Cancer metastasis is the process by which malignant cells move from the primary tumor and establish new distant sites of cancer throughout the body. This ability of cancer cells to move beyond the primary tumor is one of the hallmarks of malignant disease. Metastasis is a complex and intricate process that is responsible for treatment failure and the eventual death of most patients with cancer. The discovery of metastasis as an active process rather than a random act of nature has increased our understanding of this dynamic process and has inspired researchers to explore the sequence of events leading to metastasis.