The 2018 update of the WHO-EORTC classification for primary cutaneous lymphomas

Primary cutaneous lymphomas are a heterogeneous group of T-cell lymphomas and B-cell lymphomas that present in the skin with no evidence of extracutaneous disease at the time of diagnosis. In the last decade the 2005 WHO-EORTC consensus classification has served as a golden standard for the diagnosis and classification of these conditions. In September 2018 an updated version of the WHO-EORTC was published in the 4th edition of the WHO classification for Skin Tumours Blue Book. In this classification primary cutaneous acral CD8+ T-cell lymphoma and EBV-positive mucocutaneous ulcer are included as new provisional entities, and a new section on cutaneous forms of chronic active EBV disease has been added. The term primary cutaneous CD4 positive small/medium T-cell lymphoma was modified to primary cutaneous CD4 positive small/medium T-cell Lymphoproliferative disorder, because of its indolent clinical behavior and uncertain malignant potential. Modifications have also been made in the sections on lymphomatoid papulosis increasing the spectrum of histologic and genetic types and primary cutaneous marginal zone lymphomas recognizing two different subtypes. Herein, the characteristic features of these new and modified entities as well as the results of recent molecular studies with diagnostic, prognostic and/or therapeutic significance for the different types of primary cutaneous lymphomas are reviewed. An update of the frequency and survival of the different types of primary cutaneous lymphomas is provided.