Malignant lymphomas of bone in Japan.

Thirty-four cases of primary non-Hodgkin's lymphoma (NHL) of bone collected from hospitals in Japan were histologically and immunohistologically reviewed, and the results were compared with those in Western countries. There were no remarkable differences in age, sex, and the distribution of bone tumors between Japanese and Western cases. Sixteen cases (47%) diagnosed previously as "reticulum cell sarcoma" were reclassified as diffuse NHL of large cell (seven cases), mixed type (four cases), immunoblastic type (three cases), clear cell type (one case), and multilobated type (one case). The cases with small lymphocytic type with plasmacytoid features (lymphoplasmacytic type) were more common in Japan (35% of our cases) than in Western countries. The distribution of histologic subtypes, except for lymphoplasmacytic and T-cell lymphomas, in the current cases was similar to that in Western countries. However, immunohistochemistry showed that Japanese cases contained a much higher frequency of T-cell lymphoma (10% of all cases) than Western cases. Histologic grade according to the Working Formulation correlated well with clinical stage. There may be a tendency towards better prognosis with lower grade tumors, but this was not statistically significant.