The purpose of this study is to evaluate the efficacy and safety of lurbinectedin in combination with durvalumab for the treatment of participants with extensive stage small cell lung cancer (ES-SCLC) whose disease has not progressed after first line (1L) induction therapy.

The study will evaluate the safety and efficacy of lurbinectedin in combination with durvalumab as maintenance therapy in participants with ES-SCLC after first line induction therapy with durvalumab and platinum plus etoposide containing regimen. In order to be considered for eligibility screening for the maintenance phase, participants need to have an ongoing CR, PR, or stable disease (SD) per RECIST v1.1 criteria after completion of 4 cycles of durvalumab and platinum plus etoposide containing regimen induction treatment.

Inclusion Criteria:

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 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.

Exclusion Criteria:

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

In accordance with ICMJE requirements, Jazz Pharmaceuticals may provide qualified external researchers access to individual participant data (IPD) and clinical trial data that underlie the results of this trial upon request. Qualified researchers can submit a request on https://www.jazzpharma.com/science/clinical-trial-data-sharing/ as outlined. Jazz Pharmaceuticals reserves the right not to consider a request. For inquiries about Jazz's data sharing policy contact clinicaldatasharing@jazzpharma.com.