Figure 2.

Selected microfluidic platforms for studying breast cancer invasion, the first stage of metastasis, which occurs as cancer cells break off from the primary breast tumor to invade the surrounding tissue. As proliferation increases, cancer cells become confined, hypoxic, and metabolically starved. These factors contribute to an epithelial-to-mesenchymal (EMT) transition within the cancer cells, changing their morphology and greatly increasing their motility. Aside from the primary stimuli of invasion: (i) highly motile amoeboid, (ii) slow collective, and (iii) mesenchymal cell migration, cancer cells have also been shown to become invasive or undergo EMT in response to acidity, stromal and endothelial cell crosstalk, healthy immune cell signaling, excess ECM density, and some forms of chemo- or radiotherapy.