Aggressive NK-cell leukaemia

Definition

A systemic proliferation of NK cells. Overlaps with extranodal NK/T-cell lymphoma and may represent its leukaemic counterpart. The role of EBV in the etiology has been uncertain, but resent studies have shown positivity in both endemic and non-endemic cases1.

Synonyms

Epidemiology

Rare, more commonly found among Asian adolescent and young adults. It may occur in children.

Clinical features

Patients present with fever, constitutional symptoms Hepatosplenomegaly is common, sometimes with lymphadenopathy. Multiorgan failure may occur.

The leukaemia may be subtle. Anaemia, neutropenia and thrombocytopenia are common. There may be a coagulopathy or haemophagocytic syndrome.

Histopathology

Most commonly involves peripheral blood, bone marrow, liver and spleen. The marrow shows infiltration by neoplastic cells, sometimes with reactive histiocytes showing haemophagocytosis. The neoplastic cells often appear monotonous with round nuclei and small nucleoli. Necrosis is common. There may be angioinvasion. Involvement of the bone marrow is patchy and inconsistent2.

The circulating atypical lymphocytes are large with azurophilic cytoplasmic granules2.

Immunohistochemistry

The immunophenotype is the same as that of NK/T-cell lymphoma, nasal type.

Cytogenetics

T-cell gene rearrangements are lacking1.

Differential diagnosis

• Indolent NK-cell lymphoproliferative disorder(chronic NK-cell lymphocytosis, NK-cell large granular lymphocyte lymphocytosis). This occurs mainly in adults. Most patients are asymptomatic, but may have a vasculitis or nephrotic syndrome. There is no fever, hepatosplenomegaly or lymphadenopathy. Red cell aplasia, neutropenia and rheumatoid arthritis are not seen. The immunophenotype of the circulating cells is very similar to that of aggressive NK-cell leukaemia. Some cases transform to an aggressive phase.

• extranodal NK/T lymphoma: shows the same immunophenotype but occurs in an older age group; it usually does not involve lymph nodes or peripheral blood.

Prognosis

The course is usually highly aggressive, despite treatment.

References

World Health Organization Classification of Tumours, Tumours of the haematopoietic and lymphoid tissues, IARC Press 2001.

1VE Nava and ES Jaffe. The pathology of NK-cell lymphomas and leukamias. Adv Anat Pathol 2005;12:27-34.

This page last revised 23.3.2005.

©SMUHT/PW Bishop