Alveolar Soft Part Sarcoma
Synonyms: ASPS
Deceptively slow-growing despite high-grade histology
Quick Facts
Behaviour
Malignant
Category
Soft tissue
Grade
High
Synonyms
ASPS
Category
Soft tissue
Behaviour
Malignant
Grade
High
Gender
Female
Tissue of Origin
Unknown (possible muscle or neural crest origin)
Epidemiology
- Rare, 0.5–1% of soft tissue sarcomas
- Peak incidence in adolescents and young adults (15–35 years), but wide age range of presentation
- Slow-growing despite high-grade histology
Clinical Features
- Painless slow-growing deep soft tissue mass
- Up to 70% have metastases at presentation
- Often large at presentation due to indolent course
- Pulsatile mass or prominent vessels may be evident
- Brain metastases can present as neurological symptoms
Location
- Deep soft tissues of the extremities (thigh and buttock) most common in adults
- Head and neck (tongue, orbit) more common in children
- Rarely trunk or retroperitoneum
Imaging
- Well-defined hypervascular mass on CT and MRI
- Prominent internal and peripheral flow voids on MRI (flow vessels)
- Can mimic AV malformation on angiography
Pathology
- Large polygonal cells with an abundant eosinophilic cytoplasm
- PAS-positive diastase-resistant crystals (pathognomonic)
- Nests of tumor cells with surrounding vascular channels
Genetics
- ASPSCR1-TFE3 gene fusion (der(17)t(X;17)(p11;q25))
- Unbalanced translocation always present
- TFE3 FISH/IHC confirmatory
Treatment
- Wide surgical resection of primary lesion
- Excision of brain and lung mets may prolong survival
- Radiotherapy considered in unresectable lesions or with positive margins
- VEGFR inhibitors show strong response in metastatic disease
- Multiple immunotherapy agents being trialed
- Cytotoxic drugs have limited efficacy
Prognosis
- Indolent course but high rate of metastasis (lungs, bone, brain)
- 5-year survival 47-68%, very good in local disease (73-100%) and 20-60% in those with metastases.
- Late metastasis common (>10 years after resection)
- Brain metastases associated with very poor outcome
Key Points
- Deceptively slow-growing despite high-grade histology
- Metastatic propensity (43% at presentation)
- TFE3 rearrangement is diagnostic
- Long-term surveillance required - late metastasis well recognised
Workup - Blood Tests
FBC, U&E, LFTs - baseline
Workup - Local Imaging
MRI with contrast of primary site
Workup - Biopsy
Core needle biopsy
Workup - Staging
- CT chest/abdomen/pelvis
- MRI brain - brain metastases common
- Whole body PET-CT per LSESN guidelines
Workup - Other
MDT review with sarcoma specialist centre
Follow-up Summary
Soft Tissue Tumours - Localised Extremity - Intermediate and High Grade
Year 10+
Continue surveillance - late metastasis (lung, bone, brain) well recognised >10 years post-resection
Medical disclaimer
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