Tumors with a subgroup of cancer cells that undergo epithelial-mesenchymal transition, which downregulate some genes (such as E-cadherin, β-catenin, cytokeratin 5 and 6) and upregulate other genes (such as E-cadherin, vimentin, Snail, Slug, Twist, ZEB1 and 2, S100A4, MMP2 and 3, α-smooth muscle actin), so these tumors become metastasized, activating mobility-enhancing genes (such as S100 CBPP) and releasing cancer cells into the blood circulation that are often chaperoned by stromal cells. The gene discussed is TWIST1; the disease is cancer.