A Study With ABBV-155 Alone and in Combination With Taxane Therapy in Adults With Relapsed and/or Refractory Solid Tumors

Inclusion Criteria: * Has a histologic or cytologic diagnosis of a malignant solid tumor. * Participants enrolled in Part 2a (monotherapy, dose expansion) must have small cell lung cancer (SCLC) diagnosis; participants enrolled to Part 2b (combination therapy, dose expansion) must have either NSCLC or HR-positive/HER2-negative breast cancer. * Measurable disease defined by Response Evaluation Criteria in Solid Tumors (RECIST) criteria. * An Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to 2. * Failure of at least 1 prior systemic chemotherapy including all available standard therapies for participants in the dose-escalation phase (Parts 1a and 1b) including the safety lead-in phase (Japan only). * All participants with breast cancer for subjects in the dose-expansion phase (Part 2b only) must have the following: * Locally advanced or metastatic HR-positive/HER2-negative breast cancer after failing cyclin-dependent kinase (CDK)4/6 inhibitor-based therapy. * HR-positivity and HER-2-negativity should be confirmed based on American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) criteria. * All participants with non-small cell lung cancer (NSCLC) for participants in the dose-expansion phase (Part 2b only) must have R/R NSCLC after at least 1 line of therapy. Participants with activating mutations in EGFR, ALK/ROS1, BRAF genes, or with positive expression of PD-L1 must have been treated with the appropriate targete…