Although the presence of more than one KIT mutation has been described in patients with childhood mastocytosis (16) and in instances of acute myeloid leukemia (17) and GIST refractory to treatment (18), most patients with systemic mastocytosis present with D816V-KIT alone (1, 16), emphasizing the need for a neoplastic mast cell model expressing KIT with the single D816V-KIT mutation. This evidence concerns the gene KIT and gastrointestinal stromal tumor.