SOX2 and neoplasm: As described above, the ACP mouse model showed that WNT activation in the pituitary’s resident stem cells is a key event in ACP tumor development and growth, and that the mutated SOX2+ cells promote the proliferation of the surrounding cells, probably via paracrine signaling that also includes several WNT ligands showing upregulated gene expression (e.g., Wnt5a, Wnt6, Wnt10a) (3, 4, 32).