It is clinically important to identify bladder cancers with a high risk of intravesical recurrence after transurethral bladder tumor resection. We developed molecular markers for predicting intravesical recurrence of superficial bladder transitional cell carcinoma using oligo-microarray analysis.

Gene expression profiles associated with intravesical recurrence were analyzed by oligo-microarray in 27 superficial bladder transitional cell carcinoma samples from cases treated with transurethral resection between 2000 and 2004 at Kyoto University Hospital. Of candidate genes the expression of P21-activated kinase (Pak1) was validated by semiquantitative real-time polymerase chain reaction using another set of samples and immunohistochemistry. Furthermore, Pak1 functions in bladder cancer cells were analyzed by the transfection of constitutively active (T423E) or kinase dead (K299R) Pak1.

Microarray identified 25 genes whose expression was associated with recurrence, including Pak1. Pak1 mRNA expression was statistically associated with grade and the risk of recurrence but not with stage in 86 bladder cancers. Immunohistochemistry and multivariate analysis demonstrated that high Pak1 protein expression was an independent factor associated with recurrence (relative risk 2.27, p = 0.008). High Pak1 expression was significantly associated with a high risk of recurrence even in low stage/grade cancers. Transfection with T423E Pak1 into 253J cells progressed cell motility on wound healing assay, whereas transfection with K299R Pak1 decreased EJ cell motility.

These results suggest that Pak1 expression is associated with recurrence and it might be a useful prognostic marker for superficial bladder transitional cell carcinoma.