Figure 1.

Schematic representation of CTC generation, intravasation, circulation, extravasation, proliferation, and colonization. In the invasion process, cancer cells actively break down the basement membrane, migrate through the extracellular matrix, and enter the circulation. CTCs detach from primary tumors in the form of both single cells and cell clusters. Once the CTCs enter blood circulation, they are covered with platelets, and this coating induces the EMT phenotype in the CTCs. In secondary sites, CTCs extravasate and colonize in the tissues, where MET is induced.