The World Health Organization classification of malignant lymphomas in Japan: Incidence of recently recognized entities

New insights into the immunology and genetics of malignant lymphomas have a llowed the recognition of new entities and the refinement of previously rec ognized disease categories. The relative incidence of these subtypes of mal ignant lymphoma is also known to differ according to geographic location. I n order to clarify the current status of malignant lymphomas in Japan and t he relative incidences of their subtypes, 3194 patients were classified acc ording to the new World Health Organization (WHO) classification. Among the se were 3025 cases (94.71%) of non-Hodgkin's lymphoma (2189 cases (68.53%) of B-cell lymphoma, 796 cases (24.92%) of T-cell lymphoma) and 141 cases (4 .41%) of Hodgkin's lymphoma. The incidences of the major subtypes of non-Ho dgkin's lymphoma were 33.34% for diffuse large B-cell lymphoma, 8.45% for m arginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) ty pe, 8.05% for plasma cell myeloma, 7.45% for adult T-cell leukemia/lymphoma (ATLL), 6.7% for follicular lymphoma, 6.67% for peripheral T-cell lymphoma of unspecified type, 2.79% for mantle cell lymphoma, 2.6% for nasal and na sal-type T/NK cell lymphoma, 2.35% for angioimmunoblastic T-cell lymphoma, and 2.35% for precursor B-cell lymphoblastic leukemia/lymphoma, in decreasi ng order. The other subtypes comprised less than 2%, mainly precursor T-cel l lymphoblastic lymphoma/leukemia (1.72%), anaplastic large-cell lymphoma o f T- and null-cell types (1.53%), and B-cell chronic lymphocytic leukemia/s mall lymphocytic lymphoma (1.31%). The incidence of ATLL was influenced by its high percentage (19.20%) in the south-western Japanese island, Kyushu, an endemic area of human T-cell leukemia virus type 1 (HTLV-1), but which a ppeared to be lower than that in a previous study. The nodular sclerosis an d mixed cellularity types of Hodgkin's disease occupied 1.78% and 1.63%, re spectively. These data are distinct from those in Western countries and sim ilar in several ways to those in the East, although the relatively high rat e of ATLL was attributed to the geographical difference in the etiologic fa ctor, HTLV-1.