Epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) processes. EMT occurs through (step 1) local invasion and formation of the initial tumor, (step 2) intravasation to enter the bloodstream, (step 3) systematic transport to a metastatic site, usually another organ, (step 4) extravasation out of the bloodstream, and (step 5) colonization and formation of a metastatic tumor through cell proliferation. MET is the reversal process, which occurs in the same steps in the reverse order as labeled in this figure (steps 5 to 1)
Note. Adapted from “Epithelial–mesenchymal plasticity in carcinoma metastasis” by Tsai JH, Yang J. Genes Dev. 2013;27:2192–206 (https://genesdev.cshlp.org/content/27/20/2192.long). CC BY-NC.