[Grayzone lymphoma. Clinical relevance]

Malignant lymphomas are classified into different entities according to their morphology, immunohistochemical parameters and clinical behavior. Several important pathogenetic events can be assigned to certain lymphoma entity types. Nevertheless, some cases present overlapping morphologic and immunohistochemical characteristics and a clear-cut diagnosis cannot be made. This is particularly the case with aggressive lymphomas for which a clear distinction cannot be made between the entities of diffuse large cell lymphoma/Burkitt lymphoma or primary mediastinal B cell lymphoma/classic Hodgkin's lymphoma. In order to redress this situation, two new gray zone entities were introduced in the WHO 2008 classification. Until further knowledge regarding the therapy, behavior and prognosis of these gray zone lymphomas has been gained, they should continue to be considered as distinct entities.