CEACAM5 and neoplasm: High levels of serological tumor markers frequently found in squamous cell carcinoma include SCC-Ag (squamous cell carcinoma-associated antigen), Cyfra 21-1 (cytokeratin 19 fragment 21-1 antigen), CEA (carcinoembryonic antigen), and TrxR (Thioredoxin reductase) [6,7,8].