BACKGROUND: The gut microbiome plays a role in the development and progression of colorectal cancer (CRC). AIM AND OBJECTIVE: This review focuses on whether the gut microbiome is involved in the development and regulation of the host immune system. METHODS: The gut microbiome can influence the production and activity of immune cells and molecules that help to maintain the integrity of the intestinal barrier and prevent inflammation. Gut microbiota modulates the anti-cancer immune response. The gut microbiota can influence the function of immune cells, like T cells, that recognize and eliminate cancer cells. Gut microbiota can affect various aspects of cancer progression and the efficacy of various anti-cancer treatments. RESULTS: Gut microbiota provide promise as a potential biomarker to identify the effect of immunotherapy and as a target for modulation to improve the efficacy of immunotherapy in CRC treatment. CONCLUSION: The potential synergistic effect between the gut microbiome and anti-cancer treatment modalities provides an interest in developing strategies to modulate the gut microbiome to improve the efficacy of anti-cancer treatment.