These results indicated that there were significant differences in immune cell infiltration between the H-CEA and L-CEA groups and that CEA-associated dominant gut microbiota were significantly associated with a variety of tumor-infiltrating immune cells in CRC patients, suggesting that CEA-associated differential gut microbiota have a potential modulatory role in shaping the immune micro-environment in CRC. This evidence concerns the gene CEACAM5 and colorectal carcinoma.