Serum biomarkers, including carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9(CA19-9), are convenient to test; however, their sensitivity and specificity are suboptimal, and positivity rates have been less than 30% in early-stage CRC, thus not being good enough for clinical screening (7, 8). The gene discussed is CEACAM5; the disease is colorectal carcinoma.