Cluster 1 was composed of five out of a total of 9 OTUs that were positively associated with the tumor size in CRC/T2D samples, whereas the majority of negative associations with CEA level and tumor size were observed in cluster 2 and cluster 3 in both the CRC subgroups, except for the association between the CEA level and its correlated OTUs in the CRC/T2D group. This evidence concerns the gene CEACAM5 and type 2 diabetes mellitus.