GRP and lung cancer: Korkmaz et al. [60] studied a panel of six tumor markers (progastrin-releasing peptide (ProGRP), squamous cell carcinoma antigen (SCCAg), cytokeratin 19-fragments (CYFRA 21-1), human epididymis protein 4 (HE4), chromogranin A (CgA), and neuron-specific enolase (NSE)) to determine the role they could play in the diagnosis and classification of lung cancer.