The alveolar nature of the lesion is evident on low power.
Tongue muscle is seen in the middle and surrounded by infiltrating tumor on both sides.
The cells show uniform cytological features throughout the tumor. Image
The tumor cells have round vesicular nuclei with a prominent nucleolus, and a moderate amount of eosinophilic cytoplasm.
PAS stain highlights the cytoplasm.
Alveolar soft part sarcoma is a rare aggressive sarcoma with a propensity for lymphovascular and distant spread. It most often arises in the extremities and head and neck. In children, a substantial number of cases arise in the head and neck (e.g. orbit, tongue).
Microscopically, nests of polygonal tumor cells with clear to eosinophilic cytoplasm are invested by fibrovascular septae and delicate vascular channels. The tumor can be so vascular that a bruit can be heard clinically (Goldberg). PAS positive, diastase-resistent rod-like or rhomboid structures are characteristic.
The characteristic cytogenetic lesion seen in ASPS is an unbalanced translocation involving ASPL (alveolar soft part sarcoma locus) on chromosome 17 and the TFE3 (transcription factor 3 locus) on the X chromosome. This translocation is designated as der(17)t(x:17). This leads to upregulation of TFE3 detected as nuclear staining on IHC. TFE3 nuclear positivity is a sensitive method for supporting the diagnosis, and this is really nice because ASPS does not stain for much else. ASPS is negative for cytokeratins, EMA, chromogranin, synaptophysin, HMB45 and melanA. Vimentin is positive in 30% to 50% of cases (Folpe).
Resection is indicated if feasible. Some cases of ASPS of the tongue have shown marked intraoperative bleeding, and so pre-operative embolization is sometimes considered, especially if the tumor is located in a very posterior location.
Metastatic disease, often involving the lungs, is not uncommon at the time of presentation.
→In adults, ASPS tends to arise in the extremities. For children, the head and neck (especially the tongue) are the favored locations.
→The characteristic translocation is der(17)t(X;17).
→For IHC, TFE3 nuclear staining is a sensitive and specific marker.
Folpe AL, Inwards CY. Bone and Soft Tissue Pathology: Foundations in Diagnostic Pathology Philadelphia, PA: Elsevier; 2010: 295-8.
Goldberg JM, et al (2005). Clear cell sarcoma and alveolar soft part sarcoma: ESUN article. Liddy Shriver Sarcoma Initiative. Available at sarcomahelp.org