There are several known blood-derived tumor biomarkers, including tumor-specific antigens—PSA (prostate-specific antigen), SCCA (squamous cell carcinoma antigen), AFP (alpha-fetoprotein specific to hepatocellular carcinoma), CA125 (glycosylated mucin specific mostly to ovarian cancer), CA19-9 (carbohydrate antigen 19-9, pancreatic and colorectal cancer), and LDH (lactate dehydrogenase, melanoma, renal and colorectal cancer)—and less specific ones such as CEA (carcinoembryonic antigen) and CA 15-3 (carbohydrate antigen 15-3, mucin) (see reviews on tumor biomarkers [1,2]). The gene discussed is MUC5AC; the disease is colorectal cancer.