CD5(-) CD56(-CELL RECEPTOR SILENT PERIPHERAL T-CELL LYMPHOMAS ARE NATURAL-KILLER-CELL LYMPHOMAS() T)

Non-Hodgkin's lymphomas are divided into B- and T-cell neoplasms. The existence and the clinical relevance of lymphomas derived from the thi rd lymphocyte lineage, ie, natural killer (NK) cells are still controv ersial. NK cells are lymphocytes that mediate cytotoxicity without pri or sensitization. NK cells also have phenotypic and genotypic characte ristics: they express the NK-related antigen CD56, T-cell markers such as CD2 and CD7, but do not express CD5 and T-cell receptor (TCR) prot eins, and their TCR locus is not rearranged. Therefore, if NK cell lym phomas exist, they should express some T-cell markers, but not alpha b eta or gamma delta TCR proteins. Such lymphomas are actually called TC R silent peripheral T cell lymphomas (PTCL). To detect and characteriz e NK cell lymphomas, we investigated the immunophenotype and immunogen otype of 35 patients with TCR silent PTCL. The first group included 16 patients with a lymphoma of CD5(-) CD56(+) phenotype, which is identi cal to normal NK cells. These patients had either a nasal/nasopharynge al lymphoma (11 cases) or a lymphoma with predominant non-nasal/non-no dal initial involvement (five cases). Eight of the nine cases for whic h immunogenotypic data were available lacked clonal rearrangement of t he TCR gamma genes. Thus, these tumors are likely to be NK cell lympho mas. The second group of 15 cases had a CD5(+) phenotype (14 were CD56 (-), and 1 was CD56(+)) and clonal rearrangement of TCR gamma genes, i ndicating that they were true PTCL with unproductive TCR rearrangement . The four remaining cases were CD5(-) CD56(-) lymphomas and disclosed either a clonal (two cases) or no clonal (two cases) rearrangements o f the TCR gamma genes. Altogether these findings show that CD5(-) CD56 (+) so-called ''TCR silent PTCL'' bear the immunophenotype and immunog enotype of normal NK cells and display peculiar clinical features dist inct from true PTCL. (C) 1996 by The American Society of Hematology.