Stomach Cancer

The Bacterium Behind Most Stomach Cancer

This is the strongest evidence linking any bacterium to any cancer, and it comes from randomised trials rather than observation alone. Stomach cancer is the fifth most common cause of cancer death worldwide. For most of the twentieth century it was blamed on diet and stress. It turned out that the largest single cause was an organism living in the stomach lining, and that treating it changes who gets the disease.

An organism nobody expected to find

The stomach was long assumed too acidic for bacteria to survive.

Helicobacter pylori manages it. It burrows into the mucus layer coating the stomach lining, where conditions are less hostile, and produces an enzyme that neutralises acid immediately around itself.

Infection is usually acquired in childhood and, untreated, lasts for life. It causes chronic inflammation of the stomach lining.

Over decades that inflammation drives a recognised sequence. The lining thins, then starts producing cells resembling intestinal lining rather than stomach lining, a change called intestinal metaplasia. From there, some people progress to abnormal cells and then to cancer.

The bacterium is implicated in up to 90% of stomach cancer cases.

What happens when you remove it

Association wouldn't be enough on its own. What makes this different is that removing the bacterium has been tested repeatedly in randomised trials.

A meta-analysis pooled 11 randomised trials and 13 observational studies of people carrying the infection, with at least two years of follow-up.

Treating the infection reduced stomach cancer incidence, with a relative risk of 0.61, meaning roughly a 39% reduction.

In healthy people without existing stomach changes, seven trials covering 8,323 participants found a similar reduction in cancer and in deaths from it.

The clearest result came in people who had already had an early stomach cancer removed endoscopically. Among 910 who received eradication treatment, 5.9% developed a further stomach cancer, against 11.4% of the 931 who didn't.

Source: Eradication Therapy to Prevent Gastric Cancer in Helicobacter pylori-Positive Individuals: Systematic Review and Meta-Analysis

Why treatment isn't a complete answer

The honest reading of those numbers includes what they don't show.

Eradication reduces stomach cancer incidence by around 60% to 70% at best, not to zero. Cancer can still appear more than ten years after successful treatment, so the risk is lifelong rather than removed.

That's because the damage already done to the stomach lining doesn't fully reverse. Thinning and intestinal metaplasia largely persist, and tissue in that state carries ongoing risk regardless of whether the bacterium is still there.

Timing therefore matters enormously. Treating the infection before those changes are established does far more than treating it afterwards.

There's also a geographic caveat. Almost all these trials were run in East Asia, where stomach cancer rates are highest, so the size of the benefit elsewhere is less certain.

Source: Endoscopic risk factors to inform early detection of gastric cancer after Helicobacter pylori eradication: Meta-analysis and systematic review

Why infection alone doesn't explain everything

One more observation deserves attention, because it points at the rest of the picture.

Stomach cancer rates vary enormously between countries, and that variation isn't explained by how common the infection is. Plenty of populations carry it widely without correspondingly high cancer rates.

So something modifies whether infection progresses. Bacterial strain differences account for part of it. Inherited variation in the inflammatory response accounts for more.

Diet is the third factor, and it's the one under any individual's control. High salt intake damages the stomach lining and is consistently associated with higher risk. Diets rich in fruit and vegetables are consistently associated with lower risk.

That means infection sets the stage, and what happens next depends partly on the conditions the lining is kept in.

What this means for you

Persistent indigestion, difficulty swallowing, unexplained weight loss or vomiting blood needs prompt medical assessment, and Helicobacter pylori is detected with a breath, stool or blood test and cleared with a course of antibiotics. In addition, the research above shows that clearing this bacterium reduces stomach cancer risk substantially in randomised trials, while leaving a residual risk that depends on how much damage the lining has already taken. A varied, plant-rich diet, low in salt, supports the same conditions this research ties to slower progression of that damage. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.