A Study Assessing Adverse Event and How Oral ABBV-453 Moves Through the Body in Adult Participants With Relapsed or Refractory (R/R) Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Lymphoma (SLL)

Inclusion Criteria:

• Relapsed/refractory (R/R) chronic lymphocytic leukemia (CLL)/ small lymphocyticlymphoma (SLL) that has received at least 2 prior systemic therapies and have noavailable (or established) therapies known to provide clinical benefit and to whichthe participant would consent to receiving.

• Laboratory values meeting those listed in the protocol.

Exclusion Criteria:

• QT interval corrected for heart rate (QTc) using Fridericia's correction of > 470msec (females) or > 450 msec (males), Grade 3 arrythmia, and/or other clinicallysignificant cardiac abnormalities.

• Known to be B-cell leukemia/lymphoma 2 inhibitor (BCL-2i) refractory or has receiveda BCL-2i-containing regimen within (6 months) of starting study drug (e.g.,venetoclax, lisaftoclax, BGV-11417).

• Has active human immunodeficiency virus (HIV) infection. HIV testing is not requiredunless required locally.

• Recent history (within 6 months) of:

• Congestive heart failure (defined as New York Heart Association, Class 2 orhigher).

• Ischemic cardiovascular event.

• Cardiac arrhythmia requiring pharmacological or surgical intervention.

• Pericardial effusion.

• Pericarditis.

• Consumes known moderate or strong inhibitors of cytochrome P450 3A isoform subfamily (CYP3A) within 14 day or 5 half-lives of the drug (whichever is shorter) before thefirst dose of ABBV-453.