Acidophil stem cell tumors and immature PIT1-lineage tumors are less well differentiated and have an extremely variable clinical presentation; not all patients have GH excess and when present, it is variable; these tumors are also associated with hyperprolactinemia and, in the case of the immature PIT1-lineage neoplasms, hyperthyroidism. Here, GH1 is linked to neoplasm.