[Pathology of malignant lymphomas]

Current problems relating pathology of malignant lymphomas were reviewed. Unique geopathologic features of malignant lymphomas have been increasingly made clear. Japanese lymphomas, previously reported as having relative excess of T cell lymphomas, are now proved similar to Euro-American lymphomas with regard to T/B ratio, i.e. 75% and 20% respectively, except ATLL related with HTLV-I. Instead, characteristics of Japanese lymphomas are 1) low incidence rate of overall lymphomas and 2) scarcity of Hodgkin's disease (HD) and follicular lymphomas. These differences seems to be related to the difference in HLA composition among susceptible individuals. Since HLA haplotypes regulate host's immunoreactivity through their unique molecular structures, it is possible that "narrow" cognitive molecules could trigger the autoimmune reaction and "broad" one could accept altered cell as "self", thus leading to the late-onset lymphomagenesis. Viewing the evidences that no consistent immuno-gene rearrangements were detected in significant cases of ALCL (anaplastic large cell lymphoma) and HD, it was suggested that these lymphomas derive from the precursor cell before the rearrangement of immunogenes. Thus, lymphomas could be divided into two categories, i.e. 1) pre-rearrangement lymphomas (HD and ALCL) and 2) post-rearrangement lymphomas (common NHL).