Alveolar soft part sarcoma with neural differentiation and aberrant TLE1 expression: A case report

Alveolar soft part sarcoma (ASPS) is a rare soft tissue tumor of uncertain histogenesis. It occurs most commonly in deep soft tissues of the lower extremities. Relevant histomorphology and diffuse and strong immunoreactivity of TFE3 has been included in essential diagnostic criteria by WHO Soft tissue and Bone tumors, 5th edition. A 35 years female presented with recurrent painless posterior right thigh mass which progressed to a size of 15x15cm in 6 months. MRI of the swelling showed T1 isointense and T2 hetrointense lesion with multiple flow voids and few non enhancing areas suggestive of necrosis. Fine needle aspiration cytology showed tight clusters of round to oval tumor cells with moderate cytoplasm. Sections from the cell block revealed tumor cells arranged in an organoid pattern. Individual cells showed a round to oval nucleus with powdery chromatin and abundant eosinophilic to clear cytoplasm. Diagnosis of undifferentiated sarcoma was made. Histopathological examination of the excised lesion showed round to oval shaped cells arranged in nests and alveolar pattern. Individual cells showed mild degree of atypia with a vesicular nucleus, moderate eosinophilic cytoplasm and distinct cell borders. Increased mitoses, prominent vascularity, extensive areas of necrosis and hemorrhage were seen. Immunohistochemistry (IHC) for TFE3, TLE1, synaptophysin and BCL2 was positive and it was negative for pan cytokeratin and S100. Periodic acid‐Schiff stain for intracytoplasmic crystalline structures was negative. Based on the histomorphology and IHC, diagnosis of ASPS was made showing neural differentiation and abberent TLE1 expression. Further studies were suggested for confirmation of the diagnosis. Accurate diagnosis of ASPS requires trained pathologists and molecular testing to lead the treatment accordingly. This case is presented owing to its overlapping histomorphological and immunohistochemical findings.