KRT19 and laryngotracheoesophageal cleft: To explore the variation of serum carcinoembryonic antigen (CEA), cytokeratin 19 fragment (CYFRA21-1), and squamous cell carcinoma (SCC) antigen in patients with lung cancer (LC) and their diagnostic value with endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA).