Study to Evaluate Adverse Events and Change in Disease Activity in Adult Participants With B-Cell Malignancies Receiving Oral ABBV-525 Tablets

Inclusion Criteria:

• Dose Escalation (Part 1) Only: Participants with a documented diagnosis of one ofthe following third line or later of treatment (3L)+ mature B-cell malignancies,from the World Health Organization (WHO)-defined histologies as defined in theprotocol.

• Dose Optimization (Part 2) Only: Participants with documented diagnosis of chroniclymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) with histology based onWHO criteria, with measurable disease requiring treatment as defined by theInternational Workshop on Chronic Lymphocytic Leukemia (iwCLL).

• Dose Expansion (Part 3) Only: Participants with documented diagnosis of one of the 3L+ mature B-cell malignancies based on WHO criteria listed in the protocol, withmeasurable disease requiring treatment.

• Participant has an Eastern Cooperative Oncology Group (ECOG) Performance Status (PS)of 0, 1, or 2.

• Participant has a life expectancy >= 12 weeks.

• Adequate hematological and hepatic function as defined in the protocol.

• Must have archival or freshly collected tumor tissue for correlative studies beforestudy enrollment.

• Participants with prior central nervous system (CNS) disease that has beeneffectively treated may be eligible.

• Participants with resolved coronavirus disease 2019 (COVID-19) infection areeligible.

Exclusion Criteria:

• Known active CNS disease, or primary CNS lymphoma.

• Known bleeding disorders.

• Known history of stroke or intracranial hemorrhage within 12 months prior to firstdose of study treatment.

• Uncontrolled active systemic infection, or active cytomegalovirus infection.

• Active and/or chronic hepatitis B or C infection and/or the criteria listed in theprotocol.

• Known history of human immunodeficiency virus (HIV).

• Known active COVID-19 infection. Participant must not have signs/symptoms associatedwith COVID-19 infection or known exposure to a confirmed case of COVID-19 infectionduring screening. If participant has signs/symptoms suggestive of COVID-19infection, the participant must have a negative molecular (e.g., polymerase chainreaction) test or 3 negative antigen test results at least 24 hours apart.