This is a phase 3, open-label, multicenter, randomized study of subcutaneous (SC) vs intravenous (IV) tarlatamab in participants with relapsed extensive stage small cell lung cnacer (ES-SCLC) fter platinum-based chemotherapy. Patients will be randomized (1:1) into the investigational group for subcutaneous Tarlatamab injection or in the control group for intravenous tarlatamab injection.

Subcutaneous vs. Intravenous Tarlatamab

To demonstrate non-inferiority in PK parameters of subcutaneous versus intravenous tarlatamab administration using pharmacokinetic parameters.

1. Histologically or cytologically confirmed small-cell lung carcinoma with demonstrated radiographic progression or relapse after only 1 platinum-based regimen:

• Documented disease progression must be following first-line platinum-based systemic chemotherapy with or without anti-PD-(L)1 therapies for ES-SCLC.
• In countries where SOC first-line systemic treatment for ES-SCLC disease includes platinum containing chemotherapy in combination with PD-(L)1 inhibitor, it is required that patients have failed PD-(L)1 inhibitor as part of their first-line systemic treatment or are ineligible to receive PD-(L)1 inhibitor therapy
• Participants treated with a platinum-based regimen for LS-SCLC may be
  eligible if relapse of the disease is documented within the 6 months after last
  dose of platinum-based chemotherapy.

2. Measurable disease as defined per inverstigator according to RECIST 1.1 criteria within the 21-day screening period.
3. Paricipants with a history of CNS metastases are conditionally accepted.
4. Available tumor tissue
5. ECOG 0-1

1. Previous diagnosis of non-small cell lung cancer (NSCLC) with epidermal growth factor (EGFR) activating mutation that has transformed to SCLC, or mixed SCLC and NSCLC histology, unless NSCLC is predominant.
2. Other relevant medical conditions, suchs as myocardial infarction and/or symptomatic congestive heart failure, arterial thrombosis, pneumonitis/ILD, other malignancies, uncontrolled pleural effusion, etc.
3. Prior/concomitant therapy, such as systemic anticancer therapy within 30 days of enrollment, history of severe or life-threatening events from any immune-mediated therapy, corticosteroid therapy or any other immunosuppresive therapy, live or attenuated vaccine, other anticaner therapy for a malignancy other than SCLC.
4. More than one line of anticancer therapy for SCLC