A soft tissue tumor or sarcoma in children is a rare tumor that arises in connective tissue. Despiteoptimal treatment of non- metastatic high-grade sarcomas, 50-80% of patients relapse within 2 years and the median survival time is only 15 months. Despite several clinical trials with newer therapies, treatment has remained unchanged for the past 20 years. The rarity of the disease and the fact that more than 50 subytpes exist prevent the design of large randomized studies. Moreover, there are no markers available with which to monitor the effect of treatment. This increases the risk of non-response to therapy, the presence of side effects and the risk of relapse. In this project, we aim to address the urgent need to predict the most effective individual therapy by developing patient avatars in animal models in which the therapy response will first be extensively tested. The use of animal models that mimic human disease is of paramount importance to improve clinical decision-making. We want to anticipate individualized combination therapy. We aim to build a diverse and representative cohort of zebrafish xenograft models of sarcoma patients, providing a rich source of patient avatars for comprehensive dose-response evaluation of therapeutic strategies.