KIT and systemic mastocytosis: While MML is characterized by diffusely distributed immature cells lacking CD2 and CD25 expression and the c-KIT D816V mutation, other entities in the differential diagnosis present with distinct characteristics: systemic mastocytosis and SM-AHN typically show dense clusters of mature mast cells, mast cell leukemia demonstrates a predominance of immature mast cells, and all these classic mast cell disorders share common features including CD117 and tryptase expression, aberrant CD2 and/or CD25 expression, and the presence of c-KIT D816V mutation in most cases [4, 7, 8].