Classification of the posttransplant lymphoproliferative disorders: from the past to the present

Posttransplant lymphoproliferative disorders (PTLD) represent a histopathologic, immunophenotypic, genotypic, and clinical spectrum of disease seen in patients after solid organ and bone marrow transplantation. Because of their great heterogeneity, several classification schemes have been proposed over the past 15 years. Although originally based on morphology and limited immunophenotypic studies, more detailed immunophenotypic and genotypic studies have become increasingly important in the classification of the PTLD. The classifications proposed by Frizzera et al, Nalesnik et al, and Knowles et al are discussed. In addition, some specific types of PTLD recognized in the literature but not distinguished in any of the currently published classifications are presented.