CD2 and systemic mastocytosis: Finally, some patients with SM do not have identifiable variants in KIT (KIT wild type; KIT WT); this is particularly the case in the nearly 70% of patients who present with well-differentiated SM (WDSM), a subset of ISM characterized by the presence of compact multifocal infiltrates of round mature, CD2- and CD25-negative MC in BM [93].