Sequential Hypofractionated Radiotherapy Followed by Anti-PD-L1 Atezolizumab for SCLC

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).

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.

Based on these emerging evidences, the investigators hypothesized that local radiation therapy can enhance the effect of anti-PD-L1 monoclonal antibody through priming T-cell effector function against cancer cells. Described as above, the investigators concluded that modest dose of radiation to local site prior to immunotherapy is the best to enhance T-cell-mediated immunity.