RESUMEN
PURPOSE: This article presents new research on the role of the renowned German physician Ernst von Leyden (1832-1910) in the emergence of oncology as a scientific discipline. METHODS: The article draws on archival sources from the archive of the German Society of Haematology and primary and secondary literature. RESULTS: Leyden initiated two important events in the early history of oncology: the first international cancer conference, which took place in Heidelberg, Germany, in 1906, and the founding of the first international association for cancer research (forerunner of today's UICC) in Berlin in 1908. Unfortunately, these facts are not mentioned in the most recent accounts. Both had a strong impact on the professionalization of oncology as a discipline in its own right. CONCLUSION: Although not of Jewish origin, von Leyden was considered by the National Socialists to be "Jewish tainted", which had a lasting effect on his perception at home and abroad.