Purpose: Heparanase activity has been detected in many malignant tumors, showing a correlation with the metastatic potential. The present study was undertaken to investigate the expression of heparanase and its prognostic significance in renal cell carcinomas (RCC).

Experimental Design: Nineteen RCCs and 6 nonneoplastic renal tissues were analyzed for heparanase mRNA expression by real-time PCR. Heparanase protein expression was semiquantitatively investigated by immunohistochemistry in 70 RCCs. Involvement of heparanase in the invasiveness of RCC cell lines, 786-O and Caki-2 cells, was examined by down-regulating the gene expression with small interfering RNA (siRNA) using the Matrigel invasion assay.

Results: The expression level of heparanase mRNA was significantly higher in clear cell RCCs than in papillary RCCs, chromophobe RCCs, and nonneoplastic renal tissues. Heparanase was predominantly immunolocalized to cell surface and cytoplasm of clear cell RCCs and mean expression levels of heparanase were significantly higher in clear cell RCCs than in papillary and chromophobe RCCs. The protein expression levels were positively correlated with primary tumor stage, distant metastasis, and histologic grade. Targeting of heparanase mRNA expression in 786-O and Caki-2 cells with siRNA down-regulated the mRNA expression and inhibited the Matrigel invasion by these cells, whereas nonsilencing siRNA showed no effect. Multivariate Cox analysis revealed that elevated heparanase expression was a significant and an independent predictor of disease-specific survival (odds ratio, 8.814; P = 0.019).

Conclusions: These data suggest that heparanase plays an important role in invasion and metastasis and silencing of the gene might be a potential therapeutic target in clear cell RCCs.