Is Quantitative Real-Time RT-PCR an Adjunct to Immunohistochemistry for the Evaluation of ErbB2 Status in Transitional Carcinoma of the Bladder?

To test different approaches of evaluation of the ErbB2 status in a large series of human transitional cell carcinoma (TCC) of the bladder with the prospect of finding targeted therapies. ErbB2 status of 73 human TCC samples was analyzed by both immunohistochemistry (IHC) and by quantification of mRNA levels of expression using real-time reverse transcription-polymerase chain reaction (RT-PCR). Additionally, 18 bladder samples were studied for ERBB2 gene amplification by real-time quantitative PCR. Twenty-five tumors (34.2%) overexpressed ERBB2 mRNA compared to normal bladder samples; this alteration appeared in low-grade and low-stage tumors (pTaG1). Twenty-four (32.9%) tumors showed moderate (++) or strong (+++) immunostaining. A very strong agreement was found between the two methods (κ=0.97, 95% confidence interval, 0.90–1). ErbB2 status was not associated with tumor stage. Of the 18 bladder samples tested for ERBB2 gene amplification, only one showed ERBB2 DNA amplification. ErbB2 overexpression occurs in about one third of bladder TCCs. This overexpression can be detected by RT-PCR with a very good correlation with IHC. RT-PCR can therefore be used for cases considered doubtful on IHC rather than gene amplification studies because, in TCC, gene amplification is not the predominant mechanism of both mRNA and protein overexpression. Accurate quantification of ErbB2 status is mandatory for the use of anti-ErbB2–targeted therapies in bladder TCC.