The strong link between a reduced CEA expression and dMMR in colorectal cancer, in which 96% of mismatch repair-proficient (pMMR) but only 69% of dMMR cancers showed strong CEA staining is in agreement with data from Schiemann et al. [51] finding lower CEA serum levels in colorectal cancer patients with hereditary non-polyposis colorectal carcinomas than found in those with sporadic carcinomas. This evidence concerns the gene CEACAM5 and colorectal cancer.