For instance, prostate-specific antigen (PSA) in prostate cancer (Gilgunn et al., 2013), carcinoma antigen 125 (CA125/MUC16) in ovarian cancer (Zurawski et al., 1988), CA19-9 and carcinoembryonic antigen (CEA) in colon cancer (Goldstein and Mitchell, 2005), and aberrantly glycosylated MUC1 (also known as CA15-3) in breast cancer (Kumpulainen et al., 2002). The gene discussed is KLK3; the disease is breast cancer.