Qarziba for Patients in Relapsed/Refractory High-grade Osteosarcoma

Inclusion Criteria: * Provision of signed and dated, written informed consent from each patient or patient's legally acceptable representative, parent (s) or legal guardian in accordance with regional laws or regulations and the patient's assent, when applicable, before any study-specific activity, including screening evaluation, is performed. For patients who reach the age of legal consent during the clinical study, notification may be required and a new consent form may need to be signed by the patient. * Histologically confirmed high-grade osteosarcoma which is relapsed or refractory (ONLY patients in first or second relapse will be eligible). Histological confirmation from initial diagnosis or relapse is acceptable. * Disease status: subjects must have achieved a complete or partial response after a second or further line of systemic therapy (with or without surgery) as defined by the following criteria: * Complete Response = disappearance of all target and non-target lesions * Partial Response = at least 30% decrease in the sum of the longest diameter (LD) of target lesions, taking as reference the baseline sum LD of the last episode of relapse or recurrence. If a partial response is achieved, only patients with a focal localized disease at any site must be enrolled (for patients with lung disease a maximum of 2 lung unilateral nodules will be accepted). * Age: ≥ 1 to \< 25 years old at the time of signing the informed consent form. * Performance Level: Karnofsky Perfor…