Systemic Mastocytosis: a (slightly) Simplified Diagnostic Approach

This presentation which addresses changes and updates in mastocytosis is based on the recently published International Consensus Classification of myeloid neoplasms (Arber DA, Orazi A, Hasserjian RP, et al. Blood 2022; 140: 1200–1228). Mastocytosis is a neoplastic disease characterised by a clonal proliferation of mast cells, which accumulate in one or multiple organs. The disease includes three clinicopathologic types. It can be limited to the skin (cutaneous mastocytosis), a condition mostly occurring in childhood that usually behaves in a benign fashion. Adult patients usually present with systemic disease, i.e., systemic mastocytosis (SM). This includes indolent subtypes such as indolent SM, its subvariant termed bone marrow mastocytosis, and smoldering SM. Aggressive SM subtypes include aggressive SM and mast cell leukaemia. The latter represents a proliferation of immature and atypical mast cells (promastocytes, metachromatic blasts or pleomorphic poorly differentiated forms) which account for > 20% of the marrow aspirate cellularity. SM with an associated myeloid neoplasm represents the fifth subtype of SM. A separate type of mast cell neoplasm is mast cell sarcoma, a rare aggressive form of localised mast cell proliferation that can present in the skin, bone, and in other organs, and can progress to mast cell leukaemia. Reference 1. Leguit RJ, Wang SA, George TI, Tzankov A, Orazi A. The international consensus classification of mastocytosis and related entities. Virchows Arch 2022; doi: 10.1007/s00428-022-03423-3. Epub ahead of print. PMID: 36214901.