Fig. 3. The role of osteopontin in multi-steps of cancer cell metastasis.

The OPN overexpression induces multi-steps of cancer cell metastasis through activating different protein mediators. A primary tumour undergoes vascularisation by angiogenesis as various growth factors such vascular endothelial growth factor are secreted. Detachment of the cancerous cell then occurs followed by intravasation; the tumour cell enters and circulates the vascular system. The cell eventually attaches to the wall of the blood vessel before undergoing extravasation and leaving the blood vessel. The tumour cell then grows as a secondary tumour causing metastasis