Inclusion Criteria:

          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.

        Exclusion Criteria:

          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.