Histological classification of the non-Hodgkin's lymphoma.

The non-Hodgkin's lymphomas (NHL) are a diverse group of neoplasms which show subtle histological differences. This has led to difficulties in formulating reproducible classifications of NHL that are both histologically and clinically relevant. In this review we discuss some of the historical aspects of NHL classification leading up to the principal classifications in current use. In comparing these we put forward reasons why we regard the updated Kiel classification as that which is the most soundly based in clinical, histological and biological terms. The Kiel classification, unlike its competitors, lends itself to further updating as new clinicopathological entities become established, without loss of its essentially sound foundations. Thus the classification of T-cell lymphomas can only be regarded as provisional and certain extranodal lymphomas, which are clear clinicopathological entities, await classification. The biological foundation of the Kiel classification should allow further updating to incorporate these entities and the tighter definitions of categories of NHL that will surely result from the application of cytogenetics, molecular biology and studies of lymphocyte homing mechanisms.