INSM1

The intronless INSM1 gene is located on chromosome 20p11.23 and encodes a zinc finger transcription factor. INSM1 is primarily involved in neuroendocrine differentiation and is exoressed in neuroendocrine cells found throughout the body. In normal tissues, nuclear INSM1 immunostaining is observed in scattered neuroendocrine cells within the gut, including the mucosa of the stomach, duodenum, ileum, rectum, and appendix. Islets of Langerhans in the pancreas, cells in medulla of the thymus, adrenal gland (medullar cells), and some cell  of the adenohypophysis.

INSM1 is expressed in the majority of neuroendocrine neoplasms: Neuroendocrine tumours (NETs), small cell lung carcinoma, Merkel cell carcinoma, medullary thyroid carcinoma, pheochromocytoma and paraganglioma. Some degree of expression is also seen in Ewings sarcoma, solitary fibrous tumour, Rhabdomyosarcoma and myxoid lioposarsoma.

The primary application of INSM1 is in diagnosis and classification of neuroendocrine tumors and differentiation. INSM1 typically demonstrates a nuclear staining pattern, with a moderate to strong reaction observed in either a subset or majority of cells.