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As scientists explore the role of the gut microbiome in cancer pathogenesis and treatment response, kidney cancer has been an important area of research, noted authors of a review in the

"Among genitourinary tumors, renal cell carcinoma (RCC) has been the area of most clinical trial research into the gut microbiome since immunotherapy is a mainstay of treatment in RCC," said Ulka Vaishampayan, MBBS, and Charles Nguyen, MD, both of the University of Michigan in Ann Arbor.

"Despite the armamentarium of treatment options, a subset of patients with mRCC [metastatic RCC] will have disease progression for which additional interventions to improve responses are needed," the team added. Gut-modulating interventions being studied include probiotic dietary supplements, fecal microbiota transplant (FMT), and dietary modifications.

Vaishampayan, who is the Beverly Mitchell MD Research Professor of Medicine, Ambulatory Clinical Chief (Hem/Onc), Director of the MET (Phase I) team, and Co-Leader of the Translational Clinical Research Program at the university's Rogel Cancer Center, highlighted key research in the following interview.

What are some of the compelling data that demonstrate the impact of microbiome dysbiosis on treatment outcomes in RCC?

Vaishampayan: It started with the clinical observation that patients treated concurrently with antibiotics and immune therapy had lower chances of response and remission. Preclinical data from xenograft -- animal -- models show improved immune stimulation with a combination of gut-modulating therapy and immune checkpoint therapy.

Clinical trials were conducted and reported with CBM-588, one of the gut-modulating dietary supplements administered in combination with ipilimumab + nivolumab and with cabozantinib + nivolumab in metastatic/advanced renal cancer. The results demonstrated no additional adverse events for the combination and a promising increase in response rates and progression-free and overall survival.

How far along are gut-modulating supplements for RCC in clinical development?

Vaishampayan: CBM-588 has shown preliminary promise as per the clinical studies stated above. The next step in the development of microbiome therapy is to evaluate this in a phase III trial. Southwest Oncology group is developing a randomized clinical trial of combining frontline immune checkpoint-based therapy with CBM-588.

At the University of Michigan, we are starting clinical investigation of another prebiotic called inulin gel. A healthy volunteer study was conducted, and inulin gel will be entering an early-phase clinical trial in advanced renal cancer.

What research is being done into FMT for patients with RCC?

Vaishampayan: The application of FMT started with altering immune flora to treat refractory immune colitis toxicity. Pilot studies of FMT in metastatic melanoma receiving Immune checkpoint inhibitor (ICI) therapy resulted in initial clinical responses accompanied by enhanced T-cell activation and immune cell infiltration. Now there are multiple clinical trial efforts to evaluate efficacy of FMT strategy with ICI therapy.

The MITRIC trial (ClinicalTrials.gov identifier: ) is a phase II study evaluating the efficacy of FMT from donors with solid tumors who have responded to ICI, with FMT transplanted into patients with advanced cancers including mRCC who have not responded to ICI. The primary end points include overall response rate and safety.

In the phase I/II TACITO trial (ClinicalTrials.gov identifier: ), patients with mRCC who will be receiving ICI are randomly assigned to placebo or FMT from donors with ICI response.

How else are scientists investigating interventions to impact the gut microbiome in patients with cancer?

Vaishampayan: Correlative work with analyzing stool samples and gut microbial composition will continue to improve our understanding of the impact of gut flora in efficacy and toxicity of immune checkpoint therapy. The ultimate goal would be to create an ideal product that combines the components within gut flora that are favorable to efficacy of immune therapy across a broad range of malignancies.

The impact of diet, antibiotics, and other medications such as proton pump inhibitors will need to be carefully studied. Enrolling a diverse population is especially important in microbiome studies given the diversity in diet across different ethnicities.

Is there anything else you would like oncologists to understand about this topic?

Vaishampayan: Microbiome-impacting therapy may represent a potentially nontoxic way of improving efficacy of immune inhibitors in advanced cancers. Although there is promising preliminary data, routine use of microbiome-impacting agents in combination with immune checkpoint inhibitors is not currently recommended.

Please consider enrolling patients in clinical trials evaluating the effects of pre/probiotics and expedite clinical answers to move the field forward!

Read the review here and expert commentary about it here.