Single Arm Romiplostim to Prevent CIT

The goal of this clinical trial is to to assess the efficacy of romiplostim as a supportive care measure in patients with a new diagnosis of Ewing sarcoma receiving interval-compressed chemotherapy. The main questions it aims to answer are: 1. To demonstrate the efficacy of romiplostim in patients with newly diagnosed Ewing sarcoma, measured specifically as the rate of CIT, defined as a failure to achieve platelet recovery (≥ 75,000/µL post nadir, without transfusion, or a platelet count sufficient to resume chemotherapy per provider and institutional standard) within 7 days of planned chemotherapy cycle start, measured during the continuation phase (cycle 7 to end of cycle 13 or 16, per AEWS0031/AEWS1221, or AEWS1031 respectively) of interval-compressed chemotherapy (every 2 week vincristine/cyclophosphamide +/- doxorubicin and ifosfamide/etoposide chemotherapy) as compared to published institutional historical control rate. 2. To determine the safety of incorporation of romiplostim supportive care when given concurrently with Ewing sarcoma therapy. 3. To determine the feasibility of incorporation of romiplostim supportive care into upfront Ewing sarcoma regimens.