Figure 1

Role of Snail1 and Twist1 during mammary gland development and breast cancer progression. In females, release of ovarian hormones induces further development of the mammary gland. Snail1 and Snail2 control aromatase expression, indicating that they have a role in development of the ductal network. Somatic mutations and/or aberrant expression of oncogenes can cause proliferation of mammary epithelial cells. During malignant cancer progression, Snail1 induces an epithelial-to-mesenchymal transition (EMT) of epithelial breast cancer cells, which grants them invasive and migratory capacities. Twist1 plays a role in the development of distant metastasis by prompting cancer cells to enter the bloodstream. At distant organs, these cells undergo a mesenchymal-to-epithelial transition (MET).