Epidemiological features of B-cell lymphoma in japan.

Age-adjusted incidence rates for malignant lymphomas in eastern Asian countries except for the Kyushu district of Japan are lower than those in northern European, North and South American and Oceanian countries. Particularly, the incidence rates for Hodgkin's disease and follicular lymphoma are remarkably low in eastern Asian countries. Immunological and clinico-pathological analyses suggested that the estimated rate of incidence of extra-nodal B-cell lymphoma in Japan is not very different from that in the U.S.A. However, their primary sites differ as seen in gastrointestinal lymphomas, most of which are included in extranodal B-cell lymphoma. It is interesting epidemiologically that patients with colorectal lymphoma, whose distribution is closely correlated with that of colorectal cancer in both countries, is much rarer in Japan than in the U.S.A. From the epidemiological viewpoint, extranodal B-cell lymphoma in Japan could be classified by the difference in possible risk factors as follows; lymphoma of the alimentary tract, lymphoma of solid organs, lymphoma of the liver and spleen, medullary or extramedullary plasmacytoma, and Burkitt's lymphoma. In order to clarify the possible risk factors for each type of extranodal B-cell lymphoma including chronic lymphocytic leukemia of B-cell type, it seems necessary to conduct collaborative nationwide epidemiological studies in Japan.