t(6;11) renal cell carcinoma (RCC): expanded immunohistochemical profile emphasizing novel RCC markers and report of 10 new genetically confirmed cases.

Renal cell carcinomas (RCCs) harboring the t(6;11)(p21;q12) translocation were first described in 2001 and recently recognized by the 2013 International Society of Urological Pathology Vancouver Classification of Renal Neoplasia. Although these RCCs are known to label for melanocytic markers HMB45 and Melan A and the cysteine protease cathepsin K by immunohistochemistry (IHC), a comprehensive IHC profile has not been reported. We report 10 new t(6;11) RCCs, all confirmed by break-apart TFEB fluorescence in situ hybridization. A tissue microarray containing 6 of these cases and 7 other previously reported t(6;11) RCCs was constructed and immunolabeled for 21 different antigens. Additional whole sections of t(6;11) RCC were labeled with selected IHC markers. t(6;11) RCC labeled diffusely and consistently for cathepsin K and Melan A (13 of 13 cases) and almost always at least focally for HMB45 (12 of 13 cases). They labeled frequently for PAX8 (14 of 23 cases), CD117 (10 of 14 cases), and vimentin (9 of 13 cases). A majority of cases labeled at least focally for cytokeratin Cam5.2 (8 of 13 cases) and CD10 and RCC marker antigen (10 of 14 cases each). In contrast to a prior study's findings, only a minority of cases labeled for Ksp-cadherin (3 of 19 cases). The median H score (product of intensity score and percentage labeling) for phosphorylated S6, a marker of mTOR pathway activation, was 101, which is high relative to most other RCC subtypes. In summary, IHC labeling for PAX8, Cam5.2, CD10, and RCC marker antigen supports classification of the t(6;11) RCC as carcinomas despite frequent negativity for broad-spectrum cytokeratins and EMA. Labeling for PAX8 distinguishes the t(6;11) RCC from epithelioid angiomyolipoma, which otherwise shares a similar immunoprofile. CD117 labeling is more frequent in the t(6;11) RCC compared with the related Xp11 translocation RCC. Increased pS6 expression suggests a possible molecular target for the uncommon t(6;11) RCCs that metastasize.

Utilization of a TFE3 break-apart FISH assay in a renal tumor consultation service.

Xp11 translocation renal cell carcinomas (RCCs) are characterized by chromosome translocations involving the Xp11.2 breakpoint, resulting in gene fusions involving the TFE3 transcription factor. In archival material, the diagnosis can often be confirmed by TFE3 immunohistochemistry (IHC), but variable fixation (especially prevalent in consultation material) can lead to equivocal results. A TFE3 break-apart fluorescence in situ hybridization (FISH) assay has been developed to detect TFE3 gene rearrangements; however, the utility of this assay in a renal tumor consultation practice has not been examined. We reviewed 95 consecutive renal tumor consultation cases submitted to rule in or rule out Xp11 translocation RCC. Thirty-one cases were positive for TFE3 rearrangements by FISH. Patients ranged from 6 to 67 years of age (mean=30 y; median=28 y). Novel or distinctive morphologic features of these cases included extensive cystic change simulating multilocular cystic RCC (3 cases), sarcomatoid transformation (3 cases), oncocytic areas mimicking oncocytoma (1 case), trabecular architecture mimicking a carcinoid tumor (1 case), colonization of renal pelvic urothelium mimicking urothelial carcinoma in situ (1), and focal desmin and diffuse racemase immunoreactivity (1 case each). Twenty-six of the 31 TFE3 FISH-positive RCCs were unequivocally positive for TFE3 by IHC, but 4 were equivocal, and 1 was negative. Of the 64 cases that were negative by TFE3 FISH, 50 were negative by TFE3 IHC, and 14 were equivocal. Thirty-two of the 64 TFE3 FISH-negative cases could be classified into other accepted RCC subtypes: 23 as clear cell RCC, 5 as papillary RCC, 3 as clear cell papillary RCC, and 1 as chromophobe RCC. The other 32 cases remained unclassified, including 3 cathepsin K-positive RCC that closely resembled Xp11 translocation RCC. In conclusion, TFE3 FISH is highly useful in renal tumor consultation material, often resolving cases with equivocal TFE3 IHC results. Given the difficulty of optimizing TFE3 IHC, TFE3 FISH is for most laboratories the optimal test for establishing the diagnosis of Xp11 translocation RCC.

Molecular confirmation of t(6;11)(p21;q12) renal cell carcinoma in archival paraffin-embedded material using a break-apart TFEB FISH assay expands its clinicopathologic spectrum.

A subset of renal cell carcinomas (RCCs) is characterized by t(6;11)(p21;q12), which results in fusion of the untranslated Alpha (MALAT1) gene to the TFEB gene. Only 21 genetically confirmed cases of t(6;11) RCCs have been reported. This neoplasm typically demonstrates a distinctive biphasic morphology, comprising larger epithelioid cells and smaller cells clustered around basement membrane material; however, the full spectrum of its morphologic appearances is not known. The t(6;11) RCCs differ from most conventional RCCs in that they consistently express melanocytic immunohistochemical (IHC) markers such as HMB45 and Melan A and the cysteine protease cathepsin K but are often negative for epithelial markers such as cytokeratins. TFEB IHC has been proven to be useful to confirm the diagnosis of t(6;11) RCCs in archival material, because native TFEB is upregulated through promoter substitution by the gene fusion. However, IHC is highly fixation dependent and has been proven to be particularly difficult for TFEB. A validated fluorescence in situ hybridization (FISH) assay for molecular confirmation of the t(6;11) RCC in archival formalin-fixed, paraffin-embedded material has not been previously reported. We report herein the development of a break-apart TFEB FISH assay for the diagnosis of t(6;11)(p21;q12) RCCs. We validated the assay on 4 genetically confirmed cases and 76 relevant expected negative control cases and used the assay to report 8 new cases that expand the clinicopathologic spectrum of t(6;11) RCCs. An additional previously reported TFEB IHC-positive case was confirmed by TFEB FISH in 46-year-old archival material. In conclusion, TFEB FISH is a robust, clinically validated assay that can confirm the diagnosis of t(6;11) RCC in archival material and should allow a more comprehensive clinicopathologic delineation of this recently recognized neoplastic entity.