This study is a single-arm, open-label, proof of concept clinical trial in children, adolescent and young adult patients with unresectable pOS that have progressed, relapsed or are refractory to standard systemic therapy.~All participants will receive the study therapy and there will be dose escalation in a traditional 3 + 3 design during the Phase I study of this trial.~In the Phase II study of the trial, treatment will continue if the subject has Complete Response (CR), Partial Response (PR) or Stable Disease (SD) of pOS after every 3 cycles after the first 6 cycles but not beyond 24 cycles, unless it is judged to be in his/her best interest.~Approximately 3-9 subjects will be enrolled in the phase I part and 10-12 in the phase II part of this trial. Participants will be followed for toxicity for 30 days after treatment has been discontinued or until one of the protocol-defined reasons~This study seeks to evaluate if Natalizumab can be used safely and effectively as immunotherapy in children, adolescent and young adult patients with pOS. Natalizumab is currently Food and Drug Administration (FDA) approved for the treatment of T-cell mediated autoimmune disorders The study team will evaluate the safety and tolerability of Natalizumab as well as the clinical response associated with Natalizumab treatment and evaluate overall survival.
The purpose of this study is to evaluate the safety and tolerability of Natalizumab in children, adolescent and young adult patients with pulmonary metastatic osteosarcoma (pOS) and to assess clinical response associated with this treatment as well as overall survival.