The overlapping spectrum of nodal peripheral T-cell lymphomas (PTCL) entities.

Nodal PTCLs comprise four main entities: angioimmunoblastic T-cell lymphoma (AITL), ALK⁺anaplastic large cell lymphoma (ALCL), ALK^– ALCL and PTCL, not otherwise specified (PTCL, NOS). The only well-demarcated entity is ALK⁺ ALCL. TFH cells have recently been identified as the cell of origin of AITL, whereas the cellular origin of the other entities is not known precisely. There is a lack of specific definition criteria for PTCL, NOS, and thus substantial overlap with AITL, and ALK^– ALCL. Gene expression profiling analyses have identified traces of the TFH signature in a subset of PTCL, NOS, suggesting that the spectrum of AITL may be wider than anticipated. A small group of “follicular” PTCLs, different from AITL, might also derive from TFH cells and could be associated with a distinct translocation t(5 ;9) involving ITK and SYK. The overlap between PTCL, NOS and ALK^– ALCL is accounted by a subset of PTCLs composed of large CD30⁺ cells.