Purpose: A phase II study was performed to determine the efficacy of irinotecan (IRN) in children with refractory solid tumors. Secondary objectives were to evaluate toxicity, pharmacokinetics, pharmacodynamics, and UGT1A1 genotype.
Patients and methods: A total of 181 patients were enrolled, of whom 171 were eligible. Patients received IRN 50 mg/m2/d for 5 days repeated every 3 weeks. Pharmacokinetic studies and UGT1A1 genotyping were performed.
Results: Of 161 patients assessable for response, one patient with hepatoblastoma had a complete response, with partial responses observed in patients with medulloblastoma (n = 4), rhabdomyosarcoma (n = 1), neuroblastoma (n = 1), and germinoma (n = 1), for an overall response rate of 5%. Grade 4 neutropenia and grade 3 to 4 diarrhea occurred in less than 7% of the courses administered. Pharmacokinetic studies were available for 79 patients. The mean +/- standard deviation IRN plasma clearance was 374 +/- 148 mL/min/m2, with median relative extent of conversion and relative extent of glucuronidation of 0.05 (range, 0.01 to 0.25) and 2.24 (range, 0.39 to 9.6), respectively. No association between UGT1A1 genotype (n = 61) and toxicity or pharmacokinetic parameters was observed.
Conclusion: IRN 50 mg/m2/d for 5 days every 21 days is well tolerated, but was not effective as a single agent in a spectrum of solid tumors, with the possible exception of patients with medulloblastoma (16% response rate). There was no association between UGT1A1*28 genotype and toxicity or pharmacokinetic parameters.