The group headed by Martinez-Barbera showed in elegant studies that, when occurring in pituitary stem cells (namely SOX2+ cells), CTNNB1 mutations led to the development of clusters of cells originating from these SOX2+ cells which, in turn, are able to secrete high levels of growth factors (epidermal growth factor, fibroblast growth factor, transforming growth factor beta and cytokines (such as sonic hedgehog, IL-1 and IL-6), that will eventually promote proliferation and invasion of the surrounding epithelial cells by the tumor [44,48]. The gene discussed is CTNNB1; the disease is neoplasm.