CEACAM5 and neoplasm: This study aimed to investigate the association between baseline serum tumor markers (STMs) (carcinoembryonic antigen [CEA], neuron-specific enolase [NSE], cytokeratin-19 fragment [CYFRA21-1], carbohydrate antigen 19–9 [CA19-9], and carbohydrate antigen 125 [CA125]) and the efficacy of first-line immunotherapy in patients with advanced non-small cell lung cancer.