Mir 200 family members are exceedingly enriched in epithelial tissues. Mir 200 is not expressed in ordinary fibroblast which are of mesenchymal origin, while Mir 200 family is expressed in ordinary epithelial cells. Mir 200 family is believed to play and important role in suppressing tumor by inhibiting transition to epithelial mesenchymal, which is the initiative step of metastasis. Epithelial Mesenchymal Transition occurs as a result of embryonic development and have great similarities with cancer development. Epithelial Mesenchymal Transition make cells to lose grip and rise in motility. This occurs during the initial stages of metastasis as characterized by suppression of E-cadherin expression that happens during metastasis initial stages.
In a way of difference, Mir 200 has proven to have promoted metastasis last step in which migrating cancer cells experience Epithelial Mesenchymal Transition (MET) when distance tissues are colonizing. In a different stages of mouse mammary isogenic cancer cell lines, Mir 200 family have high expression in the cells which are able to form metastases but not in other cancer cells that are not able to colonize. Mir 200c Overexpression in metastatic cancer cells that are not ready enable Epithelial Mesenchymal Transition to colonize lung and live.