Aggressive Natural Killer Cell Leukemia in an Adult With Establishment of an NK Cell Line

Abstract

There have been many reports of cases in which chronic increases in the numbers of natural killer (NK) cells have been reported. Whether this is reactive or neoplastic in nature has been debated. We report the first case of an aggressive NK cell leukemia in an adult with establishment of an NK cell line. A 70-year-old man had two spontaneous episodes of jejunal perforation and one month later developed a severe febrile illness with moderate splenomegaly. Hemoglobin was 13.1 g/L, and WBC count was 1.8 X 10(9)/L with 2% large granular lymphocytes (LGLs). Platelet count was 143 X 10(9)/L; prothrombin time (PT) and partial thromboplastin time (PTT) were normal. Bone marrow was infiltrated with 25% to 30% LGLs; serum lysozyme was normal. Serum LDH was initially 1,191 U/L and rose to 6,408 (normal 240 to 525 U/L). Ten days later, the WBC count increased to 99.9 X 10(9)/L with 70% LGL cells; the PT and PTT increased, and the platelet count dropped. No bacterial or viral cause of fever was identified. The cells from peripheral blood were LGLs that stained positively for acid phosphatase. All of the LGLs reacted with a monoclonal antibody reactive with NK cells (LEU-11b). Functionally, the patient's peripheral blood mononuclear cells (PBMs) demonstrated 100 times more lytic activity against K562 tumor cell lines than did normal PBMs. The patient's PBMs were propagated in vitro. The cultured cells showed the morphological, cytochemical, immunological, and functional characteristics of NK cells. In addition, partial trisomy involving chromosome 1 q with duplication in regions of q21 through q31 was observed in all metaphases analyzed. The extra chromosome 1q with duplication in regions q21 through q31 was translocated to the p-terminal of chromosome 5. One percent to 5% of normal PBMs comprise NK cells; in most cases, leukemias arise from normal phenotypic counterparts. This case demonstrated that aggressive NK cell leukemia may occur in adults. In addition, the chromosomal abnormalities suggest that this is not a reactive process but a malignancy.