This study is modular in design, allowing evaluation of the preliminary efficacy, safety, tolerability, and immunogenicity of novel combinations of immunotherapies and/or deoxyribonucleic acid (DNA) damage repair inhibitors in patients with platinum refractory or resistant extensive-stage-disease SCLC. Patient who has progressive disease (PD) during first-line platinum-based chemotherapy (platinum refractory) or PD within 90 days after completing first-line platinum-based chemotherapy (platinum resistant) will be enrolled to the study. The primary objective of the study is to assess the preliminary efficacy of each treatment arm based on objective response rate (ORR).