Bispecific T-Cell Engager Tarlatamab and TROP2 Targeted Antibody Drug Conjugate Sacituzumab Govitecan in Previously Treated Extensive-Stage Small Cell Lung Cancer and Extrapulmonary Neuroendocrine Cancer

Background: Small-cell lung cancer (SCLC) is the most deadly form of lung cancer. It kills at least 250,000 worldwide each year. Extra-pulmonary neuroendocrine cancer (EP-NEC) is a similar type of cancer that develops anywhere other than the lungs. EP-NEC is also very aggressive. Better treatments are needed for these cancers. Objective: To test 2 drugs (tarlatamab combined with sacituzumab govitecan \[SG\]) in people with SCLC or EP-NEC. Eligibility: People aged 18 years and older with SCLC or EP-NEC that either did not respond to or returned after treatment. Design: Participants will be screened with a physical exam, blood tests, heart function testing, and imaging scans. Both study drugs are given intravenously (through a needle in the arm). Participants will receive a small starter dose of tarlatamab (1 mg) 2 weeks before beginning regular treatment, followed by the full dose (10 mg) one week later. Treatment then follows a repeating 4-week cycle: tarlatamab (10 mg) on days 1 and 15, and sacituzumab govitecan (7.5 or 10 mg/kg) on days 1 and 8. Treatment continues for up to 2 years, unless the cancer worsens, the participant passes away, or side effects become too severe. Participants will have regular check-ups including physical exams, blood tests, and imaging scans to monitor safety and treatment response. Blood and tumor samples will be collected for research purposes. After stopping treatment, participants will return for a safety check at 30 days, then be contacted every 3 months to check on their health and survival. Those who stop treatment for reasons other than cancer progression will continue CT scans every 8 weeks until their disease progresses.