Phase 2 trial of imatinib mesylate (IM) for treatment of recurrent or refractory pediatric solid tumors: A Children’s Oncology Group study

8520 Background: In in vitro studies, IM inhibits KIT and PDGF receptor tyrosine kinases. Clinical activity has been demonstrated against gastrointestinal stromal tumors (KIT mutations) and dermatofibrosarcoma protuberans (PDGFR rearrangements). On immunohistochemistal staining, Ewing sarcoma (EWS), osteogenic sarcoma (OS), neuroblastoma (NBL), desmoplastic small round cell (DSRCT) and synovial sarcomas (SS) often over express KIT or PDGF receptor. A pediatric phase 2 study using a 2-stage design was performed. Methods: Patients less than age 30 years of age with refractory or recurrent EWS, OS, NBL, DSRCT, SS or GIST were eligible. IM (440 mg/m2/day) was administered daily for 28 day courses. Doses larger than 600 mg were divided bid. Responses were assessed using RECIST criteria. A minimum of one response in the first 10 patients was required to proceed to the second stage of accrual. The study sought to identify diseases with at least a 25% response rate with a probability of 0.92; three or more respon...