A Study of Atezolizumab Compared With Gemcitabine Plus (+) Cisplatin or Carboplatin for PD-L1-Selected Participants With Stage IV Squamous Non-Small Cell Lung Cancer (NSCLC) (IMpower111)

Inclusion Criteria: * Histologically or cytologically confirmed Stage IV squamous NSCLC * Tumor programmed death-ligand 1 (PD-L1) expression, as determined by immunohistochemistry (IHC) assay of archival tumor tissue or tissue obtained at screening * No prior treatment for Stage IV squamous NSCLC * Measurable disease as defined by RECIST v1.1 * Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 * Adequate hematologic and end-organ function Exclusion Criteria: * Active or untreated central nervous system (CNS) metastases * Untreated or inadequately treated spinal cord compression * Leptomeningeal disease * Uncontrolled pleural effusion, pericardial effusion, or ascites * Uncontrolled tumor-related pain * Uncontrolled hypercalcemia * Any other malignancies within 5 years except those with negligible risk of metastasis or death * Pregnant or lactating women * Known hypersensitivity to any component of atezolizumab formulation or other study medication * History of autoimmune disease except controlled, treated hypothyroidism or type I diabetes * Prior allogeneic bone marrow or solid organ transplantation * Positive human immunodeficiency virus (HIV) test * Active hepatitis B or C * Active tuberculosis * Significant cardiovascular disease * Severe infection or major surgery within 4 weeks prior to randomization * Use of any approved anti-cancer therapy within 3 weeks prior to treatment * Use of an investigational agent or participation in another clinical trial within 4 weeks prior to randomization * Exposure to oral or IV antibiotics within 2 weeks or live attenuated vaccines within 4 weeks prior to randomization * Prior treatment with cluster of differentiation (CD) 137 agonists or immune checkpoint blockade therapies, anti-programmed death-1 (anti-PD-1), and anti-PD-L1 therapeutic antibodies * Treatment with immunostimulatory agents within 4 weeks or immunosuppressive agents within 2 weeks prior to randomization