Cancer

Updated 17 November 2017

What is the link between gut bacteria and cancer treatment?

There is increasing evidence that the gut microbiome plays a key role in the human immune system.

0

The type of bacteria that cancer patients harbour in the gut might affect their odds of responding to certain treatments, two early studies hint.

These trillions of bacteria and other microbes that live in the human intestines are referred to as the "microbiome".

The research, in humans and mice, adds to evidence that gut bacteria play a key role in the immune system.

Freeing up the immune system

Both studies looked at whether there's a link between patients' gut bacteria and their responses to newer cancer drugs called PD-1 inhibitors. The drugs, which include Keytruda (pembrolizumab) and Opdivo (nivolumab), work by freeing up the immune system to attack cancer cells.

The drugs are approved for several cancers, including advanced cases of melanoma, lung, bladder and stomach cancers.

In one study, researchers focused on 112 patients with advanced melanoma, the deadliest form of skin cancer. The investigators found that those who'd responded to PD-1 therapy tended to have a gut "microbiome" that was distinct from those of patients who did not respond.

The new research appears in Science.

Those who'd responded generally had more diversity in their bacteria, plus higher concentrations of common bacteria called Ruminococcus and Faecalibacterium.

Still, the researchers said the findings do not prove that those bacteria improve the odds of doing well on PD-1 therapy, and stressed that it's too soon to make recommendations to cancer patients – including whether they should take "probiotic" supplements.

Diversity of gut bacteria

"Only a clinical trial can show that. This needs to be tested," said senior researcher Dr Jennifer Wargo, an associate professor at University of Texas M.D. Anderson Cancer Center in Houston.

However, the findings build on evidence of a "clear link between the gut microbiome and immune function," she said.

Studies have found that the diversity of those bugs – particularly in the gut – is linked to the risks of various health conditions, including those related to immune function.

According to a previous Health24 article, analysing the composition of people's collection of gut bacteria can also help improve identification of those who are at risk for, or already have, colon cancer.

In general, studies have found, the more diversity in the gut microbiome, the better.

Wargo's study involved a group of melanoma patients who'd responded to a PD-1 inhibitor – meaning their cancer had stabilised or regressed for at least six months – and a group that did not respond.

Gut bacteria transplanted

Overall, the responders showed an "abundance" of Ruminococcus and Faecalibacterium. In contrast, the non-responders had a high concentration of Bacteroidales bacteria.

To test whether the microbes might have a direct influence on treatment response, the researchers transplanted gut bacteria from the patients into lab mice.

Those animals also responded better to PD-1 therapy, versus mice that had transplants from non-responding patients, according to the report.

In the second study, French researchers focused on 249 patients treated with a PD-1 inhibitor for lung, kidney or urinary tract cancers. Just over one-quarter had taken antibiotics to treat an infection shortly before or after starting PD-1 treatment. (Antibiotics are drugs that kill bacteria).

Overall, those antibiotic patients had lower survival odds. Plus, 69% of patients who responded to PD-1 treatment had detectable amounts of bacteria called Akkermansia muciniphila, versus 34% of patients who did not respond.

It all raises "exciting possibilities," Wargo said. Namely, could manipulating the gut microbiome improve the chances of responding to cancer treatment?

But there are plenty of unanswered questions. For one, "We don't really know what constitutes a 'favourable' microbiome," Wargo noted. So there is no way to tell cancer patients whether any probiotic might benefit them.

Tailoring treatment

In fact, she said, if patients were to take a random supplement, it might end up causing harm. In addition, there also needs to be more research into gut bacteria and responses to other cancer therapies, Wargo added.

Dr Nikhil Khushalani specialises in treating skin cancer at Moffitt Cancer Center, in Tampa, Florida. He cautioned that the study findings are a "first step", but also a "very intriguing" one.

Khushalani said the findings raise the possibility of testing patients' stool samples to see who has a greater likelihood of responding to PD-1 therapy. "That could help us in truly tailoring treatment," he suggested.

Then there's the possibility of actually altering patients' microbiomes – whether through probiotics or even faecal transplants, Khushalani added.

Like Wargo, he cautioned patients against self-treating with probiotics, given the unknowns.

"But that could be where we're heading," Khushalani said. "Hopefully, this will open the door to even more research in this arena."

Image credit: iStock

 

Ask the Expert

Cancer expert

CANSA’s purpose is to lead the fight against cancer in South Africa. Its mission is to be the preferred non-profit organisation that enables research, educates the public and provides support to all people affected by cancer. Questions are answered by CANSA’s Head of Health Professor Michael Herbst. For more information, visit cansa.org.za.

Still have a question?

Get free advice from our panel of experts

The information provided does not constitute a diagnosis of your condition. You should consult a medical practitioner or other appropriate health care professional for a physical exmanication, diagnosis and formal advice. Health24 and the expert accept no responsibility or liability for any damage or personal harm you may suffer resulting from making use of this content.

* You must accept our condition

Forum Rules