Epithelial mesenchymal transition (EMT) is suggested to play an important role during malignent progression of cancer. Nuclear proteins belonging to the Snail family of transcriptional repressors are of crucial importance in the regulation of EMT. To address the problem of malignant tumor development, we aim at identifying factors using functional genetic screenings that modulate epthelial differentiation and which are likely essential during tumor progression. So far, little is known of the in vivo role of Snail and Stug during cancer progression, as there are so far no adequate models to study their in vivo effects on the full malignant cascade. We have obtained different transgenic Snail and Slug mouse models, which will be crossed with relevant spontaneous cancer models. Furthermore, we want to analyse the contribution of Snail induced EMT towards cancer stemness.