We observed strong correlations between microbial OTUs and the CEA level and the tumor size in the CRC/T2D group (Spearman's correlation coefficient, 0.7 < |ρ| < 0.9; nominal p-values < 0.05); meanwhile, moderate relationships were shown in the CRC/non-T2D group (Spearman's correlation coefficient, 0.3 < |ρ| < 0.6; nominal p-values < 0.05). Here, CEACAM5 is linked to type 2 diabetes mellitus.