This is first-in-human (FIH) Phase 1, open-label (identity of assigned study drug will be known), multicenter, dose escalation study with dose expansion to identify the RP2D and to evaluate the safety, tolerability, and preliminary antitumor activity of JNJ-63709178 in adult subjects with relapsed or refractory acute myeloid leukemia (AML) who are ineligible for or have exhausted standard therapeutic options. The study is divided into 3 periods: a Screening Phase (within 28 days before the first dose of study drug), a Treatment Phase (first dose of study drug until the last dose of study drug) and a Post-treatment Follow-up Phase (up to the end of study participation or end of study). Subjects' safety will be monitored throughout the study.