and avoid immune clearance.

Source: Fusobacterium nucleatum and colorectal cancer: From phenomenon to mechanism

What its presence predicts

Being present is one thing. What matters is whether it changes outcomes.

Researchers measured how much Fusobacterium DNA was in tumour tissue and followed patients afterwards. Those with high levels had a 58% higher risk of dying from their bowel cancer.

That association held independently of the tumour's own molecular characteristics, meaning it wasn't simply a marker for a more aggressive genetic subtype.

Tumours carrying it also tended to be less well differentiated and at more advanced stages. In one study, lymph node spread was present in 59% of patients with high levels of the bacterium and in none of those with low levels.

Abundance rises with stage. Tissue and stool from people with invasive disease carried far more than samples from those with the earliest tumours.

How it makes tumours worse

Several mechanisms have been identified, and they operate together.

The FadA protein doesn't just anchor the bacterium. Binding to that surface protein disrupts the junctions holding lining cells together and switches on a growth signalling pathway that's already central to bowel cancer development.

The bacterium drives chronic inflammation through several inflammatory signals, and inflammation itself promotes tumour growth.

It causes DNA damage, both directly through reactive molecules and indirectly through that inflammation.

It also interferes with treatment. Tumours carrying it show more resistance to chemotherapy, apparently by blocking the process that would otherwise make cancer cells die. It also alters the immune environment around the tumour in ways that shield it.

Source: Unraveling the Role of Fusobacterium nucleatum in Colorectal Cancer: Molecular Mechanisms and Pathogenic Insights

What this doesn't mean

Two clarifications matter, because this is easy to overstate.

Bowel cancer isn't an infection. It develops through accumulated genetic damage over years, and inherited risk, age, smoking and alcohol all contribute. This bacterium appears to accelerate and worsen a process that has other causes.

Nobody has shown that eliminating it prevents bowel cancer in people. Targeted approaches are being developed, including viruses that infect only this species, but they're experimental.

What the evidence does support is that the bacterial environment inside a tumour affects how that tumour behaves, which wasn't part of the picture a decade ago.

What this means for you

Blood in the stool, a persistent change in bowel habit or unexplained weight loss needs urgent assessment, and taking part in bowel screening when invited is the single most effective thing available, since it finds growths before they become cancer. In addition, the research above found a mouth bacterium colonising bowel tumours, with high levels carrying a 58% higher risk of dying from the disease and driving resistance to chemotherapy. A varied, plant-rich diet supports the same gut bacteria this research ties to a community that resists colonisation by organisms that don't belong there. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.