How the Gut Microbiome Could Influence Cancer Treatment

In recent years, the gut microbiome has emerged as one of the most exciting — and unexpected — factors influencing cancer treatment. Scientists are discovering that the trillions of microbes living in your digestive tract may play a powerful role in how your body responds to therapies like immunotherapy and chemotherapy.

While we’ve long known that gut bacteria help with digestion and immune function, we now understand they may also shape treatment outcomes, side effects, and long-term recovery.

Here’s what the latest research reveals — and what it could mean for the future of personalised cancer care.

What Is the Gut Microbiome?

The gut microbiome is the complex ecosystem of bacteria, fungi, and other microbes living in your intestines. These organisms support everything from breaking down food to training your immune system to respond appropriately — not too aggressively, but not too weakly either.

Because the immune system plays such a critical role in fighting cancer, researchers began exploring whether the microbiome might be influencing this process too. The answer: it is.

Why the Microbiome Matters in Cancer Therapy

Several studies now show that the balance of microbes in your gut can affect how well you respond to cancer treatments — particularly:

●       Immunotherapy (like immune checkpoint inhibitors such as Keytruda or Opdivo)

●       Chemotherapy

●       Radiation therapy (in select cases)

Some bacteria seem to help activate the immune system to better target tumours. Others may interfere with that process or increase the risk of side effects like inflammation or infection.

This discovery is shifting how clinicians think about personalising cancer treatment.

How the Microbiome Is Measured

Microbiome testing typically involves:

1. Stool Sample Collection

A small stool sample is collected and sent to a lab for analysis.

2. Microbial Sequencing

Advanced DNA sequencing tools — like 16S rRNA or full metagenomic analysis — identify which microbial strains are present and in what quantities.

3. Clinical Interpretation

The results are interpreted alongside current research to understand how your unique microbial makeup might support or hinder cancer therapy.

4. Targeted Recommendations

Depending on your profile, clinicians may suggest:

●       Adding specific probiotics or prebiotics

●       Adjusting your diet to encourage helpful bacteria

●       Avoiding certain antibiotics during treatment

●       In some cases, considering a fecal microbiota transplant (FMT) to restore healthy microbial diversity

What the Research Says

●       Melanoma and the MicrobiomeA UK-led study in 2024 found that patients with higher levels of Bifidobacterium pseudocatenulatum, Roseburia spp., and Akkermansia muciniphila responded better to immune checkpoint inhibitors.

●       FMT as a Tool to Improve TreatmentThe Wellcome Sanger Institute is studying how fecal microbiota transplants might boost immunotherapy effectiveness and reduce side effects in cancer patients.

●       Predictive Microbial Signatures Ongoing clinical trials (MITRE and MELRESIST) are using microbial profiles to predict treatment success in melanoma, lung, and kidney cancers.

●       Long-Term Outcomes and the Microbiome A 2024 study published in Nature Medicine showed that microbial strain-level profiles could predict response to therapy and progression-free survival at 12 months.

●       Immune Modulation via Microbes A review published in PMC highlights how gut microbes help regulate immune responses — a key pathway in anti-cancer defence.

The Future of Personalised Cancer Support

While microbiome analysis is still emerging in mainstream oncology, its potential is enormous. By understanding an individual’s gut microbiome, healthcare teams can increasingly tailor treatment plans to support the body’s natural defences, improve therapeutic response, and reduce side effects.

If you or a loved one is preparing for cancer therapy — especially immunotherapy — exploring the gut microbiome could offer an additional layer of insight. It’s not a replacement for treatment, but a way to personalise and support it more intelligently.