Study to Evaluate Adverse Events and Movement of Intravenously (IV) Infused ABBV-787 in Adult Participants With Relapsed/Refractory (R/R) Acute Myeloid Leukemia (AML)

Inclusion Criteria: Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Laboratory Criteria matching those outlined in the protocol. QT interval corrected for heart rate (QTc) <= 470 msec using Fridericia's correction, and no other clinically significant cardiac abnormalities. Documented diagnosis of non-promyelocytic acute myeloid leukemia (AML), per 2022 European Leukemia Net (ELN) criteria. Participants with relapsed/refractory (R/R) acute myeloid leukemia (AML) who have been treated with up to 3 prior lines of therapy and are refractory to or intolerant of all established AML therapies that are known to clearly provide clinical benefit at the judgement of the investigator. Must have a white blood cell (WBC) count < 25 × 10^9 /L prior to initiation of study drug (Note: Hydroxyurea or leukapheresis is permitted to meet this criterion and for use through Cycle 3 to control for hyperleukocytosis.). Exclusion Criteria: Have received a CD33-targeting therapy within 3 months prior to the first dose of ABBV-787. Stem cell transplant within 3 months prior to first dose of study drug. Have received anticancer therapy including chemotherapy, radiation therapy, immunotherapy, biologic, or any investigational therapy within 14 days or 5 half-lives of the drug (whichever is shorter) prior to the first dose of ABBV-787. History of documented pneumonitis that required treatment with systemic steroids within the last 6 months, nor any evidence of active pneumonitis. Unresolved toxicity of Grade >= 2 from prior anticancer therapy, or to levels dictated in the eligibility criteria, with the exception of alopecia. Known active severe or poorly controlled acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.