A Study of Lurbinectedin in Combination With Durvalumab for the Treatment of Participants With ES-SCLC

1. Participant has histologically or cytologically confirmed ES-SCLC (per Veterans Administration Lung Study Group staging system). 2. Participant has received 4 cycles of definitive platinum-based chemotherapy with at least 3 cycles of durvalumab 3. Has Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1. 4. Must have a life expectancy of ≥ 12 weeks as assessed by the treating physician. 5. Adequate hematologic and end-organ function for at least 7 days prior to dosing. 6. Has a body weight \> 30 kg. 7. Adequate contraceptive precautions.

1. Clinically confirmed leptomeningeal carcinomatosis. 2. Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures 3. Significant cardiovascular disease within 3 months prior to enrollment 4. History of another primary malignancy 5. Presence or history of Central Nervous System (CNS) metastases 6. History of allogeneic organ transplantation. 7. History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on the screening chest CT scan. 8. Any concurrent chemotherapy, study intervention, biologic, or hormonal therapy for cancer treatment. 9. Receipt of live attenuated vaccine within 30 days prior to the first dose of study intervention. 10. Pregnant or breastfeeding or intending to become pregnant during the study or within 6 months after the last dose of study intervention.