In this case report, we describe two patients with systemic mastocytosis with an associated haematological neoplasm. The KIT c.2447A>T;p. (Asp816Val) (D816V) mutation, the original driver mutation of mastocytosis, can, in combination with additional genetic abnormalities, drive the clonal evolution towards an additional myelodysplastic or myeloproliferative neoplasia. When patients present with a dominant phenotype of the latter neoplasia, which is often the cause in chronic myelomonocytic leukaemia (CMML) or acute myeloid leukaemia (AML), the original mastocytosis could be overlooked, missing therapeutic opportunities.

(BELG J HEMATOL 2023;14(4):178–82)