or the lymphatics or through both routes. The most common sites of metastases are the lungs, liver, brain, and the bones.

Currently, three main theories have been proposed to explain the metastatic pathway of cancer: the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) hypothesis, the cancer stem cell hypothesis, and the macrophage-cancer cell fusion hybrid hypothesis. Some new hypotheses