Expression of μ-BCR-ABL transcripts in chronic neutrophilic leukemia

The classification of chronic neutrophilic leukemia (CNL) is controversial. Our purpose was to correlate clinical, pathologic, and molecular analyses in 2 cases of CNL. In both cases, the patients were referred because of a substantially increased peripheral WBC count noted during routine examination. Bone marrow biopsies and aspirate smears revealed hypercellularity with myeloid/erythroid ratios of 4:1 and 11:1, respectively. The bone marrow aspirate results were as follows: case 1: blasts, 2%; promyelocytes, 2%; myelocytes, 6%; metamyelocytes, 16%; band neutrophils, 13%; segmented neutrophils, 34%; and case 2: blasts, 1%; promyelocytes, 2%; myelocytes, 15%; metamyelocytes, 20%; band neutrophils, 24%; neutrophils, 19%. Reverse transcriptase in situ polymerase chain reaction studies demonstrated expression of μ-BCR-ABL transcripts in 13% and 25% of the bone marrow cells, respectively. In both cases, the positive signal was noted mainly in the early granulocytic precursors and was present in occasional mature neutrophils. To our knowledge, this is the first in situ demonstration of μ-BCR-ABL expression in CNL. Our findings reinforce the usefulness of this messenger RNA as a molecular marker of CNL.