Fig. 2

Kaplan-Meier survival curves for overall survival in different subgroups of stage IV NSCLC patients. CEA, carcinoembryonic antigen; CYFRA 21 − 1, cytokeratin-19 fragments; EGFR-TKIs, epidermal growth factor receptor tyrosine kinase inhibitors; NSE, neuron-specific enolase; ProGRP, progastrin-releasing peptide