A Phase III, Open-Label Study of Maintenance Lurbinectedin in Combination With Atezolizumab Compared With Atezolizumab in Participants With Extensive-Stage Small-Cell Lung Cancer

Inclusion Criteria for the Induction Phase: * ECOG PS of 0 or 1 * No prior systemic therapy for ES-SCLC * 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 * Histologically or cytologically confirmed ES-SCLC * Adequate hematologic and end-organ function to receive 4 cycles of induction treatment with carboplatin, etoposide and atezolizumab * Measurable disease, as defined by RECIST v1.1 * Negative HIV test and no evidence of active Hepatitis B or Hepatitis C at screening Exclusion Criteria for the Induction Phase: * Presence or history of CNS metastases * Active or history of autoimmune disease or deficiency * History of malignancies other than SCLC within 5 years prior to enrollment * Prior treatment with CD137 agonists or immune checkpoint blockade therapies, including anti-CTLA-4, anti-PD-1, and anti-PD-L1 therapeutic antibodies, or lurbinectedin or trabectedin * 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 * Treatment with investigational therapy within 28 days prior to enrollment Inclusion Criteria for the Maintenance Phase: * ECOG PS of 0 or 1 * Ongoing response or stable disease per RECIST 1.1 after 4 cycles of induction therapy * Toxicities attributed to prior induction anti-cancer therapy or PCI resolved to Grade \<=1 * Adequate hematologic and end-organ function Exclusion Criteria for the Maintenance Phase: * Presence or history of CNS metastases * Receiving consolidative chest radiation * Severe infection within 2 weeks prior to randomization into the maintenance * Treatment with therapeutic oral or IV antibiotics at the time of randomization