Potential role of intratumor bacteria outside the gastrointestinal tract: More than passengers

INTRODUCTION: Tumor‐associated bacteria and gut microbiota have gained significant attention in recent years due to their potential role in cancer development and therapeutic response. This review aims to discuss the contributions of intratumor bacteria outside the gastrointestinal tract, in addition to exploring the mechanisms, functions, and implications of these bacteria in cancer therapy. METHODS: We reviewed current literature on intratumor bacteria and their impact on tumorigenesis, progression, metastasis, drug resistance, and anti‐tumor immune modulation. Additionally, we examined techniques used to detect intratumor bacteria, precautions necessary when handling low microbial biomass tumor samples, and the recent progress in bacterial manipulation for tumor treatment. RESULTS: Research indicates that each type of cancer uniquely interacts with its microbiome, and bacteria can be detected even in non‐gastrointestinal tumors with low bacterial abundance. Intracellular bacteria have the potential to regulate tumor cells' biological behavior and contribute to critical aspects of tumor development. Furthermore, bacterial‐based anti‐tumor therapies have shown promising results in cancer treatment. CONCLUSIONS: Understanding the complex interactions between intratumor bacteria and tumor cells could lead to the development of more precise cancer treatment strategies. Further research into non‐gastrointestinal tumor‐associated bacteria is needed to identify new therapeutic approaches and expand our knowledge of the microbiota's role in cancer biology.