INSM1 – Antibody Lexicon

Synonyms: Insulinoma-associated protein 1

by Jan Klos

Background

Insulinoma-associated protein 1 (INSM1) is coded by the gen with the same name INSM1. The protein functions as a repressor of transcription which regulates entry into cell cycle and controls neuroendocrine differentiation. It is a sensitive marker for neuroendocrine differentiation considered more sensitive and more specific than Synaptophysin, Chromogranin A or CD56. It is considered a potential neuroendocrine biomarker for the development of novel cancer therapeutics against neuroendocrine tumors.

Positivity in normal tissues

All neuroendocrine cells except parathyroid gland.

Positivity in tumors

All tumors with neuroendocrine differentiation except parathyroid tumors. Reactivity is present in circa 90% extraskeletal myxoid chondrosarcomas (with rearrangements of the NR4A3 gene), providing strong evidence for neuroendocrine differentiation. Potential pitfall are INSM1-positive tumors without evidence of neuroendocrine differentiation like Ewing sarcoma (30 %+), ossifying fibromyxoid tumor (30 %+), chordoma (10 % +), soft tissue myoepithelioma (5 %+). Basal cell carcinoma of the skin which stains positive with Chromogranin A in >70% is negative for INSM1, may be interpreted as argument against wide neuroendocrine differentiation in these tumors.

Staining pattern

Nuclear

Antibody clone

Control tissue

Application

Sensitive and specific marker for identification of neuroendocrine phenotype in normal and neoplastic tissues and immature neuronal differentiation in central nervous system
High expression seems to be a negative prognostic indicator in neuroendocrine neoplasms in gastro-intestinal tract and positive prognostic indicator in small cell carcinomas of the lung.

by Jan Klos

Background

Positivity in normal tissues

Positivity in tumors

Staining pattern

Antibody clone

Control tissue

Application

Selected references