Although originally thought to have high sensitivity and specificity for CRC, CEA is more sensitive in patients with advanced disease than those with early stage disease; indeed, less than 40% sensitivity has been observed in patients with early stage CRC (i.e., A and B rated cancers according to Dukes classification), that is, the very population, that is, the target of screening programs [21]. Here, CEACAM5 is linked to colorectal carcinoma.