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Olaratumab is a monoclonal antibody that specifically binds to platelet‐derived growth factor receptor alpha (PDGFRα) and blocks receptor activation. We conducted a phase 1 trial to evaluate the safety of olaratumab and determine a recommended dose in combination with three different chemotherapy regimens in children. Patients 25% of patients included neutropenia, anemia, leukopenia, lymphopenia, and thrombocytopenia. Pharmacokinetic profiles of olaratumab with chemotherapy were within the projected range based on adult data. There was one complete response (rhabdomyosarcoma [Part B vincristine/irinotecan arm]) and three partial responses (two rhabdomyosarcoma [Part A doxorubicin arm and Part C doxorubicin arm]; one pineoblastoma [Part B vincristine/irinotecan arm]). Olaratumab was tolerable and safely administered in combination with chemotherapy regimens commonly used in children and adolescents., Observed pharmacokinetic (PK) data and model predicted PK profiles by weight in pediatric patients treated with olaratumab. The overlay was limited to the first seven cycles where observed data were available to provide meaningful comparison. Overall, there was general agreement between the observed and model predicted serum concentrations as the observed values (colored circle) overlap with the prediction interval (shaded region) from the PK model. The colored circles correspond to each patient in the study. The shaded region represents the 90% prediction interval and the solid line represents the median of predicted concentration.