Pediatric Osteosarcoma

This clinical study is the initiative of the FOSTER (Fight OsteoSarcoma Through European Research) consortium and Gustave Roussy, which is the sponsor. Its aim is to evaluate the biology of tumour in greater depth by collecting samples of the tumour during the biopsy at diagnosis, and blood samples. This study is a platform study that evolves over time. This means that it allows for the evaluation of several treatments or therapeutic strategies within a single clinical trial, which can be modified and adapted over time. The FOSTER evolving study platform aim to implement a comprehensive strategy of clinical, biological, radiological, therapeutic integrated research from diagnosis to relapse, with the aim to improve survival of osteosarcoma patients of all age, through randomised therapeutic questions at different phase of treatment from diagnosis to relapse. The platform study makes it possible to evaluate several treatments for the same disease, on an ongoing basis, using a main protocol with adaptable arms. The FOSTER-CabOS trial (part 2 of FOSTER study) is a European Phase III clinical study . It assesses the efficacy of cabozantinib, a tyrosine kinase inhibitor, as a maintenance therapy post-standard treatment in osteosarcoma patients. The trial is randomized against Best Supportive Care to determine the effectiveness of cabozantinib in improving event-free survival. This maintenance therapy aims to prevent relapse among patients who have already received standard treatment for osteosarcoma.

The purpose of this study is to assess the safety, feasibility, and effectiveness of a consolidative B7-H3 CAR T cell therapy in patients with newly diagnosed high-risk osteosarcoma who have undergone upfront standard chemotherapy. Primary Objectives: \- To evaluate 1-year RFS from the time of SJCARB7H3-41BBL infusion for patients with newly diagnosed metastatic osteosarcoma who received standard chemotherapy. Secondary Objectives: * To evaluate the OS from time of SJCARB7H3-41BBL infusion for patients with newly diagnosed metastatic osteosarcoma who received standard chemotherapy. * To evaluate the feasibility of delivering SJCARB7H3-41BBL at the end of standard therapy in patients with newly diagnosed metastatic osteosarcoma. * To describe the safety of autologous SJCARB7H3-41BBL therapy when delivered at the end of standard therapy in patients with newly diagnosed metastatic osteosarcoma.