PDGFRB and systemic mastocytosis: However, almost one third of such responding cases corresponded to patients with SM associated with either HES/CEL (n = 11/37) [32, 34, 37, 45–47] or chronic basophilic leukemia (n = 1/37) [68] carrying rearrangements of PDGFRα/PDGFRβ; in turn, another 10/37 patients only showed improvement of MC-mediator release-associated symptoms and/or skin lesions [32, 48, 51, 52, 55, 57] Among the remaining 15 cases, 5 fulfilled criteria for CR [18, 49, 51, 53, 54] and 10 were reported to have PR [32, 45, 49, 50, 56].