Oncology · Bone Tumors
The facts most likely to be tested
Ewing sarcoma is characterized by the t(11;22)(q24;q12) translocation, which results in the EWS-FLI1 fusion protein.
Radiographic imaging typically reveals a diaphyseal lesion with a classic onion-skin periosteal reaction.
Histopathology demonstrates small round blue cells that are CD99 positive and PAS positive.
Patients frequently present with localized bone pain and systemic symptoms such as fever, weight loss, and anemia.
The tumor most commonly arises in the diaphysis of long bones, particularly the femur, tibia, and humerus.
Ewing sarcoma is the second most common primary malignant bone tumor in children and adolescents.
Management requires a multimodal approach consisting of neoadjuvant chemotherapy, surgical resection, and radiation therapy.
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A 14-year-old male presents with a 3-month history of progressive mid-shaft thigh pain and intermittent low-grade fevers. Physical examination reveals localized tenderness and soft tissue swelling over the mid-femur. Laboratory studies show an elevated erythrocyte sedimentation rate (ESR) and leukocytosis. Radiographic imaging of the femur demonstrates a moth-eaten appearance with a lamellated onion-skin periosteal reaction in the diaphysis.
What is the most likely diagnosis?
Ewing Sarcoma
The combination of a diaphyseal lesion, systemic symptoms (fever), and the classic 'onion-skin' periosteal reaction on X-ray is pathognomonic for Ewing sarcoma, which is confirmed by the t(11;22) translocation.
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Etiology / Epidemiology
Second most common primary bone malignancy in children/adolescents; peak incidence 10–20 years.
Clinical Manifestations
Localized bone pain and swelling; onion-skin periosteal reaction on imaging.
Diagnosis
Biopsy is the gold standard; look for small round blue cell tumor.
Treatment
Multimodal therapy: Chemotherapy followed by surgical resection or radiation.
Prognosis
Metastasis at presentation is the most significant negative prognostic factor.
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Epidemiology & Etiology
Predominantly affects Caucasian males in the second decade of life. It is rarely seen in patients over age 30. Unlike osteosarcoma, it is not associated with Paget disease or prior radiation exposure.
Pertinent Anatomy
Most commonly arises in the diaphysis of long bones, particularly the femur, tibia, and humerus. It can also involve the pelvis and chest wall, which often presents with more aggressive clinical features.
Pathophysiology
Characterized by the t(11;22)(q24;q12) translocation, resulting in the EWS-FLI1 fusion protein. This oncogenic transcription factor drives uncontrolled cellular proliferation. Histology reveals sheets of uniform small round blue cells with scant cytoplasm.
Clinical Manifestations
Patients present with localized pain and a palpable mass, often mimicking osteomyelitis. Systemic symptoms like fever, weight loss, and anemia are common. Pathologic fractures may occur at the site of the lesion.
Diagnosis
Plain radiographs show a classic onion-skin periosteal reaction. Biopsy is the definitive diagnostic test. MRI is the gold standard for evaluating the extent of soft tissue involvement and marrow infiltration.
Treatment
Standard of care is neoadjuvant chemotherapy (e.g., vincristine, doxorubicin, cyclophosphamide) to shrink the tumor. Avoid radiation as primary therapy if surgical resection is possible due to secondary malignancy risk. Surgical resection is preferred for local control.
Prognosis
Five-year survival is approximately 70% for localized disease but drops significantly with distant metastasis. Pulmonary metastasis is the most common site of spread and requires aggressive surveillance.
Differential Diagnosis
Osteosarcoma: sunburst periosteal reaction and Codman triangle
Osteomyelitis: elevated inflammatory markers and positive blood cultures
Eosinophilic granuloma: punched-out lytic lesions
Lymphoma of bone: typically older patients with permeative bone destruction
Metastatic disease: usually older patients with a known primary malignancy