Ewing's sarcoma is the common name for primitive neuroectodermal tumor. It is a rare disease in which cancer cells are found in the bone or in soft tissue. The most common areas in which it occurs are the pelvis, the femur, the humerus, and the ribs. James Ewing (1866-1943) first described the tumor, establishing that the disease was separate from lymphoma and other types of cancer known at that time. Ewing's sarcoma occurs most frequently in teenagers. Ewing's sarcoma is the result of a translocation between chromosomes 11 and 22, which fuses the EWS gene of chromosome 22 to the FLI1 gene of chromosome 11.

Clinical Findings

Ewing's sarcoma usually presents in childhood or early adulthood, with a peak between 10 and 20 years of age, although it can occur in younger children and older adults. It can occur anywhere in the body, but most commonly in the pelvis and proximal long tubular bones. The metaphysis and diaphysis of the femur are the most common sites, followed by the tibia and the humerus. Thirty percent are overtly metastatic at presentation.

The most common clinical findings are pain and swelling.

Imaging Findings

On conventional radiographs, the most common osseous presentation is a permeative lytic lesion with periosteal reaction. The classic description of lamellated or "onion skin" type periosteal reaction is often associated with this lesion. Plain films add valuable information in the initial evaluation or screening. The wide zone of transition (e.g. permeative) is the most useful plain film characteristic in differention of benign versus aggressive or malignant lytic lesions.

MRI should be routinely used in the work-up of malignant tumors. MRI will show the full bony and soft tissue extent and relate the tumor to other nearby anatomic structures (e.g. vessels). Gadolinium contrast is not necessary as it does not give additional information over noncontrast studies.

CT can also be used to define the extraosseous extent of the tumor, especially in the skull, spine, ribs and pelvis. Both CT and MRI can be used to follow response to radiation and/or chemotherapy.

Bone scintigraphy can also be used to follow tumor response to therapy.

Differential Diagnosis

Other entities that may have a similar radiologic presentation include osteomyelitis, osteosarcoma (especially telangiectatic osteosarcoma) and eosinophilic granuloma. Soft tissue neoplasms such as malignant fibrous histiocytoma that erode into adjacent bone may also have a similar appearance.

Treatment

Because almost all patients with apparently localized disease at diagnosis have occult metastatic disease, multidrug chemotherapy as well as local disease control with surgery and/or radiation is indicated in the treatment of all patients (2). Treatment often consists of adjuvant chemotherapy generally followed by wide or radical excision, and may also include radiotherapy. Complete excision at the time of biopsy may be performed if malignancy is confirmed at that time.

Prognosis

Staging attempts to distinguish patients with localized from those with metastatic disease. Most commonly, metastases occur in the chest, bone and/or bone marrow. Less common sites include the central nervous system and lymph nodes.

Survival for localized disease is 65-70% when treated with chemotherapy. Survival for metastatic disease is 25-30%.

Useful Links

National Cancer Institute listing for Ewing's sarcoma