2.5 Safety and Efficacy Assessments
Routine clinical and laboratory assessments, physical examinations, EKGs, echocardiograms, and tibial growth plate x-rays were conducted at baseline and prespecified intervals. Adverse events were graded using National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE), version 5. Imaging studies and tumor assessments were obtained at baseline, after cycle 2, after cycle 4, and then every 4 cycles until documented progression for patients with complete response (CR), partial response (PR), or stable disease (SD). Response was assessed using Response Evaluation Criteria in Solid Tumors (RECIST) guideline (version 1.1). Patients with an overall best objective response of CR or PR prior to any local measures were categorized as responders, and all other patients as non-responders.
2.6 Correlative Biology Evaluations
Serial plasma samples were obtained to quantify and characterize ctDNA over time in response to protocol therapy. Peripheral blood samples were collected in cell-stabilizing tubes at baseline, Cycle 1 Day 3, Cycle 1 Day 5, Cycle 2 Day 1, and then at times of subsequent of disease evaluation. Plasma was isolated and processed to collect cell free DNA as previously described [18]. TranSS-Seq to detect EWSR1 andFUS fusions was used to quantify ctDNA for patients with Ewing sarcoma and ultra-low passage whole genome sequencing (ULP-WGS) to detect aneuploidy was used for patients with osteosarcoma. Detailed methods are as previously reported [18].