In recent years, many studies have shown that radiation therapy can be a useful treatment as a combining treatment with immunotherapy. The abscopal effect refers to the ability of radiation delivered radiation delivered to a local site to treat the other diseases outside radiation field (Tang et al., 2014). A recent study described that abscopal effect was observed in a malignant melanoma patient treated with CTLA4 antagonist and radiotherapy (Postow et al., 2012). Moreover, an animal study presented that blockade of PD-L1 and ionizing radiation showed synergism (Deng et al., 2014). Based on these emerging evidences, the investigators hypothesized that local radiation therapy can enhance the effect of anti-PD-L1 monoclonal antibody through increasing T-cell effector function against tumors. Atezolizumab, which is a humanized anti-PD-L1 monoclonal antibody, act as an inhibitor the interaction between PD-L1 and PD-1, and eventually restore suppressed T-cell immunity leading elimination of cancer cells. In this study, the investigators will investigate the combining effect of hypofractionated-sublethal dose of radiation therapy followed by anti-PD-L1 monoclonal antibody, atezolizumab, for SCLC patients who are recurrent or refractory for initial platinum-based chemotherapy.