A Study of Durvalumab Plus Tremelimumab With Chemotherapy in Untreated ES-SCLC

1. Age ≥ 18 years old at time of study entry (consent) and adult male or female (For Nebraska, ≥19 years old) 2. Histologically or cytologically confirmed ES-SCLC 3. Tumor biopsy or cytology should be obtained within 8 weeks of initiation of treatment. 4. Brain metastases; must be asymptomatic or treated and stable, off steroids for at least 1 month prior to study treatment. 5. Have not received any prior therapy for SCLC, except palliative radiation. If the patient received radiation, there must be measurable disease outside the radiation field. 6. Measurable disease or evaluable disease based on RECIST Version 1.1. 7. Eastern Cooperative Oncology Group ECOG = 2 8. Body weight \> 30 kg 9. No active secondary malignancy. Patients with other prior malignancies will be included, provided they have been disease-free for at least five years. 10. Adequate hematologic and end organ function 11. Women of childbearing potential must have a pregnancy test (urine or serum) proven negative within 14 days prior to registration.

1. Participation in another clinical study with an investigational product during the last 28 days. 2. Any previous chemotherapy and /or immunotherapy for SCLC 3. Current or prior use (≤ 14 days before first doses of study drugs) of immunosuppressive medication. 4. Any concurrent chemotherapy, IP, biologic, or hormonal therapy for cancer treatment. 5. History of another primary malignancy except for malignancy treated with curative intent and with no known active disease ≥5 years before the first dose of IP 6. History of leptomeningeal carcinomatosis 7. Paraneoplastic syndrome (PNS) of autoimmune nature, requiring systemic steroids or clinical symptomatology suggesting worsening of PNS 8. Active infection including tuberculosis, HIV, hepatitis B and C. 9. Active or prior documented autoimmune or inflammatory disorders 10. Uncontrolled cardiovascular disease 11. History of active primary immunodeficiency 12. Pregnant or lactating women 13. Known allergies, hypersensitivity, or intolerance to any of the study medications, excipients, or similar compounds.