Fig. 1.

Cartoon depiction of the metastatic process. (a) To metastasize, cells in the (1) primary tumor, located at position 1; (2) separate and undergo EMT; (3) invading through local tissues surrounding the initial lesion before (4) intravasating from the basement membrane into the vasculature or lymphatic system. Metastatic cells then begin to travel as CTCs or CTM through the vasculature. (b) Cells in the metastatic cluster (5) adhere to the basement membrane and then (6) exit at a distal location in a process called extravasation to (7) form a tumor at a secondary site. Arrows indicate direction of migration.