PURPOSETo estimate the maximum-tolerated dose (MTD) of erlotinib administered during and after radiotherapy, and to describe the pharmacokinetics of erlotinib and its metabolite OSI-420 in patients between 3 and 25 years with newly diagnosed high-grade glioma who did not require enzyme-inducing anticonvulsants.EXPERIMENTAL DESIGNFive dosage levels (70, 90, 120, 160, and 200 mg/m(2) per day) were planned in this phase I study. Dose-limiting toxicities (DLT) were evaluated during first 8 weeks of therapy. Local radiotherapy (dose between 54 and 59.4 Gy) and erlotinib started preferentially on the same day. Erlotinib was administered once daily for a maximum of 3 years. Pharmacokinetic studies were obtained after first dose and on day 8 of therapy. Mutational analysis of EGFR kinase domain, PIK3CA, and PTEN was done in tumor tissue.RESULTSMedian age at diagnosis of 23 patients was 10.7 years (range, 3.7-22.5 years). MTD of erlotinib was 120 mg/m(2) per day. Skin rash and diarrhea were generally well controlled with supportive care. Dose-limiting toxicities were diarrhea (n = 1), increase in serum lipase (n = 1), and rash with pruritus (n = 1). The pharmacokinetic variables of erlotinib and OSI-420 in children were similar to those described in adults. However, there was no relationship between erlotinib dosage and drug exposure. No EGFR kinase domain mutations were observed. Two patients with glioblastoma harbored mutations in PIK3CA (n = 1) or PTEN (n = 1).CONCLUSIONSAlthough the MTD of erlotinib in children with newly diagnosed high-grade glioma was 120 mg/m(2) per day, pharmacokinetic studies showed wide interpatient variability in drug exposure.