Osteopontin (OPN) is a multifunctional phosphoprotein secreted by various cells.OPN serves in both cell attachment and cell signaling by interacting with integrins in various pathological conditions.OPN expression has been demonstrated in a variety of human carcinomas.The recent studies showed that OPN expressed by tumor cells was associated with the motile and invasive behaviors of tumor cells,suggesting that OPN might contribute to invasion and metastasis of tumors.