Detection of Kit D816V Mutation in the Peripheral Blood of Patients with Systemic Mastocytosis Correlates with the Involvement of Multiple Hematopoietic Cell Lineages and Disease Severity
O Simakova, TM Wilson, D Maric, W Fu, J Woelfel, P Noel, DD Metcalfe, I Maric. NIH, Bethesda, MD
Background: Detection of the KIT D816V mutation in patients with systemic mastocytosis (SM) generally requires bone marrow testing; however, in some patients the mutation is also detectable in peripheral blood (PB). Patients with SM do not have circulating mast cells, and the cell type(s) carrying the KIT mutation in PB are not well characterized.
Design: We analyzed purified hematopoietic cell lineages from PB of 21 patients with SM classified according to the WHO criteria (13 indolent, 1 smoldering, 2 SM-AHNMD, 5 aggressive). All 21 patients tested positive for KIT D816V mutation in bone marrow aspirates. Peripheral blood neutrophils, monocytes, eosinophils, T-lymphocytes and B-lymphocytes were separated using flow cytometric sorting and tested for KIT D816V mutation by nested RT-PCR/RFLP.
Results: No increase in circulating mast cells or CD34 positive cells (average 0.03%) was observed in PB of any patient. Three patients had no detectable KIT D816V mutation in any of the 5 investigated cell types. Six patients were positive in only 1 cell type, six patients were positive in 2, four patients were positive in 3, one patient was positive in 4 and one was positive in all 5 (see table). Eosinophils were the most common carrier of the mutation (61% of positive cases), followed by neutrophils (50%) and monocytes (44%). Lymphocytes, particularly B cells were the least common carrier (28%). The number of cell types carrying the mutation significantly correlated with SM variant. Patients with indolent SM had either no detectable mutation or fewer cell lineages involved as compared to patients with more severe disease (1 vs. 2.5 cell types with the mutation; p=0.039). Multilineage involvement significantly correlated with increased serum tryptase levels and the extent of bone marrow mast cell infiltrate.
|Number of KIT positive PB cell types||% of total patients||% of patients with non-indolent SM||% mast cells in BM biopsies (median)||Serum tryptase level (median) ng/ml|