Liquid Biopsy in Ewing Sarcoma and Osteosarcoma is a study to understand if a special blood test can tell us if a type of bone cancer called Ewing sarcoma or osteosarcoma might come back after treatment. The test looks for tiny pieces of tumor genes in the blood called circulating tumor DNA (or ctDNA). The study is divided into two parts.

Part A involves about 90 people providing blood samples at certain times to help find changes in genes linked to these cancers. The results from these tests won't be shared with the participants.

Part B will compare different ctDNA tests and will involve about 60 people. In this part, some results may be shared with doctors and patients. This part will include tests from a company called Foundation Medicine.

• The study will take place in multiple locations and is funded by Dana-Farber Cancer Institute and other organizations.
• Participants must be at least one year old and not older than 50 years.
• People who have already received certain types of cancer treatments or have other types of tumors cannot participate.

Before joining, patients should discuss eligibility with their doctor and consider the requirements and commitments involved.