KIT and systemic mastocytosis: Unlike classic SM, which is characterized by aberrant MC morphology, such as spindle shapes and hypogranulation, and associated with the KIT D816V mutation [1], a subgroup of patients (<10% of all SM) present with well-differentiated SM (WDSM), characterized by a mature MC morphology (round, fully granulated) and a reduced frequency of KIT D816V mutations compared with other forms of SM (29% vs. 93%) [18,19].