Background: Enoblituzumab, is an Fc optimized humanized IgG1 monoclonal antibody that binds to B7-H3 (CD276), a member of the B7 family. It is Fc-engineered to enhance effector function including antibody dependent cellular cytotoxicity (ADCC). IHC analyses with the parental anti-B7H3 mAb specificity incorporated in enoblituzmab revealed limited B7-H3 expression in normal tissues but high expression in many cancers (Loo et al., 2012). Among pediatric solid tumors, high expression of B7-H3 has been reported in neuroblastoma, rhabdomyosarcoma, osteosarcoma, Wilms tumor, Ewing’s sarcoma and desmoplastic small round cell tumor. B7-H3 overexpression correlates with poor prognosis in a broad range of cancers in adults suggesting a potential role in enabling tumor immune escape. ADCC and potential modulation of T cell function resulting in enhanced antitumor immune response are presumed mechanisms of action of enoblituzumab. Methods: This is an open-label, dose escalation / cohort expansion phase 1 study (NCT02982941) designed to characterize the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of enoblituzumab in children and young adults with B7-H3-expressing relapsed or refractory malignant solid tumors. A 3+3 design is used in escalating dose cohorts of weekly intravenous (IV) enoblituzumab starting at 10 mg/kg. Response is first determined at 8 weeks. irRECIST is used for response assessment for patient management. Enoblituzumab may continue up to 2 years based on response. Cohort expansion phase, to further define the safety and initial antitumor activity of enoblituzumab, will start after maximum tolerated dose is determined. The patients are assigned to 1 of 5 cohorts based on disease type as follows: 1) neuroblastoma - measurable disease, 2) neuroblastoma - non-measurable disease, 3) rhabdomyosarcoma, 4) osteosarcoma, and 5) Ewing’s sarcoma, Wilms’ tumor and desmoplastic small round cell tumors. Enrollment is ongoing. Ref : Development of an Fc-enhanced anti-B7-H3 monoclonal antibody with potent antitumor activity. Loo D, Alderson RF, Chen FZ, Huang L et al. Clin Cancer Res. 2012; 18:3834-45. Clinical trial information: NCT02982941