Liquid Biopsy in Ewing Sarcoma and Osteosarcoma as a Prognostic And Response Diagnostic: LEOPARD

The purpose of this study is to evaluate whether ctDNA in the blood can provide information about the chances of Ewing sarcoma or osteosarcoma coming back after treatment. This research study is evaluating a new advanced laboratory test to detect small pieces of tumor genes in the peripheral blood known as circulating tumor DNA (ctDNA). Part A : During this part of the research study (Part A) participants will be asked to provide blood samples at pre-defined times. These blood samples may help find specific genetic alterations commonly seen in Ewing sarcoma or osteosarcoma that may allow investigators to learn more about the uses of ctDNA. The results of the ctDNA analysis will not be returned to participants. Approximately 90 patients will take part in this study across multiple centers. Part B: This research study is evaluating new advanced laboratory tests to detect small pieces of tumor genes in the peripheral blood known as circulating tumor DNA (ctDNA). Part B of the research study, which focuses on ctDNA tests that can be returned to providers and patients with Ewing sarcoma. This part of the study will allow comparison of commercial ctDNA testing from Foundation Medicine to our research testing. It is expected that about 60 people with Ewing sarcoma will take part in Part B of this research study. The sponsor of this protocol is Dana-Farber Cancer Institute and is providing funding for the study. Additional funding for this study is provided by the Conquer Cancer Foundation of the American Society of Clinical Oncology, Alex's Lemonade Stand Foundation, Boston Children's Hospital Office of Faculty Development, the Friends of Dana-Farber Cancer Institute, The Harvard Catalyst Program, and the Spada Pediatric Sarcoma Foundation