Ewing sarcoma is a small, round, blue cell tumor that primarily affects bone and soft tissue. It is often metastatic and has been found in a variety of organs. It typically presents with bone or soft tissue pain. Ewing sarcoma most commonly affects adolescent males. It is considered a poorly-differentiated malignancy on the primitive neuroectodermal tumor (PNET) spectrum. Ewing sarcoma is categorized as a "small round blue cell tumor" due to its histologic appearance, which it shares with other types of malignancies. Ewing sarcomas may be differentiated from these other tumors by CD99 positivity, presence of rosettes on microscopy, and a t(11;22) translocation, which nearly all Ewing sarcomas contain.

Treatment consists of systemic chemotherapy and surgical excision of the primary tumor. Radiotherapy is also sometimes utilized. Prognosis depends on multiple factors, but Ewing sarcoma can be curable even when metastatic.