Drs. Diwakar Davar and Ben Boursi discuss the role of the gut microbiome in the outcome of cancer immunotherapy and the prevention of immunotherapy-related adverse events, as well as compelling research on nutritional interventions to improve response to immune checkpoint inhibitors. TRANSCRIPT   Dr. Diwakar Davar: Hello, and welcome to the ASCO Daily News Podcast. I'm your guest host, Dr. Diwakar Davar. I'm an associate professor of medicine and the clinical director of the Melanoma and Skin Cancer Program at the University of Pittsburgh's Hillman Cancer Center.   Researchers have shown that microorganisms in the gut can impact the effectiveness of immunogenic chemotherapy for patients with cancer. Although microbial therapies for cancer are still at a very early stage of clinical development, compelling research in recent years has shown that changing the gut microbiome can help improve outcomes in patients receiving treatments for cancer enduring immune checkpoint inhibition.  My guest today is Dr. Ben Boursi, a GI medical oncologist at the Sheba Medical Center at Tel Aviv University in Israel. Dr. Boursi is also an adjunct professor at the Center for Clinical Epidemiology and Biostatistics at the University of Pennsylvania. He joins me today to discuss his pivotal research on the role of the gut microbiome in mediating its effects on immunotherapy. And again, I want to highlight that we're recording this on October 9th, and as you may well know, many recent events over the last couple of days have happened in Israel, and so Dr. Boursi has joined us at a very difficult time. So, we're very grateful for him taking time out of his suddenly very busy schedule to join us at a time that is fraught for all. You'll find our disclosures in the transcript of this episode. You'll also find the disclosures of all guests on the podcast at asco.org/DNpod. Ben, it's great to have you on the podcast today. Thank you for being here at such a difficult time, sharing what will, I think, be a great episode.  Dr. Ben Boursi: Thanks for having me, Diwakar. Dr. Diwakar Davar: Ben, the gut microbiome and its role in terms of mediating effects and side effects of cancer immunotherapy has gotten a lot of interest recently. You've done some fundamental work in this space. Why don't you briefly summarize for the audience, firstly, what is the gut microbiome and what are the major themes in relation to cancer immunotherapy?  Dr. Ben Boursi: Well, the microbiome is the ecosystem of microorganisms, bacteria, phages, fungi, that are crucial for immunologic, metabolic and hormonal homeostasis of the host. In the last decade, we began to understand the central role of the gut and tumor microbiome in tumorigenesis, metastasis, treatment efficacy and toxicities, and in 2022, polymorphic microbiomes became one of the hallmarks of cancer, in addition to previous hallmarks that focused mainly at the cellular/genetic levels. The initial studies in mice models showed that therapeutic efficacy of immunotherapy depends on both the presence and composition of the microbiota (In germ-free or antibiotic treated mice, immunotherapy is ineffective), and following these studies, three observational studies in human patients showed that the gut microbiome can predict response to immunotherapy and that response to immunotherapy could be transferred to germ-free mice by fecal microbiota transplantation (FMT) from responding patients.  These studies helped us to define three main research questions regarding the possible role of microbial modulation in cancer treatment. First, can microbial modulation overcome resistance to immunotherapy, both primary and secondary resistance? And this question was the focus of the initial proof of concept studies. Second, can microbial modulation improve response to immunotherapy in treatment-naive patients? And third, can microbial modulation prevent or treat immune related adverse events? The initial positive results