Proteases in tumor invasion and metastasis

Metastatic cells comprise only a small, particular sub-populatation of highly malignant cells which pre-exist with a primary tumor [1–3]. The metastatic spread of cancer appears to be a selective process which is dependent upon complex interactions between metastatic cells and host properties [1, 4] including, for example, either effective or compromised anti-metastatic immune reactivity. Discrete sequential steps contribute to the mechanism of metastatic tumor growth, and cells with metastatic potential must survive and complete each step in order to successfully establish secondary tumor foci [1].