September 2016—In December 2007, American hematopathologist Tracy I. George, MD, spent a weekend in the small town of Ansbach in central Bavaria in the laboratory of Hans-Peter Horny, MD, whom she calls “the father of mast cell pathology.” Dr. Horny was at that time a privately practicing hematopathologist after having spent most of his career in academia. Plans for an international clinical trial were underway to evaluate the investigational drug midostaurin in advanced systemic mastocytosis, a rare group of diseases for which there was no effective therapy, and Dr. Horny would be the study pathologist. Dr. George, who had been diagnosing mast cell diseases for several years, wanted to take part as well.