Associations of the colon tissue microbiome and circulating bile acids with colorectal adenoma among average-risk women: possible implications for racial disparities

The gut microbiome and bile acids (BAs) may act individually or interact to influence colorectal cancer (CRC) development. The gut microbiome is likely influenced by multiple exposures, including social determinants of health, and in turn may underlie higher CRC risk among Black individuals. We investigated overall and race-specific associations of the colon tissue microbiome and circulating BAs with colorectal adenoma prevalence in the multi-center Colorectal Neoplasia Screening with Colonoscopy in Average-Risk Women Regional Navy/Army Medical Centers study (CONCeRN). We individually matched women with adenoma (n=143 cases) to those without adenoma (n=279 controls), including 56 Black women. We extracted DNA and sequenced the V4 region of the 16S rRNA gene. We calculated alpha and beta diversity, taxonomic abundance (focused on a priori-selected bacteria), and co-abundance groups (CAGs). Fasting serum collected before colonoscopy underwent targeted quantitative liquid chromatography-tandem mass spectrometry to measure 13 primary and secondary BAs. We used multivariable conditional logistic regression to estimate interrelationships between the gut microbiome, BAs, and adenoma prevalence. Oral-originating Parvimonas and Porphymonas were inversely associated with adenoma presence (odds ratios [ORs] and 95% confidence intervals [CIs]=0.77 [0.63-0.94; P=0.01] and 0.82 [0.69-0.97; P=0.02], respectively). BAs were not strongly associated with adenoma prevalence. Race was associated with beta diversity differences, abundance of several CRC-related bacteria (Peptostreptococcus and Prevotella), and multiple CAGs. Overall, we found that selected oral-originating bacteria were associated with adenoma prevalence. We noted multiple racial differences in the microbiome metrics, highlighting the need for further research into the microbiome, which is potentially modifiable, among diverse populations.