OS and CSS for the high-grade LCNEC and SCLC patients in the SEER stage subgroup using Kaplan-Meier analysis and log-rank test. (A) OS in localized stage subgroup: LCNEC vs. SCLC, P < 0.001; (B) OS in regional stage subgroup: LCNEC vs. SCLC, P < 0.001; (C) OS in distant stage subgroup: LCNEC vs. SCLC, P = 0.03; (D) CSS in localized stage subgroup: LCNEC vs. SCLC, P < 0.001; (B) CSS in regional stage subgroup: LCNEC vs. SCLC, P < 0.001; (C) CSS in distant stage subgroup: LCNEC vs. SCLC, P = 0.02. Abbreviations: LCNEC, large cell neuroendocrine carcinoma; SCLC, small cell lung carcinoma; OS, overall survival; CSS, cancer-specific survival; SEER, Surveillance Epidemiology and End Results database.