Ewing sarcoma is a rare, aggressive bone cancer that primarily affects children and young adults, with early symptoms often mimicking common injuries or infections. It typically arises in long bones like the femur, tibia, or pelvis, and may present with localized pain, swelling, and systemic signs such as fever and fatigue.
The disease belongs to the Ewing family of tumors, which share a characteristic genetic translocation-most commonly t(11;22)(q24;q12)-that fuses the EWSR1 gene with the FLI1 gene. This mutation drives uncontrolled cell growth and is detectable via molecular testing, though symptoms usually precede diagnosis by weeks to months.
Pain is the most frequent initial symptom, occurring in over 80% of cases. It typically begins subtly, worsening at night or during activity, and may be misattributed to sports injury or growing pains. Swelling develops in about 60% of patients, often near the affected bone, and can be mistaken for a sprain or strain.
Fever occurs in 20-30% of patients and is often low-grade and persistent. Unlike infection-related fevers, it does not respond to antibiotics. Fatigue, unintentional weight loss, and decreased appetite are also reported, especially in advanced cases.
A 14-year-old male presented with six weeks of right thigh pain and a 2 cm lump near the mid-shaft of his femur. He had no trauma history. Initial X-ray showed a permeative lytic lesion with a "sunburst" pattern and a soft tissue mass. MRI confirmed a 7 cm tumor extending into surrounding muscle. Biopsy revealed small round blue cells positive for CD99 and EWSR1-FLI1 fusion. Diagnosis: Ewing sarcoma.
Neurological deficits can occur if the tumor compresses nearby nerves. Sciatica-like pain, foot drop, or numbness in the lower limb may signal spinal or pelvic involvement. Pathological fractures-breaks due to weakened bone-are seen in 10-15% of cases, particularly in the femur or pelvis.
Metastasis at diagnosis happens in 20-25% of patients, most commonly to the lungs or other bones. A cough, hemoptysis, or bone pain in distant sites should raise suspicion. One study found that 15% of patients with pulmonary metastases had normal chest X-rays initially, underscoring the need for CT scans in suspected cases.
When symptoms persist beyond two weeks despite rest and anti-inflammatory treatment, especially in adolescents, malignancy should be ruled out. Delayed diagnosis correlates with poorer survival-median time from symptom onset to diagnosis is 6-8 weeks in many cases.
Ewing sarcoma is frequently mistaken for osteomyelitis (bone infection), especially in younger patients. Both conditions cause pain, swelling, and elevated inflammatory markers like CRP and ESR. However, Ewing sarcoma rarely causes pus formation or drainage, and imaging shows distinct patterns.
Osteosarcoma, another primary bone tumor, typically affects older teens and young adults (ages 10-25) and presents with pain and swelling, but more often in the distal femur or proximal tibia. Ewing sarcoma favors the diaphysis and metaphysis of long bones and shows a more aggressive radiographic appearance.
Table: Distinguishing Features of Bone Tumors in Adolescents
| Tumor Type | Typical Age | Common Location | Imaging Findings | Key Lab Markers |
|---|---|---|---|---|
| Ewing sarcoma | 10-20 years | Femur, pelvis, ribs | Lytic lesion with "onion-skin" periosteal reaction | Normal LDH, elevated CRP/ESR |
| Osteosarcoma | 10-25 years | Distal femur, proximal tibia | "Codman's triangle," sunburst pattern | Often elevated alkaline phosphatase |
| Benign osteoid osteoma | 10-20 years | Long bone cortex | Central nidus with surrounding sclerosis | Normal inflammatory markers |
One non-obvious distinction: Ewing sarcoma rarely causes hypercalcemia or elevated serum calcium levels, unlike some other bone cancers. This helps differentiate it from metastatic disease or paraneoplastic syndromes.
Initial evaluation includes plain X-ray, which reveals a permeative lytic lesion with a characteristic "onion-skin" periosteal reaction in 70% of cases. This pattern results from alternating layers of new bone formation beneath the periosteum, driven by tumor-induced inflammation.
MRI is essential for assessing tumor extent, soft tissue involvement, and neural compression. PET-CT is used to detect occult metastases, particularly in the lungs or spine. A negative PET scan reduces the likelihood of distant spread, while a positive scan changes staging and treatment plans.
I recall reviewing a case where a 16-year-old girl had persistent hip pain and a slight limp. Her X-ray showed a subtle periosteal reaction in the ilium. MRI confirmed a 5 cm mass involving the pelvic bone with extension into the sciatic nerve. Biopsy confirmed Ewing sarcoma. The lesion was not visible on initial X-ray, highlighting the importance of clinical context and follow-up imaging.
Genetic confirmation via FISH or RT-PCR testing for EWSR1-FLI1 fusion is required for definitive diagnosis. Immunohistochemistry for CD99 (MIC2) is positive in nearly all cases, but not specific-other tumors like primitive neuroectodermal tumors (PNETs) can also express it.
If a child or adolescent experiences unexplained bone pain lasting more than two weeks, especially with swelling or fever, medical evaluation is warranted. Pain that worsens at night or disrupts sleep is a red flag. Any palpable mass near a long bone should prompt imaging.
Early referral to a pediatric oncology center improves survival. Five-year survival rates exceed 70% for localized disease but drop to 20-30% with metastasis at diagnosis. Treatment involves multimodal therapy: chemotherapy, radiation, and surgery or targeted therapy.