Rationale of a new classification for the group of primary cutaneous lymphomas

In the last decade many studies showed that primary cutaneous lymphomas have another clinical behavior and prognosis, and therefore require a different therapeutic approach, as compared with their primary nodal equivalents. Because, until recently, classification systems for non-Hodgkin's lymphomas were purely based on histologic criteria, and did not recognize the special character of these lymphomas, primary cutaneous lymphomas were not uncommonly diagnosed incorrectly and/or treated inappropriately with unnecessarily aggressive therapies. For that reason the Cutaneous Lymphoma Group of the European Organization for Research and Treatment of Cancer (EORTC) proposed a separate classification for the group of primary cutaneous lymphomas. This EORTC classification is consistently based on a combination of clinical, histologic, immunophenotypical and genetic criteria, and includes well-defined and recognizable disease entities. It contains a limited number of cutaneous T-cell lymphomas and cutaneous B-cell lymphomas, which together constitute more than 95% of all primary cutaneous lymphomas. Herein, the rationale and the basic principles of the EORTC classification are presented, and the relationship between the EORTC classification and other recent classification systems, such as the Revised European-American Classification for Lymphoid Neoplasms (REAL classification) and the proposed World Health Organization classification, are discussed.