Mast cell leukemia with novel BRAF variant and concomitant atypical KIT variant.

Mast cell leukemia (MCL) is a leukemic variant of systemic mastocytosis defined by mast cells ≥ 20% of marrow nucleated cells. Its incidence is < 1% of all systemic mastocytosis cases [1]. Clinical characteristics and treatment of the disease are not well established and overall prognosis is very poor. We report a case of de novo mast cell leukemia with novel BRAF variant, concomitant KIT exon 9 missense mutation and complex cytogenetic abnormalities. After careful review of the literature we have not found any prior reports of concomitant BRAF and KIT variants, and complex cytogenetic abnormalities in MCL. This case provides evidence that MCL can have wide spectrum of genetic abnormalities as well as accumulation of mutations in various genes including BRAF. This finding may have significant implications for the understanding of pathogenesis, diagnosis, as well as targeted therapy of MCL.