What is already known on this topic
A form of skin tumor, melanoma is one of the most common and aggressive cancers. Immunotherapy drugs, which help the immune system to recognize and kill tumor cells, have been transformative in melanoma, but for many people, these drugs fail to stop tumor growth. And although several studies have suggested that the gut microbiota can influence the response to immunotherapy, the role of diet and probiotic supplements has not been well studied.
What this research adds
By analyzing the gut microbiota profiles of people with melanoma, researchers found that those who reported eating more fiber-rich foods when they began immunotherapy treatment survived longer without cancer growth than people with insufficient dietary fiber intake. In contrast, use of probiotics — live microorganisms consumed as a supplement to improve gut health — appeared to reduce the effectiveness of immunotherapy. Similar results were observed in mice implanted with tumors.
The findings support the idea that the microbiota modulates a person’s response to immunotherapy and suggest that this response is impaired in those receiving probiotics and a low-fiber diet.
A form of skin tumor, melanoma is one of the most common and aggressive cancers. Now, new research suggests that a diet rich in fiber influences the gut microbiota in ways that may help some people with melanoma to better respond to cancer treatment.
The study, published in Science, supports the idea the microbiota modulates a person’s response to cancer immunotherapy — a type of treatment that helps the immune system to recognize and kill tumor cells. The findings could also inform clinical trials, says study co-senior author Jennifer Wargo at the University of Texas MD Anderson Cancer Center. “These results provide further support for clinical trials to modulate the microbiome with the goal of improving cancer outcomes using dietary and other strategies,” she says.
Immunotherapy drugs have been transformative in melanoma, but for many people, these drugs fail to stop tumor growth. And although several studies have suggested that the gut microbiota can influence a person’s response to immunotherapy, the role of diet and probiotic supplements has not been well studied.
To fill this knowledge gap, Wargo and her colleagues assessed the gut microbiota profiles of melanoma patients and mouse models of the disease.
First, the researchers analyzed 438 people with melanoma, the majority of whom had received immunotherapy. As the study participants began therapy, they were asked to complete a dietary questionnaire and a survey of usage of antibiotics and probiotics.
The researchers found no difference in progression-free survival for people who took probiotics compared to those who didn’t. But people who reported eating more fiber-rich foods when they began immunotherapy treatment survived longer without cancer growth than people with insufficient dietary fiber intake.
Next, the team assessed whether dietary fiber and probiotics could affect clinical outcomes. They found that melanoma patients benefitted from a combination of a high-fiber diet and no use of probiotic supplements.
Towards the clinic
Finally, the researchers conducted a study involving mice implanted with tumors. Also in this case, the most pronounced benefits were observed in animals on a fiber-rich diet and no probiotic intake.
In general, probiotic use was associated with reduced response to immunotherapy, larger tumors, lower gut microbiota diversity and less immune cells able to kill tumors, the researchers found. In contrast, a high-fiber diet was linked to slower tumor growth and improved response to immunotherapy.
These results suggest that anti-tumor immunity is strongest with a high-fiber diet and no probiotics, the researchers say. “The data suggest that one can target the composition of the gut microbiota and affect the ability of the patient to respond to immunotherapy,” adds study co-senior author Giorgio Trinchieri at the National Institutes of Health. “Consuming a diet rich in fiber, like fruits, vegetables, and legumes, could improve your ability to respond to immunotherapy.”