Clinical characteristics and prognostic factors of surgically resected combined small cell lung cancer: a retrospective study

•SCLC/LCNEC was the most common type of C-SCLC.•SCLC/LCNEC patients' DFS and OS were also longer than other combined types.•Adjuvant chemotherapy of EP/EC regiments are the main treatment for surgical C-SCLC.•Patients with increased NSE were significantly associated with longer DFS and OS.•Pleura invasion, lymphatic metastasis, adjuvant chemotherapy were prognostic factors.