ABSTRACT

Metastasis is a common biological process of solid epithelial tumors. This process was vividly described as the ‘seed and soil’ theory by Stephen Paget in 1889 (Paget 1889). During tumor metastasis, tumor cells shed from the primary tumor and invade the surrounding tissue, enter either the blood or the lymphatic circulation, extravasate and fi nally grow at a distant tissue (Steeg 2006). Metastasis is the main cause of death for cancer patients. It is necessary to develop an effective method to monitor and treat tumor metastasis, as traditional treatments such as surgery and radiographic imaging aim at the primary tumor, and chemotherapy and hormonal therapy usually act as palliative care.