KIT and systemic mastocytosis: Recently, two new categories previously not included in the World Health Organization classification system were described: clonal mast cell activation disorders characterized by recurrent episodes of idiopathic anaphylaxis, absence of skin lesions and the presence of only one or two minor World Health Organization criteria for systemic mastocytosis;15,16,17 and well differentiated systemic mastocytosis characterized by mast cells with normal morphology, absence of CD25 and CD2 expression and detection of KIT mutations other than D816V.