The primary objective of this study is to evaluate the safety and tolerability of subcutaneous (SC) tarlatamab.

Inclusion Criteria:

• Participants ≥ 18 years of age (or ≥ legal adult age within country if it is older than 18 years) at time of signing informed consent.
• Participants with histologically or cytologically confirmed ES-SCLC that progressed or recurred following at least one line of platinum-based anti-cancer therapy for SCLC.

Note: Participants with prior treatment for LS-SCLC should have also received another regimen for their recurrent, ES-SCLC disease.

• Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) of 0 or 1.
• Participants must have adequate organ function (cardiac, pulmonary, kidney, and liver).
• Participants must be able to have SC injections administered in the abdomen.
• Participants without measurable disease or tumor tissue (fresh biopsy or archival) available may be permitted after discussion with and approval by Amgen Medical Monitor.

Exclusion Criteria:

• Participants that have received prior DLL3 targeted therapy.
• Participants with untreated or symptomatic brain metastases or those requiring therapy with steroids.
• Note: Participants with asymptomatic brain metastatic lesions are allowed following definitive treatment (Amgen Medical Monitor may approve untreated, asymptomatic brain metastasis if local therapy is not required per investigator judgment).
• Participants with leptomeningeal disease.
• Participants with baseline oxygen requirement.

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.