Osteopontin expression correlates with prognostic variables and survival in clear cell renal cell carcinoma

Background and Objectives: Osteopontin (OPN) is a phosphorylated glycoprotein with diverse functions including tumorigenesis and tumor cell metastasis. Recently, it has been detected in a growing number of human tumors, and assessed as a potential prognostic marker. The aim of this study was to analyze the expression of OPN in normal renal tissue and clear cell renal cell carcinomas (CRCCs), and to assess its prognostic significance. Methods: The expression of OPN protein was immunohistochemically analyzed in 171 CRCCs and compared to usual clinicopathological parameters such as tumor size, nuclear grade, pathological stage, Ki-67 proliferation index, and cancer-specific survival. Results: In normal renal parenchyma, the expression of OPN was seen in distal tubular epithelial cells, calcifications, and some stromal cells. The upregulation of OPN was observed in 61 CRCCs (35.7%) in the form of cytoplasmic granular staining of various intensities. Statistical analysis showed correlation of the OPN expression with tumor size (P < 0.001), Fuhrman nuclear grade (P < 0.001), pathological stage (P = 0.011), and Ki-67 proliferation index (P < 0.001). Moreover, patients with OPN-positive tumors had significantly worse prognosis in comparison to patients with tumors lacking OPN protein (P = 0.004). Conclusion: Our results suggest that overexpression of OPN is involved in the progression of CRCC.