16S rRNA sequencing of gut microbiota from patients of papillary thyroid cancer and healthy controls

Purpose: Emerging evidence indicates that gut microbial dysbiosis contributes to cancer development through metabolic regulation. The gut microbial and metabolic characteristics of papillary thyroid cancer (PTC) remain incompletely characterized, and the role of microbial dysbiosis in PTC tumorigenesis is not well understood.Methods: This study recruited 70 PTC patients and 70 healthy controls (HCs) and performed 16S rRNA se-quencing and LC-MS/MS metabolomic analysis of fecal samples.Results: The PTC group demonstrated significantly greater microbial diversity and richness compared to the HC group. Substantial differences in microbiota composition were also observed between the two groups. Analysis revealed 19 differentially expressed bacterial taxa in PTC patients relative to HCs, including enriched pathogens (Collinsella, Carnobacterium, and Moryella) and depleted protective bacteria (Lacticaseibacillus, Faecalibac-ulum, Coprobacter, Anaerotruncus, Leuconostoc, and Acetanaerobacterium). These differentially abundant bacterial taxa discriminated PTC from HC with an area under the curve (AUC) of 77.71%. Microbial co-occurrence network analysis demonstrated stronger correlations between bacterial taxa in PTC compared to HC. Metabolomic profiling identified 20 significantly differentially expressed metabolites in PTC, including ele-vated levels of ornithine and lysine. Further investigation revealed associations between tumor-associated mi-crobes and metabolites involved in ornithine and lysine metabolic pathways, suggesting a potential mechanism through which gut microbiota may correlate with tumorigenesis. Finally, we conducted comparative analysis of microbial and metabolic profiles between BRAF mutation (BRAFmut) and BRAF wild-type (BRAFwt) patients. Integrative analysis indicated that BRAFmut-enriched Halomonas was negatively correlated with leucine and lysine, providing a plausible hypothesis for microbial-mediated mutagenic effects.Conclusion: This study elucidates the distinctive distribution and correlation patterns of gut metabolites and microbiota in PTC, offering valuable insights into the pathogenesis and progression of thyroid cancer.