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| Photo credit National Institutes of Health |
CANCER DIGEST – Jan. 8, 2022 – In an unusual study involving humans and mice, researchers have found that a high fiber diet may improve the treatment of melanoma.
The unusual study design involved an observational study of hundreds of melanoma patients being treated with immune checkpoint blockade or ICB, a relatively recent treatment that blocks proteins on cancer cells that keep the body’s cancer killing T cells from doing their job, and a parallel mouse study involving mice implanted with melanoma tumors. The findings were published in the journal Science on Dec. 23, 2021.
The massive study led by Christine Spencer, PhD, at the University of Texas, Houston along with more than 80 other researchers at UT and other institutions around the country including the National Institutes of Health and Oregon State University studied the intestinal microbiome, or the trillions of bacteria that inhabit the gut in hundreds of patients undergoing ICB therapy. They also analyzed dietary habits and the use of probiotics and compared disease course and treatment outcomes.
In the observational part of the study the researchers found higher dietary fiber intake was associated with slowing the disease progression for patients treated with ICB. There were similar effects among patients taking probiotics or a combination of the two. The biggest benefits, in terms of slowing the disease, however, were among patients with high fiber intake but no probiotic use.
An observational study, however, cannot show a cause for the observed effect since there may be other factors going on with the patients being observed that couldn’t or weren’t measured. For example, it is extremely difficult and expensive to design a study that controls all the food participants consume. That’s where the parallel mouse study comes in.
The diet of the mice could be controlled and measured with different diets being compared. The effects of ICB treatment on the different groups of mice fed high fiber diets, high fiber and probiotics, and probiotics alone showed similar results as those shown in the humans.
“We showed that dietary fiber and probiotic use, both known to impact the gut microbiome, are associated with differing ICB outcomes,” Andriy Morgun, associate professor of Pharmacogenomics at Oregon State University, said in a press release. “From the human cohort results we can’t assign causality – there may have been other things going on with those patients that we didn’t measure in this study.”
Morgun said the results in the mouse study, however, support the idea that anti-tumor immunity is strongest with a high-fiber diet and no probiotics.
Morgan noted that network analysis in mice showed a family of bacteria, called Ruminococcaceae, among the organisms increased by the high-fiber diet. That same bacteria were found in the current study involving humans and in previous, related research with people.
Confirming the results of this study will take a double-blind, randomized dietary intervention study to determine whether a targeted, achievable diet change at the start of ICB therapy can improve patient outcomes, Morgan added.
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