Mastocytosis: immunophenotypical features of the transformed mast cells are unique among hematopoietic cells.

Mastocytosis is a disease of bone marrow origin histologically characterized by compact tissue infiltrates of atypical mast cells never seen in reactive states. Most patients with mastocytosis have transformed mast cells carrying an activating point mutation at codon 816 of KIT and also show an elevated serum tryptase level. In this article immunophenotypical features of mast cells are described. Based on these features, mast cells are not closely related to other myeloid cells. Using the knowledge on aberrantly expressed antigens by mast cells, the hematopathologist should be able to recognize the disease even in the presence of unusual morphologic findings or an associated hematologic non-mast cell lineage disease.