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-Hod gkin's lymphoma with a highly aggressive clinical course and strong associa tion with Epstein-Barr virus (EBV) infection. Although no recurrent chromos ome aberrations have been identified in NK-cell lymphoma, deletions of 6q a nd trisomy 7 have been described repeatedly in this type of lymphoma. In th is study we attempted to determine the immunophenotypes of tumour cells wit h certain chromosome aberrations, i.e. deletions of 6q and trisomy 7, in th ree cases of NK cell lymphomas by means of combined immunophenotyping and f luorescence in situ hybridization (FISH). Tn all three cases clonal chromos ome aberrations were detected only in CD56(+) cells but not in CD3(+) or CD 5(+) cells. However, not all CD56(+) cells were shown to contain these chro mosome aberrations, Double immunophenotyping combined with FISH confirmed t hat the chromosome aberrations occurred only in CD56(+)CD3(-) cells. This s tudy indicates that chromosome aberrations in NK-cell lymphomas are restric ted to the CD56(+), CD3(-) and CD5(-) cell population and that NK-cell lymp homas are indeed derived from mature true NK cells and not from T lymphocyt es.