Insulinoma-associated protein 1 immunostaining on cytology specimens: an institutional experience

Abstract

© 2018 Elsevier Inc. Neuroendocrine tumors (NETs) are epithelial neoplasms with prominent neuroendocrine differentiation. Cytologic examination and utilization of immunohistochemical (IHC) markers are important diagnostic tools for the evaluation of these tumors. Herein we report our experience with the application of INSM1 in cytology samples. We searched our pathology system for cytologic specimens with INSM1 IHC performed from 2017 to 2018. Patients' demographics were recorded, and cytology materials were reviewed including all neuroendocrine IHC markers performed. A total of 134 (67 male, 67 female) specimens with INSM1 IHC were identified. Specimens included 91 (68.2%) NETs or tumors with neuroendocrine features (TNEFs), 33 (24.3%) nonneuroendocrine lesions (non-NET), and 10 (7.5%) nonneoplastic diagnoses. INSM1 was positive in 90 (99%) of the NET/TNEFs and negative in 32 (97%) non-NETs. CD56 was positive in 42 (95.5%) of the NET/TNEFs and negative on 9 (69.2%) of the non-NETs. The sensitivity of INSM1 was 99% and specificity was 97%, whereas the sensitivity of CD56 was 95.5% and specificity was 69.2%. Chromogranin had the lowest sensitivity (82.5%), and synaptophysin had the lowest specificity (66.7%). Both positive and negative predictive values of INSM1 were higher than CD56 (99% versus 91.3% and 97% versus 81.8%, respectively). INSM1 is a sensitive and specific marker for detection of NETs in cytology samples independent of primary site.