The association of systemic mastocytosis with another hematologic neoplasia of myeloid or lymphoid origin is recognized as an advanced subvariant of mastocytosis. Here, we report the association of indolent or smoldering systemic mastocytosis with three cases of myelodysplastic/myeloproliferative neoplasms with ring sideroblasts and thrombocytosis, a recently recognized disease characterized by SF3B1 mutations. The hierarchical pattern of KIT, SF3B1, JAK2, and additional mutations was studied in whole and fractionated subpopulations of peripheral blood cells and whole bone marrow. In two cases, we could demonstrate a multilineage D816V KIT mutation, involving all myeloid lineages in one patient and also the lymphoid series in the other. Two patients displaying both SF3B1 and V617F JAK2 mutations had a very poor prognosis. Another patient bearing SF3B1, but not V617F JAK2 mutation, had a favorable response to erythropoietin treatment and long survival.
