A Phase 1b Study Evaluating the Safety, Tolerability, Pharmacokinetics, and Efficacy of Tarlatamab in Combination With AB248 in Participants With Extensive Stage Small Cell Lung Cancer (DeLLphi-311)

Inclusion Criteria: 1. Participant has provided informed consent before initiation of any study-specific activities/procedures. 2. Participants ≥ 18 years (or ≥ legal age within the country if it is older than 18 years) at the time of signing the informed consent. 3. Participants with histologically or cytologically confirmed ES-SCLC that has progressed or recurred following at least 1 line of anti-cancer therapy for ES-SCLC. 4. Participants must have at least 1 measurable lesion as defined by RECIST 1.1 within 21-day screening period, not previously irradiated. 5. Participants must have adequate organ function (hematological, coagulation, cardiac, pulmonary, kidney, and liver). 6. Participants must submit a fresh tumor biopsy at screening unless a new biopsy cannot be performed safely or is infeasible. Participants who cannot provide fresh tissue may provide archival tissue that was collected after last anticancer therapy. Exclusion Criteria: 1. Symptomatic central nervous system (CNS) metastases. 2. Participants with brain metastases may be eligible if criteria defined in the protocol are met. 3. Prior therapy with any delta-like ligand 3 (DLL3)-directed therapy (including tarlatamab). 4. Prior interleukin (IL)-2, IL-7 or IL-15 targeted therapy. 5. Baseline (at rest) requirement of supplemental oxygen.