HTLV‐positive and ‐negative T‐cell lymphomas. Morphological and immunohistochemical differences between european and HTLV‐positive japanese T‐cell lymphomas

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Abstract
A total of 56 cases of malignant lymphoma presumed to be of peripheral T‐cell origin were investigated with regard to histological and immunohistochemical features. The goal of the study was to determine whether virus‐associated T‐cell lymphomas can be morphologically or immunohistochemically distinguished from presumably virus‐negative T‐cell lymphomas. The cases came from endemic and nonendemic regions of Japan, the United Kingdom (including 4 Caribbean cases) and the Federal Republic of Germany. Sera of all Japanese and Caribbean patients and 8 German patients were tested for antibodies to adult T‐cell leukaemia virus‐associated antigen HTLV‐A. In all cases sections were examined blind by 5 welltrained histopathologists. In most cases cryostat sections could be prepared from fresh tissue specimens and stained with a large panel of monoclonal antibodies. All HTLV‐A‐positive cases were morphologically classifiable as the pleomorphic type of T‐cell lymphoma. Approximately 70% of the tested cases of pleomorphic T‐cell lymphoma, however, showed a positive serum reaction for HTLV‐A. All other types of peripheral T‐cell lymphoma (T‐immunoblastic lymphoma, chronic lymphocytic leukaemia of T type, T‐zone lymphoma, “AILD type” and lymphoepithelioid cell lymphoma) were HTLV‐A‐negative and mostly observed in European patients. Thus virus‐associated T‐cell lymphomas appear to be invariably of the pleomorphic type; but pleomorphism is not specific to HTLV‐A‐positive cases. This was also evident from the results of an experiment in which 2 Japanese histopathologists attempted to recognize HTLV‐A positivity in a blind study of pleomorphic T‐cell lymphomas. A maximum of about 80% of cases were correctly identified, with about 10% false‐positive diagnoses (in HTLV‐A‐negative or presumably negative cases) and 10% false‐negative diagnoses. The immunohistochemical analysis revealed not only many common features but also 2 distinct differences between HTLV‐A‐positive and ‐negative T‐cell lymphomas. All but one of the HTLV‐A‐positive cases showed reactivity with anti‐Tac and all cases in the virus‐positive group were negative for TÜ14. All other cases were Tac‐negative and approximately 65% of these cases exhibited reactivity with TÜ14. Preliminary cytogenetic observations suggest that there are also differences in specific chromosome aberrations.