| Dysbiosis refers to a disturbed gut microbial state characterized by reduced microbial diversity, loss of beneficial commensals, expansion of potentially pathogenic organisms, and altered production of microbial metabolites. In IBD, dysbiosis is closely linked to impaired mucosal tolerance, barrier dysfunction, exaggerated immune activation, and persistence of chronic intestinal inflammation. In cancer, especially colorectal and inflammation-associated cancer, dysbiosis may contribute to tumor initiation and progression by promoting epithelial injury, microbial translocation, genotoxic or pro-inflammatory signaling, altered bile acid and short-chain fatty acid metabolism, and an immune environment that supports carcinogenesis. Thus, dysbiosis is best viewed as a microbiome-level pathogenic factor connecting barrier failure, chronic inflammation, and cancer risk.
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