Immunotherapy and The Microbiome

Last updated: March 2019

Recently you may have heard discussion about the organisms that live in your digestive system, and the fact that they play a role in your health. You may have heard about prebiotics and probiotics, and are wondering what they have to do with your health, and the immunotherapy that you are using for your cancer treatment.

Defining some key terms

First, let’s define some of these terms:

  1. Microbiome: This term refers to the trillions of bacteria, fungi, viruses and parasites that live in or on a specific region of your body (for example, your skin, or your intestines).1 These organisms live in harmony with your body, or symbiotically, where both our organs and the bacteria benefit from the relationship.
  2. Probiotics: Probiotics refers to a group of live organisms, usually bacteria, that you consume, usually in foods or as a supplement, to add to the bacteria that already live in your system.2 These can be found in food sources such as yogurt or other fermented foods like sauerkraut, kombucha, or kimchi. They are also available in capsule or tablet forms.
  3. Prebiotics: Prebiotics refers to plant fibers, such as complex carbohydrates, that stimulate the growth of healthy bacteria in the gut. Since your body cannot digest these carbohydrates, the microbes in your intestines digest them as they pass along your system. While prebiotics are usually found in fruit and vegetables, they are also available in supplement form.
  4. Immunotherapy: This term refers to medications that are created from living organisms. While these drugs have many uses, they are becoming very common in the treatment of many cancers, and is used often in treating skin cancer.3

Now that you understand what these terms mean, you are probably wondering, “What does the gut microbiome have to do with cancer treatments?” Researchers are currently trying to understand that very question. Currently, it appears that the microbes in your stomach and intestines could influence how well many skin cancer immunotherapy treatments work.4

Immunotherapy and the microbiome

Researchers have known for a while that certain drugs and chemotherapies can change how the gut microbiome works. Certain drugs, like the chemotherapy agent Cyclophosphamide, actually change the structure of the stomach, allowing gut microbes to help fight cancers.4 Researchers also noted that in studies with mice who have no microbiome, immunotherapeutic agents like PD-1 inhibitors didn’t work to fight cancer cells, but mice who had certain types of bacteria responded to the immunotherapeutic agents. Medications like antibiotics can kill both good and bad bacteria and can change the microbiome of the gut.4

How diversity in your microbiome helps

Studies show that patients who have a diverse microbiome, or many different kinds of microbes in their gut, seem to respond better to cancer immunotherapy treatments.5 Beyond that, it appears that people who continued to have diverse microbiome after treatment were more likely to have a longer progression-free survival, or remission, of their cancer.

What does it mean?

Researchers are in the process of conducting larger studies about this connection between the gut microbiome and treatment response. While there is a lot of hope around this discovery and the possibilities of increasing response to treatment, there is also worry about drastically changing a patient’s microbiome to induce this response. Changing a patient’s microbiome may come with other side effects such as weight gain, or even obesity. There are also worries about using single strains of bacteria to change a microbiome. Currently, studies have been inconsistent in finding exactly which strains of bacteria are helpful in increasing drug response.5

Maybe try plant food over probiotics

What does this mean for you or a cancer patient you love? It means that researchers have found promising results in how we can increase response in cancer treatment. If you are interested in this research, talk to your healthcare team. They may have suggestions about changes in diet that can benefit your microbiome. Eating healthy, prebiotic, plant-fiber based diets are usually a great idea to increase your microbiome but ask your healthcare provider if this change is right for you. If you or someone you love is interested in this research, you can find out if there are any trials about the microbiome near you. You can find active trials at

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