Introduction
Cutaneous T-cell lymphoma (CTCL) is a type of extranodal non-Hodgkin’s lymphoma (NHL), a disease of the skin caused by clonal proliferation of T lymphocytes, and consists of a group of diseases with different clinical manifestations, histological features, and prognosis [1]. Cutaneous T-cell lymphomas account for 75-80% of all primary cutaneous lymphomas. In the last decade, as the understanding of lymphoma has improved, some new types have been discovered, while the staging of lymphoma is constantly updated and progressing. Compared with other sites of lymphoma, skin lymphoma lesions are easy to detect and can be biopsied in a timely manner, playing an important role in the diagnosis, classification and treatment of the disease.
Classification
With the increasing understanding of cutaneous T-cell lymphoma, the proper classification of such a complex and diverse spectrum of the disease has become an important issue. The latest classification system combines two sets of classifications from the World Health Organization (WHO) and the European Organization for Research and Treatment of Cancer (EORTC) based on the clinical manifestations of the disease, the morphology of the tumor cells, and the biology of the cells, and a new classification of cutaneous T-cell lymphoma was developed in 2005 (WHO-EORTC classification) [2], as shown in Table 1. In the new classification, the Sézary syndrome, which was once classified as a subtype in MF, was separated into a new type.
Table 1. 2005 WHO-EORTC classification of cutaneous T-cell lymphomas
Mycosis fungoides granulomatosis
Variant subtypes of mycosis fungoides
Mycosis fungoides pro-follicular granuloma
Paget-like reticulocytic hyperplasia
Granulomatous skin laxity
Sézary’s syndrome
Adult T-cell leukemia/lymphoma
Primary cutaneous CD30+ lymphoproliferative disorder
Primary cutaneous progressive large cell lymphoma
Lymphomatoid papulosis
Subcutaneous lipofuscinosis-like T-cell lymphoma
Extranodal NK/T-cell lymphoma, nasal type
Primary cutaneous peripheral T-cell lymphoma, unspecified type
Primary cutaneous aggressive pro-epidermal CD8+ T-cell lymphoma*
Cutaneous gamma/δ T-cell lymphoma*
Primary cutaneous CD4+ small/moderate size pleomorphic T-cell lymphoma*
* Tentative classification