KIT and mastocytosis: Researches have demonstrated KIT mutation D816V as one of the most common resistance to imatinib and sunitinib,[19] while dasatinib has been shown to overcome the resistance.[20] In a clinical trial involving 50 patients with advanced GIST, dasatinib was proven to increase 6-month progression-free survival by 30%.[21] Therefore, we chose dasatinib to treat systemic mastocytosis in this case.