Alveolar Soft-part Sarcoma of the Urinary Bladder With Urethral Recurrence: A Unique Case With Emphasis on Differential Diagnoses and Diagnostic Utility of an Immunohistochemical Panel Including TFE3

Alveolar soft-part sarcoma (ASPS) is a rare, clinically, morphologically, ultrastructurally, and cytogenetically distinctive malignant mesenchymal tumor that most classically occurs in the extremities of adolescents and young adults, but has also been described in a number of unusual sites. The molecular signature of ASPS is a specific der(17)t(X;17)(p11.2;q25) translocation, which results in the fusion of TFE3 transcription factor gene (from Xp11) with ASPL at 17q25. The ASPL-TFE3 fusion protein encoded by the fusion transcript can be detected immunohistochemically with commercially available antibodies to the carboxy terminus of TFE3. Herein, we report a unique case of ASPS presenting in the bladder with subsequent urethral recurrence in a 25-year-old woman. We emphasize the differential diagnoses engendered by ASPS including common, not-so-common, and rare tumors involving the urinary bladder that have a nested architecture, and both clear and eosinophilic cytoplasm, and demonstrate the utility of a broad immunohistochemistry panel including TFE3 for diagnosis.