Peripheral T-cell lymphoma classification: the matter of cellular derivation.

Peripheral T-cell lymphomas (PTCLs) represent approximately 12% of all non-Hodgkin's lymphomas in Western countries. They are quite heterogeneous as far as morphology and phenotype are concerned. Furthermore, until now, PTCLs could not be referred to specific normal counterparts, in contrast to B-cell-derived non-Hodgkin's lymphomas. In particular, in the last edition of the WHO classification of Tumors of the Hematopoietic and Lymphoid Tissues, for the majority of nodal PTCLs (including the not otherwise specified type and anaplastic large-cell lymphoma), the postulated cell of origin remained undefined. However, in the last few years, high-throughput genomic techniques, especially gene-expression profiling, have allowed us to better define the relationship between some entities and the different T-cell subpopulations. Consequently, it has become possible to clearly define, for example, the association between angioimmunoblastic T-cell lymphoma and T-follicular helper cells. In addition, within PTCLs/not otherwise specified, different subgroups were identified based on their similarity to different cellular counterparts, including T-helper, T-cytotoxic and T-follicular helper cells. In this article, based on their own experience as well as up-to-date literature, the authors revise the concept of PTCL classification by specially focusing on their cellular counterparts and discuss the possible clinical relevance of such an approach.