A Trial of Tarlatamab in Patients With Pretreated Extensive-stage Small Cell Lung Cancer (ES-SCLC) and ECOG PS 2

Inclusion Criteria: * Histologically or cytologically confirmed ES-SCLC. * Previous treatment with only one line of platinum-etoposide doublet chemotherapy with immune-checkpoint inhibition for SCLC. Patients treated with a platinum-etoposide doublet chemotherapy for prior limited stage (LS)-SCLC may be eligible for the study if the disease has progressed on treatment or within 6 months from chemotherapy completion (i.e. during durvalumab consolidation): the platinum-etoposide line of therapy will count as one prior line of therapy. * Progressive disease on or after the first-line treatment for SCLC. * ECOG Performance Status 2. * Age ≥18 years. * Adequate haematological, renal and liver function. * Coagulation function: Prothrombin time (PT)/international normalised ratio (INR) and partial thromboplastin time (PTT) or activated partial thromboplastin time (aPTT) ≤1.5x ULN, except for patients receiving anticoagulation, who must be on a stable dose of anticoagulation therapy for 6 weeks prior to enrolment. * Pulmonary function: * No clinically significant pleural effusion. Pleural effusion managed with indwelling pleural catheter (e.g., PleurX) are allowed. * Baseline oxygen saturation \>90% on room air. * Cardiac function: Left ventricular ejection fraction (LVEF) ≥50%, no clinically significant pericardial effusion as determined by an echocardiogram (ECHO) or multigated acquisition (MUGA) scan (preferred), and no clinically significant electrocardiogram (ECG) findings. * Women of childbearing potential, must have a negative urinary or serum pregnancy test within 5 weeks before enrolment. Pregnancy test must be repeated within 3 days before the first dose of tarlatamab treatment. * Written Informed Consent must be signed and dated by the patient and the investigator prior to any trial-related intervention. Exclusion Criteria: * Symptomatic CNS metastases Patients with untreated asymptomatic brain metastases and patients with treated and stable brain metastases are eligible. * Diagnosis or evidence of leptomeningeal disease or spinal cord compression * Prior history of immune-checkpoint inhibitor treatment resulting in: * any severe or life-threatening immune-mediated adverse event, * history of immune-mediated encephalitis or another immune-mediated CNS event (any grade), * grade ≥2 immune-mediated recurrent pneumonitis, * infusion-related reactions leading to permanent discontinuation of the immunotherapy agent. Exception: patients with a history of immune-checkpoint inhibitor-induced endocrinopathy which is clinically stable on replacement therapy. * 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. * Treatment with live virus, including live-attenuated vaccination within 14 days prior to enrolment and inactive vaccines (e.g., non-live or non-replicating agent) and live viral non-replicating vaccines (e.g., Jynneos for Monkeypox infection) within 3 days prior to enrolment. * History of other malignancy within the past 2 years, with the following exceptions: * Low-risk malignancy treated with curative intent and with no known active disease present for ≥1 year before enrolment and believed to be at low risk for recurrence per investigator discretion. * Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease. * Adequately treated cervical carcinoma in situ without evidence of disease. * Adequately treated breast ductal carcinoma in situ without evidence of disease. * Prostatic intraepithelial neoplasia without evidence of prostate cancer. * Adequately treated urothelial papillary non-invasive carcinoma or carcinoma in situ. * Myocardial infarction and/or symptomatic congestive heart failure (New York Heart Association \>class II) within 12 months prior to enrolment. * History of arterial thrombosis (e.g., stroke or transient ischemic attack) within 12 months prior to enrolment. * Presence/history of an uncontrolled viral infection: * Known uncontrolled human immunodeficiency virus (HIV) infection. * Active hepatitis C infection (patients with detectable hepatitis C antibody \[HCV Ab\] and HCV RNA viral load above the limit of quantification). * Patients with presence of HCV Antibodies and HCV RNA viral load below the limit of quantification (HCV RNA negative) with or without prior treatment are allowed. * Active hepatitis B infection (presence of hepatitis B surface antigen \[HBsAg\] and hepatitis B virus \[HBV\] DNA viral load above the limit of quantification \[HBV DNA positive\]). * Patients with resolved HBV infection defined as absence of HBsAg and presence of HBV core antibody (anti-HBc) followed by an HBV DNA viral load below the limit of quantification (HBV DNA negative) are allowed, with a requirement for regular monitoring for reactivation for the duration of treatment on the study and assessing the need for HBV prophylaxis therapy per local or institutional guidelines. * Patients with chronic HBV infection inactive carrier state defined as presence of HBsAg and HBV DNA viral load below the limit of quantification \[HBV DNA negative\] are allowed, with a requirement for regular monitoring for reactivation for the duration of treatment on the study and assessing the need for HBV prophylaxis therapy per local or institutional guidelines. * Receiving systemic corticosteroid therapy or any other form of immunosuppressive therapy within 7 days prior to first dose of study treatment. * Prophylactic dexamethasone for the management of tarlatamab-related adverse events and any anti-emetic therapies are allowed. * Low-dose corticosteroids (prednisone ≤10 mg per day or equivalent) is permitted during the trial. * Patients with symptoms and/or clinical signs and/or radiographic signs that indicate an acute and/or uncontroll