LAUSR

Abstract Background Oncogenic driver alterations in FGFR are present in a subset of pediatric gliomas. Debio1347 is an orally available, highly selective FGFR 1–3 inhibitor that had a favorable safety profile and encouraging preliminary clinical activity in an adult phase 1 study. Methods Five children with progressive/refractory CNS tumors harboring an FGFR gene alteration following prior therapy were treated with Debio1347 at Memorial Sloan Kettering Cancer Center on single patient use protocols. Patients were treated using the 20 mg tablet formulation at the adult recommended phase 2 dose (80 mg/1.73 m2 * BSA once daily). Toxicities were graded using CTCAEv5.0 and imaging response assessments were performed every 8–12 weeks. RESULTS All AEs were grade 1–2. Most common treatment-related adverse events were hyperphosphatemia, ALT increased and hypoalbuminemia (4 patients). Two patients met criteria for partial response and two patients had stable disease. A 13 month-old patient with a spinal cord high-grade glioma harboring two FGFR1 mutations (V592M, K687E) had tumor reduction of 91.7% maintained for 12 months. A 26-month-old patient with a pilomyxoid astrocytoma harboring an FGFR1-TACC1 fusion had a tumor reduction of 74.5% maintained for 9 months. Molecular characterization of recurrent tumor from this patient demonstrated an NF1 deletion as a novel molecular mechanism of acquired resistance to FGFR inhibition. Prolonged disease stabilization was noted in an eight year-old patient with metastatic suprasellar pilomyxoid astrocytoma harboring an FGFR1 mutation (9 months) and in a 14 year-old patient with posterior fossa glioneuronal tumor harboring an FGFR3-TACC3 fusion (24 months and ongoing). Conclusions Debio1347 demonstrated tolerable toxicity and promising anti-tumor efficacy in pediatric patients with refractory FGFR altered gliomas. Specific attention to growth velocity and clinical symptoms with incorporation of imaging assessment of bone growth is warranted. Candidate biomarkers (FGFR1 V592M and K687E SNVs, FGFR-TACC fusions) may guide patient selection. Further studies in this population are warranted.