Inclusion Criteria:
* Participant has provided informed consent prior to initiation of any study specific activities/procedures.
* Participant must be a resident in China, and of Chinese ancestry ≥ 18 years of age (or legal adult age within country) at the time of signing the informed consent.
* Histologically or cytologically confirmed small cell lung cancer.
* Extensive-stage SCLC participants who progressed on or recurred following 1 platinum-based regimen as 1L therapy (including a PD-1/PD-\[L\]1) and at least 1 other prior line of therapy.
* Measurable lesions as defined per RECIST 1.1 within 21 days prior to the first dose of study drug.
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1.
* Minimum life expectancy of 12 weeks.
* Adequate organ function.
Exclusion Criteria:
Disease Related
* Any previous diagnosis of transformed non-small cell lung cancer (NSCLC), epidermal growth factor receptor (EGFR) activating mutation positive NSCLC that has transformed to SCLC.
* Symptomatic central nervous system (CNS) metastases.
* Diagnosis or evidence of leptomeningeal disease.
* Prior history of severe or life-threatening events from any immune-mediated therapy.
Other Medical Conditions
* Active autoimmune disease that has required systemic treatment (except replacement therapy) within the past 2 years or any other diseases requiring immunosuppressive therapy while on study.
* History of solid organ transplantation.
* Evidence of interstitial lung disease or active, non-infectious pneumonitis.
* History of other malignancy within the past 2 years, with certain exceptions
* Myocardial infarction and/or symptomatic congestive heart failure (New York Heart Association \> class II) within 12 months of first dose of study drug.
* History of arterial thrombosis (eg, stroke or transient ischemic attack) within 12 months of first dose of study drug.
* Participants with symptoms and/or clinical signs and/or radiographic signs that indicate an acute and/or uncontrolled active systemic infection within 7 days prior to the first dose of study drug.
* HIV, Hepatitis B, and Hepatitis C, with certain exceptions.
* Major surgery within 28 days of first dose study drug. Prior/Concomitant Therapy
* Currently or previously enrolled in a tarlatamab study.
* Prior therapy with any selective inhibitor of the DLL3 pathway.
* Prior anti-cancer therapy within 21 days prior to first dose of study treatment, with certain exceptions.
* Receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug, with certain exceptions.
* Treatment with live virus, including live-attenuated vaccination, within 14 days prior to the first dose of study drug. Inactive vaccines (eg, non-live or non-replicating agent) and live viral non-replicating vaccines (eg, Jynneos for mpox infection) within 3 days prior to first dose of study drug.
Prior/Concurrent Clinical Study Experience
• Currently receiving treatment in another investigational device or drug study, or less than 30 days since ending treatment on another investigational device or drug study(ies). Other investigational procedures while participating in this study are excluded.
Other Exclusions
* Female participants of childbearing potential unwilling to use protocol-specified method of contraception during treatment and for an additional period of time after the last dose of study drug as specified in the study protocol.
* Female participants who are breastfeeding or who plan to breastfeed while on study and for an additional period of time after the last dose of study drug as specified in the study protocol.
* Female participants planning to become pregnant or donate eggs while on study and for an additional period of time after the last dose of study drug as specified in the study protocol.
* Female participants of childbearing potential with a positive pregnancy test assessed at screening by a highly sensitive serum pregnancy test.
* Male participants with a female partner of childbearing potential who are unwilling to practice sexual abstinence (refrain from heterosexual intercourse) or use contraception during treatment and for an additional period of time after the last dose of study drug as specified in the study protocol.
* Male participants with a pregnant partner who are unwilling to practice abstinence or use a condom during treatment and for an additional period of time after the last dose of study drug as specified in the study protocol.
* Male participants unwilling to abstain from donating sperm during treatment and for an additional period of time after the last dose of study drug as specified in the study protocol.
* Participants has known sensitivity to any of the products or components to be administered during dosing.
* Participants likely to not be available to complete all protocol-required study visits or procedures, and/or to comply with all required study procedures.
* History or evidence of any other clinically significant disorder, condition, or disease that, in the opinion of the investigator or medical monitor if consulted, would pose a risk to participant safety or interfere with the study evaluation, procedures, or completion.
