Phase 3 Trial of Tarlatamab (SC vs IV) in Extensive-Stage Small Cell Lung Cancer After Platinum based First-line Chemotherapy (ES-SCLC)DeLLphi-315

- Participant has provided informed consent prior to initiation of any study specific activities/procedures. - Age ≥ 18 years (or legal adult age within country, whichever is older) at the time of signing the informed consent. - Histologically or cytologically confirmed SCLC with demonstrated progression or relapse. - Participants who progressed or recurred following 1 platinum-based regimen. - Measurable disease as defined per RECIST 1.1 within the 21-day screening period. - Eastern Cooperative Oncology Group (ECOG) PS of 0 or 1. - Minimum life expectancy of 12 weeks. - Adequate organ function. - History of central nervous system (CNS) metastases are allowed with considerations defined in the protocol.

Disease Related - Any previous diagnosis of non-small cell lung cancer (NSCLC), epidermal growth factor receptor (EGFR) activating mutation that has transformed to SCLC, or mixed SCLC and NSCLC histology, with exceptions defined in the protocol. Other Medical Conditions - Myocardial infarction and/or symptomatic congestive heart failure (New York Heart Association > class II) within 6 months prior to first dose of study treatment. - History of arterial thrombosis (e.g., stroke or transient ischemic attack) within 6 months prior to first dose of study treatment. - Current evidence or history of non-infectious pneumonitis/ILD (interstitial lung disease) that required steroids or other immunosuppressive treatment. - History of other malignancy within the past 2 years, with exceptions defined in the protocol. - Presence or history of viral infection based on criteria per protocol. - History of solid organ transplantation. - Symptoms and/or radiographic signs that indicate an acute and/or uncontrolled active systemic infection requiring antibiotics within 7 days prior to the first dose study treatment. - Known sensitivity or a contraindication to any of the products or components. - Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures. Prior/Concomitant Therapy - Prior systemic anticancer therapy within 30 days of enrolment - Prior history of severe or life-threatening events from any immune-mediated therapy. - Receiving systemic corticosteroid therapy or any other form of immunosuppressive therapy within 14 days prior to first dose of study treatment. - Live and live-attenuated vaccines within 28 days prior to the start of study treatment. - Receiving another anticancer therapy for a malignancy other than SCLC. - More than 1 prior line of anticancer therapy for SCLC. - Participation in a tarlatamab clinical trial or prior therapy with any selective inhibitor of the delta-like ligand 3 (DLL3) pathway. - Treatment in an alternative investigational trial within 28 days prior to enrolment. - History of allergy or hypersensitivity to similar products (eg, drugs with a similar chemical structure or other monoclonal antibody) or any excipient. Other Exclusions - Participants unable to have SC injections administered in the abdomen or thigh. - Participant unlikely to be able to complete all protocol-required procedures, restrictions and requirements. - History or evidence of any other clinically significant disorder, condition, or disease that, in the opinion of the investigator, would pose a risk to participant safety.