A Phase I and Pharmacokinetic Study of Oral Dabrafenib in Children and Adolescent Patients with Recurrent or Refractory BRAF V600 Mutation–Positive Solid Tumors

Purpose: The 2-part, phase I/IIa, open-label study (NCT01677741) sought to determine the safety, tolerability, pharmacokinetics, and preliminary activity of dabrafenib in pediatric patients with advanced BRAF V600–mutated cancers. Patients and Methods: This phase I dose-finding part treated patients ages 1 to <18 years with BRAF V600 mutation–positive tumors with oral dabrafenib 3 to 5.25 mg/kg/day to determine the RP2D based on safety and drug exposure target. Results: Between May 2013 and November 2014, 27 patients [12 male; median age, 9 years (range, 1–17 years)] with BRAF V600–mutant solid tumors recurrent/refractory to treatment (low- or high-grade glioma, Langerhans cell histiocytosis, neuroblastoma, or thyroid cancer) were enrolled. The median treatment duration was 75.6 weeks (range, 5.6–148.7 weeks), with 63% treated for >52 weeks and 52% undergoing treatment at data cutoff date. The most common grade 3/4 adverse events suspected to be related to study drug were maculopapular rash and arthralgia (2 patients each). No dose-limiting toxicities were observed. Pharmacokinetic analyses showed a dose-dependent increase in AUC0–12 and achievement of adult exposure levels at the recommended phase II doses of 5.25 mg/kg/day (age <12 years) and 4.5 mg/kg/day (age ≥12 years) divided into 2 equal doses daily, not exceeding 300 mg daily. Conclusions: In this first clinical trial in pediatric patients with pretreated BRAF V600–mutant tumors, dabrafenib was well tolerated while achieving target exposure levels; the average treatment duration was >1 year with many patients still on treatment. The phase II component is also closed and will be reported separately.