Peripheral T/NK-cell lymphoma: a report of the IX^th Workshop of the European Assocation for Haematopathology

In April 1998, The European Association for Haematopathology organized the IX^th workshop on peripheral T-cell and NK-cell lymphomas and leukaemias. The workshop focused on unusual subtypes of these rare malignancies, allowing evaluation of the recently published WHO classification of neoplastic diseases of the lymphoid tissues.

 One-hundred and three cases were centrally immunophenotyped and hybridized for EBER1/2 of Epstein–Barr virus. All cases were reviewed by a panel of experienced haematopathologists and classified according to the new WHO classification for lymphoid neoplasms. Three cases were considered as precursor T-cell and 95 cases as peripheral T/NK-cell lymphoma/leukaemia. Although the cases represented a selected series of unusual cases, the following conclusions could be made: (i) Most lymphomas except the hepatosplenic γ/δ T-cell lymphomas showed a rather broad morphological spectrum, with differences both between and within individual tumours. (ii) This heterogeneity was also reflected by the immunophenotype, for instance a variable expression of CD30 was found in many enteropathy type T-cell lymphomas. (iii) Exceptions in phenotype were regularly found in almost all categories, indicating that phenotype should not be the final determining factor in classification. (iv) The great majority of T-cell lymphomas expressed the α/β T-cell receptor, with the exception of all but one hepatosplenic T-cell lymphomas and a few other extranodal peripheral T cell lymphomas. (v) Malignancies of precursor cells, blastic NK-cell lymphoma/leukaemia, adult T-cell lymphoma/leukaemia and most AIL-type T-cell lymphomas did not express cytotoxic molecules such as TIA1 and granzyme-B. In contrast, all five aggressive NK/T-cell lymphomas/leukaemias, a single case of large granular lymphocyte leukaemia and 40 of 47 primary extranodal lymphoma/leukaemias expressed these molecules. In hepatosplenic γ/δ T-cell lymphoma, five of six cases showed expression of TIA1 but not of granzyme-B. (vi) Seven tumours developed after organ-transplant, four cases being EBV-positive. No distinct phenotype could be attributed to these cases.

Most peripheral T/NK cell lymphomas could be categorized as distinct entities as described in the recently proposed WHO classification for lymphoid neoplasms.