Synergistic induction of cell death by LSD1 and HDAC inhibitors has previously been described for glioblastoma,32, 33 AML34 and breast cancer.35, 36 Our study not only reveals a synergism of concomitant LSD1 and HDAC inhibition in RMS, but – more importantly – elucidates the molecular mechanisms underlying this synergistic induction of cell death. The gene discussed is KDM1A; the disease is breast cancer.