Aggressive mature natural killer cell neoplasms: from epidemiology todiagnosis

Mature natural killer (NK) cell neoplasms are classified by the World Health Organization into NK/T cell lymphoma, nasal type (NKTCL), aggressive NK-cellleukemia (ANKCL) and chronic lymphoproliferative disorders of NK-cells, thelatter being considered provisionally. NKTCL and ANKCL are rare diseases, withhigher prevalence in Asia, Central and South America. Most NKTCL presentextranodal, as a destructive tumor affecting the nose and upper aerodigestivetract (nasal NKTCL) or any organ or tissue (extranasal NKTCL) whereas ANKCLmanifests as a systemic disease with multiorgan involvement and naturallyevolutes to death in a few weeks. The histopathological hallmark of theseaggressive NK-cell tumors is a polymorphic neoplastic infiltrate withangiocentricity, angiodestruction and tissue necrosis. The tumor cells havecytoplasmatic azurophilic granules and usually show a CD45^+bright,CD2⁺, sCD3^-, cytCD3epsilon⁺,CD56^+bright, CD16^−/+, cytotoxic granulesmolecules⁺ phenotype. T-cell receptor genes are in germ-lineconfiguration. Epstein-Barr virus (EBV) -encoded membrane proteins and earlyregion EBV RNA are usually detected on lymphoma cells, with a pattern suggestiveof a latent viral infection type II. Complex chromosomal abnormalities arefrequent and loss of chromosomes 6q, 11q, 13q, and 17p are recurrentaberrations. The rarity of the NK-cell tumors limits our ability to standardizethe procedures for the diagnosis and clinical management and efforts should bemade to encourage multi-institutional registries.