Biomarkers that can be detected and validated in cancer patients with advanced disease may lack specificity and sensitivity for early detection, for example, carcinoembryonic antigen (CEA), which is currently used to monitor colorectal carcinoma treatment, and can also be present at raised levels in gastric, pancreatic, lung, and breast cancer, as well as in some non-neoplastic conditions. Here, CEACAM5 is linked to cancer.