This classification recognises five PA subtypes, depending on the aberrant hormone immunostaining: prolactin tumour (PRL), growth hormone tumour (GH), adrenocorticotropic hormone tumour (ACTH), thyroid-stimulating hormone tumour (TSH, α-subunit (SU)) and gonadotroph hormone tumour (follicle-stimulating hormone (FSH), luteinising hormone (LH) or SU) [8]. The gene discussed is GH1; the disease is neoplasm.