Malignant Lymphomas in Yamagata Prefecture

The incidence and preferential sites of malignant lymphomas were retrospectively investigated by reviewing archived pathological files (1985 to 1996) in 11 major hospitals in Yamagata Prefecture, a HTLV-1-nonendemic area of Japan. In addition, re-evaluation of 212 recent cases based upon the newly-published WHO classification was performed. The following results were obtained: 1) the actual number of lymphoma patients was increasing annually, 2) the incidence rate of extranodal lymphomas was 61.3%, with the gastro-intestinal tract and Waldeyer's ring being the major preferential sites, 3) the incidence of extranodal lymphomas seemed to be increasing annually, whereas that of nodal lymphomas was not, 4) B-cell lymphomas were dominant (69.8%), in a percentage similar to that of a previous nationwide investigation, 5) major categories among the B-cell lymphomas were diffuse large B-cell lymphoma, follicular lymphoma and extranodal B-cell lymphoma of MALT, 6) the percentage of T-cell lymphomas was less than that of the nationwide investigation, 7) angioimmunoblastic T-cell lymphoma was a major subtype of T-cell lymphoma, and 8) the incidence rate of Hodgkin lymphoma was 5.7% of total malignant lymphomas.