Mature natural killer (NK) cell neoplasms are classified by the World Health
Organization into NK/T cell lymphoma, nasal type (NKTCL), aggressive NK-cell
leukemia (ANKCL) and chronic lymphoproliferative disorders of NK-cells, the
latter being considered provisionally. NKTCL and ANKCL are rare diseases, with
higher prevalence in Asia, Central and South America. Most NKTCL present
extranodal, as a destructive tumor affecting the nose and upper aerodigestive
tract (nasal NKTCL) or any organ or tissue (extranasal NKTCL) whereas ANKCL
manifests as a systemic disease with multiorgan involvement and naturally
evolutes to death in a few weeks. The histopathological hallmark of these
aggressive NK-cell tumors is a polymorphic neoplastic infiltrate with
angiocentricity, angiodestruction and tissue necrosis. The tumor cells have
cytoplasmatic azurophilic granules and usually show a CD45+bright,
CD2+, sCD3-, cytCD3epsilon+,
CD56+bright, CD16−/+, cytotoxic granules
molecules+ phenotype. T-cell receptor genes are in germ-line
configuration. Epstein-Barr virus (EBV) -encoded membrane proteins and early
region EBV RNA are usually detected on lymphoma cells, with a pattern suggestive
of a latent viral infection type II. Complex chromosomal abnormalities are
frequent and loss of chromosomes 6q, 11q, 13q, and 17p are recurrent
aberrations. The rarity of the NK-cell tumors limits our ability to standardize
the procedures for the diagnosis and clinical management and efforts should be
made to encourage multi-institutional registries.