Natural Killer Cell Lymphoblastic Leukaemia/Lymphoma: Case Report and Review of the Recent Literature.

Natural killer (NK) cell lymphoblastic leukaemia/lymphoma is a rare haemopoietic tumour currently defined in the 2008 WHO classification under the category of acute leukaemias of ambiguous lineage. A diagnosis of this type of leukaemia is considered in cases expressing CD56 along with immature T-cell-associated markers such as CD2 and CD7 with absence of B-cell and myeloid markers; in addition, blastic plasmacytoid dendritic cell leukaemia should be excluded. Prior to 2008, these precursor NK cell lymphoblastic leukaemias/lymphomas were categorized as myeloid/NK cell acute leukaemia with a phenotype identical to acute myeloid leukaemia with minimal differentiation. While the new classification has merit in having excluded myeloid expression, there is still persistent confusion in the literature and on a practical level with regard to precursor NK cell neoplasms. There is a paucity of recent case reports in the literature after the new WHO classification of this neoplasm. Due to the rarity of this neoplasm, an accurate pathological diagnosis is often difficult. In this article, we describe a case of precursor NK cell lymphoblastic leukaemia/lymphoma presenting with unique morphological features and conflicting immunophenotypes. We also review all case reports of this neoplasm after the WHO 2008 classification.