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.