The article reviews the concept, development, and potential sources of intratumoral microbiota, which are microorganisms found in tumor tissues. These microorganisms can colonize tumors through mucosal destruction, adjacent tissue migration, and hematogenic invasion, affecting tumor behavior as part of the tumor microenvironment. Intratumoral microbiota promote tumor initiation and progression by inducing genomic instability, mutations, epigenetic modifications, inflammation, immune evasion, metabolic regulation, and invasion and metastasis. The review highlights the potential of intratumoral microbiota in early cancer diagnosis, prognosis, and therapy, particularly in immunotherapy. It also discusses the challenges and research prospects in this field. The article provides a comprehensive overview of the characteristics, diversity, and roles of intratumoral microbiota in various cancers, including lung, liver, colorectal, gastric, breast, pancreatic, and oral cancers. Additionally, it explores the prognostic value of intratumoral microbiota in predicting cancer survival and therapeutic efficacy.The article reviews the concept, development, and potential sources of intratumoral microbiota, which are microorganisms found in tumor tissues. These microorganisms can colonize tumors through mucosal destruction, adjacent tissue migration, and hematogenic invasion, affecting tumor behavior as part of the tumor microenvironment. Intratumoral microbiota promote tumor initiation and progression by inducing genomic instability, mutations, epigenetic modifications, inflammation, immune evasion, metabolic regulation, and invasion and metastasis. The review highlights the potential of intratumoral microbiota in early cancer diagnosis, prognosis, and therapy, particularly in immunotherapy. It also discusses the challenges and research prospects in this field. The article provides a comprehensive overview of the characteristics, diversity, and roles of intratumoral microbiota in various cancers, including lung, liver, colorectal, gastric, breast, pancreatic, and oral cancers. Additionally, it explores the prognostic value of intratumoral microbiota in predicting cancer survival and therapeutic efficacy.