Target-driven exploratory study of imatinib mesylate in children with solid malignancies by the Innovative Therapies for Children with Cancer (ITCC) European Consortium

Aim: To explore imatinib efficacy and pharmacokinetics in children and adolescents with refractory/relapsing solid tumours, expressing imatinib-sensitive receptor tyrosine kinases. Methods: Exploratory study on imatinib in tumours expressing, at least, one of the receptors KIT or platelet-derived growth factor receptor (PDGFR). Standard radiological response evaluation, pharmacokinetics, gene mutations and positron emission tomography imaging were assessed. Results: Thirty-six patients (median age: 13.7 years) with brain (12), mesenchymal/bone (14) or other solid tumours, received imatinib 340 mg/m²/d over a total of 255 months. Fifteen tumours expressed KIT in ≥30% cells, 19 expressed PDGFRA and 25 expressed PDGFRB. Twenty patients experienced grades 1-2 treatment-related toxicities. Ten patients achieved stable disease; one chordoma had metabolic response. Pharmacokinetic data showed high inter-patient variability (variation coefficient: 44% and 53% for plasma imatinib and CGP 74588 AUCs, respectively). Conclusions: Imatinib was tolerated well, but failed to show efficacy according to standard criteria in paediatric malignancies expressing KIT or PDGFR.