The role of intratumoral microbiota in the occurrence and progression of tumors and its implications for guiding tumor treatment

In recent years, the presence of microbiota in tumors has been discovered through extensive research, overturning the longstanding belief that "tumors are sterile." Advanced techniques such as 16S rRNA gene sequencing, fecal microbiota transplantation, and the construction of mouse models specific to different tumor types have been utilized to validate the existence of microbiota within various tumors. The intratumoral microbiota significantly influences tumor development by modulating immune responses, mediating inflammatory reactions, and interfering with or enhancing immunotherapy or chemotherapy. For instance, Aspergillus sydowii in lung adenocarcinoma promotes immunosuppression via the Dectin-1/CARD9 pathway, while colibactin-producing Escherichia coli in colorectal cancer facilitates tumor progression through lipid metabolism dysregulation. Moreover, intratumoral microbiota can predict patient prognosis and guide personalized cancer treatment strategies, highlighting their potential as therapeutic targets. This review synthesizes current evidence on the roles of intratumoral microbiota across multiple cancer types and discusses their clinical implications.