Impact of the intratumoral resident microbiome on the immune microenvironment of malignant tumors (Review)

Advances in cancer research have highlighted the importance of tumor‑intrinsic factors, including tumor type, immune environment, immunogenicity, metabolic demands and the intratumoral microbiome. Together, these factors have reshaped the current understanding of cancer immunity and systemic therapies, particularly targeted treatments and immune checkpoint inhibitors that act on cancer cells, blood vessels and immune cells within the tumor microenvironment (TME). Among these, the presence of bacteria within tumors has emerged as a critical modulator of the TME, influencing tumor progression and antitumor responses across various cancer types. With the rapid expansion of cancer immunotherapies, advanced detection and sequencing technologies are increasingly applied to elucidate interactions between intratumoral microbiota and immune cells. The present review focuses on the mechanisms by which tumor bacteria modulate immune responses, supported by validations from <i>in vitro</i> and <i>in vivo</i> studies. The potential of intratumoral microbiota as biomarkers for prognosis and immunotherapy response is also discussed, alongside emerging biotechnological tools for microbiota profiling. By examining the dual roles of intratumoral microbiota in cancer biology, the current review provides a comprehensive overview of their implications and practical applications in cancer‑related research.