CEACAM5 and lung cancer: Currently, serum biomarkers such as cytokeratin 19 fragment (CYFRA21-1), pro-gastrin releasing peptide (ProGRP), carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), and squamous cell carcinoma-associated antigen (SCCA) have shown potential clinical utility for diagnosing lung cancer [52].