Role of oral microbiome in cancer immunotherapy

The oral microbiome is comparable to the gut microbiome in ecological complexity and is now recognized as a contributor to anticancer immune responses. Although the relationship between the gut microbiome and anticancer immunity is well established, the connection between the oral microbiome and anticancer immunity has received increasing attention, with accumulating evidence pointing to the direct effects of the oral microbiome on immune cell populations. The relationship between cancer and the oral microbiome is bidirectional: each influences the behavior of the other. The tumor microenvironment (TME) and oncological therapies such as chemotherapy and radiation can cause oral microbiome dysbiosis. Once dysbiosis is established, it creates conditions that favor tumor initiation and recurrence through chronic inflammation and impaired immune surveillance. Furthermore, the oral microbiome indirectly affects distant cancers and contributes to systemic inflammation and microbial dissemination through gastrointestinal, respiratory, hematogenous, neurological, and lymphatic pathways. Prebiotics, probiotics, postbiotics, and microbiota transplantation represent promising therapies targeting this microbial community to enhance the efficacy of cancer immunotherapy.