[Morphology, immunohistochemistry and genetics of peripheral T cell lymphomas]

T-cell lymphomas are relatively rare in our material; they comprise less than 20% of all non-Hodgkin's lymphomas. A definitive classification of the T-cell lymphomas still does not exist. Nonetheless, it is now possible to distinguish thymic and prethymic, i.e. lymphoblastic lymphomas, from postthymic, i.e. peripheral T-cell lymphomas. Of the peripheral T-cell lymphomas the following are relatively well defined: chronic lymphocytic leukemia of T type (T-CLL) and prolymphocytic leukemia of T type (T-PLL), mycosis fungoides and Sézary's syndrome, lymphoepithelioid lymphoma (Lennert's lymphoma), T-zone lymphoma T-immunoblastic lymphoma, and large cell anaplastic lymphoma (so-called Ki1 lymphoma). Recently, a T-cell lymphoma termed lymphogranulomatosis X (AILD)-type was defined whose chromosomal abnormalities and rearrangement of the beta-chain of the T-cell receptor appear to distinguish it from cases of non-neoplastic lymphogranulomatosis X. Histological and cytochemical criteria enable the identification of many cases of T-cell lymphoma. By contrast, the large number of available monoclonal antibodies can do little more than confirm the T-cell nature and proliferation rate of the tumor cells. DNA rearrangement techniques now make it possible to distinguish between polyclonal and monoclonal T-cell proliferations. Lymphoepithelioid lymphoma, lymphogranulomatosis X and large cell anaplastic lymphoma (Ki1 lymphoma) are treated in detail. The boundary between Hodgkin's disease and peripheral T-cell lymphoma is not as distinct as textbooks would make it appear.