a new study shows.
Investigators found that the patients who reported consuming at least 20 g of dietary fiber daily had significantly better progression-free survival (PFS) than those who reported consuming lower amounts of dietary fiber. However, patients who took a probiotic supplement in the past month had slightly shorter PFS, but the results were not statistically significant.
And after adjusting for clinical factors, each 5-g increase in daily dietary fiber intake corresponded to a 30% lower risk of disease progression, according to the analysis, published online Dec. 23, 2021, in Science.
“Our study sheds light on the potential effects of a patient’s diet and supplement use when starting treatment with immune checkpoint blockade,” co–lead study author Jennifer Wargo, MD, professor of genomic medicine and surgical oncology at University of Texas MD Anderson Cancer Center, Houston, said in a press release. “These results provide further support for clinical trials to modulate the microbiome with the goal of improving cancer outcomes using dietary and other strategies.”
Previous research has suggested that the microbiome can influence patients’ response to immunotherapy. One recent analysis, for instance, found that fecal microbiota transplant can improve response to immunotherapy in advanced melanoma. And a small 2019 analysis from Dr. Dr. Wargo and colleagues hinted that a high-fiber diet may enhance patients’ ability to respond to immunotherapy in advanced melanoma, while probiotics appear to dampen that response.
Still, the role diet and probiotic supplements play in treatment response remains poorly understood.
In the current study, Dr. Wargo and colleagues assessed fecal microbiota profiles and dietary habits, including fiber intake and probiotic use, in 158 patients with advanced melanoma who received immune checkpoint blockade inhibitors.
In the cohort, 31% (49 of 158) of late-stage melanoma patients reported taking a commercially available probiotic in the past month. When assessing whether probiotic use influenced patient outcomes, the investigators observed a shorter but not statistically significant difference in PFS in those who took a probiotic (median, 17 months) versus those who did not (23 months).
Higher dietary fiber, however, was associated with significantly improved PFS in a subset of 128 patients. The team divided patients into a higher-fiber intake group (those consuming at least 20 g/day) and a low-fiber group (those consuming less than 20 g).
The 37 patients reporting higher fiber intake demonstrated improved PFS, compared with those in the low-intake group (median PFS not reached vs. 13 months), plus a 30% lower risk of disease progression or death for each additional 5 g consumed each day.
“The observed protective effect of dietary fiber intake in relation to PFS and response remained consistent among the subset of patients treated with anti–PD-1 monotherapy, with the exclusion of patients reporting recent antibiotic use,” the authors noted.
When assessing fiber and probiotic intake together, the researchers found that immunotherapy response rate was higher (82%) in the 22 patients who reported sufficient dietary fiber intake with no probiotic use versus 59% in 101 patients who reported either insufficient fiber intake or probiotic use.
Overall, the research suggests that “consuming a diet rich in fiber, like fruits, vegetables, and legumes, could improve your ability to respond to immunotherapy,” co–lead author Giorgio Trinchieri, MD, chief of the Laboratory of Integrative Cancer Immunology in the National Cancer Institute’s Center for Cancer Research, Bethesda, Md., said in a press statement. “The data also suggest that it’s probably better for people with cancer receiving immunotherapy not to use commercially available probiotics.”
The investigators also explored whether dietary fiber intake enhanced treatment response in preclinical mouse models of melanoma. In this instance, mice receiving a fiber-rich diet showed delayed tumor growth after anti–PD-1 treatment, compared with mice given a low-fiber diet or probiotics.
According to the authors, “our preclinical models support the hypothesis that dietary fiber and probiotics modulate the microbiome and that antitumor immunity is impaired in mice receiving a low-fiber diet and in those receiving probiotics – with suppression of intratumoral [interferon-gamma] T-cell responses in both cases.”
Dietary fiber may exert beneficial effect by increasing specific types of bacteria in the gut, such as Ruminococcaceae, which “produce high levels of certain short-chain fatty acids that have an antitumor effect,” Dr. Trinchieri explained.
However, “the impact of dietary fiber and probiotics on the gut microbiota is only part of the bigger picture,” Dr. Trinchieri said in a press release. “Many factors can affect the ability of a patient with melanoma to respond to immunotherapy” but, according to this analysis, “the microbiota seems to be one of the dominant factors.”
While Jeffrey S. Weber, MD, PhD, applauded the “innovative and interesting” research, he believes the patient population is too small to confirm that a high-fiber diet does indeed contribute to improved immunotherapy response and PFS in patients with advanced melanoma.
Additional data are needed to clarify these findings. “I will believe it if I could see it replicated in a larger study,” Dr. Weber, professor and deputy director of the Laura and Isaac Perlmutter Cancer Center, New York University, said in an interview.
Dr. Wargo noted that a randomized clinical trial exploring how diets with varying fiber content affect the microbiome and immune response is currently enrolling patients with stage III and IV melanoma receiving immunotherapy.
This study was supported by the Melanoma Moon Shot, among others. Dr. Wargo is a collaborator on a U.S. patent application that covers methods to enhance immune checkpoint blockade responses by modulating the microbiome. Dr. Weber reported relationships with Bristol-Myers Squibb, GlaxoSmithKline, Genentech BioOncology, Merck, Novartis, EMD Serono, Celldex, CytomX, Nektar, Roche, Altor, Daiichi Sankyo, and Eli Lilly, and is named on patents filed for biomarkers for ipilimumab and nivolumab.
A version of this article first appeared on Medscape.com.