Lung Cancer

What the Gut Has to Do With Lung Tumours

The evidence here is strong and clinically consequential, having already changed how some oncologists prescribe. Lung cancer treatment now often includes immunotherapy, which works by removing the brakes on immune cells so they can attack tumours. Whether that works depends heavily on the state of the immune system, and the largest single influence on immune training sits in the intestine.

The antibiotic finding

Researchers examined patients with non-small-cell lung cancer and kidney cancer receiving immunotherapy, and asked a simple question about who had recently taken antibiotics.

Patients given antibiotics shortly before starting treatment, or early during it, had significantly shorter survival.

The effect was consistent enough that a later review of 95 clinical studies published between 2015 and 2025 confirmed it. That review identified the 30-day window around starting treatment as the period mattering most.

That finding has a limitation worth naming. People needing antibiotics are often sicker, so some of the difference could reflect their underlying condition rather than the drugs. The researchers acknowledged it, and it's why the animal work mattered.

Source: Gut microbiome influences efficacy of PD-1-based immunotherapy against epithelial tumors

The bacterium that was missing

The team went looking for what antibiotics were removing.

Comparing gut bacteria between patients whose tumours responded and patients whose didn't, one organism stood out. Non-responders had low levels of Akkermansia muciniphila.

That's a bacterium living in the mucus layer coating the gut wall, where it helps maintain the barrier rather than sitting in the gut contents.

The test came next. Mice were given antibiotics, which destroyed their response to immunotherapy. Giving those mice Akkermansia muciniphila by mouth restored it.

So a single species, replaced after the community had been damaged, was enough to bring the treatment back.

How a gut bacterium reaches a lung tumour

Nothing travels from gut to lung directly, so the route runs through the immune system.

Immune cells are trained in the gut wall, where the largest concentration of them in the body sits alongside the bacterial community. Cells primed there circulate throughout the body.

Compounds bacteria produce from fibre act on those cells, influencing how readily they activate and how long they stay active.

Gut bacteria also set the background level of inflammatory signalling. Persistent low-grade inflammation is associated with immune cells becoming exhausted, meaning less responsive to stimulation, which is exactly the state immunotherapy is trying to reverse.

So the gut doesn't act on the tumour. It acts on the cells that act on the tumour.

What this has changed and what it hasn't

Two things are worth separating.

What has changed is prescribing behaviour. Many oncologists now avoid unnecessary antibiotics around the start of immunotherapy, and the microbiome is being investigated as a way to predict who will respond. Machine learning models using bacterial profiles predict response with reasonable accuracy in research settings.

What hasn't changed is treatment. No microbiome-based therapy is approved for lung cancer. Stool transplant trials are running in melanoma rather than lung cancer, and results there don't automatically transfer.

One finding deserves particular caution. Over-the-counter mixed probiotic supplements have consistently correlated with worse immunotherapy outcomes, apparently by disturbing the varied community the response depends on. This is not a situation where taking a supplement is a low-risk bet.

Diet-based work is at an earlier stage, though pilot studies of high-fibre eating patterns have improved immune cell infiltration into tumours.

Source: Clinical Evidence for Microbiome-Based Strategies in Cancer Immunotherapy: A State-of-the-Art Review

What this means for you

A persistent cough, coughing blood, breathlessness or unexplained weight loss needs urgent assessment, and stopping smoking remains by far the largest single influence on lung cancer risk. In addition, the research above found antibiotics around the start of immunotherapy tracking with shorter survival, and restoring one missing gut bacterium bringing the treatment's effect back in animals. A varied, plant-rich diet supports the same gut bacteria this research ties to better immunotherapy response, while over-the-counter probiotic supplements tracked with worse outcomes. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.