The primary objective for dose exploration and dose expansion is to evaluate the safety and tolerability of tarlatamab in combination with AB248.

The primary objective for dose exploration only is to determine the recommended dose for expansion and/or maximum tolerated combination dose (MTCD) of AB248 in combination with tarlatamab.

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.

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request.

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors. If not approved, a Data Sharing Independent Review Panel will arbitrate and make the final decision. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the URL below.