INSM1

INSM1 (insulinoma‑associated protein 1) is a nuclear transcription factor and a highly sensitive and specific marker of neuroendocrine differentiation. In IHC, it shows strong nuclear staining and reliably identifies a broad spectrum of neuroendocrine neoplasms, including small cell carcinoma, large cell neuroendocrine carcinoma, well‑differentiated neuroendocrine tumours, Merkel cell carcinoma, medullary thyroid carcinoma, paraganglioma/pheochromocytoma, and olfactory neuroblastoma. INSM1 also stains normal neuroendocrine tissues such as adrenal medulla, pancreatic islets, thyroid C cells, and gastrointestinal enterochromaffin cells. It is particularly useful when traditional neuroendocrine markers (synaptophysin, chromogranin, CD56) are negative, and has been shown to be equal in sensitivity and specificity compared to these markers (1).

Recommended Controls

Criteria for assessing INSM1 staining as satisfactory: expected staining is nuclear. Recommended controls to include a paraganglioma which will be strongly positive and for the negative control, a section of appendix, mainly negative but will also show a moderate staining pattern in the neuroendocrine cells of the mucosa.

Expected staining pattern

Paraganglioma

Appendix

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.