Combination of immunohistochemistry, FISH and RT-PCR shows high incidence of Xp11 translocation RCC: comparison of three different diagnostic methods

We evaluated the frequency of translocation renal cell carcinoma (RCC) by reverse transcription polymerase chain reaction (RT-PCR) and how well the TFE3 immunoreactivity is concordant with TFE3 gene translocation status proved by fluorescence in situ hybridization (FISH) assay and RT-PCR. TFE3 and Cathepsin K expression was analyzed by immunohistochemistry in 185 RCC cases, and 48 cases either of more than weak expression of TFE3 or of positivity for Cathepsin K were done for FISH analysis and RT-PCR. All the RT-PCR positive cases were confirmed by cloning and sequencing. Of the 14 cases with strong nuclear TFE3 expression, 12 showed a break-apart signal by FISH. ASPL- and PRCC-TFE3 translocations were detected in 13 and one case, respectively, by RT-PCR. Of 21 cases with weak TFE3 expression, five were translocation-positive by FISH. ASPL-, PRCC-, and PSF-TFE3 translocations were detected by RT-PCR (n=3, 3, and 1, respectively). All 13 TFE3-negative/cathepsin K-positive cases were negative by FISH and two each harbored ASPL- and PRCC-TFE3 translocations that were detected by RT-PCR. A high rate of TFE3 immunoreactivity (8.6%) was confirmed by RT-PCR (13.5%) and FISH (9.7%). Higher translocation rate of RT-PCR means RT-PCR detected translocation in TFE3 weak expression group and only cathepsin K positive group more specifically than FISH. Thus, RT-PCR would complement FISH analysis for detecting translocation RCC with fusion partners.