In fact, most of the currently available cancer biomarkers are based on the detection of glycans, including the sialyl Lewis A antigen (CA19-9) and the STn (CA72-4), or glycoproteins, such as the alpha-fetoprotein (AFP), the prostate-specific antigen (PSA), mucin 16 (CA125), mucin 1 (CA15-3) and the carcinoembryonic antigen (CEA), which are used to follow both patient treatment response and tumor recurrence in several types of cancers (as reviewed in [3,4,209]). The gene discussed is CEACAM5; the disease is cancer.