EPSTEIN-BARR-VIRUS (EBV) IN EXTRANODAL T-CELL NON-HODGKINS-LYMPHOMAS (T-NHL) - IDENTIFICATION OF NASAL T-NHL AS A DISTINCT CLINICOPATHOLOGICAL ENTITY ASSOCIATED WITH EBV

T-cell Non-Hodgkin's lymphomas (T-NHL) can be defined as clonal malign ant proliferations related phenotypically and functionally to normal T -cell populations of the lymphoid tissue. There is increasing evidence that T-NHL with similar morphology but originating from different sit es differ in their clinical behaviour, immunophenotypic features, onco gene expression and relation with oncogenic viruses such as HTLV-I and EBV. Indeed, it has been shown that the prevalence of EBV in T-NHL is related to the site of origin. Thus, EBV was found in nearly all nasa l T-NHL but only in a proportion of primary nodal, lung, gastrointesti nal and Waldeyer's ring T-NHL while it was undetectable in most primar y cutaneous T-NHL. Besides their constant association with EBV, nasal T-NHL display peculiar clinical, histological, immunophenotypic and ge notypic features. They present clinically as lethal midline granuloma and histologically as pleomorphic malignant tumours variably associate d with angiocentricity, angioinvasion and necrosis. Moreover, they fre quently exhibit extensive loss of T-cell antigens, including CD3 and T CR alpha beta and gamma delta proteins, usually express the Natural Ki ller (NK)-related CD56 antigen and frequently show absence of clonal r earrangements of TCR beta, gamma and delta loci. Therefore, among T-NH L, nasal T-NHL can be regarded as a distinct clinicopathologic entity associated with EBV, which could be derived either from immature T-cel ls or from NK cells.