The most commonly used markers, specific for cancer cells, are the CEA and the CK-20 for gastric and colorectal cancer [155, 156], and the C1P83, CA 19–9, 17–1-A, C54–0, KL-1 for pancreatic adenocarcinoma [157, 172]. The gene discussed is CEACAM5; the disease is colorectal cancer.