GH1 and pituitary tumor: Pituitary tumors that cause GH excess have several variants, including pure somatotroph tumors that can be densely-granulated or sparsely granulated, or plurihormonal tumors that include mammosomatotroph, mixed somatotroph-lactotroph tumors and mature plurihomonal Pit1-lineage tumors, as well as the rare acidophil stem cell tumors and poorly-differentiated Pit1-lineage tumors.