Cutaneous lymphomas: new entities and rare variants

Abstract

Primary cutaneous lymphomas are the second most common group of extranodal non-Hodgkin lymphomas. Recently several new variants and entities have been described but have not yet become part of the World Health Organization (WHO) classification. These forms include the granulomatous form of mycosis fungoides, which is associated with a poorer prognosis, as well as indolent CD8+ lymphoproliferations on the head and at acral localizations. Within the group of cutaneous CD30+ lymphoproliferative disorders, new histological types of lymphomatoid papulosis have been identified, such as type D (CD8+ epidermotropic) and typeE (angioinvasive) which simulate aggressive lymphomas. Cutaneous peripheral T-cell lymphomas are a prognostically heterogeneous group of cutaneous lymphomas. The cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma and cutaneous gamma/delta T-cell lymphoma are very aggressive neoplasms, whereas cutaneous CD4+ small to medium-sized T-cell lymphoma in its solitary or localized form represents an indolent lymphoproliferation: the terminology, histogenesis and differentiation from nodular T-cell pseudolymphoma are still a matter of debate. Among B-cell lymphomas, disorders associated with Epstein-Barr virus (EBV) are discussed focusing on EBV diffuse large B-cell lymphoma of the elderly and EBV-associated mucocutaneous ulcer. This review describes the clinical, histological and immunophenotypic features of new and rare entities and variants of cutaneous lymphomas and highlights the impact of the clinicopathological correlation in the diagnostic process.