MUC16 and ovarian cancer: CEA was the first serum tumor biomarker to be identified, in 1965; it is overexpressed in, for example, most colon cancer patients and some breast cancer patients.[10] CA125 is a biomarker for ovarian cancer, and it has been shown to be upregulated in breast cancer tissues.[11] CA15-3 is a transmembrane glycoprotein that is overexpressed in carcinomas of epithelial origin, including breast, ovarian, and pancreatic cancers.