Cross-sectional gut microbiota and serum metabolite differences across clinically defined groups in colorectal cancer.

Colorectal cancer (CRC) is a prevalent malignancy associated with alterations in the gut microbiota and host metabolic profiles. This cross-sectional study aimed to characterize gut microbiota and serum metabolite differences among healthy controls (HC), patients with non-metastatic colorectal cancer (CRC-nm), and patients with metastatic colorectal cancer (CRC-m). Stool metagenomic sequencing and untargeted serum metabolomics were performed in 107 participants, followed by exploratory differential analyses and internally cross-validated modeling to identify candidate microbial and metabolic features and evaluate their discriminatory performance. Differential analyses identified two CRC-m-enriched species-level features (Enterocloster clostridioformis and Lactobacillus crispatus) and two CRC-m-depleted features (Megamonas rupellensis and Phocaeicola plebeius) across comparisons with both CRC-nm and HC groups. Metabolomic analysis identified eight pathway-mapped metabolites, mainly involved in amino acid-related metabolic pathways. In modeling analyses, metabolite-only models provided the primary discriminatory signal, whereas adding bacterial features did not improve predictive performance. Integrated microbiota-metabolite models showed lower internal performance than metabolite-only models in some comparisons, including CRC-m versus CRC-nm. Overall, these findings suggest that observed discriminatory performance was primarily driven by serum metabolite features rather than additional bacterial features, and highlight candidate microbial and metabolic markers for future validation. Because all CRC-m cases were stage IV and all CRC-nm cases were stages I-III, these results should be interpreted as exploratory cross-sectional group differences that may reflect disease stage, tumor burden, or broader progression-related changes rather than metastasis-specific biology.