SNAI1 and neoplasm: The specific action of EMT‐TFs and their context dependence are also supported by lineage tracing experiments to evaluate tumor initiation in different genetically engineered knock‐in reporter breast cancer mouse lines, which demonstrated that the EMT program mediated by Snail2 (Slug) is required for normal mammary stem cells, while Snail1‐induced EMT accounts for the acquisition of stemness and tumor‐initiating properties of neoplastic lesions (Ye et al., 2015).