GRP and neoplasm: Commonly used primary lung cancer markers that are currently recommended by the American Association for Clinical Biochemistry and the European Group on Tumor Markers include carcinoembryonic antigen (CEA), neuron‐specific enolase (NSE), cytokeratin fragment (Cyfra21‐1), pro‐gastrin‐releasing peptide (ProGRP), and squamous cell carcinoma antigen (SCC).6