The assessment of the well-investigated classic tumour markers for GI malignancies, such as carbohydrate antigen 19.9 (CA 19.9) and 72.4 (CA 72.4) as well as carcinoembryonic antigen (CEA), is helpful in monitoring cancer progression but not useful in the early detection of these malignancies due to the insufficient diagnostic sensitivity and specificity offered by the above markers. The gene discussed is CEACAM5; the disease is cancer.