Prospective Evaluation of Dynamic Serum ProGRP for Treatment Response Monitoring in Ewing Sarcoma

This single-center prospective observational study aims to evaluate whether longitudinal changes in serum pro-gastrin-releasing peptide (ProGRP) reflect treatment response in patients with newly diagnosed Ewing sarcoma. Serum ProGRP levels will be measured before systemic treatment, during neoadjuvant chemotherapy, before local treatment, and after local treatment. Changes in ProGRP will be compared with radiographic tumor response assessed according to RECIST version 1.1. The study will also explore the ability of early ProGRP changes to predict objective radiographic response and the association between ProGRP patterns and event-free survival. ProGRP results obtained for research purposes will not be used to guide clinical treatment decisions.

Inclusion Criteria: * Age 10 to 60 years. * Histologically confirmed Ewing sarcoma. * Newly diagnosed disease and scheduled to initiate first-line systemic therapy at Peking University People's Hospital. * No prior systemic chemotherapy for Ewing sarcoma and no prior radiotherapy to the primary tumor. * At least one evaluable lesion on baseline imaging; at least one measurable lesion according to RECIST version 1.1 is required for the primary outcome analysis. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 2. * Estimated life expectancy greater than 3 months. * Written informed consent provided by the participant or the participant's legally authorized representative. Exclusion Criteria: * History of another malignant tumor within the previous 3 years, except for an adequately treated malignancy with a negligible risk of recurrence, as determined by the investigator. * New York Heart Association (NYHA) class III or IV heart failure. * Uncontrolled concomitant illness, including uncontrolled diabetes mellitus or an active infection. * Severe infection requiring intravenous antimicrobial treatment within 4 weeks before enrollment. * Clinically significant bleeding or a clear bleeding tendency within 3 months before enrollment. * Severe renal impairment, defined as an estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73 m². * Pregnancy or breastfeeding. * Any condition that, in the investigator's judgment, may compromise participant safety, interfere with study assessments, or prevent compliance with the protocol.