A Phase 1b Study Evaluating the Safety, Tolerability, Pharmacokinetics, and Preliminary Anti-Tumor Activity of Subcutaneous Tarlatamab in Subjects With Extensive Stage Small Cell Lung Cancer (DeLLphi-308)

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.