EMT and back again: Visualizing the dynamic phenotypes of metastasis

To what extent does the acquisition of mesenchymal phenotypes by tumor epithelial cells contribute to metastasis? A definitive answer to this question has remained elusive despite much experimentation and debate. Recently, an influential study based on fluorescence-based lineage tracing technology provided evidence that very few of the cells that populate experimental metastases in fact undergo the epithelial-to-mesenchymal transition. Persistent questions regarding the concordance between marker conversion and cell phenotypes prompted Lourenco and colleagues to complement their lineage tracking system with single-cell analysis. This granular approach provides an unprecedented view of the phenotypic transitions that take place during metastasis and their striking heterogeneity.