Peripheral T-cell lymphomas: an historical perspective.

Peripheral T-cell lymphomas (PTCL) remain largely unexplored due to disease rarity and biological heterogeneity as well as relatively recent recognition in modern classification systems. Before 1970, classifications of non-Hodgkin’s lymphomas (NHL) were based on morphology. The discovery of distinct T-, Band natural killer (NK)–cell lineages led to two immunologically based classification systems proposed in 1974: the European Kiel and the North American Lukes-Collins. In 1982, the Working Formulation (WF), based on clinical and morphologic criteria, was developed in the United States. The updated Kiel classification separated Band Tcell lymphomas but still failed to address some disease types.