We Partner 4 Research

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

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