**Study of Tarlatamab and AB248 for Small Cell Lung Cancer** This study aims to find out how safe and tolerable a drug combination (tarlatamab and AB248) is for people with a type of lung cancer called Extensive Stage Small Cell Lung Cancer (ES-SCLC). The study will also help decide the best dose amount for these drugs. **Key Points:** - **Duration and Visits:** The study requires participants to undergo a screening period of 21 days and provide a fresh tumor biopsy. - **Eligibility:** Participants must be 18 or older, have a confirmed ES-SCLC that has worsened after treatment, and have at least one measurable tumor. - **Exclusions:** People with certain brain problems or who need extra oxygen cannot join. The study also excludes those who have used similar therapies before. Informed consent is necessary, meaning participants agree to take part after understanding the study details. Participants must have good organ function and may provide older tumor samples if new ones are not possible. This study is crucial for finding better ways to treat ES-SCLC.