Osteosarcoma Maintenance Therapy With OST31-164

This is a Phase 2, open-label, multicenter, single-arm study in patients (12-39 years) with a recent history of pulmonary recurrent osteosarcoma that has been completely resected. Planned enrollment is a maximum of 45 patients who will receive OST31-164 as a single agent every 3 weeks for 48 weeks with 4 doses constituting 1 treatment cycle (12 weeks per cycle). Each patient will receive treatment at a dose of 1x109 CFU until week 48 or until disease progression, unacceptable toxicity, or the patient meets any other treatment discontinuation criteria. Following treatment discontinuation, all patients will enter a 3-year survival follow-up period. Exploratory evaluation of immune response will be conducted. If available, tissue from the recent resection will be sent to the COG Biobank for future genomic and pathologic analysis by the COG.