CEACAM5 and ovarian cancer: The currently most widely used serological biomarkers include carcinoembryonic antigen (CEA) and carbohydrate antigen 19.9 for gastrointestinal cancer [3-5]; CEA, cytokeratin 19 fragment, neuron-specific enolase, tissue polypeptide antigen, progastrin-releasing peptide and squamous cell carcinoma antigen for lung cancer [6]; CA 125 for ovarian cancer [2]; and prostate-specific antigen (PSA, also known as kallikrein-related peptidase (KLK) 3) in prostate cancer [7].