A Study of Atezolizumab Plus Carboplatin and Etoposide With or Without Tiragolumab in Patients With Untreated Extensive-Stage Small Cell Lung Cancer

Inclusion Criteria: * Histologically or cytologically confirmed extensive-stage small cell lung cancer (ES-SCLC) * No prior systemic treatment for ES-SCLC * Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1 * Measurable disease, as defined by Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) * Adequate hematologic and end-organ function * Treatment-free for at least 6 months since last chemo/radiotherapy, among those treated (with curative intent) with prior chemo/radiotherapy for limited-stage SCLC Exclusion Criteria: * Symptomatic or actively progressing central nervous system (CNS) metastases * Malignancies other than small cell lung cancer (SCLC) within 5 years prior to randomization, with the exception of those with a negligible risk of metastasis or death treated with expected curative outcome * Active or history of autoimmune disease or immune deficiency * History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography (CT) scan * Positive test result for human immunodeficiency virus (HIV) * Active hepatitis B or hepatitis C * Severe infection at the time of randomization * Treatment with any other investigational agent within 28 days prior to initiation of study treatment * Prior treatment with CD137 agonists or immune checkpoint blockade therapies, anti-cytotoxic T lymphocyte-associated protein 4 (anti-CTLA-4), anti-TIGIT, anti-PD-1, and anti-PD-L1 therapeutic antibodies * Treatment with systemic immunostimulatory agents within 4 weeks or 5 drug elimination half-lives prior to randomization