Regular ArticlesSystemic Mastocytosis Associated with Chronic Idiopathic Myelofibrosis: A Distinct Subtype of Systemic Mastocytosis-Associated Clonal Hematological Nonmast Cell Lineage Disorder Carrying the Activating Point Mutations KITD816V and JAK2V617

In ∼20 to 30% of patients with systemic mastocytosis (SM), an associated clonal hematological nonmast cell lineage disorder (AHNMD) is diagnosed. Although SM may be considered to be closely related to the myeloproliferative disorders (MPDs), it is unknown whether JAK2V617F+ MPD may occur as AHNMD in patients with SM. We here describe five patients with SM and co-existing chronic idiopathic myelofibrosis (SM-CIMF). In five of five patients, we detected the SM-related KIT mutation D816V, and in four of five patients, the MPD-related JAK2 mutation V617F. Surprisingly, JAK2V617F was found not only in the AHMMD component of the disease but also in microdissected mast cells in all four JAK2V617F-positive cases. Conversely, in two of the five patients, KITD816V was found not only in neoplastic mast cells but also in microdissected CD15+ neoplastic myeloid cells. Control experiments showed that 10 indolent SM patients without associated MPD did not carry the JAK2 mutation V617F and that 15 CIMF patients without SM did not carry the KIT mutation D816V. Altogether, these data suggest that KITD816V+ SM can co-exist with JAK2V617F+ CIMF and that, in some of these SM-CIMF cases, the two mutations are present in the neoplastic cells of both disease components.