SM is further subclassified as indolent mastocytosis, SM with associated clonal hematological non-mast-cell lineage disease, aggressive mastocytosis, mast cell leukemia, mast cell sarcoma, and extracutaneous mastocytoma. Cytogenetics: no specific abnormality; ∼30% reported to have clonal abnormalities, del(20q), del(11q) is the most frequently reported.⁴⁶  Patients with SM with associated clonal hematological non-mast-cell lineage disease may exhibit cytogenetic abnormality of the associated neoplasm. Molecular genetics: most cases have the KIT D816V mutation, but detection depends on the sensitivity of the method and the number of neoplastic cells in the specimen. Mutations of TET2 occur in ∼30% of SM often associated with monocytosis with or without mutated KIT. Less frequent mutations include JAK2 V617 and N-RAS.²²