Advanced systemic mastocytosis—Revised classification, new drugs and how we treat

Mastocytosis constitutes the neoplastic proliferation of mast cells and is broadly classified into systemic mastocytosis (SM), cutaneous mastocytosis and mast cell sarcoma. SM is further partitioned into advanced (AdvSM) and non-advanced (SM-non-Adv) subcategories. AdvSM includes aggressive SM (ASM), SM with an associated haematological neoplasm (SM-AHN) and mast cell leukaemia (MCL). In 2022, two separate expert committees representing the 5th edition of the World Health Organization (WHO5) and the International Consensus (ICC) classification systems submitted revised classification criteria for SM, highlighted by the ICC-proposed incorporation of mast cell cytomorphology in the diagnostic criteria for MCL and myeloid-lineage restriction for the AHN component in SM-AHN. Recent developments in SM also include the introduction of KIT-targeting tyrosine kinase inhibitors (KITi), including midostaurin and avapritinib, both drugs have shown potent activity in reducing mast cell and mutant KIT burden and alleviating mast cell-associated organopathy and mediator symptoms; however, their overall impact on survival or superiority over pre-KITi era treatment options (e.g. cladribine) has not been studied in a controlled setting. In the current review, we provide a summary of recent changes in disease classification and an analysis of recent clinical trials and their impact on our current treatment approach in AdvSM.