T-ALL natural killer cell leukemia (T-ALL NK), diagnosed in a 50-year old male, had an immunophenotypic picture showing CD45 bright+ as well as cytoplasmic myeloperoxidase (cMPO)-negative blasts and marked leukocytosis with 85-90% large-sized lymphoid cells (having high N:C ratio, clumped chromatin and cytoplasmic granules with 1-2 prominent gated nucleoli). The gene discussed is MPO; the disease is aggressive NK-cell leukemia.