Colorectal Cancer Anal and Stool Microbiome
Few studies have explored the microbiome's relationship to early-onset CRC (<50 year old; EOCRC) and later-onset CRC (LOCRC) or the molecularly distinct proximal and distal CRC. Furthermore, obtaining stool samples for human gut microbiome analyses in time-consuming and inconvenient for patients; so we tested the utility of anal swabs as a microbiome sampling method and used it to characterize EOCRC versus LOCRC and proximal versus distal CRC. Anal swabs (n=71) and stool samples (n=148) were collected from adult patients with advanced or metastatic CRC at the University of Iowa. The microbiome was profiled by sequencing the 16S rRNA V3-V4 region. Initial visit phylum abundance correlations between stool and anal samples were calculated using Spearman tests, and diversity and differential abundance testing were conducted with Wilcoxon tests. Linear mixed effect models (LMEM) were used to perform these analyses across multiple visits. Anal swabs were obtained from patients twice as successfully as stool samples. Correlation analysis demonstrated significant correlation of Fusobacterium, Verrucomicrobiota, and Desulfobacteriota between anal swabs and stool samples. LMEM analysis of anal swab microbiomes revealed enriched Negativicoccus, Dialister, Murdochiella, Porphyromonas, and Lawsonella in proximal cancers and enriched Paludicola in distal cancers. This analysis also found EOCRC to be enriched in Dialister and Corynebacterium. Anal swabs demonstrate a strong correlation in abundances of major gut phyla, suggesting their potential utility in ascertaining gut microbial composition. Further studies are needed to better understand the role of the anal microbiome in CRC and its differing phenotypes.