Alveolar soft part sarcoma (ASPS) is a rare, highly vascular, deep soft tissue mesenchymal malignancy that is classically seen in the lower extremities of young adults. They account for <1% of all soft tissue sarcomas.
There is a slight female predilection in patients less than 30 years old 1.
Though it can occur anywhere in the body, it is most frequently seen in the deep tissues of the lower extremities (thigh and buttock), followed by the trunk and upper extremities in adults. Rarely, it can occur within the female genital tract (e.g. uterus). Whereas in infants and children, the majority of cases occur in the head and neck 6.
Distant metastases at the time of diagnosis is a relatively common feature, with metastases often spreading hematogenously to the lungs, bone, and brain1,4.
ASPS derives its name from its histological appearance1. It is characterized by well-defined nests of large round or polygonal tumor cells with generous eosinophilic cytoplasm, separated by fibrous stroma7. They are arranged in the classic alveolar growth pattern with minimal to no mitotic figures. Vascular invasion is a common feature.
The cells are PAS-positive with diastase-resistant intracytoplasmic inclusions1.
There is strong strong nuclear staining by an antibody directed against the C‐terminus of the transcription factor E3 (TFE3) gene, which shows sensitivity and specificity of 92% for ASPS 11.
Slightly hyperdense soft tissue mass on non-contrast CT, and on contrast-enhanced CT, a vascular mass with heterogeneous enhancement 8. CT angiography will demonstrate a hypervascular mass with multiple, enlarged tortuous vessels feeding the tumor 8.
MRI is recommended for imaging evaluation, where they present as a large, highly vascular mass 9:
- T1: isointense or slightly hyperintense
- T2 hyperintense; associated vascular signal voids are common secondary to large peritumoral blood vessels.
- T1C+: heterogeneous contrast enhancement
Treatment and prognosis
For localized disease without metastases, aggressive treatment with surgery and radiation is indicated 5. For patients presenting with distant metastases, surgery alone is the preferred treatment option 5.
Alveolar soft part sarcoma is highly malignant, with a relatively indolent, yet relentless course. The overall prognosis is poor given the high frequency of metastatic disease 1. A large study indicated that the median survival time was 3 years if metastatic disease was present at diagnosis and 11 years without metastatic disease at presentation 2,4. Another study showed survival rates of 77% at 2 years, 60% at 5 years, 38% at 10 years and only 15% at 20 years 10.
Differential diagnosis includes:
- malignant fibrous histiocytoma: MRI shows necrosis, cystic regions and edema 3
- synovial sarcoma: slow-growing and superficial tumor, without flow voids on MRI, and with calcification, necrosis and hemorrhage often noted on CT 3
- angiosarcoma: more common in males
- osteosarcoma: typical sunburst appearance on radiographs and is usually centered within the bone
- vascular malformations (e.g. AVM): demonstrates pure vascular tissue and no accompanying solid tumor 3
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