PRIMARY OBJECTIVE:~I. To estimate the proportion of patients with recurrent measurable osteosarcoma treated with trastuzumab deruxtecan (DS-8201a) who are event free (%EF) at 24 weeks.~SECONDARY OBJECTIVES:~I. To assess the safety of DS-8201a in patients with recurrent osteosarcoma. II. To describe the pharmacokinetics of DS-8201a in patients with recurrent osteosarcoma.~III. To estimate the objective response rate (ORR), event free survival (EFS), overall survival (OS) and duration of response (DOR) of patients with recurrent, measurable osteosarcoma.~EXPLORATORY OBJECTIVES:~I. To describe the relationship between potential biomarkers and response to DS-8201a.~II. To evaluate quantitative circulating tumor deoxyribonucleic acid (DNA) (ctDNA) and circulating tumor cells (CTCs) as a surrogate markers of response in recurrent osteosarcoma.~OUTLINE:~Patients receive trastuzumab deruxtecan intravenously (IV) over 30-90 minutes on day 1. Treatment repeats every 21 days for 35 cycles in the absence of disease progression or unacceptable toxicity.~After completion of study treatment, patients are followed up at 6 months.
This phase II trial studies the effects of trastuzumab deruxtecan in treating patients with HER2 positive osteosarcoma that is newly diagnosed or has come back (recurrent). Trastuzumab deruxtecan is a monoclonal antibody, called trastuzumab, linked to a chemotherapy drug called deruxtecan. Trastuzumab attaches to HER2 positive cancer cells in a targeted way and delivers deruxtecan to kill them.