A Study of DCLL9718S in Participants With Relapsed or Refractory Acute Myeloid Leukemia (AML) or DCLL9718S in Combination With Azacitidine in Participants With Previously Untreated AML Unsuitable for Intensive Induction Chemotherapy

Inclusion Criteria: * Diagnosis of AML per World Health Organization (WHO) criteria (except acute promyelocytic leukemia) * Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0, 1, or 2 * Adequate end-organ function * Willing and able to undergo a pre-treatment bone marrow aspirate and biopsy and subsequent bone marrow aspirates and biopsies during treatment Specifically for participants in Arm A: * Age greater than or equal to (\>/=) 18 years * Relapsed or refractory acute myeloid leukemia * Participants cannot have received more than two prior regimens Specifically for participants in Arm B: * Treatment-naive participants with AML who are \>/=75 years old * Treatment-naive participants unfit for induction chemotherapy for AML due to comorbidities who are \>/=65 years old Exclusion Criteria: * Diagnosis of acute promyelocytc leukemia * Prior allogeneic stem cell transplant or solid organ transplant * Active central nervous system (CNS) involvement by leukemia * History of idiopathic pulmonary fibrosis, organizing pneumonitis (for example \[e.g.\], bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis * Treatment with investigational therapy within 14 days prior to Cycle 1, Day 1 * Treatment with a monoclonal antibody within 30 days prior to Cycle 1, Day 1 * Positive for hepatitis C virus (HCV) antibody at screening * Active hepatitis B virus (HBV) infection * Known positivity for human immunodeficiency virus (HIV) * History of other malignancy within 2 years prior to screening * Family history of long QT syndrome, with a QTc interval greater than (\>) 480 millisecond (msec) at screening, or taking concurrent medications known to prolong QT/QTc interval