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

CytoLyt fixation impedes insulinoma-associated protein 1 (INSM1) immunoreactivity compared to formalin fixation

INTRODUCTION

Insulinoma-associated protein 1 (INSM1) is an immunohistochemical marker commonly used to confirm cytomorphological concordant neuroendocrine tumors/carcinomas (NETs/NECs), demonstrating high utility in small samples. Previous reports have suggested comparable INSM1 staining in CytoLyt-fixed cell blocks and formalin-fixed surgical pathology specimens. This study aimed to assess INSM1 immunoreactivity using both fixation methods and investigate potential factors contributing to its variable expression.

MATERIALS AND METHODS

A retrospective query was performed (03/31/21-05/31/22) for NET/NEC cases that had both formalin- and CytoLyt-fixed cell blocks. We collected clinical data and reporting of immunostains for each case. INSM1 staining was evaluated in both fixation methods, and reported as positive, negative, or equivocal. Equivocal INSM1 staining was further scored as a percentage of 1%-100% and intensity of weak (faint staining), moderate (darker staining), and strong (dense staining).

RESULTS

Our search identified 20 cases from diverse body sites, including mediastinal lymph nodes (40%), pancreas (35%), lung (20%), and porta hepatis lymph nodes (5%). All cases exhibited a widespread positivity (over 90%) in formalin-fixed cell blocks. In contrast, CytoLyt fixed cells showed a negative stain in 65% of cases and 30% exhibited an equivocal positivity.

CONCLUSIONS

While INSM1 is previously reported as a sensitive (75%-100%) and specific (82.7%-100%) marker for NET/NECs, our study found a reduced immunohistochemical staining in CytoLyt-fixed cell blocks. Consequently, false negative INSM1 immunohistochemical results in CytoLyt-fixed cell block material may pose a pitfall in the diagnosis of NET/NEC.

Recommendations for optimizing the use of cytology in the diagnosis and management of patients with lung cancer

Non-small cell lung cancer (NSCLC) is one of the oncological entities with the greatest evolution in molecular diagnosis due to the large number of diagnostic biomarkers and new treatments approved by international regulatory agencies. An accurate, early diagnosis using the least amount of tissue is the goal for the establishing and developing precision medicine for these patients. Rapid on-site evaluation (ROSE) provides cytological samples of optimal quantity and quality for a complete diagnosis of NSCLC. The usefulness of cytological samples has been demonstrated, not only for massive parallel sequencing but also for the quantification of the expression of programmed death-ligand 1 (PD-L1) and tumour mutational burden (TMB). Pre-analytical, analytical, and post-analytical recommendations are made for the management and appropriate use of cytological samples in order to obtain all the information necessary for the diagnosis and treatment of patients with NSCLC according to current quality parameters.

Insulinoma-Associated Protein 1 (INSM1): Diagnostic, Prognostic, and Therapeutic Use in Small Cell Lung Cancer

Small cell lung carcinoma (SCLC) is an aggressive and difficult to treat cancer. Although immunohistochemistry is not mandatory for a SCLC diagnosis, it might be required, especially in small samples. Insulinoma-associated protein 1 (INSM1) is expressed in endocrine and nervous tissues during embryogenesis, generally absent in adults and re-expressed in SCLC and other neuroendocrine neoplasms. Its high specificity propelled its use as diagnostic biomarker and an attractive therapeutic target. Herein, we aim to provide a systematic and critical review on the use of INSM1 for diagnosis, prognostication and the treatment of SCLC. An extensive bibliographic search was conducted in PubMed® focusing on articles published since 2015. According to the literature, INSM1 is a highly sensitive (75–100%) and specific (82–100%) neuroendocrine immunohistochemical marker for SCLC diagnosis. It can be used in histological and cytological samples. Although advantageous, its standalone use is currently not recommended. Studies correlating INSM1 expression and prognosis have disclosed contrasting results, although the expression seemed to entail a worse survival. Targeting INSM1 effectively suppressed SCLC growth either as a suicide gene therapy regulator or as an indirect target of molecular-targeted therapy. INSM1 represents a valuable biomarker for a SCLC diagnosis that additionally offers vast opportunities for the development of new prognostic and therapeutic strategies.

Exploration of INSM1 and hASH1 as additional markers in lung cytology samples of high-grade neuroendocrine carcinoma with indeterminate neuroendocrine differentiation

BACKGROUND

Traditional neuroendocrine (NE) markers synaptophysin, chromogranin, and CD56 play an integral role in affirming the diagnosis of high-grade lung NE carcinoma, however promising markers, INSM1, and hASH1, have been identified. We investigated the utility of these markers in pulmonary cytology specimens, particularly in cases where results of traditional NE markers were equivocal.

METHODS

A retrospective search of cytology cases obtained via endobronchial ultrasound (EBUS)-guided FNA revealed 26 cases of high-grade lung carcinoma where an indeterminate diagnosis of small-cell lung carcinoma (SCLC) was based on equivocal IHC staining with traditional NE markers. A separate cohort of 23 cases positive for all traditional markers with a definitive diagnosis of SCLC was also selected. Cytology cellblock sections were immunostained with INSM1 and hASH1 and analyzed using H-score methodology (score range 0-300). A score of ≥95 was considered "positive."

RESULTS

INSM1 was positive in 19/24 (79.2%) of cases of high-grade lung carcinoma with indeterminate NE differentiation, while hASH1 was positive in 6/24 (25.0%). Chromogranin was seen only focally positive (<10% of cells) in 4/24 (16.7%), synaptophysin positive in 16/24 (66.7%), and CD56 positive in 14/21 (66.7%). Among unambiguous cases, INSM1 was positive in all cases with an average score of 233.9, while hASH1 was positive in 21/23 (91.3%) with an average score of 196.3.

CONCLUSION

Compared with traditional NE stains and to hASH1, INSM1 was expressed in a higher number of cases of high-grade lung NE carcinomas in cytology cellblock specimens, making it a superior, more sensitive NE marker.

INSM1, a Novel Biomarker for Detection of Neuroendocrine Neoplasms: Cytopathologists’ View

Background: Insulinoma-associated protein 1 (INSM1) has been considered as a novel immunostain for neuroendocrine tumors (NETs) and is hypothesized to be more reliable than first-generation NET biomarkers, such as CGA (chromogranin A), SYP (synaptophysin) and CD56 (neural cell adhesion molecule). In this review, we summarize existing literature on INSM1′s reliability as an immunostain for detection of various NETs, its results in comparison to first-generation NET biomarkers, and its expression in both non-NETs and benign tissues/cells on cytology specimens (cell blocks/smears).

Perspectives on the diagnostic, predictive and prognostic markers of neuroendocrine neoplasms (Review)

Neuroendocrine neoplasms (NENs) are a heterogeneous group of rare tumors with different types of physiology and prognosis. Therefore, prognostic information, including morphological differentiation, grade, tumor stage and primary location, are invaluable and contribute to the formulation of treatment decisions. Biomarkers that are currently used, including chromogranin A (CgA), serotonin and neuron-specific enolase, are singular parameters that cannot be used to accurately predict variables associated with tumor growth, including proliferation, metabolic rate and metastatic potential. In addition, site-specific biomarkers, such as insulin and gastrin, cannot be applied to all types of NENs. The clinical application of broad-spectrum markers, as it is the case for CgA, remains controversial despite being widely used. Due to limitations of the currently available mono-analyte biomarkers, recent studies were conducted to explore novel parameters for NEN diagnosis, prognosis, therapy stratification and evaluation of treatment response. Identification of prognostic factors for predicting NEN outcome is a critical requirement for the planning of adequate clinical management. Advances in ‘liquid’ biopsies and genomic analysis techniques, including microRNA, circulating tumor DNA or circulating tumor cells and sophisticated biomathematical analysis techniques, such as NETest or molecular image-based biomarkers, are currently under investigation as potentially novel tools for the management of NENs in the future. Despite these recent findings yielding promising observations, further research is necessary. The present review therefore summarizes the existing knowledge and recent advancements in the exploration of biochemical markers for NENs, with focus on gastroenteropancreatic-neuroendocrine tumors.

Insulinoma-associated protein 1(INSM1) is a superior marker for the diagnosis of gastroenteropancreatic neuroendoerine neoplasms: a meta-analysis

PURPOSE

An increasing number of studies have shown that insulinoma-associated protein 1 (INSM1) is a robust marker for the diagnosis of gastroenteropancreatic neuroendocrine neoplasms (GEP-NEN). The overall diagnostic accuracy of INSM1 for GEP-NEN remains unclear. The purpose of this study is to estimate the diagnostic value of INSM1 for GEP-NEN through a meta-analysis.

METHODS

We searched relevant studies addressing the accuracy of INSM1 in the diagnosis of GEP-NEN from PubMed, Web of Science, Embase, Cochrane Library and China National Knowledge Infrastructure (CNKI) as well as from reference lists since the establishment of the database to January 12, 2021. Pooled sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and summary receiver operating characteristic (SROC) curves were used to comprehensively evaluate the diagnostic value of INSM1 for GEP-NEN. Statistical analysis was performed by Stata 15.0 and RevMan 5.4.

RESULTS

Nine studies with a total of 393 patients were included in the meta-analysis. The meta-analysis results showed that the pooled sensitivity and specificity of INSM1 for the diagnosis of GEP-NEN were 0.99 (95% CI: 0.87-1.00) and 0.96 (95% CI: 0.93-0.98), respectively. The PLR and NLR were 23.3 (95% CI: 13.3-40.8) and 0.01 (95% CI: 0.00-0.14), respectively. The DOR was 380.31 (95% CI: 164.14-881.21), and the area under the curve (AUC) of SROC curve was 0.98 (95% CI: 0.96-0.99).

CONCLUSIONS

The results show that INSM1 is an effective marker for the diagnosis of GEP-NEN with high sensitivity and specificity. INSM1 is recommended for clinical application to improve the diagnostic accuracy of GEP-NEN. However, more high-quality studies are needed to confirm these findings.

Diagnostic Utility of INSM1 in Medullary Thyroid Carcinoma

Insulinoma-associated protein 1 (INSM1) is shown to be an excellent marker for neuroendocrine differentiation. However, the diagnostic utility of INSM1 in medullary thyroid carcinoma (MTC) has not yet been extensively investigated. INSM1 staining was performed on 21 MTCs, 7 MTC mimickers (including 3 papillary carcinomas, 2 poorly differentiated carcinomas, 1 follicular adenoma, and 1 nodular plasma cell hyperplasia), and 3 cases of C-cell hyperplasia. INSM1 staining of these cases was compared with the traditional MTC markers including calcitonin (CT), monoclonal carcinoembryonic antigen (mCEA), chromogranin A (CgA), and synaptophysin (Syn). The H-score was generated using the QuPath program, an open-source image analysis software. All 21 MTC cases and 3 C-cell hyperplasia cases were positive for all markers. The MTC mimickers were entirely negative for INSM1. INSM1 and Syn displayed, more consistently, high expression with minimal variability than CgA that showed a wide range of expression with significant variability. mCEA and CT exhibited mostly a high expression with some variability. Being a nuclear stain, interpretation was easier with INSM1 compared to other cytoplasmic markers. INSM1 is an excellent marker for neuroendocrine differentiation, entirely applicable in the diagnosis of MTC and C-cell hyperplasia with high sensitivity and specificity. In comparison with the traditional MTC markers, INSM1 is unique in the crisp nuclear staining pattern with a consistent, diffuse, and strong expression. INSM1 can be potentially combined with CT or mCEA as a dual stain, especially when the lesional tissue is limited for a panel of immunostains.

Clinical Routine Application of the Second-generation Neuroendocrine Markers ISL1, INSM1, and Secretagogin in Neuroendocrine Neoplasia: Staining Outcomes and Potential Clues for Determining Tumor Origin

Neuroendocrine neoplasms (NENs) have traditionally been identified via expression of proteins associated to the regulation of secretory vesicles and granules. We report the clinical usage of the "second-generation" proteins ISL LIM homeobox 1 (ISL1), INSM transcriptional repressor 1 (INSM1), and secretagogin (SECG) as immunohistochemical markers of neuroendocrine differentiation since their introduction in clinical routine and compare the results with the established proteins chromogranin A (CGA) and synaptophysin (SYP). In total, 161 tumors, including 139 NENs and 22 "non-NENs" (unrelated tumors with an initial suspicion of NEN), were informatively stained for ISL1, and subsets were also interrogated for INSM1 and/or SECG. Diffuse or focal positive immunoreactivity was noted for ISL1 in 91/139 NENs (65%) and in 6/22 (27%) non-NENs, for INSM1 in 76/85 NENs (89%) and in 2/5 (40%) non-NENs, and for SECG in 49 out of 64 NENs (77%) and in 0/5 non-NENs (0%). Generally, ISL1, INSM1, and SECG exhibited sensitivities in line with or slightly below that of CGA and SYP-largely attributable to tissue-specific patterns regarding tumoral origin. Moreover, for pancreatic and small intestinal NENs, the two largest subgroups, ISL1 staining results were consistent irrespectively of tumor source and WHO grade. We verify previously suggested immunohistochemical schemes of neuroendocrine markers of first- and second-generations to facilitate the diagnostic process for NENs and confirm that the second-generation neuroendocrine markers display tissue-specific patterns. We therefore recommend their implementation in tertiary endocrine pathology centers, not least to aid in the identification of primary tumors when analyzing metastases.

INSM1 expression in a subset of thoracic malignancies and small round cell tumors: rare potential pitfalls for small cell carcinoma

INSM1 is a diagnostic marker for neuroendocrine tumors originating in multiple anatomic sites. In the lung, INSM1 shows 76-97% sensitivity for neuroendocrine tumors overall. Our aim was to characterize INSM1 as a diagnostic marker for small cell carcinoma in the context of its epithelial, lymphoid, and mesenchymal morphologic mimics. Immunohistochemistry was performed on 231 tumors, including lung neuroendocrine tumors, nonneuroendocrine carcinomas of the thoracic cavity, diffuse large B-cell lymphomas, and small round cell sarcomas, using an anti-INSM1 mouse monoclonal antibody. Extent (0-100%) and intensity (1-3+) of nuclear INSM1 staining was multiplied in each case to calculate an H-score. Demographic and clinical information was obtained from the medical record. INSM1 had an overall sensitivity and specificity of 81.5% and 82.7% for small cell carcinoma, respectively, using a threshold established with a receiver operating characteristic curve. 40/48 (82.7%) small cell carcinomas were positive for INSM1, including 19/24 (79%) small cell carcinomas that were negative for chromogranin and synaptophysin. 5/5 carcinoids and 21/28 (75%) large cell neuroendocrine carcinomas showed INSM1 expression. Among nonneuroendocrine tumors, 7/38 (18%) lung adenocarcinomas, 2/17 (12%) lung squamous cell carcinomas, 4/10 (40%) thymic carcinomas, 4/12 (33%) adenoid cystic carcinomas, 1/19 (5%) diffuse large B-cell lymphomas, 4/11 (36%) alveolar rhabdomyosarcomas, and 4/23 (17%) Ewing sarcomas were positive for INSM1. No synovial sarcomas or desmoplastic small round cell tumors were positive. Weak, focal INSM1 expression alone is insufficient as a diagnostic marker for small cell carcinoma, but is sensitive and specific, easy to interpret in small biopsies, and makes a valuable addition to a diagnostic panel.

Insulinoma-associated protein 1 immunostaining for various types of neuroendocrine tumors on FNA smears

BACKGROUND

Insulinoma-associated protein 1 (INSM1) has recently emerged as a reliable nuclear immunostaining marker for detecting neuroendocrine tumors (NETs) in paraffin-embedded surgical samples and cytologic cell blocks, but the reliability of INSM1 staining on cytologic smears is understudied. This study investigated the performance of INSM1 staining on cytologic smears for the detection of various NETs in comparison with chromogranin (CG) and synaptophysin (SYN).

METHODS

INSM1, CG, and SYN were stained on cytologic smears of 70 NETs, including 20 pancreatic NETs, 10 lung carcinoid tumors, 11 small cell lung carcinomas (SCLCs), 10 medullary thyroid carcinomas, 10 Merkel cell carcinomas, 4 thymic atypical carcinoid tumors, and 5 olfactory neuroblastomas. The detection rate, the percentage of positive cells, and the staining intensity were recorded.

RESULTS

The overall detection rate of INSM1 (94%) was higher than the rates of CG (79%) and SYN (89%). The detection rate of INSM1 was higher than the rates of CG and SYN in SCLC, Merkel cell carcinoma, and olfactory neuroblastoma; higher than the rate of CG and equal to the rate of SYN in pancreatic NETs and medullary thyroid carcinoma; equal to the rate of CG and higher than the rate of SYN in thymic atypical carcinoid tumors; and equal to the rate of CG and lower than the rate of SYN in lung carcinoid tumors. INSM1 staining was easier to interpret than CG and SYN staining, especially in high-grade NETs.

CONCLUSIONS

INSM1 can be reliably stained on cytologic smears and outperforms CG and SYN in the verification of clinically or radiologically suspected NETs.

Expression of novel neuroendocrine marker insulinoma-associated protein 1 (INSM1) in genitourinary high-grade neuroendocrine carcinomas: An immunohistochemical study with specificity analysis and comparison to chromogranin, synaptophysin, and CD56

Confirmation of genitourinary high-grade neuroendocrine carcinomas (GU-HGNECs) often requires immunohistochemical staining. Here we evaluated a novel neuroendocrine marker, insulinoma-associated protein 1 (INSM1), in GU-HGNECs with comparison to chromogranin, synaptophysin and CD56. Immunohistochemical expression of INSM1, chromogranin, synaptophysin, and CD56 was evaluated in 39 GU-HGNECs using full tissue sections [4 in kidney, 28 in urinary bladder, and 7 in prostate; 31 small cell carcinomas (SmCCs), 6 large cell neuroendocrine carcinomas (LCNECs), 2 mixed SmCC-LCNECs]. In 33 SmCCs/components, INSM1 showed similar sensitivity (93.9 %) to chromogranin (87.8 %), synaptophysin (93.9 %) and CD56 (87.8 %), and stained a similar percentage of tumor cells (52 %) to chromogranin (49 %) and CD56 (52 %), but lower than synaptophysin (87 %) (p < 0.0001). In 8 LCNECs/components, INSM1 is similar to chromogranin, synaptophysin or CD56 in sensitivity (62.5 %, 62.5 %, 75 %, 62.5 %, respectively) and the mean percentage of positively stained tumor cells (21 %, 44 %, 48 %, 37 %, respectively). INSM1 is more sensitive for SmCCs than LCNECs (93.9 % vs. 62.5 %, p = 0.015). INSM1 showed 97.4 % specificity upon analyzing 273 genitourinary non-neuroendocrine tumors on tissue microarrays. Our study indicates that INSM1 is a sensitive marker for genitourinary HGNECs with high specificity. For genitourinary SmCCs, INSM1 shows similar sensitivity to chromogranin, synaptophysin and CD56 but stains a lower percentage of tumor cells than synaptophysin. For genitourinary LCNECs, INSM1 showed similar sensitivity to chromogranin, synaptophysin and CD56. INSM1 is more sensitive for genitourinary SmCCs than LCNECs. Our result and literature review indicate that whether INSM1 is more sensitive than conventional neuroendocrine markers for HGNECs depends on the tumor primary sites.

Insulinoma-associated protein 1 (INSM1): a potential biomarker and therapeutic target for neuroendocrine tumors

BACKGROUND

Insulinoma-associated protein 1 (INSM1), a transcriptional regulator with a zinc-finger DNA-binding domain, has been validated as a cytoplasmic marker for neuroendocrine differentiation of tumor cells. Next to its abundant expression in the fetal pancreas, it is expressed in brain tumors, pheochromocytomas, medullary thyroid carcinomas, insulinomas and pituitary and small-cell lung carcinomas. INSM1 is not expressed in normal adult tissues and/or most non-neuroendocrine tumors. It regulates various downstream signaling pathways, including the Sonic Hedgehog, PI3K/AKT, MEK/ERK1/2, ADK, p53, Wnt, histone acetylation, LSD1, cyclin D1, Ascl1 and N-Myc pathways. Although INSM1 appears to be a subtle and specific biomarker for neuroendocrine tumors, its role in tumor development has remained unclear.

CONCLUSIONS

Here, we highlight INSMI expression, as well as its diagnostic significance and use as a therapeutic target in various neuroendocrine tumors. Targeting signaling pathways or gene expression alterations associated with INSM1 expression may be instrumental for the design of novel therapeutic strategies for neuroendocrine tumors.

Insulinoma-associated protein 1 (INSM-1) expression in medullary thyroid carcinoma FNA: a multi-institutional study

INTRODUCTION

Insulinoma-associated protein 1 (INSM-1) is expressed in both normal tissues and neoplasms with neuroendocrine differentiation such as small cell lung carcinoma and pancreatic neuroendocrine tumors. The aim of this study was to evaluate the INSM-1 expression in medullary thyroid carcinoma (MTC) in the aspirated material and its preoperative diagnostic value.

MATERIALS AND METHODS

MTC cases with available cytological material from 5 institutions were retrospectively identified. INSM-1 expression was analyzed in 48 cell blocks prepared from fine-needle aspiration samples from histologically confirmed cases of MTC. Twenty-nine samples were aspirates from primary thyroid lesions and 19 from secondary lesions lymph node or liver lesions. INSM-1 immunostain was done using the Ventana Automatic System (Ventana Medical Systems, Tucson, AZ). The control group consisted of 20 samples from histologically confirmed cases of papillary, follicular, and anaplastic thyroid carcinomas and secondary thyroid malignancies (squamous cell carcinoma, malignant melanoma).

RESULTS

The male to female (M:F) ratio in MTC group was 1:1.5 and the average age was 55.6 years (range: 24-84 years). INSM-1 nuclear staining in at least 5% of cells was considered positive. Forty-five (93.75%) MTC samples were positive including all primary tumor aspirates. All control samples were negative.

CONCLUSIONS

INSM-1 nuclear positivity is a reliable marker of MTC neuroendocrine differentiation on cytology material from both primary tumor and metastases. INSM-1 can also discriminate MTC from other primary and secondary thyroid carcinomas when there are cytomorphologic overlaps.

Immunohistochemistry in the diagnosis and classification of neuroendocrine neoplasms: what can brown do for you?

This review is based on a presentation given at the Hans Popper Hepatopathology Society companion meeting at the 2019 United States and Canadian Academy of Pathology Annual Meeting. It presents updates on the diagnosis and classification of neuroendocrine neoplasms, with an emphasis on the role of immunohistochemistry. Neuroendocrine neoplasms often present in liver biopsies as metastases of occult origin. Specific topics covered include 1. general features of neuroendocrine neoplasms, 2. general neuroendocrine marker immunohistochemistry, with discussion of the emerging marker INSM1, 3. non-small cell carcinoma with (occult) neuroendocrine differentiation, 4. the WHO Classification of neuroendocrine neoplasms, with discussion of the 2019 classification of gastroenteropancreatic neoplasms, 5. use of Ki-67 immunohistochemistry, 6. immunohistochemistry to assign site of origin in neuroendocrine metastasis of occult origin, 7. immunohistochemistry to distinguish well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma, 8. lesions frequently misdiagnosed as well-differentiated neuroendocrine tumor, and 9. required and recommended data elements for biopsies and resections with associated immunohistochemical stains. Next-generation immunohistochemistry, including lineage-restricted transcription factors (e.g., CDX2, islet 1, OTP, SATB2) and protein correlates of molecular genetic events (e.g., p53, Rb), is indispensable for the accurate diagnosis and classification of these neoplasms.

Insulinoma-associated protein 1 (INSM1) is a robust marker for identifying and grading pancreatic neuroendocrine tumors

BACKGROUND

Pancreatic neuroendocrine tumor (PNET) is a diagnostic challenge with limited samples in not only identification but grading. Prior studies have shown insulinoma-associated protein 1 (INSM1) to be a robust marker in identifying PNETs from other solid pancreatic tumors on resection specimens. In this study, we investigated the utility of INSM1 not only for identifying PNETs but also for grading in cell blocks (CBs) and surgical resections (SRs).

METHODS

A search for PNET cases between 2000 and 2019 identified 55 samples (26 CBs and 29 SRs) that were further separated into high (2 CBs, 3 SRs), intermediate (4 CBs, 7 SRs), and low (20 CBs, 19 SRs) grades based on their final pathology report and Ki-67 level. Immunohistochemical (IHC) staining for INSM1 (C-8, Santa Cruz Biotechnology [1:100]) was performed and quantified using an H score of 0 to 300. Non-PNET solid pancreatic tumors were compared and included acinar cell carcinoma, solid pseudopapillary neoplasm, and ductal adenocarcinoma.

RESULTS

All 55 cases of PNET demonstrated nuclear INSM1 staining. The average H scores for INSM1 staining of PNET were 254 and 252 in CB and SR, respectively. The H scores decreased with increasing tumor grade, with low-grade (G1), intermediate-grade (G2), and high-grade (G3) tumors showing average INSM1 H scores of 229 and 253, 266 and 253, and 30 and 33 in both CB and SR, respectively.

CONCLUSION

IHC with INSM1 plays a role in identifying and potentially grading PNETs.