TFE3 (MRQ-37)

Xp11 translocation renal cell carcinomas (RCC) are a recently recognized subset of RCC, characterized by chromosome translocations involving the Xp11.2 break point and resulting in gene fusions involving the TFE3 transcription factor gene that maps to this locus.1 Xp11 translocation RCC represents the most common type of RCC in children, but is less frequent on a percentage basis in adults.2 Morphologically, these neoplasms frequently show papillary architecture and clear cytoplasm, and frequently have associated psammoma bodies. Immunohistochemically, these neoplasms under-expresses epithelial markers such as anti-cytokeratin and anti-epithelial membrane antigen (anti-EMA) compared with typical adult type RCC. The most sensitive and specific immunohistochemical marker for the Xp11 translocation RCC is nuclear labeling of TFE3 protein, which reflects over-expression of the resulting fusion proteins relative to native TFE3.3 Alveolar soft part sarcoma (ASPS) is an uncommon soft tissue sarcoma of undertain differentiation. It presents in younger patients, often in the extremities. Despite relatively high rates of metastasis, patients often experience prolonged survival in the metastatic setting relative to others. The hallmark of ASPS is a chromosomal rearrangement at 17q25 and Xp11.2 engendering an ASPSCR1-TFE3 fusion gene responsible for an aberrant transcription factor presumably enabling pathogenesis.4 This aberrant chimeric transcription factor retains the N-terminal DNA binding domain encoded by TFE3 while the ASPSCR1 encoded portion probably provides domain(s) modulating gene expression.4 The presence of this super-activated transcription factor may induce the expression of numerous molecules contributing to ASPS diagnosis, progression, and metastasis.4