This is a phase 1b study to assess the safety and tolerability of tarlatamab in combination with programmed death ligand (PD-L1) inhibition with and without chemotherapy.

Inclusion Criteria:

• Participant has provided informed consent prior to initiation of any study specific activities/procedures.
• Age greater than or equal to 18 years old at the same time of signing the informed consent.
• Histologically or cytologically confirmed Extensive Stage Small Cell Lung Cancer (ES-SCLC) and no prior systemic treatment for ES-SCLC.
• Participants with prior treatment for limited-stage SCLC (LS-SCLC) are permitted.
• Eastern Cooperative Oncology Group (ECOG) 0 to 1.
• Participants with treated asymptomatic brain metastases are eligible provided they meet defined criteria.
• Adequate organ function as defined in protocol.

Exclusion Criteria:

• History of other malignancy within the past 2 years with exceptions.
• Major surgery within 28 days of study day 1.
• Untreated or symptomatic brain metastases and leptomeningeal disease.
• Participants who experienced recurrent grade 2 pneumonitis or severe or life-threatening immune-mediated adverse events or infusion-related reactions including those that lead to permanent discontinuation while on treatment with immuno-oncology agents.
• History of immune-related colitis.
• History or evidence of interstitial lung disease or active, non-infectious pneumonitis.
• Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose of study treatment.
• 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 treatment
• Participant has known active infection requiring parenteral antibiotic treatment. Upon completion of parenteral antibiotics and resolution of symptoms, the participant may be considered eligible for the study from an infection standpoint
• NOTE: Simple urinary tract infections and uncomplicated bacterial pharyngitis are permitted if responding to an active treatment and after consultation with Medical Monitor. Participants requiring oral antibiotics who have been afebrile for >24 hours, have no leukocytosis, nor clinical signs of infection are eligible. Screening for chronic infectious conditions is not required.
• History of hypophysitis or pituitary dysfunction.
• History of solid organ transplantation or allogeneic hematopoietic stem cell transplantation.
• 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. Participants with Type I diabetes, vitiligo, psoriasis, hypo- or hyper-thyroid disease not requiring immunosuppressive treatment are permitted.

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.