AbstractThe gastrointestinal tract greatly contributes to global cancer burden and cancer‐related deaths. The microbiota represents the population of microorganisms that live in and around the body, located primarily in the gastrointestinal tract. The microbiota has been implicated in colorectal cancer development and progression, but its role in cancer therapy for the gastrointestinal tract is less defined, especially for extra‐intestinal cancers. In this review, we discuss the past 5 years of research into microbial involvement in immune‐related therapies for colorectal, pancreatic, hepatic, and gastric cancers, with the goal of highlighting recent advances and new areas for investigation in this field.