TFE3 [MD227R]

Xp11 translocation renal cell carcinoma (RCC) is 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. Xp11 translocation RCC represents the most common type of RCC in children, but is less frequent on a percentage basis in adults. Morphologically, the neoplasm frequently shows papillary architecture and clear cytoplasm, and frequently has associated psammoma bodies. Immunohistochemically, the neoplasm under-expresses epithelial markers such as cytokeratin and epithelial membrane antigen compared with typical 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 TFE3. Alveolar soft part sarcoma (ASPS) is an uncommon soft tissue sarcoma which affects predominantly young patients, often in the extremities. ASPS has the specific molecular translocation der(17)t(X;17)(p11.2;q25), which fuses the TFE3 transcription factor gene at 17q25 to ASPL, a gene at 17q25 to form a fusion transcript of ASPL-TFE3. The diagnosis of ASPS can be problematic due to histologic overlap with other tumors, particularly in small biopsies, as well as when the detection of a metastasis is prior to identification of a primary, or when presenting at unusual primary sites such as bone. Moreover, there has previously been a lack of specific diagnostic markers. The differential diagnoses include, in particular, paraganglioma, granular cell tumor, metastatic renal cell carcinoma, hepatocellular carcinoma, melanoma, and adrenal cortical carcinoma. Carcinomas can be separated by the expression of cytokeratins. Paraganglioma shows very strong positivity with anti-synaptophysin. Melanomas can be distinguished by strong positivity with antibodies against HMB-45, S100, and Melan A. These markers generally are all negative in ASPS. Anti-TFE3 has been shown to be highly specific and sensitive for ASPS.