The cell of origin for pituitary tumours can be one of the five differentiated cell types: growth hormone- (GH-) secreting, adrenocorticotrophic hormone- (ACTH-) secreting, prolactin- (PRL-) secreting, thyroid-stimulating hormone- (TSH-) secreting, or nonfunctioning pituitary cells (NFA) within the pituitary gland [167]. The gene discussed is PRL; the disease is pituitary tumor.