T-cell chronic lymphocytic leukaemia: the spectrum of mature T-cell disorders

Mature (post-thymic) T-cell malignancies comprise a heterogeneous group of diseases with distinct clinical, morphological and immunophenotypic features. As some of these features overlap in the various disorders, it is essential to use a number of diagnostic criteria to define the clinicopathological entities, namely: membrane markers, morphology by light and electron microscopy, clinical features, seroepidemiology of HTLV-I, histopathology, cytogenetic studies and DNA analysis. The latter, which is necessary to document clonality and confirm T-lineage, examines the rearrangement of the T-cell receptor beta, gamma and delta genes. By means of this multiparameter approach, it is possible to distinguish within the post-thymic leukaemias 4 disease entities: T-chronic lymphocytic leukaemia or large granular lymphocyte leukaemia, T-prolymphocytic leukaemia, adult T-cell leukaemia/lymphoma and Sézary syndrome.