The bacteria that live in your gut could have a major say in how effective cancer treatments like chemotherapy are on your body. In two papers published today in Science, researchers say that gut bacteria was found to have a major impact on how cancer treatments perform in mice. Though bacteria's relevance to such therapies may seem unlikely, this is actually just the latest in a series of preliminary discoveries surrounding the impact of the gut microbiota, the complex mixture of bacteria that lives inside you.

Mice with no gut bacteria were less responsive to cancer treatments

"What was really a surprise was with the chemotherapy," Romina Goldszmid, a National Institutes of Health researcher and corresponding author on one of the papers, tells The Verge. "What we were not really expecting was that the molecules important to causing damage [to the tumor] are … also from the gut bacteria."

The research teams behind both papers saw that mice with reduced levels of bacteria in their gut were less responsive to treatments than mice that had a normal microbiota. The next step will be to learn why. NIH researchers now want to determine exactly which bacteria is having such a noticeable impact — potentially giving physicians another tool for battling cancer.

"If one wants to use this information to manipulate the gut microbiota to favor or dampen a certain response depending on the setting, we need to understand which bacteria do what," Goldszmid says. Her research team is continuing to study bacteria in mice, but they’re also taking a crucial next step: looking for these same effects in humans.

"We need to validate these results in humans."

"The bacteria in the gut of the mouse are not the same [ones in] the gut in the human," Goldszmid says. "We need to validate these results in humans." Goldszmid thinks that a similar response will be seen in people, but the exact types of bacteria that play a role will likely differ. More broadly, she says physicians will also have to start considering how various treatments impact the gut. "Any type of treatment that will affect the composition of the microbiota may have an impact that we were not aware of."

Though that may mean more variables to be concerned with, understanding them could lead to better treatments for cancer down the road. "I think the microbiota will have an impact," Goldszmid says. "Whether it’s going to be the same type of bacteria, that we can’t really tell. But we can certainly expect that the microbiota will play a role."