Phase II Trial of Vandetanib in Children and Adults With Wild-Type Gastrointestinal Stromal Tumors

Background: * Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumor of the gastrointestinal tract, resistant to cytotoxic chemotherapy and radiation therapy. KIT and platelet derived growth factor receptor alpha (PDGFRA) mutations have been identified as tumor initiating events in 85% of adult patients with GIST, but 85% of GISTs in pediatric patients lack KIT and PDGFRA mutations (wild-type) and imatinib is not as effective in eliciting objective responses. * Recent work in the Pediatric and Wild-Type (wt) GIST Clinic at the National Cancer Institute (NCI) led to the identification of succinate dehydrogenase (SDH) germline mutations in 12% patients with wt-GIST (6/34). SDH protein expression evaluated using immunohistochemistry (IHC) was markedly decreased or absent in 18/18 patients with pediatric wt-GIST. Thus the majority of wt-GIST are SDH-deficient. Vandetanib (ZACTIMA; ZD6474; AstraZeneca) is an oral small molecule antineoplastic drug that inhibits vascular endothelial growth factor receptor 2 (VEGFR2), estimated glomerular filtration rate (EGFR), and rearranged during transfection (RET)-dependent signaling. Preliminary preclinical data demonstrate marked growth inhibition of SDH-mutant/deficient renal cell carcinoma cell lines when treated with vandetanib. Objective(s): -Primary: To assess the clinical activity (radiographic response Response Evaluation Criteria in Solid Tumors (RECIST v1.1) of vandetanib in children and adults with wt-GIST using RECIST (v1.1). Eligibility: -Adults and children with measurable localized or metastatic wt-GIST confirmed in a Clinical Laboratory Improvement Amendments (CLIA) laboratory will be eligible for trial participation. Patients must have measurable disease by RECISTv1.1 and adequate organ function. Design: * This phase II trial will determine whether daily oral vandetanib is active in patients with wt-GIST. Vandetanib activity will be assessed primarily by radiographic response of measurable disease using RECISTv1.1. * Vandetanib will be administered orally once daily continuously in the absence of toxicity or disease progression, using a 28-day cycle. * Patients will be carefully monitored for toxicity and response. A small, optimal two-stage phase II design with a target response rate of 25% will be used. Nine evaluable patients will be enrolled initially. If 1 or more of the first 9 have a response, then accrual would continue until a total of 24 patients have enrolled. If there are 3 or more responses in 24 (12.5% or more) patients, then this would be sufficiently interesting activity to warrant further study.