[Worldwide consensus: the way from the KIEL classification to the REAL classification to the WHO classification]

The history of lymphoma classification has been long and controversial. However, within the last thirty years much has been learned about the biology of lymphoma. The concept of classifying malignant lymphoma according to the (proposed) normal counterpart was developed in the KIEL classification. In 1994, the so-called revised European/American lymphoma classification was published as a consensus of pathologists from both sides of the Atlantic. Its clinical significance was proven in the International Lymphoma Classification Project. The upcoming WHO-Classification is based on the principle to define disease entities that can be recognized by the pathologists and are of clinical relevance. Within these entities, histopathological variants and clinical subtypes are described, which may or may not bear prognostic relevance. Prognostic factors can be defined within an entity, on a clinical, morphological, immunohistochemical or genetic basis.