Ewing sarcoma is a type of cancer that may be a bone sarcoma or a soft-tissue sarcoma. Symptoms may include swelling and pain at the site of the tumor, fever, and a bone fracture. The most common areas where it begins are the legs, pelvis, and chest wall. In about 25% of cases, the cancer has already spread to other parts of the body at the time of diagnosis. Complications may include a pleural effusion or paraplegia.

The cause of Ewing sarcoma is unknown. Most cases appear to occur randomly. It is sometimes grouped together with primitive neuroectodermal tumors, in a category known as the Ewing family of tumors. The underlying mechanism often involves a genetic change known as a reciprocal translocation. Diagnosis is based on biopsy of the tumor.

Treatment often includes chemotherapy, radiation therapy, surgery, and stem cell transplant. Targeted therapy and immunotherapy are being studied. Five-year survival is about 70%. A number of factors, however, affect this estimate.

James Ewing in 1920 established that the tumor is a distinct type of cancer. It affects about one in a million people per year in the United States. Ewing sarcoma occurs most often in teenagers and young adults and represents 2% of childhood cancers. Caucasians are affected more often than African Americans or Asians. Males are affected more often than females.