Aleukemic variant of mast cell leukemia.

A woman was admitted with fatigue, icterus, thrombocytopenia (77 109/L), normocytic anemia (9.8 g/dL), and a normal white blood cell count (8.5 109/L). The peripheral blood smear showed metamyelocytes, myelocytes, monocytes, erythroblasts, and atypical cells with bilobulated nuclei resembling basophil granulocytes (left panel of figure). In the bone marrow there was a nearly complete infiltration with atypical, partly degranulated mast cells expressing surface markers (CD2, CD25, and CD117; right panel of figure). These cells were also positive for c-KIT mutation (D816V). Tryptase levels in serum were elevated (719 g/L, normal value: 0-11.4 g/L) in the absence of symptoms arising from mediator release.