A case of bilateral renal cell carcinoma associated with long-term dialysis showing false-positive immunoreactivity for TFE3 as Xp11 translocation renal cell carcinoma

Renal carcinomas associated with Xp11.2 translocations/transcription factor 3 (TFE3) gene fusion (Xp11 translocation RCC) are a rare subtype of renal cell carcinoma. A middle-aged Japanese man, who had a medical history of dialysis for more than 12 years, had bilateral renal cancers with a background of acquired cystic disease of the kidney and remarkable deposition of calcium oxalate in the tumorous area. The right renal tumor showed papillary architecture of clear cells with diffuse and strong immunoreactivity for TFE3 and focal and weak positivity for cathepsin K, suggesting a possibility of Xp11 translocation RCC. However, RT-PCR failed to detect any type of the reported fusion genes involving TFE3. Thus, the sample was sent for a TFE3 break-apart FISH assay in a renal tumor consultation service, which reported no evidence of TFE3 gene rearrangement. The right renal tumor was finally diagnosed as papillary renal cell carcinoma with cystic change. We report here a case of bilateral renal cell carcinoma in a patient undergoing long-term dialysis, which showed false-positive immunoreactivity for TFE3 immunostaining. Titration of TFE3 immunohistochemical staining (IHC) should be performed and cross-referenced with the FISH or RT-PCR results to avoid the misinterpretation of TFE3 IHC results.