Furthermore, the KIT D816V tissue mutation burden was significantly higher in advanced than in indolent systemic mastocytosis (p=0.001), predicted survival of patients in multivariate analyses independently, and was significantly reduced after response to cytoreductive therapy.
The presence of the KIT D816V mutation in PB of ISM patients is associated with (early) involvement of circulating CD34<sup>+</sup> HPC and multiple myeloid cell subpopulations, KIT-mutated PB CD34<sup>+</sup> HPC potentially contributing to early dissemination of the disease.
Based on all these results, it is hypothesized that KIT D816V as a single hit may be sufficient to cause indolent systemic mastocytosis, whereas additional defects may be required to induce aggressive mast cell disorders.
To our knowledge, this is the first report on the clinical impact of the fraction of KIT D816V mutation positive cells in ISM, which in the present study does not seem to correlate with clinical manifestations of the disease.
Monoclonality for both ISM and B-CLL could be confirmed by demonstrating the typical activating c-kit point mutation D816V in bone marrow MC, and a monoclonal IgH rearrangement in bone marrow B cells.
To study the lineage relationship and the extent of expansion of cells derived from the mutated clone, we examined the occurrence of the Asp816Val c-kit mutation in genomic DNA of individual sorted peripheral blood T cells, B cells, and monocytes in patients with indolent systemic mastocytosis.
However, the KIT D816V mutation was detected using mutation-specific qPCR in both bone marrow and peripheral blood in all 25 cases, demonstrating for the first time that the KIT D816V mutation is consistently present in non-mast cells in indolent systemic mastocytosis and that these cells are circulating in peripheral blood.