Figure 3.

During tumor progression, EMT positive tumor cells from primary tumor gain the ability of migration and invasion and their proliferation is inhibited which are thought to be dormant tumor cells. They are colored gray. After systemic dissemination, only a small portion of circulating tumor cells arrive at their target organ and they have to undergo MET to accomplish colonization. Until now, there are two different viewpoints concerning the following stages. (A) when EMT positive tumor cells arriving at target organ, the MET program induce their colonization and activation. The activated tumor cells then proliferate into macrometastasis. They are colored red. (B) when EMT positive tumor cells arriving at target organ, the MET program may just promote their colonization or formation of micrometastasis that stay in dormant stage. Then the secondary partial EMT is thought to induce their activation and turn the dormant micrometastasis into macrometastasis.