Patients' Gut Bugs May Play Role in Cancer Care

From - November 2, 2017

Patients' Gut Bugs May Play Role in Cancer Care

THURSDAY, Nov. 2, 2017 -- The type of bacteria that cancer patients harbor in the gut might affect their odds of responding to certain treatments, two early studies hint.

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

But experts stressed it's too soon to make recommendations to cancer patients -- including whether they should take "probiotic" supplements.

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.

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.

"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.

The "microbiome" refers to the trillions of bacteria and other microbes that dwell in the human body.

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.

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 stabilized or regressed for at least six months -- and a group that did not respond.

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.

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