Aggressive NK-cell leukemia

Synonyms and related key words: Aggressive Natural Killer cell leukemia

Overview
Aggressive NK-cell leukemia is a disease with an aggressive, systemic proliferation of natural killer cells (NK cells) and a rapidly declining clinical course.

It is also called aggressive NK-cell lymphoma, or large granular lymphocyte leukemia, NK-cell type

Synonyms
Aggressive NK-cell leukemia/lymphoma, large granular lymphocyte leukemia, NK-cell type

ICD-O code
9948/3

Definition
Aggressive NK-cell leukemia is a disease with an aggressive, systemic proliferation of natural killer cells (NK cells) and a rapidly declining clinical course.

Epidemiology
This rare form a leukemia is more common among Asians in comparison to other ethnic groups. It is typically diagnosed in adolescents and young adults, with a slight predominance in males.

Etiology
This disease has a strong association with the Epstein-Barr virus (EBV), but the true pathogenesis of this disease has yet to be described. The cell of origin is believed to be an NK cell. Blastoid NK cell lymphoma appears to be a different entity and shows no association with EBV.

Presentation
Patients usually present with constitutional symptoms (malaise, weight loss, fatigue), and hepatosplenomegaly is commonly found on physical exam. Lymphadenopathy is also found to a lesser extent. Due to the aggressive nature of the disease, patients may initially present at a more advanced stage, with coagulopathies, hemophagocytic syndrome, and multi-organ failure.

Laboratory findings
Leukemic cells are invariably present in samples of peripheral blood to a variable extent. Pancytopenia (anemia, neutropenia, thrombocytopenia) is commonly seen as well.

Sites of involvement
This disease is typically found and diagnosed in peripheral blood, and while it can involve any organ, it is usually found in the spleen, liver, and bone marrow.

Peripheral blood
The leukemic cells have a diameter mildly greater than a large granular lymphocyte (LGL) and have azurophilic granules and nucleoli of varying prominence. Nuclei may be irregular and hyperchromatic.

Bone marrow
Bone marrow involvement runs the spectrum between an inconspicuous infiltrate to extensive marrow replacement by leukemic cells. Reactive histiocytes displaying hemophagocytosis can been seen interspersed in the neoplastic infiltrate.

Other organs
Leukemic involvement of organs is typically destructive on tissue sections with necrosis and possibly angioinvasion, and the monotonous infiltrate may be diffuse or patchy.

Immunophenotype
The immunophenotype of this disease is the same as extranodal NK/T-cell lymphoma, nasal type and is shown in the table below. CD11b and CD16 show variable expression.

Genetic findings
Due to the myeloid lineage, clonal rearrangements of lymphoid (T cell receptor; B cell receptor) genes are not seen. The genome of the Epstein Barr virus (EBV) is detected in many cases, along with a variety of chromosomal abnormalities.

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