[788] Development of a TFEB Break-Apart Fluorescence In Situ Hybridization (FISH) Assay for Diagnosis of the t(6;11)(p21;q12) Renal Cell Carcinomas Harboring the Alpha-TFEB Gene Fusion in Archival Material

Pedram Argani, Raluca Yonescu, George J Netto, Peter B Illei, Constance A Griffin. Johns Hopkins Medical Institutions, Baltimore, MD

Background: Renal cell carcinomas (RCC) harboring the t(6;11)(p21;q12) chromosome translocation were first described in 2001, and subsequently have been shown to harbor a specific Alpha-TFEB gene fusion resulting in upregulation of native TFEB protein. Fewer than 20 genetically confirmed cases have been reported. Immunohistochemistry for TFEB protein is a highly sensitive and specific marker for the presence of the Alpha-TFEB gene fusion in optimally processed archival material; however, it is highly sensitive to variable fixation and thus often yields nondiagnostic results in consultation material. Break-apart florescence in situ hybridization (FISH) assays, such as those reported for the related TFE3 gene used for the diagnosis of Xp11 translocation RCC, are typically less sensitive to fixation than immunohistochemical assays, and may resolve immunohistochemically-ambiguous cases. A break-apart FISH assay for TFEB gene fusions has not been reported.
Design: Using a cytogenetically confirmed t(6;11)(p21;q12) RCC, we developed a break-apart TFEB FISH assay. We used bacterial artificial chromosome (BAC) probes, 3 centromeric to and 2 telomeric to TFEB. The assay was validated on 6 additional confirmed cases of t(6;11)(p21;q12) RCC consisting of 2 additional genetically confirmed cases, and 4 morphologically typical cases which showed robust TFEB immunoreactivity. We also studied as negative controls 11 unrelated RCCs and normal tissues. For each case, 6 different observers counted signals derived from the BAC probes centromeric and telomeric to TFEB in 100 cells. The mean percentage of split signals per case among the observers was recorded.
Results: All 7 confirmed t(6;11)(p21;q12) RCC (patient ages 3-37 years; mean age 19) demonstrated a high percentage of cells with split signals (mean= 45%, range among cases, 30-60%). Of note, one of the cases had been resected 46 years before the TFEB FISH assay was performed, demonstrating the stability of the FISH assay in archival material. None of 11 unrelated RCC demonstrated a high percentage of cells with split signals (mean=5%; range among cases, 2-11%).
Conclusions: We report the development of a TFEB break-apart FISH assay for diagnosis of the t(6;11)(p21;q12) RCC which harbor the Alpha-TFEB gene fusion. This assay should allow more definitive identification of the t(6;11)(p21;q12) RCC in archival material, and permit further clinicopathologic studies to be performed on this distinctive neoplasm.
Category: Genitourinary (including renal tumors)

Tuesday, March 20, 2012 9:30 AM

Poster Session III # 147, Tuesday Morning

 

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