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2541 Background: BXQ-350 is a novel agent composed of the multifunctional, lysosomal activator protein Saposin C (SapC) and dioleoyl- phosphatidylserine (DOPS) and has demonstrated antitumor effects in both in vitro and in vivo preclinical models. Many tumors, including high-grade glioma and diffuse intrinsic pontine glioma (DIPG), and cells of tumor vasculature have aberrantly exposed phosphatidylserine (PS)-rich domains on the cell surface. BXQ-350 is an anti-tumor agent in development from Bexion Pharmaceuticals, Inc. that selectively targets tumor cell PS, particularly those translocated to the outer leaflet of the plasma membrane in tumor cells. BXQ-350 activates and participates in various cellular processes, including apoptosis and necrosis, and may also exhibit novel mechanisms leading to cell death that require further investigation. Methods: Nine refractory solid (2) and central nervous system (7) tumor patients (5F:4M, age 4-23 years of age) were enrolled in a 2-site dose escalation phase I first-in-pediatric trial ( NCT03967093 ) which completed in 2019. All patients received at least one dose of BXQ-350 which was administered as an intravenous infusion. Dosing began at 1.8 mg/kg and escalated to the highest planned dose level of 3.2mg/kg. Results: There were no BXQ-350-related serious adverse events, dose limiting toxicities, or withdrawals. The highest planned dose of 3.2 mg/kg was achieved safely but a maximum tolerated dose was not established. One osteosarcoma patient had progressive disease prior to completing cycle one of treatment and was removed from trial. Eight patients (DIPG-3, HGG-1, GBM-1, Pineoblasotoma-1, Ependymoma-1, Osteosarcoma-1) completed at least one cycle, with one DIPG patient completing cycle five. Conclusions: BXQ-350 was well tolerated with no significant dose-limiting toxicities at the highest planed dose level. A pediatric phase I trial in newly diagnosed patients is planned for 2nd quarter 2020. Clinical trial information: NCT03967093 .

10009 Background: Entrectinib is a CNS-penetrant oral inhibitor of TrkA/B/C, ROS1 and ALK tyrosine kinases. We report the efficacy of entrectinib in children with recurrent/refractory solid or CNS tumors. Methods: Patients ≤ 20y old with recurrent/refractory solid tumors were eligible. After determination of the recommended dose in all-comers, disease-specific expansion cohorts of CNS and solid tumors harboring target aberrations in NTRK1/2/3, ROS1 or ALK, and neuroblastoma (NBL), regardless of mutation spectrum, were enrolled. Response, assessed by Investigator, was classified as complete response (CR), partial response (PR), stable disease (SD) or progressive disease (PD) using RANO for CNS tumors, RECIST for solid tumors, and Curie score for NBL. Results: Between May 2016 and October 2018, 29 patients aged 4.9m–20y (median 7y) were enrolled and 28 were evaluated for response. Entrectinib was well tolerated. Dose limiting toxicities were elevated creatinine, dysgeusia, fatigue and pulmonary edema. The recommended dose was 550 mg/m2 daily. All responses occurred at doses ≥ 400 mg/m2. In CNS tumors (n = 6), all high-grade with gene fusions: 1 achieved a CR ( ETV6-NTRK3); 3 achieved a PR ( TPR-NTRK1, EEF1G-ROS1, EML1-NTRK2); 1 achieved an unconfirmed PR ( GOPC-ROS1); and 1 has yet to be evaluated ( KANK1-NTRK2). In extracranial solid tumors (n = 8), 6 had a fusion of whom 1 achieved a CR ( DCTN1-ALK) and 5 achieved a PR ( TFG1-ROS1, EML4-NTRK3, ETV6-NTRK3, KIF5B-ALK, ETV6-NTRK3). In NBL (n = 15): 1 achieved a CR ( ALK F1174L). Median duration of therapy was 85d (6–592d) for all patients; 56d (6–338d) for non-responders; and 281d (56–592d) for responders. Median time to response was 57d (30–58d). Conclusions: Entrectinib produced striking, rapid and durable responses in all children with refractory CNS and solid tumors harboring NTRK1/2/3, ROS1 or ALK fusions (11 out of 11) as well as in an ALK-mutated NBL. No responses were seen in tumors lacking aberrations in target kinases. These results support the continued evaluation of entrectinib as a targeted therapeutic in solid tumors with NTRK1/2/3, ROS1 and ALK fusions, especially in high-grade CNS neoplasms. Clinical trial information: NCT02650401.

e18226 Background: Children diagnosed with cancer in low- and middle-income countries (LMIC) have markedly inferior outcomes compared to those in high income countries. While some of these issues can be resource availability, a major problem is the quality of training and traditional methods of clinical practice where decision making is centered on the most senior person on the team. To ensure real change, highly-trained locally based specialists with a strong emphasis on problem-solving and critical thinking using evidence-based approaches are needed. Methods: The Children’s Cancer Hospital Egypt (CCHE-57357) and Dana-Farber Boston Children’s Hospital (DFBCH) at Harvard Medical School developed a 30 month pediatric oncology fellowship training program following the American Academy of Pediatrics fellowship guidelines. The primary objective of the program was to implement a shared education model to develop highly educated physicians who are able to follow evidence-based approaches and who are committed to sustained practice in LMIC. Results: DFBCH staff provide ongoing education to the fellows through visits to CCHE-57357 every 2-3 months, weekly video sessions with the fellows for case presentation and journal clubs, and weekly conference calls with the fellowship program staff to ensure that the goals and objectives for each fellow and the program are met. Each of the current 15 fellows spend 6 weeks/year in Boston participating in evidence-based multi-disciplinary based rounds; the remainder of the curriculum takes place at CCHE-57357 and incorporates an array of individual, small group and e-learning modules specifically created for the program. Three classes of fellows have been enrolled and the senior class will graduate in the spring of 2017. Conclusions: Training of fellows following the same standards and methods as those applied to North American candidates is feasible and has the potential to advance the quality of education and expertise in LMIC. By focusing on the education of the next generation of clinicians, the opportunity to implement many of the important principles of clinical care can be realized.