10502Background: Outcomes for children with relapsed and refractory neuroblastoma are dismal. The combination of I/T has activity in patients with relapsed disease, and the toxicity profile of I/T makes it an excellent backbone for study of new agents. Temsirolimus (TEM) and dinutuximab (DIN) were selected for testing in combination with I/T in subjects with relapsed, progressive or refractory neuroblastoma. Methods: COG ANBL1221, a randomized Phase II selection design trial, compared response and toxicity in subjects treated with I/T in combination with either TEM (Arm A) or DIN/GM-CSF (Arm B). Patients were eligible at first relapse/progression or first designation of primary refractory disease. Randomization was stratified based on prior therapy and MYCNstatus. Cycles were administered every 21 days. Partial and complete responses (PR, CR) were confirmed centrally. Results: Thirty-five eligible patients were enrolled. Median age was 5.7 years (range 2.1-16.2), 24 pts had measurable disease (12 per arm)...