Does Ewing's Sarcoma Metastasize?
Yes, Ewing's sarcoma has a high potential for metastasis, with approximately 20-25% of patients presenting with detectable metastatic disease at diagnosis, and metastatic disease at presentation represents the single most significant adverse prognostic factor for this malignancy. 1
Metastatic Patterns and Frequency
At initial diagnosis:
- Approximately 20-25% of patients have detectable metastases at presentation 1
- The most common metastatic sites are lungs (10%), bone (10%), and bone marrow (10%), with 5% presenting with combinations or other sites 1
- Subclinical metastatic disease is thought to be present in almost all patients at diagnosis, even when not overtly detectable 2
Common metastatic sites in order of frequency:
- Lungs are the most frequent site of metastasis 1
- Bone represents the second most common site 1
- Bone marrow is the third most common site 1
- Uncommon sites include brain, liver, spleen, and small bowel, which carry particularly poor prognosis 1, 2
Impact on Survival
The presence of metastases dramatically alters prognosis:
- Patients with localized disease achieve 60-75% five-year survival with current multimodal therapy 1, 3
- Patients with metastatic disease at diagnosis have only 22% five-year relapse-free survival compared to 55% for those without metastases 1
- Among metastatic patients, lung-only metastases confer better prognosis (30-50% five-year survival) compared to bone metastases or combined lung/bone metastases (approximately 10% five-year survival) 1, 4
Clinical Implications for Workup
Because metastatic disease is so common and prognostically critical, complete staging before biopsy is mandatory:
- CT chest with or without contrast to detect pulmonary metastases 1
- Whole body FDG-PET/CT (preferred) and/or bone scan with 96% sensitivity and 92% specificity for detecting metastases 1
- Bone marrow biopsy and/or screening MRI of spine and pelvis to detect bone marrow involvement 1
- Contrast-enhanced MRI of the primary site 1
The high sensitivity (100%) and specificity (96%) of FDG-PET for staging may eliminate the need for bone marrow biopsy in some cases 1.
Aggressive Biological Behavior
Ewing's sarcoma demonstrates highly aggressive metastatic potential:
- Metastatic disease can progress rapidly to cause life-threatening complications 2
- The tumor is thought to have subclinical metastases present in nearly all patients at diagnosis, explaining why systemic chemotherapy is mandatory even for apparently localized disease 2, 5
- Relapse after initial treatment occurs in the majority of patients, with lung and bone being the most common sites of recurrence 6
Age-Related Metastatic Risk
Younger patients (≤10 years) demonstrate better outcomes even with metastatic disease, possibly due to more favorable distribution of primary tumor sites, with 39% having rib primaries compared to only 16% in older patients 6.