Michael Heuser, MD, Hannover Medical School, Hannover, Germany, discusses the aims, methods and findings of his study of the in vivo efficacy of the mutant IDH1 inhibitor HMS-101 and the structural resolution of a distinct binding site. This interview took place at the 5th International Congress on Controversies in Stem Cell Transplantation and Cellular Therapies (COSTEM) 2019, held in Berlin, Germany.