As histone demethylase LSD1 (KDM1A) is a rational therapeutic target in AML, we conducted a phase I trial (“rolling‐six design”) with the LSD1 inhibitor tranylcypromine (TCP, dose levels [DL] 20, 40, 60, 80 mg p.o. d1‐28) combined with fixed‐dose ATRA (45 mg/m2 p.o. d10‐28) and low‐dose cytarabine (LDAC, 40 mg s.c. The gene discussed is KDM1A; the disease is acute myeloid leukemia.