Ewing sarcoma

Ewing sarcoma
Specialty	Oncology

Ewing's sarcoma is a malignant round-cell 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.

Because a common genetic locus is responsible for a large percentage of Ewing's sarcoma and primitive neuroectodermal tumors, these are sometimes grouped together in a category known as the Ewing family of tumors. The diseases are, however, considered to be different: peripheral primitive neuroectodermal tumors are generally not associated with bones, while Ewing's sarcomas are most commonly related to bone.

Ewing's sarcoma occurs most frequently in male teenagers, with a male/female ratio of 1.6:1.

Although usually classified as a bone tumor, Ewing's sarcoma can have characteristics of both mesodermal and ectodermal origin, making it difficult to classify.

Eponym

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.

Causes

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.

EWS/FLI functions as the master regulator.

Clinical findings

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

It is positive for CD99 and negative for CD45.

Imaging findings

Genetic exchange between chromosomes can cause cells to become cancerous, like these cells from metastasized Ewing's sarcoma

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, though some current researchers argue that dynamic, contrast enhanced MRI may help determine the amount of necrosis within the tumor, thus help in determining response to treatment prior to surgery.

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 clinical 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.

Epidemiology

The frequency in the United States depends on the patient's age, with a rate of 0.3 case per 1,000,000 children in those younger than 3 years of age to as high as 4.6 cases per 1,000,000 in adolescents aged 15-19 years. Internationally the annual incidence rate averages less than 2 cases per 1,000,000 children. In the United Kingdom an average of six children per year are diagnosed, mainly males in early stages of puberty. Due to the prevalence of diagnosis during teenage years, there may possibly be a link between the onset of puberty and the early stages of this disease, although no research is currently being conducted to confirm this theory.

Treatment

Because almost all patients with apparently localized disease at diagnosis have occult metastatic disease, multidrug chemotherapy (often including ifosfamide and etoposide) as well as local disease control with surgery and/or radiation is indicated in the treatment of all patients.

Treatment often consists of neo-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. Treatment lengths vary depending on location and stage of the disease at diagnosis. Radical chemotherapy may be as short as 6 treatments at 3 week cycles, however most patients will undergo chemotherapy for 6-12 months and radiation therapy for 5-8 weeks.

Antisense oligodeoxynucleotides have been proposed as possible treatments.

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 70% to 80% when treated with chemotherapy. Long term survival for metastatic disease can be less than 10% but some sources state it is 25-30%. .

External links

• humpath #3402
• Template:DMOZ