LAUSR

BACKGROUND & AIMS Gut microbial dysbiosis has pivotal involvement in colorectal cancer (CRC). However, the intratumoural microbiota and its association with CRC progression remains elusive. Hence, we aimed to determine the microbial community architecture within a neoplasia (CRC or adenoma) and its contribution to colorectal carcinogenesis. METHODS We collected 436 tissue biopsies from patients with CRC (n = 36) or adenoma (n = 32) (2-6 biopsies from a neoplasia plus 2-5 biopsies from adjacent normal tissues per individual). Microbial profiling was performed by 16S rRNA gene sequencing with subsequent investigation of microbiota diversities and heterogeneity. The correlation between microbial dysbiosis and host genetic alterations (KRAS mutation and microsatellite instability (MSI)) in all neoplasia biopsies was also analysed. RESULTS We discovered that intra-neoplasia microbial communities are heterogeneous. Abundances of some CRC-associated pathobionts (Fusobacterium, Bacteroides, Parvimonas and Prevotella) were found to be highly varied within a single neoplasia. Correlation of such heterogeneity with CRC development revealed alteration in microbial communities involving microbes with high intra-neoplasia variation in abundance. Moreover, we found that the intra-neoplasia variation in abundance of individual microbes changed along the adenoma-carcinoma sequence. We further determined significant difference in intra-neoplasia microbiota between biopsies with and without KRAS mutation (P < 0.001) or MSI (P < 0.001) and illustrated the association of intratumoural microbial heterogeneity with genetic alteration. CONCLUSIONS We demonstrated that intra-neoplasia microbiota is heterogeneous and correlated with colorectal carcinogenesis. Our findings provide new insights on the contribution of gut microbiota heterogeneity to CRC progression.