Gut Power: How Your Microbes Support Cancer Therapy

Cancer has touched nearly all of us, whether through our own diagnosis, a relative's treatment, or supporting a friend through their diagnosis. Learning how the immune system works, how various cancer treatments function, and how we can support the body’s defenses can provide a greater sense of control in uncertain times.

Here's something most people don't know: the microbes in your gut help train your immune system — shaping how it recognizes abnormal cells, maintains balance, and reacts when something goes wrong. This emerging field is changing how scientists think about long-term health and modern cancer therapies.

In this blog, we'll explore how your gut bacteria support your immune system, their role in cancer therapy, and what this means for long-term wellness.

The immune system’s role in cancer therapy

Your immune system is always on the lookout for cells that look damaged, infected, or unstable [1]. Most potential cancer cells are removed by the immune system long before they ever become a problem.

But sometimes cancer cells learn how to hide or shut down the alarms that would typically expose them [2]. When this happens, these cells can grow quietly for years. 

Here are several immune cells that help protect the body [3]:

• T cells: targeted immune cells that kill cells bearing abnormal or harmful proteins.
• Dendritic cells: messenger cells that indicate to T cells where threats are in the body.
• Natural Killer (NK) cells: fast-acting cells that destroy cells that look stressed or abnormal.

Many cancer therapies work by helping these immune cells do their jobs more effectively. This connection is integral to the design of modern treatments.

• CTLA-4 inhibitors (Ipilimumab) help T cells start a more potent attack.
• PD-1 (Pembrolizumab, Nivolumab) and PD-L1 (Atezolizumab) inhibitors prolong T-cell activation by blocking inhibitory signals that suppress T cells.
• Combination therapies use both types of inhibitors to enhance T-cell activation.
• NK-cell therapies strengthen fast-reacting NK cells.
• Chemotherapy directly attacks fast-growing cancer cells.

Cancer treatments: how the microbiome gets involved

Research shows that the gut microbiome can affect how well people respond to cancer treatments. In many studies, individuals with higher gut microbiome diversity (greater bacterial variety) respond better to therapy [4]-[7].

Everyone’s microbiome is unique, and research methods aren’t all the same either—studies may differ in how samples are collected, how bacteria are measured, or who is included. As a result, the specific microbes associated with improved treatment responses can vary across studies. Rather than searching for a single “magic microbe,” researchers focus on consistent patterns that signal when a microbiome helps the immune system remain strong.

Though the specific microbes vary, many influence immune pathways in similar ways. For example, short-chain fatty acids, produced by several bacterial species, enhance the function of T cells and NK cells during cancer treatment [8]-[10].

CTLA-4 inhibitors

• Certain helpful bacteria from the Firmicutes phylum, including Faecalibacterium, appear more often in people who respond well to this type of therapy [11]. People with this microbiome profile also had stronger T-cell activation during treatment.

PD-1 and PD-L1 inhibitors

• Across cancer types, bacterial taxa such as Bifidobacterium, Collinsella, Faecalibacterium, Roseburia, Blautia, Enterococcus, and Akkermansia are associated with a positive response to therapy [4]-[6], [12]-[16]. These bacteria are also linked to a more active T-cell immune response.

Combination therapies: 

• Taxa such as Bifidobacterium, Roseburia, Faecalibacterium, Bacteroides, Holdemania, and Akkermansia were more abundant in patients who responded well to treatment [14], [17].

Chemotherapy

• In metastatic colorectal cancer, people who responded well to therapy often had higher levels of Ruminococcus, a beneficial bacteria [18]. Those with poorer outcomes tended to have more Fusobacterium, a disruptive bacteria that's been linked to colorectal cancer in other research [18], [19].

How therapy can change the microbiome

Your gut microbiome and immune system are deeply connected. So when you’re going through cancer treatment, the balance of bacteria in your gut often shifts too. Different treatments affect the microbiome in distinct ways:

• CTLA-4 treatment can lower levels of Bacteroidales and Burkholderiales, with an increase of Clostridiales [20].
• PD-1 treatment led to a reduction in Firmicutes, Lachnospiraceae, and Ruminococcaceae, with an increase in Bacteroidaceae [21].
• After a combination PD-1 treatment, Solobacterium moorei and Parvimonas micra were reduced, but only in patients who responded positively to treatment [22].
• Chemotherapy can decrease bacteria like Firmicutes, Solibacillus, and Enterococcaceae, and increase Rhodobacterales, Proteobacteria, Bacteroidota and Paracoccus [23], [24]. Chemotherapy can also harm the lining of the gut [25]. When this protective wall is damaged, it becomes easier for irritation and inflammation to develop.

Understanding your unique gut for long-term wellness

The connection between gut health and cancer therapy response is still unfolding, but what we already know is encouraging. Microbes play an active role in training your immune system, and that foundation matters long before treatment ever begins. 

The everyday choices you make now — like eating a fiber-rich, whole-food diet and getting adequate sleep — can help build a diverse, resilient gut that supports your long-term well-being.  

If you're curious about where your microbiome stands today, a Gut Health Test can provide valuable insights and personalized strategies to help strengthen your gut's ability to support your immune system for prevention, treatment preparation, and recovery. 

While gut health testing should never replace standard cancer care, it can be a supportive part of preparing for treatment and recovering afterward.