PDGFRA and systemic mastocytosis: Ripretinib potently blocked proliferation and KIT phosphorylation and induced apoptosis in GIST cell lines derived from treatment-resistant patients, cell lines of other cancers with KIT or PDGFRA mutations (e.g., systemic mastocytosis and acute myeloid leukaemia) and cell lines transfected with KIT- or PDGFRA-activating mutations [4, 8].