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).

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.
All participants with SCLC in the dose-expansion phase (Part 2a only) must have R/R SCLC from at least 1 line of therapy which includes a platinum-based therapy with or without an anti-PD-1/PD-L1 therapy.

All participants with either breast cancer or NSCLC must have the following if exposed to prior taxane-based therapy:

No history of taxane allergy (Part 1b and Part 2b only).
Disease that has relapsed or progressed at least 2 months after most recent exposure to any taxane-based therapy.
Available tumor tissue suitable for immunohistochemistry testing.
Adequate kidney, liver, and hematologic laboratory values as described in the protocol.

Exclusion Criteria:

Untreated brain or meningeal metastases (participants with a history of metastases may be eligible based on details described in the protocol).
Grade 2 or higher peripheral neuropathy (only applies to participants who would receive taxane therapy).
Unresolved Grade 2 or higher toxicities related to previous anticancer therapy except alopecia.
Known active infection of hepatitis B, hepatitis C, or human immunodeficiency virus with exceptions as described in the protocol.
Recent history (within 6 months) of congestive heart failure (defined in the protocol), ischemic cardiovascular event, cardiac arrhythmia requiring pharmacological or surgical intervention, pericardial effusion, or pericarditis.
Any history of hypersensitivity to any ingredients of ABBV-155 will be excluded. For combination therapy only (Parts 1b and 2b), no history of serious allergic reaction to any taxane or any ingredients used in taxane formulation (e.g., cremaphor).