Insulinoma- Associated Protein 1 ( INSM1) Expression in Neuroendocrine Neoplasms: A Newly Discovered Diagnostic Marker

Introduction Neuroendocrine neoplasms (NENs) are heterogeneous group of neoplasms with relatively low incidence. Diagnosis of NENs requires an integrated approach of histology, immunohistochemistry, and molecular study. In the present study, we evaluated insulinoma-associated protein 1 (INSM1) expression in NENs and correlated it with other established neuroendocrine markers. Materials and Method Retrospective cross-sectional study was conducted in a tertiary care center. Consecutively, 100 cases from year November 2019 to January 2021 were enrolled in the study and all relevant data were noted. Results The mean (+/- standard deviation) age of the patients was 55.5 (+/- 10.6) years with a male preponderance. Total 59% of the tumors were located in the lung of which 67% were poorly differentiated neuroendocrine carcinoma. INSM1 were positive in 97% cases, while synaptophysin (SYN) in 96% and chromogranin A (CgA) in 86%. Correlation of INSM1 expression with SYN and CgA was statistically significant (p-value< 0.05). Mean H-score of INSM1 was significantly higher than SYN and CgA and it was statistically significant (p-value< 0.001). Conclusion In the present study, the expression of INSM1 was seen in 97% cases of NENs. A statistically significant association was found between INSM1 and traditional NE markers. As a nuclear marker it is easy to interpret and it showed higher H- score. We conclude that INSM1 is a highly sensitive marker and recommend to incorporate it in the routine practice to aid in the diagnostic workup. However, a larger cohort is required to establish the organ-specific sensitivity and specificity of INSM1.