The human microbiome in cancer: Not just a sidekick anymore

The human microbiome is increasingly recognized as a dynamic element in cancer biology. Studies across breast, prostate, lung, colorectal, and cervical tumors reveal that microbial communities influence carcinogenesis, immune regulation, and treatment outcomes. When the balance of these microorganisms is altered, inflammation becomes chronic, metabolism is disrupted, and signaling pathways such as NF-κB, IL6-STAT3, and β-catenin are activated. Bacterial metabolites and genotoxins, including colibactin and bile acids, may damage DNA and reshape the epigenetic landscape. Distinct microbial profiles have been linked to prognosis and to patient responses to chemotherapy and immunotherapy. The presence of beneficial taxa, such as Akkermansia muciniphila and Ruminococcus, has been associated with improved response to immune checkpoint inhibitors. At the same time, antibiotic-induced depletion of gut microbiome can reduce therapeutic efficacy. Strategies that help restore microbial balance, including probiotics, dietary interventions, and fecal microbiota transplantation, are being explored as complementary therapies. Although methodological differences and contamination remain challenges, the growing body of evidence indicates that the microbiome is a measurable and modifiable component of tumor ecosystems with strong potential for diagnostic, prognostic, and therapeutic applications in precision oncology.