Inclusion Criteria:

1. Histologically or cytologically documented extensive-stage small cell lung cancer (ES-SCLC) and extensive-stage disease (American Joint Committee on Cancer, 8th edition, Stage IV [T any, N any, M1a, M1b, or M1c], or T3-4 due to multiple lung nodules that are too extensive or tumor or nodal volume that is too large to be encompassed in a tolerable radiation plan)
2. Participants taking part in the separate PET tracer sub-study must provide a fresh tumor biopsy from any disease site (primary or metastatic)
3. Archived tumor specimens, in the form of blocks or sectioned slides, are mandatory for all participants except those participating in the separate PET tracer sub-study for whom the archived tumor specimen is optional
4. Eastern Cooperative Oncology Group performance status (ECOG PS) 0 or 1
5. At least 1 measurable lesion by computed tomography (CT) or magnetic resonance imaging (MRI) per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1) criteria
6. Adequate hematologic and end organ function
7. Must agree to follow specific methods of contraception, if applicable

Exclusion Criteria:

1. Women who are pregnant or breastfeeding. Japan only: participation in the study is not allowed even if breastfeeding is suspended
2. Prior chemotherapy, radiation therapy, or biologic therapy for SCLC. Previously treated limited stage SCLC (LS-SCLC) participants are also excluded
3. Symptomatic brain or other central nervous system (CNS) metastases
4. Paraneoplastic autoimmune syndrome requiring systemic treatment
5. History of idiopathic pulmonary fibrosis, drug-induced pneumonitis, idiopathic pneumonitis, organizing pneumonia, or evidence of active pneumonitis on screening chest CT scan
6. Grade ≥ 2 peripheral sensory neuropathy at study entry
7. Significant uncontrolled cardiovascular disease
8. Active, known or suspected autoimmune disease or inflammatory disorder

Other protocol-defined inclusion/exclusion criteria apply