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New research suggests that a diet that's full of fiber appears to lead to more diverse intestinal bacteria (microbiome). In turn, a thriving gut microbiome is linked to a stronger response to an immune therapy for the aggressive skin cancer.
"We found that patients eating a high-fiber diet at the start of therapy were about five times more likely to respond to the anti-PD-1 immunotherapy," said study author Christine Spencer. She's a research scientist with the Parker Institute for Cancer Immunotherapy in San Francisco.
Anti-PD-1 immunotherapy helps the immune system recognize cancer cells as dangerous cells that need to be destroyed, according to the American Cancer Society (ACS). The cancer drugs Keytruda and Opdivo are examples of this type of immunotherapy.
Several recent studies have suggested that a healthy and diverse gut microbiome might improve the response to melanoma immunotherapy treatments, the researchers said. What wasn't known was how certain diets might improve the microbiome and boost the response to melanoma treatment.
To see what difference diet might make, the researchers collected fecal samples from more than 100 people being treated for melanoma at the MD Anderson Cancer Center, in Houston. With these samples, the researchers could learn what types of bacteria people had in their gut microbiome, as well as how diverse the bacteria in the microbiome were.
The investigators then compared these findings to a previously completed diet/supplement survey to see what type of diet was linked to a more robust gut microbiome.
The findings showed that a high-fiber diet -- one full of vegetables, fruits and whole grains -- was associated with the types of bacteria that had already been linked to a better response to anti-PD-1 therapy.
The researchers also noted that about 40 percent of the people in the study were taking a probiotic supplement. Probiotics contain live bacteria believed to be helpful to maintaining the balance of the microbiome. However, the researchers found that probiotic use was actually linked to lower diversity of the gut microbiome.
And, a lower diversity of the microbiome has been linked to a poorer response to melanoma immunotherapy, the researchers noted.
The study team also looked at a group of almost 50 patients who had complete information on diet and gut microbiome, and found that those on a high-fiber diet were about five times more likely to respond to anti-PD-1 treatment than people eating a low-fiber diet.
Dr. Marcel van den Brink, head of the division of hematologic malignancies at Memorial Sloan Kettering Cancer Center in New York City, said, "This study found a high-fiber diet would lead to better diversity in the gut flora, and greater diversity gave you better outcomes," at least for anti-PD-1 immunotherapy.
"In clinical medicine, we do a great job of monitoring a lot of parameters. But when it comes to monitoring what people eat and effects of diet, we're doing a lousy job," he added.
"Patients and family members ask about diet, and we say, 'Just eat healthy,' and we don't have much more specific guidelines," van den Brink explained.
"So, these types of studies are intriguing. Diet may work in a collaborative way with immune therapy. But, we're not there yet. This was a small study. The research is early," he noted.
Still, van den Brink said that he suspected -- from this study and others, including his own research on the microbiome in blood cancers -- that the gut microbiome likely influences the immune system throughout the body, and he thinks the microbiome "will be relevant for most, if not all, immune therapies in cancer."
Spencer said hers was the first study on diet and melanoma immunotherapy. She agreed more research is needed before doctors can make specific recommendations on diet.
The findings were scheduled for presentation at the American Association for Cancer Research annual meeting, in Atlanta, March 29 to April 3. Research presented at meetings should be viewed as preliminary until published in a peer-reviewed journal.
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SOURCES: Christine Spencer, Ph.D., research scientist, Parker Institute for Cancer Immunotherapy, San Francisco; Marcel van den Brink, M.D., medical oncologist and head, division of hematologic malignancies, Memorial Sloan Kettering Cancer Center, New York City; Feb. 27, 2019, presentation preview, American Association for Cancer Research annual meeting, March 29-April 3, 2019, Atlanta