['Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) are the standard first-line treatment regimen for EGFR mutated non-small cell lung cancer (NSCLC) patients. However, the efficacy of EGFR-TKIs widely varies. The aim of this study is to determine whether the pretreatment serum cytokeratin-19 fragments (CYFRA21-1) and carcinoembryonic antigen (CEA) are associated with the efficacy of EGFR-TKIs in EGFR-mutated NSCLC patients.', 'We retrospectively enrolled 194 NSCLC patients harboring EGFR mutations who received EGFR-TKIs. Clinical characteristics were collected, and the relation between the efficacy of EGFR-TKIs and pretreatment serum CYFRA21-1 and CEA was analyzed.', 'In all cases, progression-free survival (PFS) in patients with high CYFRA21-1 level was significantly shorter than PFS in patients with normal CYFRA21-1 (7.0 vs 11.9 months, P<0.001). Overall survival (OS) in patients with high CYFRA21-1 was significantly shorter than in the normal-CYFRA21-1 group (12.6 vs 28.0 months, P<0.001). In adenocarcinoma patients, PFS in the high-CYFRA21-1 level group was significantly shorter than in patients with normal CYFRA21-1 (7.0 vs 12.0 months, P<0.001). OS in patients with high CYFRA21-1 was significantly shorter than that in the normal-CYFRA21-1 group (13.1 vs 28.1 months, P<0.001). Among squamous carcinoma patients, CYFRA21-1 level did not affect survival. No significant difference in PFS and OS was observed between patients with high CEA and patients with normal CEA.'] Is [ Serum CYFRA21-1 Correlated with the Efficacy of Epidermal Growth Factor Receptor-tyrosine Kinase Inhibitor in Non-small Cell Lung Cancer Patients Harboring EGFR Mutations ]?