Fig. 6. Schematic representation of EMT during the metastatic cascade.

Tumor cells can undergo gradual or full EMT (E, E/m, M/e, and M) that is associated with decreased proliferation, loss of EpCAM expression, and increased migration. In the metastatic cascade, M > M/e > E/m cells have increased ability to intravasate into the lymphovascular system. Once tumor cells intravasate into blood vessels, they are termed CTCs. E- and E/m-type CTCs have enhanced capacity to adhere, hence to extravasate into distant site. After homing into distant organs, including the bone marrow, systemic tumor cells are termed DTCs. E and E/m systemic tumor cells are associated with improved capacity in proliferation and metastatic outgrowth, and M/e- and M-type cells are related to long-term tumor recurrence.