Loss of E-cadherin expression has been well known as a hallmark of epithelial-mesenchymal transition (EMT), which is linked to increased risk of cancer metastasis. However, it was less clear whether E-cadherin and its downstream signaling pathways are functionally involved in driving EMT and the prometastatic phenotype. A study by Onder and colleagues in 2008 discovered that E-cadherin loss not only helps tumor cells detach from each other by breaking down cell-cell junctions but also elicits intracellular signaling events to confer a mesenchymal cell state and metastatic phenotype. This study established E-cadherin as an important global regulator, rather than just a marker, of EMT. The discovery inspired further investigation in the following decade that significantly deepened our understanding of E-cadherin and its diverse functions and more broadly of cellular plasticity in different stages and contexts of cancer metastasis.See related article by Onder and colleagues, Cancer Res 2008;68:3645-54. ©2021 American Association for Cancer Research.