TWIST1 and carcinoma: During carcinoma development, growth factors (e.g., epidermal growth factor and transforming growth factor β1) produced by tumor or normal cells trigger the PI3K/AKT and/or the MAPK/ERK pathway; this leads to the activation of the ZEB1, ZEB2, Snail, Slug or Twist transcription factors which, in turn, induce transformed epithelial cells to acquire a mesenchymal phenotype through a process termed epithelial-to-mesenchymal transition (EMT) (Figure 2) [85,86].