PDGFRB and aggressive systemic mastocytosis: Two of these patients only had transient improvement of symptoms [35], one had CM associated with HES and actually showed CR of HES with persistence of (cutaneous) mastocytosis lesions [31], one ASM patient with an associated eosinophilia and PDGFRβ gene rearrangement achieved CR [63], and the remaining patient showed PR consisting of 50% reduction of BM MC counts after therapy [64].