The primary objective of this study is to evaluate the safety and tolerability of tarlatamab in combination with YL201 with or without anti-PD-L1.

Inclusion Criteria:

• Participants ≥ 18 years of age (or legal adult age within country) at time of signing informed consent.
• Participants with histologically or cytologically confirmed ES-SCLC.
• For Parts 1 and 2, subjects must have ES-SCLC that has progressed or recurred following at least 1 prior line of platinum-based anti-cancer therapy received either for LS-SCLC or ES-SCLC.
• For Part 3, subjects must have ES-SCLC and no prior systemic treatment for ES SCLC other than 1 cycle of platinum-based chemotherapy, and etoposide, and with or without PD-(L)1 inhibitor in the first-line setting.
• At least 1 measurable lesion as defined by RECIST 1.1.
• Participants must have adequate organ function (cardiac, pulmonary, kidney, bone marrow, and liver).

Exclusion Criteria:

• Prior delta-like ligand 3 (DLL3) or B7 homolog 3 (B7-H3) targeted therapy.
• Prior exposure to topoisomerase I inhibitors or antibody-drug conjugate (ADC) with topoisomerase I inhibitor payload.
• Symptomatic central nervous system (CNS) metastases. Note: Participants with asymptomatic brain metastases are eligible as defined in the protocol.
• History of (non-infectious) interstitial lung disease (ILD)/pneumonitis that required corticosteroids, current ILD/pneumonitis, or suspected ILD/pneumonitis that cannot be ruled out by imaging at screening.
• Baseline requirement of supplemental oxygen.

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