CEACAM5 and squamous cell carcinoma: Serum tumor biomarkers, such as carcinoembryonic antigen (CEA), carbohydrate antigen125 (CA125), cytokeratin‐19‐fragment (Cyfra21‐1), squamous cell carcinoma (SCC), and neuron‐specific enolase (NSE), are also widely used in the diagnosis and prognostic monitoring of lung cancer.13, 14, 15