A new International Consensus Classification (ICC) has been published on myeloid neoplasms, including systemic mastocytosis (SM), and acute leukemia. The report, published in Blood, represents a major revision since the last update in 2016.

“Using a multiparameter approach, the main objective of the consensus process was the definition of real disease entities, including the introduction of new entities and refined criteria for existing diagnostic categories, based on accumulated data,” the authors wrote.

“The ICC is aimed at facilitating diagnosis and prognostication of these neoplasms, improving treatment of affected patients, and allowing the design of innovative clinical trials.”

In the new classification, the SM subtype previously known as SM with an associated hematologic neoplasm (SM-AHN) has been changed to SM with an associated myeloid neoplasm (SM-AMN). Additionally, a variant of the indolent SM (ISM) subtype has been described and named bone marrow mastocytosis (BMM).

Read more about SM differential diagnosis

A major refinement of the new ICC involves changes in the criteria for diagnosing SM, which are primarily based on morphology. To ensure proper identification of mast cells, tryptase and KIT (CD117) immunoreactivities have been added to the criteria, given that mast cell aggregates are sometimes not easily recognized in stained sections.

Because CD30 is often aberrantly expressed in SM, it has been added to the second minor criteria as an immunophenotypic finding. Additionally, the identification of a tyrosine kinase gene fusion in association with a myeloid/lymphoid neoplasm with eosinophilia excludes a diagnosis of SM.

Finally, the criteria used to differentiate ISM from smoldering SM, known as the “burden of disease” criteria (“B” findings), have been simplified. The “C” findings remain unchanged.


Arber DA, Orazi A, Hasserjian RP, et al. International Consensus Classification of myeloid neoplasms and acute leukemias: integrating morphologic, clinical, and genomic data. Blood. 2022;140(11):1200-1228. doi:10.1182/blood.2022015850