A Study to Evaluate Adverse Events and Change in Disease Activity of Intravenous ABBV-706 Versus Standard of Care in Adult Participants With Relapsed/Refractory Small Cell Lung Cancer

Inclusion Criteria: * Diagnosis of histologically or cytologically confirmed Relapsed/Refractory (R/R) Small Cell Lung Cancer (SCLC). * Participants must have progressed on prior systemic therapy, with CPI (if eligible) and prior tarlatamab, defined as: * In the 1L and 2L setting respectively, platinum-based chemotherapy (i.e., carboplatin or cisplatin and etoposide with CPI, if eligible for CPI) and 2L tarlatamab; or * In the 1L and 2L setting, platinum-based chemotherapy (i.e., carboplatin and etoposide with atezolizumab and lurbinectedin in combination with atezolizumab maintenance and 2L tarlatamab; or * In the 1L setting, platinum-based chemotherapy (i.e., carboplatin or cisplatin and etoposide with CPI if eligible) in combination with tarlatamab in frontline induction and/or maintenance * Participants must be considered suitable to receive SOC comparator (topotecan, lurbinectedin, or amrubicin). * Participants must have an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 to 1 during the screening period prior to the first dose of study treatment. * Participants must have measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1. Target lesions situated in a previously irradiated area are considered measurable if progression has been demonstrated in such lesions. * Participants with brain metastasis from an extracranial solid tumor are eligible if the brain metastases are: * Previously treated and not requiring anticonv…