KRT19 and lung cancer: A variety of serologic markers were now used in lung cancer diagnosis and prognosis, including carcinoembryonic antigen (CEA) [21], carbohydrate antigen 19-9 (CA 19-9) [22], cancer antigen 12-5 (CA125) [23], neuron-specific enolase (NSE), and cytokeratin 19 fragments (Cyfra21-1) [24]; however, most of these markers showed better sensitivity only in advanced stages lung cancer patients (III + IV) and had limited value in early lung cancer diagnosis [25].