Small cell lung cancer (SCLC), accounting for 10% of all lung cancers (Torre et al., 2015), shows poor outcomes with 7-10 months of median survival in advanced cases (Jett et al., 2013). Despite novel treatment strategies including targeted therapy and immunotherapy for non-small cell lung cancer (NSCLC) have been introduced, the treatment options for SCLC still remain limited. Many clinical trials, which tested the efficacy of molecular targeted agents for SCLC, failed to show clinical benefit compared with conventional platinum-based chemotherapy (Koinis et al., 2016). Nevertheless, recent studies demonstrated that immunotherapy using anti-CTLA-4 or anti-PD1 monoclonal antibody can be novel therapeutic strategies for SCLC (Ott et al., 2015; Reck et al., 2013; SJ et al., 2015).