Xp11 translocation renal cell carcinoma

A case of Xp11 translocation renal cell carcinoma (RCC) is reported in a pediatric patient, 5 years postchemotherapy for Wilms tumor. The tumor showed nested architecture with numerous psammomatous calcifications. Cytologically, the cells had voluminous clear cytoplasm with prominent nucleoli. While cytokeratin and epithelial membrane antigen stains were negative, TFE3 immunostain (a sensitive and specific marker for these neoplasms) displayed diffuse nuclear immunoreactivity. The clinical history, morphology, and immunohistochemistry were consistent with an Xp11 translocation RCC. These neoplasms all have translocations involving a breakpoint at Xp11.2, resulting in gene fusions involving the TFE3 transcription factor gene, which maps to this locus. Multiple different genes have been identified as TFE3 fusion partners in these RCC, including the same one (ASPL) found in alveolar soft part sarcoma. Xp11 translocation RCC likely comprises the majority of pediatric RCCs. While uncommon on a percentage basis in adults, adult cases may outnumber pediatric cases due to the much higher overall incidence of RCCs in the adult population. Prior exposure to chemotherapy is a distinct risk factor for its development. The tumor can metastasize decades after its initial presentation, so long-term follow-up is necessary.