Atezolizumab and Cabozantinib for the Treatment of Adolescents and Young Adults With Recurrent or Metastatic Osteosarcoma, TACOS Study

Inclusion Criteria: * Signed informed consent form * Age \>= 12 years at time of signing informed consent form * Ability to comply with the study protocol, in the investigator's judgment * Histologically confirmed diagnosis of osteosarcoma * Metastatic or unresectable locally advanced disease * Patients must have relapsed or become refractory to conventional therapy including some combination of cisplatin, doxorubicin, methotrexate, and/or ifosfamide * Measurable disease per RECIST version (v)1.1 (Note: Previously irradiated lesions can be considered as measurable disease only if progressive disease has been unequivocally documented at that site since radiation) * Availability of a representative tumor specimen for exploratory biomarker research. Archival samples are permitted if the tumor samples been obtained within 6 months prior to enrollment and the patient has not received intervening therapy * A formalin-fixed paraffin-embedded (FFPE) tumor specimen in a paraffin block (preferred) or at least 15 slides containing unstained, freshly cut, serial sections should be submitted along with an associated pathology report prior to study enrollment. If only 10-14 slides are available, the patient may still be eligible for the study, after principal investigator confirmation has been obtained * If archival tumor tissue is unavailable or is determined to be unsuitable for required testing, tumor tissue must be obtained from a biopsy performed at screening * Eastern Cooperati…