Steroid treatment within seven (7) days prior to study treatment. Patients that require intermittent use of bronchodilators, topical steroids or local steroid injections will not be excluded from the study. Patients who have been stabilized to 10 mg Prednisolone PO QD (or equivalent), daily (or less) at least seven (7) days prior to study drug administration are allowed. Phase 2 Tumor-specific Eligibility Criteria Phase 2 patients must meet the cohort-specific inclusion/exclusion criteria in addition to the general inclusion/exclusion criteria for Phase 1 and Phase 2 study listed above. Cohort 1: Patient Population: Relapsed/Refractory SCLC PHASE I INCLUSION CRITERIA PHASE II INCLUSION CRITERIA: ECOG performance status of 0-1 PHASE II INCLUSION CRITERIA: Hemoglobin > 9 g/dL PHASE II INCLUSION CRITERIA: Absolute neutrophil count > 1.5 x 10^9/L PHASE II INCLUSION CRITERIA: Platelet counts > 100 x 10^9/L PHASE II INCLUSION CRITERIA: Serum bilirubin < 2 x ULN PHASE II INCLUSION CRITERIA: Life expectancy of at least 3 months PHASE II INCLUSION CRITERIA: Women must not be pregnant or breastfeeding SCREENING PHASE INCLUSION CRITERIA DOSE EXPANSION PHASE ADDITIONAL INCLUSION CRITERIA INDUCTION PHASE INCLUSION CRITERIA: RESEARCH PHASE INCLUSION CRITERIA: In patients with suspected liver disease, bilirubin must be =< 2.5 mg/dL ECOG performance status of 0-2 Inclusion Criteria for Phase 2 Sub-study Cohort: INCLUSION CRITERIA SEARCH PHASE INCLUSION CRITERIA FOR TRANSPLANT PHASE SPECIFIC INCLUSION CRITERIA FOR PHASE II INCLUSION CRITERIA FOR CONTINUING THERAPY ON THE EXTENSION PHASE: Additional inclusion criteria for phase 2 Subjects only: Criteria for the Phase 1b: INCLUSION CRITERIA (EXPANSION PHASE ONLY) Participants with measurable disease per RECIST v1.1 Additional Inclusion Criteria for Participants Who Backfill Cleared Cohorts of Phase 1a and Phase 1b: PHASE II REGISTRATION - INCLUSION CRITERIA PHASE I INCLUSION CRITERIA: PHASE II INCLUSION CRITERIA: PHASE III INCLUSION CRITERIA: INCLUSION CRITERIA FOR FOCUS GROUPS (PHASE I) INCLUSION CRITERIA FOR PILOT-TESTING (PHASE II) ECOG ? 3 Phase 2 Inclusion Criteria: PHASE II: Meet all the Phase 1 inclusion criteria Inclusion criteria for intervention phase