Enoblituzumab (MGA271) in Children With B7-H3-expressing Solid Tumors

General Inclusion Criteria: * Age at treatment 1 to 35 years. * Relapsed or refractory malignant solid tumors of any histology for which no standard curative therapy is available (escalation phase). * Histologically proven: neuroblastoma, rhabdomyosarcoma, osteosarcoma, Ewing's sarcoma/ primitive neuroectodermal tumor, Wilms tumor, desmoplastic small round cell tumor or malignant solid tumors of any other histology that test positive for B7-H3 . * Must have malignant solid tumors that demonstrate B7-H3 expression at 2+ or greater levels on the membranous surface of at least 10% of tumor cells or ≥ 25% of tumor vasculature by IHC. * With the exception of patients with non-measurable neuroblastoma patients must have measurable disease as per RECIST 1.1 * Karnofsky (patients ≥ 16 years)/Lansky (patients \< 16 years) index ≥ 70. * Acceptable laboratory parameters and adequate organ reserve. Exclusion Criteria: * Patients are to be excluded from the study if they have any of the following: * Patients with a history of symptomatic central nervous system (CNS) unless they have been treated and are asymptomatic. * Patients with any history of known or suspected autoimmune disease with the specific exceptions of vitiligo, resolved childhood atopic dermatitis, psoriasis not requiring systemic treatment within the past 2 years, and patients with a history of Grave's disease that are now euthyroid clinically and by laboratory testing. * History of prior allogeneic bone marrow/stem-cell or solid organ transplantation. * Patients receiving autologous stem cell transplantation must wait 8 weeks before initiation of study drug administration. * Treatment with systemic chemotherapy or investigational therapy within 4 weeks of first study drug administration; other agents (e.g., biologics) within 2 weeks; radiation within 2 weeks; patients receiving 131I-MIBG therapy must wait 6 weeks prior to the initiation of study drug administration; corticosteroids (≥ 0.2 mg/kg/day prednisone or equivalent) or other immune suppressive drugs within the 2 weeks prior to the initiation of study drug administration. * History of clinically significant cardiovascular disease * Active viral, bacterial, or systemic fungal infection requiring parenteral treatment within 7 days prior to the initiation of study drug. * Known positive testing for human immunodeficiency virus or history of acquired immune deficiency syndrome. * Known history of hepatitis B or hepatitis C infection or known positive test for hepatitis B surface antigen, hepatitis B core antigen, or hepatitis C polymerase chain reaction. * Second primary invasive malignancy that has not been in remission for greater than 2 years. * History of severe trauma or major surgery within 4 weeks prior to the initiation of study drug administration. * Known hypersensitivity to recombinant proteins, polysorbate 80 or any excipient contained in the drug formulation for enoblituzumab * Patients in Canada may not have a history or evidence of latent or active tuberculosis infection.