The distinct roles of and in proximal- and late-onset colorectal cancer.

Despite the emerging role of the gut microbiome in colorectal cancer (CRC), its significance in early-onset CRC (EOCRC, < 50 y) versus late-onset CRC (LOCRC) and the molecular differences between proximal and distal CRC remain poorly understood. To circumvent the logistical and patient compliance challenges of stool collection, we explored the utility of anal swabs as a convenient alternative for characterizing gut microbiome signatures in CRC. We profiled the CRC microbiome using anal swabs ( = 76) and stool samples ( = 33) by 16S rRNA sequencing. Diversity indices were compared using Wilcoxon tests, compositional differences assessed by PERMANOVA, and correlations were performed in paired samples. Correlation analysis revealed strong associations between microbial phyla (Bacteroidetes,  = 0.86,  = 4.7 × 10⁻⁶; Firmicutes,  = 0.65,  = 3.4 × 10⁻³; Verrucomicrobiota,  = 0.81,  = 4.8 × 10⁻⁵; and Fusobacterium,  = 0.80,  = 7.3 × 10⁻⁵) and major genera (,  = 0.88,  = 1.7 × 10⁻⁵; ,  = 0.75,  = 1.5 × 10⁻³; ,  = 0.77,  = 8.5 × 10⁻⁴; and ,  = 0.81,  = 3.3 × 10⁻⁴) across sample types, validating the use of anal swabs. However, Actinobacteriota and were not correlated, likely reflecting the perianal skin-associated microbiota and underscoring the need for validation against stool or mucosal biopsies. Importantly, anal swabs revealed associations between and proximal CRC ( = 0.047) and between the Fusobacteriota phylum and LOCRC ( = 0.042), suggesting subtype-specific CRC subtypes. In mechanistic studies, using the mucous-secreting HT-29 MTX cell line, we observed that was associated with activation the RAS/MAPK pathway, upregulated c-MYC, KRAS, MAPK1, and Cyclin D1 (< 0.05) and increased proinflammatory cytokines (IL-8) (< 0.05), thereby increasing cell proliferation. In contrast, modulates the WNT/β-catenin pathway, increasing -catenin and AXIN1 (< 0.05), promoting cell migration (< 0.05), and extracellular matrix (ECM) remodeling. These findings highlight distinct microbial contributions to CRC pathogenesis, with influencing proliferation and inflammation, whereas promotes migration and invasion. Understanding these pathways offers potential for harnessing the gut microbiome's diagnostic and therapeutic power in CRC.