The researchers analyzed gut bacteria in 39 patients with melanoma who were treated with immunotherapies and found that individuals with certain types of gut bacteria had a better response.

Bacteria in the gut may influence how effective cancer immunotherapies are, according to researchers at the Harold C. Simmons Comprehensive Cancer Center at University of Texas Southwestern Medical Center. The results of the study were published in Neoplasia .

“Our research suggests there were certain good-guy bacteria that are needed to optimize the effectiveness of checkpoint inhibitors,” senior author Andrew Koh, MD, associate professor of pediatrics and microbiology with the Simmons Cancer Center, said in a statement. “These bacteria somehow prime your immune system so that it’s better able to attack cancer cells and kill them.”

The patients in the study were treated with 1 of 4 regimens: ipilimumab, nivolumab, ipilimumab plus nivolumab, or pembrolizumab.

Patients with 3 types of common bacteria found in the intestinal tract— bacteroides thetaiotaomicron, faecalibacterium prausnitzii, and holdemania filiformis—responded well to immunotherapy.

After noticing this connection, the researchers began to look for the reason for the association. They found a correlation between anacardic acid and the good gut bacteria. This type of acid is present in mangoes and cashews, and the researchers were interested to note that 5 of the 6 patients with the highest anacardic acid levels consumed cashews at least once a week.

The researchers plan to pursue larger follow-up clinical studies and more laboratory investigations to determine how to better optimize patient response to cancer immunotherapies.

“While these preliminary observations do not establish a firm causal connection between gut microbes and immunotherapy efficacy, they may lead eventually to a probiotic cocktail that could be given along with immunotherapy to enhance the chance of response,” said Koh.