Gut bacteria can impact cancer treatments
Gut Microbiome microbiota Checkpoint Inhibitor

Gut bacteria can impact cancer treatments

Dr. Talia Henkle
Dr. Talia Henkle

In 10 seconds? Evidence is emerging that your gut microbiota may impact how well cancer treatments work. Scientists are actively teasing apart what factors set patients up for success.

What exactly is the gut microbiota? Our digestive system is chock full of different types of  bacteria that help us derive nutrients from our food and shape our immune system. The populations of bacteria in your gut are referred to as your gut microbiota. Scientists can determine what your gut microbiota consists of by performing DNA sequencing analyses on your stool and are using these data to decipher what constitutes a ‘good’ combination of gut bacteria.

So what does this have to do with cancer? Immune checkpoint inhibitors, which are cancer treatments that aim to boost your immune system’s ability to tackle cancer, have revolutionized cancer care in the last decade. Still, only a fraction of patients treated with these drugs see long-lasting improvements–and scientists still can’t precisely say what factors contribute to success or failure. When data emerged in 2015 that altering the gut microbiota of mice with cancer could improve their ability to respond to checkpoint inhibitors, it paved the way for scientists to investigate if that strategy held any promise for human patients.

So what have they found? Results are promising but still inconclusive. For example, a recent study showed that altering the gut microbiota of advanced stage skin cancer patients whose cancer had previously failed to respond to checkpoint inhibitor treatment could help a subset of them (6/15) to respond better to subsequent checkpoint inhibitor treatment.

That’s cool! How exactly did they go about changing their gut microbiota? Since researchers don’t know the exact ‘recipe’ to concoct a ‘good batch’ of gut bacteria, they looked to the guts of patients whose cancers had gone away or shrunk after checkpoint inhibitor therapy. Luckily, there’s an easy and non-invasive way to ascertain the bacterial components of your gut. They gathered stool samples and created a personalized gut bacteria cocktail (appetizing, right?) to give to patients whose cancer had previously failed to respond to checkpoint inhibitor treatment.

Gut bacteria is thought to influence cancer patients' responses to cancer treatments through bacteria's ability to modulate metabolism and immunity, although the exact mechanisms are still unclear. Source: Yu ZY, et al. BMC Cancer. 2021 Aug 19;21(1):934

Eww. But, OK. So what have they learned? Progress in this field is slow but steady. This study and others provide more evidence that gut bacteria plays a role in human cancers, but the key players remain elusive. The composition of the gut microbiota is vastly different from one ‘good-responder’ to another, which makes it difficult for researchers to identify the factors or bacterial species that drive success.

Well, how will they figure that out? Some scientists suggest that deeper analyses of the metabolites (AKA certain chemical compounds) produced by gut bacteria may paint a clearer picture of what’s important than the exact species of bacteria. Others suggest the microbiota of the tumor itself may play a more important role predicting success of cancer treatment than the gut microbiota–with data showing that certain microbes in tumors can play a role in tumor chemotherapy resistance. Researchers are hacking away at these questions in the many clinical trials currently underway.

What should I eat to have a healthy gut microbiota?

It’s known that your diet significantly impacts your gut microbiota to a greater extent than genes. But without having a clear idea of what ‘good gut bacteria’ even is, it’s impossible to confidently recommend any dietary approach.

One study showed that skin cancer patients who ate a high fiber diet responded well to immunotherapy while those who took over the counter probiotics fared worse. The best dietary advice most doctors give is the most general– to avoid processed foods and eat vegetables.

Dr. Talia Henkle has distilled 5 papers saving you 17.5 hours of reading time.

The Science Integrity Check of this 3-min Science Digest was performed by Flávia Oliveira Geraldes

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