Mast cells are primary effector cells in allergic inflammation, where they cause symptoms related to mediators produced and released after mast cell activation. Understanding mast cell growth and differentiation is critical for deciphering the pathophysiology of allergic inflammation and developing new therapies [1]. Mastocytosis is a condition characterized by a pathologic accumulation of mast cells in tissues. It offers a unique opportunity to study the growth and differentiation of mast cells and their contribution to various pathologic processes. The molecular pathways regulating the proliferation and survival of mast cells are strikingly similar between normal mast cells and mast cells involved in mastocytosis. KIT, a transmembrane receptor for stem cell factor (SCF) is critical for normal mast cell growth and differentiation, and yet activating mutations in c-kit are often implicated in the etiology of mastocytosis [2].