Immunotherapy in Solid Tumors and Gut Microbiota: The Correlation—A Special Reference to Colorectal Cancer
Laboratory of Translational Oncology, School of Medicine, University of Crete, 70013 Heraklion, Greece
Medical School, University of Cyprus, 20537 Nicosia, Cyprus
Department of Anatomy, School of Medicine, University of Crete, 70013 Heraklion, Greece
Department of Medical Oncology, University Hospital of Heraklion, 71110 Heraklion, Greece
Authors to whom correspondence should be addressed.
Cancers 2021, 13(1), 43; https://doi.org/10.3390/cancers13010043
Received: 26 November 2020 / Revised: 16 December 2020 / Accepted: 22 December 2020 / Published: 25 December 2020
(This article belongs to the Special Issue Breakthroughs in Cancer-Related Immunotherapy)
Immunotherapy and immune checkpoint inhibitors have become the breakthrough treatment with extended responses and survival rates in various neoplasms. They use the immune system to defeat cancer, while gut microbiota seems to play a significant role in that attempt. To date, colorectal cancer patients have gained little benefit from immunotherapy. Only mismatch repair-deficient/microsatellite-unstable tumors seem to respond positively to immunotherapy. However, gut microbiota could be the key to expanding the use of immunotherapy to a greater range of colorectal cancer patients. In the current review study, the authors aimed to present and analyze the mechanisms of action and resistance of immunotherapy and the types of immune checkpoint inhibitors (ICIs) as well as their correlation to gut microbiota. A special reference will be made in the association of immunotherapy and gut microbiota in the colorectal cancer setting.
Over the last few years, immunotherapy has been considered as a key player in the treatment of solid tumors. Immune checkpoint inhibitors (ICIs) have become the breakthrough treatment, with prolonged responses and improved survival results. ICIs use the immune system to defeat cancer by breaking the axes that allow tumors to escape immune surveillance. Innate and adaptive immunity are involved in mechanisms against tumor growth. The gut microbiome and its role in such mechanisms is a relatively new study field. The presence of a high microbial variation in the gut seems to be remarkably important for the efficacy of immunotherapy, interfering with innate immunity. Metabolic and immunity pathways are related with specific gut microbiota composition. Various studies have explored the composition of gut microbiota in correlation with the effectiveness of immunotherapy. Colorectal cancer (CRC) patients have gained little benefit from immunotherapy until now. Only mismatch repair-deficient/microsatellite-unstable tumors seem to respond positively to immunotherapy. However, gut microbiota could be the key to expanding the use of immunotherapy to a greater range of CRC patients.