Classification and treatment of rare and aggressive types of peripheral T-cell/natural killer-cell lymphomas of the skin

The classification of cutaneous lymphomas has been contentious. Two major competing classifications were the World Health Organization (WHO) and the European Organization for Research and Treatment of Cancer (EORTC). The principal authors met for a consensus meeting resulted in a combined classification called WHO-EORTC Classification of Cutaneous Lymphoma. We review the classification of "mature" or peripheral T-cell lymphoma (PTCL) with high predilection to the skin as published by the WHO-EORTC. We also highlight new information and changes from the previous classifications of cutaneous PTCL according to the WHO classification or the EORTC classification. Finally, the salient findings are compared with similar-looking nodal PTCLs with a high frequency of skin involvement. This review focuses on a rare group of cutaneous PTCLs other than mycosis fungoides or its variants. Changes from the previous classifications are discussed, and the rare group of nodal PTCLs with high predilection to the skin are presented. The salient findings, diagnostic features, and treatments are included, along with summary tables and clinical-histopathologic images. This review may serve as a guide for hematologists, oncologists and dermatologists in the diagnosis and management of these rare, aggressive, and often difficult to diagnose lymphomas. Although cutaneous lymphomas are morphologically identical to systemic lymphomas, the former behave differently, require divergent management, and should be recognized as separate entities. The consensus WHO-EORTC classification presents unified terminology and definitions to promote conformity in diagnosing and treating these cases, to foster a multidisciplinary approach to these often-obscure diseases, and to lead to more advances in identifying molecular targets specific to these entities.