Background and Objectives: The human microbiome, as a complex ecosystem of symbiotic microorganisms, plays a fundamental role in maintaining homeostasis and preventing diseases, including cancer. Growing evidence indicates that microbial imbalance (dysbiosis) can contribute to the pathogenesis of various cancers. This review study aimed to investigate the dual role of the microbiome, from stimulating tumorigenesis to its protective effects.
Subjects and Methods: This review study was conducted in 2024. A comprehensive search of national and international scientific databases was performed to identify studies published between 2013 and 2025. Inclusion criteria encompassed studies related to: 1) the pathogenesis and mechanisms of microbiome-cancer interactions, 2) organ-specific microbiomes in cancer, 3) the microbiome as a diagnostic biomarker, 4) the influence of the microbiome on response to cancer therapies, and 5) general principles of the microbiome-cancer relationship. Out of 147 initially identified articles, and after refinement using specialized keywords and assessment based on inclusion and exclusion criteria, 112 relevant articles were ultimately selected for final analysis.
Results: The present review demonstrated that the microbiome plays a pivotal and dual role in carcinogenesis. The microbiome influences oncogenic processes through diverse mechanisms, including modulation of the tumor microenvironment, regulation of host immune responses, and production of bioactive metabolites. A key finding is that microorganisms can exert opposing roles, whereby specific species, such as Fusobacterium nucleatum in colorectal cancer and Helicobacter pylori in gastric cancer, act as pro-tumorigenic agents, while genera such as Lactobacillus exhibit protective and tumor-suppressive effects.