Study of Tarlatamab as Maintenance Treatment After Chemo-radiotherapy for Limited Stage SCLC Patients

Inclusion Criteria: * Histologically or cytologically documented new diagnosis of LS-SCLC by histology or cytology from brushing, washing, or needle aspiration. Mixed tumors are not eligible. * Patients who: 1. were treated with sequential chemo-radiotherapy 2. were treated only with chemotherapy * Have at least one lesion that meets criteria for being measurable or non-measurable, as defined by RECIST 1.1. * Has completed chemo-radiation or chemotherapy alone without progression of disease per RECIST v1.1 * Be male or female ≥18 years of age inclusive, on the day of signing informed consent. * Have a life expectancy of at least 3 months from the study start. * Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2 within 7 days prior to the first dose of study intervention. * Toxicities attributed to chemo-radiotherapy treatment have to be resolved to grade ≤1, unless otherwise specified. * No clinically significant electrocardiogram (ECG) findings * Correct pulmonary function without oxygen supplementation * Have voluntarily agreed to participate by giving written consent for the study prior to any specific protocol procedures. * Have adequate organ function (hematological and biochemistry parameters). Exclusion Criteria: * Patients expected to require any other form of radiation therapy for LS-SCLC as concurrent radiotherapy. * Extensive-stage SCLC (ES-SCLC) or any previous diagnosis of transformed non-small cell lung cancer. Mixed tumors (SCLC-NSCLC) are not eligible. * Has known history of, or active, neurologic paraneoplastic syndrome of autoimmune nature. * Has had major surgery within 4 weeks prior to first dose of study interventions. * Is currently participating in or has participated in a study of an investigational agent or has used an investigational device within 4 weeks prior to the first dose of study intervention. * Has known history of a second malignancy other than SCLC, unless potentially curative treatment has been completed with no evidence of malignancy for at least 3 years since the initiation of that therapy. * Uncontrolled intercurrent active infection at the time of enrollment requiring systemic therapy. * Evidence of interstitial lung disease or active, non-infectious pneumonitis. * History of solid organ transplantation. * Myocardial infarction and/or symptomatic congestive heart failure (New York Heart Association \>class II) within 6 months prior to first dose of study treatment. * Has a known history of Human Immunodeficiency Virus (HIV) infection. * Has a known history of Hepatitis B or known active Hepatitis C virus infection. * Has a known history of active tuberculosis. * Has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the subject's participation for the full duration of the study, or is not in the best interest of the subject to participate, in the opinion of the treating investigator. * Has known psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial. * Has serious nonhealing wound, ulcer, or bone fracture within 28 days before first dose of study intervention. * Female subjects of childbearing potential unwilling to use protocol specified method of contraception during treatment and for an additional 60 days after the last dose of study treatment. * Female subjects who are breastfeeding or who plan to breastfeed while on study through 60 days after the last dose of study treatment. * Female subjects planning to become pregnant or donate eggs while on study through 60 days after the last dose of study treatment. * Female subjects of childbearing potential with a positive pregnancy test assessed at screening by a highly sensitive serum pregnancy test. * Male subjects with a female partner of childbearing potential who are unwilling to practice sexual abstinence or use contraception during treatment and for an additional 60 days after the last dose of study treatment. * Male subjects with a pregnant partner who are unwilling to practice abstinence or use a condom during treatment and for an additional 60 days after the last dose of study treatment. * Subject has known sensitivity to any of the products or components to be administered during dosing.