Background: Modern oncology is undergoing a paradigmatic shift, moving away from viewing tumors as isolated tissue masses toward perceiving them as elements of a complex, multispecies ecosystem. Central to this environment are the gut microbiota and the recently characterized intratumoral microbiome, both of which serve as critical regulators of host-tumor dynamics. Aim: This review aims to provide a comprehensive analysis of the microbiome-host axis, specifically evaluating its role in shaping anti-tumor immunity and modulating the efficacy and toxicity of current chemotherapy and immunotherapy regimens. Materials and Methods: A systematic synthesis was conducted utilizing 57 seminal literature sources. The analysis incorporates high-impact data published up to early 2026, focusing on longitudinal clinical cohorts, metagenomic functional profiling, and mechanistic models of host-microbe crosstalk. Results: Specific bacterial consortia and their bioactive metabolites—notably inosine, short-chain fatty acids, and tryptophan derivatives—are identified as essential prerequisites for the success of immune checkpoint inhibitors. Beyond systemic immunity, the review highlights the role of bacterial enzymes, such as cytidine deaminase, in local drug degradation and chemoresistance. Furthermore, the emerging "micro-genderome" is established as a pivotal factor in driving sex-specific variations in therapeutic response and toxicity profiles. Conclusions: Microbiome stratification and therapeutic modification represent a necessary evolution in personalized oncology. Integrating microbial monitoring into standard clinical protocols is essential for protecting a patient's "microbial capital," thereby maximizing survival rates and long-term quality of life for cancer survivors.
Łysiak et al. (2026) studied this question.