Abstract:As one of the common and deadly malignant tumors worldwide, colorectal cancer (CRC) poses a serious threat to public health and causes a heavy burden to the society. The influences of microorganisms on the occurrence and development of CRC has received much attention from researchers, whereas most of the available studies have focused on gut microorganisms. In recent years, with the rapid development of next-generation sequencing, intratumoral microorganisms of CRC have been discovered and gradually opened up new research areas. We review the research progress in intratumoral microorganisms of CRC and their effects on the course of CRC and compare the relative abundance and community composition of intratumoral microorganisms of CRC with different molecular subtypes, at different stages of adenoma-carcinoma progression, and at different locations. Intratumoral microorganisms mainly affect CRC development by influencing colonic epithelial cells, tumor cells, and immune cells, with the pathogenic mechanisms including DNA damage, metabolic reprogramming, and oncogenic non-coding RNAs. Different intratumoral microorganisms exert dual effects on CRC. In the future, comprehensive experimental protocols and suitable in vitro models should be established to overcome the limitations of existing studies and elucidate the functioning mechanisms of intratumoral microorganisms, which will lay a foundation for the clinical application of microorganisms-targeted therapies for CRC and even other tumors.
