Ivanna Honcharyuk, Bruna Caridi, Paola Pinco, Sara Ferri, Alessandra De Giani, Alberto Baeri, Chiara Amoroso, Sara Massironi, Federica Facciotti
INTRODUCTION: The intratumor microbiome is a key component of the tumor microenvironment, influencing oncogenesis, immune modulation, and therapeutic responses. Bacteria, fungi, and viruses infiltrate tumor tissues, modulating local immunity and potentially conditioning the efficacy of immune checkpoint inhibitors. While mucosal-origin tumors exhibit an expected microbial presence, sterile organ tumors, such as brain and breast, reveal less intuitive microbial infiltration. AREAS COVERED: This review evaluated the interplay between the intratumoral microbiota and the immune system across different stages of carcinogenesis, including initiation, progression, and metastasis. Sources included PubMed, Embase, and Google Scholar; searches covered December 2024 to October 2025. We examine microbial metabolites, immune hijacking, and routes of dissemination. We also overview technologies for tumor microbiome characterization, including next-generation sequencing, spatial transcriptomics, and artificial intelligence (AI), with machine learning and deep learning, to support diagnostics, prediction of treatment response, and personalized oncology. EXPERT OPINION: Defining the spatial localization and functions of intratumoral microorganisms is crucial for robust biomarkers and tailored interventions. Integrating AI with spatial and multi-omics data offers major opportunities but faces obstacles - data heterogeneity, model interpretability, and ethical issues. Priorities include standardized protocols, high-resolution spatial profiling, external validation, and expertly annotated datasets to unlock microbiome-informed precision oncology.