The classification of these tumours is usually based on the types of pituitary hormones they produce, such as prolactin (PRL), growth hormone (GH), adrenocorticotropic hormone (ACTH), luteinising hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and others (Levy, 2004). The gene discussed is GH1; the disease is neoplasm.