TWIST1 and pancreatic neuroendocrine tumor: Twist was not found in this stages of islet cell tumor development (Figure 4E and F), whereas Vimentin (Figure 4G and H) was strongly expressed in the tumor stroma.These observations demonstrate that Snail is expressed in islet cell tumors of Rip1Tag2 mice, therefore providing a valid target for the Snail inhibitor PEG.