Our gut microbiome—the diverse community of microorganisms, including bacteria, archaea, viruses, and eukaryotes such as fungi, that inhabit the gastrointestinal (GI) tract—can affect our entire body’s health. Most people’s microbiomes have a healthy balance of organisms that stay contained in the GI tract because of the lining’s tight epithelial cell junctions. But from the gut, bacteria are capable of generating a range of vitamins, synthesizing amino acids, and breaking down and metabolizing indigestible carbohydrates. And a growing body of evidence—including studies conducted by oncology nurse scientists—is uncovering how the gut microbiome can influence a patient’s response to cancer treatment and their overall outcomes.