Figure 1.

Formation of tumor microemboli. CTC clusters in vessels can originate from a proliferation or gathering of single CTCs, or from direct fall-off from tumor embolization. CTC clusters are prone to be intercepted and form micro-tumor emboli in capillaries, vessels undergoing vasospasm or vessels with thrombosis. Hypoxia caused by micro-tumor embolization or/and TGF-β released by platelets can induce the EMT of tumor cells, enhancing their invasion capacity and resulting in extravasation to ectopic organs (e.g., the lungs). CTC, circulating tumor cell; TGF-β, transforming growth factor-β; EMT, epithelial-mesenchymal transition.