KIT and neoplasm: Prior molecular analysis is crucial in order to prevent patients with less sensitive or resistant tumours (e.g. PDGFRA D842V mutations) from receiving therapy with imatinib, and also to allow appropriate dosing for patients with KIT exon 9 mutated tumours, i.e. 800 mg daily, if permitted, and potentially patients with PDGFRA D842V mutations which in the future may be pre-treated with avapritinib, or other new agents as they become available (see section on systemic treatment below).