A Study of Atezolizumab and Tiragolumab Compared With Durvalumab in Participants With Locally Advanced, Unresectable Stage III Non-Small Cell Lung Cancer (NSCLC)

Inclusion Criteria:

   - Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1

   - Histologically or cytologically documented NSCLC with locally advanced, unresectable
   Stage III NSCLC of either squamous or non-squamous histology

   - Whole-body Positron Emission Tomography-Computed Tomography (PET-CT) scan, performed
   prior and within 42 days of the first dose of concurrent chemoradiotherapy (cCRT)

   - At least two prior cycles of platinum-based chemotherapy administered concurrently
   with radiotherapy (RT), which must be completed within 1 to 42 days prior to
   randomization in the study (one cycle of cCRT is defined as 21 or 28 days)

   - The radiotherapy (RT) component in the cCRT must have been at a total dose of
   radiation of 60 (±10 percent [%]) gray (Gy) (54 Gy to 66 Gy) administered by intensity
   modulated RT (preferred) or 3D-conforming technique

   - No progression during or following concurrent platinum-based CRT

   - A known PD-L1 result

   - Life expectancy >/= 12 weeks

   - Adequate hematologic and end-organ function

   - Female participants must be willing to avoid pregnancy for 90 days after the final
   dose of tiragolumab and 5 months after the final dose of atezolizumab, or for 3 months
   after the final dose of durvalumab

   - Male participants must remain abstinent or use a condom during the treatment period
   and for 90 days after the final dose of tiragolumab

   - Male participants must not donate sperm during the treatment period and for 90 days
   after the final dose of tiragolumab

Exclusion Criteria:

   - Any history of prior NSCLC and/or any history of prior treatment for NSCLC
   (participants must be newly diagnosed with unresectable Stage III disease)

   - NSCLC known to have a mutation in the epidermal growth factor receptor (EGFR) gene or
   an anaplastic lymphoma kinase (ALK) fusion oncogene

   - Any evidence of Stage IV disease

   - Treatment with sequential CRT for locally advanced NSCLC

   - Participants with locally advanced NSCLC who have progressed during or after the
   definitive cCRT prior to randomization

   - Any Grade >2 unresolved toxicity from previous CRT

   - Grade >= 2 pneumonitis from prior CRT

   - 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

   - History of malignancy other than NSCLC within 5 years prior to screening with the
   exception of malignancies with a negligible risk of metastasis or death

   - Prior allogeneic stem cell or solid organ transplantation

   - Active Epstein-Barr virus (EBV) infection or known or suspected chronic active EBV
   infection at screening

   - Treatment with investigational therapy within 28 days prior to initiation of study
   treatment

   - Prior treatment with CD137 agonists or immune checkpoint blockade therapies, including
   anti-cytotoxic T lymphocyte-associated protein 4, anti-T-cell immunoreceptor with Ig
   and ITIM domains (anti-TIGIT), anti-PD-1 and anti-PD-L1

   - Any prior Grade >/= 3 immune-mediated adverse event or any unresolved Grade > 1
   immune-mediated adverse event while receiving any previous immunotherapy agent other
   than immune checkpoint blockade agents

   - Treatment with systemic immunosuppressive medication

   - Women who are pregnant, or breastfeeding