Near missed aggressive natural killer cell leukaemia – importance of extensive immunophenotyping

Aggressive natural killer cell leukaemia (ANKL) is a rare neoplasm of NK cells with poor prognosis, varied morphology and positivity for CD2, CD3 epsilon and CD56, negative for surface CD3 and CD5. A 32-yearold man presented with high grade fever, generalized weakness, significant weight loss in the last 2 months and a lower limb mass, diagnosed elsewhere as Ewing sarcoma. He initially presented with TLC of 8000/uL which drastically increased to 52000/uL, with presence of atypical lymphoid cells. Bone marrow aspiration and biopsy was performed, bone marrow aspirate showed 44% atypical lymphoid cells that were 1.5 to 2 times the size of red blood cells with scant blue agranular cytoplasm, clumped chromatin and inconspicuous nucleoli, and flow cytometric immunophenotyping showed atypical lymphoid cells that were positive for CD45, CD38 and CD 56 and negative for CD34, CD3, CD4, CD5, CD7, CD8, CD20, CD10, CD19, CD138, kappa and lambda. Since a definitive diagnosis could not be reached on this, IHC on bone marrow biopsy was done, which showed the atypical lymphoid cells to be positive for CD45, CD3, CD2, CD56, CD38 and negative for CD117, CD5, CD7, CD30, CD20, CD57 and EBV. A diagnosis of aggressive natural killer lymphoma was reached. The diagnosis was difficult as the morphology and flow cytometry did not show any specific features of ANKL. The diagnosis was made after extensive immunophenotyping on bone marrow biopsy. This highlights the importance of doing NK cell markers when basic panel of antibodies are not supportive.