THE WORLD HEALTH ORGANIZATION CLASSIFICATION OF MALIGNANT LYMPHOMAS AT SHOWA UNIVERSITY HOSPITAL

Abstract

The classification of malignant lymphomas has been controversial in the past two decades. Developing knowledge in the immunology and molecular biology of malignant lymphomas has yielded new entities of these diseases and restructured previously recognized disease categories. The relative incidence of these subtypes of malignant lymphoma is also known to differ according to geographic location. In order to clarify the current status of malignant lymphomas at Showa University Hospital and the relative incidences of their subtypes, 582 patients were classified according to the new World Health Organization classification. Among these were 556 cases (95.5%) of non-Hodgkin's lymphoma (453 cases (77.8%) of B-cell lymphoma, 86 cases (14.8%) of T-cell lymphoma) and 24 cases (4.1%) of Hodgkin's lymphoma. The incidences of the major subtypes of non-Hodgkin' s lymphoma were 46.1% for diffuse large B-cell lymphoma, 11.7% for follicular lymphoma, 11.3% for extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue, 5.5% for peripheral T-cell lymphoma (unspecified), 3.1% for mantle cell lymphoma, and 2.1% for adult T-cell leukemia lymphoma, in decreasing order. The nodular sclerosis and mixed cellularity types of Hodgkin lymphoma occupied 1.9% and 1.0%, respectively. These data are distinct from those in Western countries and similar to the result of a Japanese mass study. We believe that the current data of the relative incidence of lymphoma subtypes at Showa University Hospital will contribute to future studies of malignant lymphomas.