Chromosome aberrations are restricted to the CD56⁺, CD3^- tumour cell population in natural killer cell lymphomas: A combined immunophenotyping and FISH study

Natural killer (NK) cell lymphomas are a newly recognized entity of non- Hodgkin's lymphoma with a highly aggressive clinical course and strong association with Epstein-Barr virus (EBV) infection. Although no recurrent chromosome aberrations have been identified in NK-cell lymphoma, deletions of 6q and trisomy 7 have been described repeatedly in this type of lymphoma. In this study we attempted to determine the immunophenotypes of turnout cells with certain chromosome aberrations, i.e. deletions of 6q and trisomy 7, in three cases of NK cell lymphomas by means of combined immunophenotyping and fluorescence in situ hybridization (FISH). In all three cases clonal chromosome aberrations were detected only in CD56⁺ cells but not in CD3⁺ or CD5⁺ cells. However, not all CD56⁺ cells were shown to contain these chromosome aberrations. Double immunophenotyping combined with FISH confirmed that the chromosome aberrations occurred only in CD56⁺CD3^- cells. This study indicates that chromosome aberrations in NK-cell lymphomas are restricted to the CD56⁺, CD3^- and CD5^- cell population and that NK-cell lymphomas are indeed derived from mature true NK cells and not from T lymphocytes.