The current markers widely used in the clinical screening or diagnosis of lung squamous cell carcinoma, adenocarcinoma, and small cell carcinoma include carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCC), neuron-specific enolase (NSE), carbohydrate antigen 125 (CA125), cytokeratin-19 fragment (CYFRA21-1), and prosecretin-releasing peptide (proGRP) [12]. Here, ENO2 is linked to small cell carcinoma.