Figure 4.

Selected microfluidic platforms for studying breast cancer extravasation, the process by which CTCs exit the vasculature in remote host organs. Individual CTCs resist immune system attacks through a myriad of mechanisms, such as the degradation of apoptotic receptors and the expression of attack-arresting surface markers. However, individual CTCs may undergo apoptosis under the influence of immune cytokines and fluid shear forces, and undergo anoikis upon loss of attachment to the extracellular matrix (ECM) and neighboring cells due to a lack of fibronectin mediation. CTCs that aggregate have been shown to be more resilient, particularly when the aggregates include platelets and neutrophils which disguise them. At remote sites, solitary carcinoma cells can extravasate through either endothelial poration or pericyte-mediated recruitment; they then may remain solitary (micrometastasis) or form a new secondary tumor through EMT (macrometastasis).