alveolar soft part sarcoma

unknown tissue of origin. Epidemiology: - ~0.5% - 0.9% of soft tissue sarcomas in adults - ~0.8% - 1.8% of soft tissue sarcomas in children - most common between 15 and 35 years - most commonly occurs in extremities especially deep soft tissues of thigh - most common site in children is head & neck region especially orbit and tongue Pathology: - poorly circumscribed - necrosis and hemorrhage common - early metastasis is characteristic - most common sites - lung, bone & brain - lymph node metastasis is uncommon Microscopic Pathology: - nests of large loosely arranged polygonal, uniform epitheliod cells surrounded by delicate connective tissue with endothelial lined vascular channels - in some instances may grow as sheets of cells - rhomboid or rod-shaped intracellular crystalline inclusions - variable amounts of glycogen and diastase resistent granules - infrequent mitoses - vascular invasion almost invariable Immunopathology: desmin sometimes + s100, neuron specific enolase + in ~1/4 cases synaptophysin - chromogranin - neurofilament proteins - cytokeratin - EMA - Genetics: - der(17)t(X;17)(p11;q25) fusion of TFE3 transcription factor gene (Xp11) with ASPL gene (ASPSCR1) at 17q25 Clinical manifestations: - slowly growing painless mass - early metastasis is characteristic feature

References

WHO Classification Tumours of Soft Tissue and Bone Fletcher, Unni & Mertens Eds. IARC Press 2002