Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via inhibition of the release of numerous secondary hormones. This antibody is a useful marker of D-cells of pancreatic islet cells which can be used to identify hyperplasia of the pancreatic islets as well as islet cell tumors, including somatostatinomas. Somatostain is also expressed in gastrointestinal and bronchopulmonary endocrine cells, thymic endocrine cells, and thyroid C cells.