To Evaluate the Efficacy and Safety of Naxitamab in Patients With Refractory Ewing's Sarcoma

The study includes:

1. Biology screening: to estimate expression on GD2 on Ewing sarcoma cells from tumor tissue from archival material. Availability of tumor tissue is required for pre-screening testing to determine GD2 expression. To be screened for potential enrollment into the study patients or their legal representatives must have signed the pre-screening informed consent form (ICF) to consent to using their archival tumor sample to test the expression of GD2 in their tumor. The expression level of GD2 will be characterized in tumor tissue by immunohistochemistry (IHC) at a local and a central diagnostic testing laboratory.
2. Standard stratifying diagnostic tests (laboratory assessment: morphology, blood chemistry including ALT, AST, eGFR, creatinine, sodium, potassium, coagulation, urine analysis including pH, blood, protein, leukocytes, glucose, urobilinogen, bilirubin, ketones, nitrites, specific gravity, vital signs (body temperature, systolic and diastolic blood pressure, and pulse rate), ECG, cardiac function test, imaging test: CT/MRI scan).
3. Patients with GD2 expression will be randomized in proportions (2:1) to the experimental (D) and control groups (S). The cohort D will consist of 16 subjects, the cohort S 8 subjects. The exploratory cohort D will receive the experimental regimen in 3-week cycles consisting of irinotecan given intravenously (iv) 50 mg/m2 after oral temozolomide 100 mg/m2 on days 1-5 and naxitamab administered iv 2.25 mg/kg/day over 30 - 60 minutes, days 2, 4, 8 and 10 (up to 150 mg/day; total 9 mg/kg per cycle), and GM-CSF 250 mg/m2/day subcutaneously, days 6-10. Patients randomized to arm S will receive IT alone. Treatment cycles will be repeated every 21 days summary to 6 cycles or until disease progression, or subsequent relapsed, or occurrence of intolerable toxicity, or any event making impossible treatment continuation, or investigator's judgment, or withdrawal of consent. All activities are presented in Schedule of Assessments (SoA) at the end of the study synopsis.
4. Patients will be recalculated according to the intent to treat (ITT) rule.
5. The study will be conducted in accordance to GCP and after EC approval of the protocol.