A process called the epithelial-to-mesenchymal transition allows cancer cells to invade nearby tissue and metastasize. Katz et al.investigated the molecular underpinnings of this process and determined that tumors with a more epithelial gene signature expressed higher amounts of the Musashi (Msi) family of RNA-binding proteins as compared to tumors with a more mesenchymal profile. High amounts of Msi proteins locked mammary cells in a state that was less mobile and incapable of differentiation. Reducing Msi expression allowed breast cancer cells to transition into a mesenchymal-like form. Msi proteins may impose an undifferentiated state on cancers, as these proteins are also abundant in neural stem cells….