If the link between certain types of gut bacteria and improved effectiveness of certain cancer treatments can be leveraged, then medical laboratories could soon have another diagnostic tool to use in supporting physicians with cancer care
From improving treatments for chronic diseases to extending lives, gut microbiome (bacteria that is part of human microbiota) has been at the forefront of developing clinical laboratory testing and anatomic pathology diagnostic technologies in recent years. Now, two studies recently published in the online journal Science confirm research that the “composition” of gut bacteria may have a significant influence on the effectiveness of certain cancer drugs.
The goal of both studies was to determine whether there was a link between gut bacteria and the efficacy of cancer drugs known as PD-1 inhibitors. These drugs are used for several types of cancer, including:
- Bladder; and,
- Stomach cancers.
They function by freeing up the immune system to attack cancer cells.
Greater Bacterial Diversity in Gut Brings Improved Response to PD-1 Inhibitors
One of the studies, “Gut Microbiome Modulates Response to Anti–PD-1 Immunotherapy in Melanoma Patients,” found that a microbiome populated with “good” bacteria can elevate the potency of certain drug treatments. The researchers discovered that the gut bacteria in patients who responded well to PD-1 inhibitors differed from that found in patients who did not respond to the treatment.
For this study, researchers at the MD Anderson Cancer Center at the University of Texas collected oral, gut, and fecal microbiome samples and tumor biopsies from 112 patients with advanced melanoma. Clinical laboratorians took the samples before and after PD-1 treatments. They divided the patients into two groups—responders and non-responders—and profiled each microbiome using genetic sequencing.
“What we found was impressive: There were major differences both in the diversity and composition of the gut microbiome in responders versus non-responders,” Jennifer Wargo, MD, MMSc, leader of the study, told STAT. “Those who did well had greater bacterial diversity in their gut, whereas those whose tumors didn’t much shrink had fewer varieties of microbes present.”
Melanoma patients who experienced success with PD-1 therapy had a more diverse microbiome and higher concentrations of bacteria known as Ruminococcus and Faecalibacterium. Patients involved in the study who did not respond well to PD-1 therapy had the presence of another bacterium called Bacteroidales.
Antibiotics Can Reduce Effectiveness of PD-1Therapy
The other study, “Gut Microbiome Influences Efficacy of PD-1-based Immunotherapy Against Epithelial Tumors,” discovered that some drug therapies were less effective in patients who were also taking antibiotics to treat infections shortly before beginning treatment with PD-1 drugs.
Researchers for this study, led by Laurence Zitvogel, MD, PhD, of the Gustave Roussy Cancer Campus in Villejuif, France, examined 249 patients who were given a PD-1 inhibitor for lung, kidney, or urinary tract cancers. A little over one fourth of these patients had recently taken antibiotics, which can strip the gut of essential bacteria necessary to treat infections.
The team found that patients who had ingested an antibiotic relapsed faster and did not live as long as patients who had not taken an antibiotic before receiving PD-1 therapy. When they analyzed variances between patients who responded well to treatment versus patients who did not, they detected the presence of Akkermansia muciniphila, a mucin-degrading bacterium, in the responders.
Personalized Treatment Based on Each Patient’s Gut Microbiome
The culmination of this type of research raises questions about how cancer medications may interact with microbiomes.
“Should we be profiling the gut microbiome in cancer patients going into immunotherapy?” asked Wargo in the STAT article. “And, should we also be limiting, or closely monitoring, the antibiotic use in these patients?
“This is all very context-specific, and multiple different factors need to be considered on how best to change the microbiome,” she continued. “When it comes to optimizing cancer therapy, treatments will have to be heavily personalized, based on what a patient’s gut microbiome looks like already.”
Diagnostic tests that could determine whether a certain drug will be beneficial for a patient would perform a critical role in healthcare decision-making. Since cancer drug treatments can cost tens of thousands of dollars or more, it would be advantageous to know which therapies would be optimal for individual patients. The hope is that in the future, clinicians, working with anatomic pathologists and clinical laboratories, will have the tools needed to ascertain if patient’s microbiomes will best work with a particular drug and if they would likely encounter any side effects.