A combined subtype of small cell lung cancer and adenocarcinoma with epidermal growth factor receptor (EGFR) mutation responds to EGFR tyrosine kinase inhibitors

Lung cancer is the leading cause of cancer death worldwide (1). Non-small cell lung cancer (NSCLC) causes 85% of the cases, and small cell lung cancer (SCLC) accounts for the other 15% (2). Activating alterations of epidermal growth factor receptor (EGFR) lead to 10–15% and 30–40% of NSCLC, especially adenocarcinoma, in Caucasus and Asian patients (3). In contrast, EGFR mutations are extremely rare in SCLC (4). However, some patients exhibit a combination subtype of SCLC and adenocarcinoma with EGFR mutation, which have been poorly investigated in terms of effective targeted therapeutic strategy.