胃肠道微生物对人体的生理功能具有重要影响。近年，人们发现微生物在肿瘤发生发展中亦起到关键作用。异常细菌定植和菌群比例失调不仅能诱发胃肠道局部上皮组织的癌变，还可能影响黏膜下淋巴组织甚至远端器官的癌变。一些微生物可通过产生遗传毒素或活性氧损伤 DNA和干扰细胞 DNA修复机制，引起细胞遗传学不稳定而诱导细胞转化。此外，胃肠道微生物还影响宿主免疫系统功能，构成免疫抑制的微环境，或者诱导慢性炎症反应促进肿瘤发生。胃肠道微生物通过多种机制共同促进肿瘤的发生发展，显示出其与肿瘤的密切关系。

Gastrointestinal microbiota has an important impact on physiological functions of human body. In recent years, the importance of gastrointestinal microbiota in tumorigenesis has emerged. Aberrant location and proportion of microbiota can canot only carcinogenesis of local epithelia, but also tumorigenesis in submucous tissues or even distant organs. Certain microbes can produce genotoxin or generate reactive oxygen species to caDNA damage and affect DNA damage repair, which leads to genetic instability and induces cell transformation. Moreover, gastrointestinal microbiota is able to affect the function of host immune system and form an immunosuppressive microenvironment, while some other pathogenic bacteria can cachronic inflammation and may be involved in tumor immune escape. Based on the above, gastrointestinal microbiota is oncogenic and closely linked to tumorigenesis.