title: Renal cell carcinoma with t(6:11) (p21;q12). A case report highlighting distinctive immunohistologic features of this rare tumor.
abstract: BACKGROUND
  Renal cell carcinoma (RCC) with t(6:11) (p21;q12) are extremely rare, fewer than 30 cases have been reported in literature. These tumors are characterized by specific chromosomal translocation involving TFEB, as against the more commonly known TFE3 (Xp11.2) translocation associated RCCs. The distinctive immnohistologic features are helpful in enabling a diagnosis of this rare tumor, otherwise diagnosed by fluorescence in situ hybridization assay, specific for detecting TFEB gene rearrangement.
  
  
  METHODS
  Herein, we report a case of this rare tumor in a 11 years old boy, with the objective of highlighting distinctive light microscopic and immuno-phenotypic features of this rare sub-type of translocation associated renal cell carcinoma, otherwise diagnosed by fluorescence in situ hybridization technique. Morphologically tumor showed distinctive biphasic population of cells, large epitheloid cells with voluminous eosinophillic cytoplasm and smaller cells with much lesser amount of cytoplasm and small rounded nuclei. The smaller cells at places clustered around hyaline pink material forming "pseudorosettes". population. Immunohistochemically both types of tumor cells showed negativity for pan CK (cytokeratin), EMA (epitheleal membrane antigen) and TFE3 (transcription factor E3). HMB 45 (human melanoma black 45) and Melan- A /MART 1 (melanoma antigen recognized by T cells) were moderate to strongly expressed.
  
  
  CONCLUSIONS
  On review of literature, most RCCs with t(6;11) translocation have been reported to be negative for pan cytokeratins and EMA. Published literature also shows that the most distinctive immunohistochemical feature of t(6;11) translocation RCC is nuclear staining for TFEB protein. Immunostains for TFE3 have always been negative in the reported cases. It is noteworthy that immunoreactivity for melanocytic markers HMB45 and Melan A and immunonegativity for epithelial markers pan CK and EMA may lead to misdiagnosis of angiomyolipoma to the unwary.
  
  
  CONCLUSIONS
  Knowledge of distinctive morphological and immuno-histochemical features of this tumor can help in establishing a diagnosis of this rare subset of translocation associated RCC on routine hematoxylin and eosin (H and E) staining and immunophenotyping.
authors.affiliation: Department of Surgical Pathology And Cytology, Breach Candy Hospital Trust, 60 A Bhulabhai Desai Road,Mumbai 400026, India. Electronic address: drsarabjeetkaur@breachcandyhospital.org.
authors.forename: Sarabjeet Kaur
authors.initials: SK
authors.lastname: Arneja
authors.affiliation: Department of Surgical Pathology And Cytology, Breach Candy Hospital Trust, 60 A Bhulabhai Desai Road,Mumbai 400026, India. Electronic address: drneeraj.gujar@breachcandyhospital.org.
authors.forename: Neeraj
authors.initials: N
authors.lastname: Gujar
keywords: Immuno-histology; RCC; Renal cell carcinoma; TFE3; TFEB; q12); renal cell carcinoma; t(6:11) (p21;; translocation factor E3; translocation factor EB