Insulinoma-associated 1: A novel nuclear marker in Merkel cell carcinoma (cutaneous neuroendocrine carcinoma)

Comparison of insulinoma-associated protein 1 (INSM1) with traditional neuroendocrine markers in gastrointestinal and pancreatic mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs)

The traditional diagnostic markers for mixed neuroendocrine-non-neuroendocrine neoplasms (MiNENs) are synaptophysin (SYP), chromogranin A (CHGA) and CD56. However, there is still a lack of a large series of article focused on the expression of insulinoma-associated protein 1 (INSM1) in gastrointestinal and pancreatic MiNENs. This study compared the expression of INSM1 and traditional neuroendocrine markers in MiNENs. In this study, we collected 46 cases of gastrointestinal and pancreatic MiNENs and performed immunohistochemical staining for INSM1, SYP, CHGA, and CD56. Histologically, the neuroendocrine components of MiNENs were all neuroendocrine carcinomas, with small cell neuroendocrine carcinomas accounting for 15.2% (7/46) and large cell neuroendocrine carcinomas accounting for 84.8% (39/46). With respect to immunohistochemical expression, the overall sensitivity of INSM1 was 80.4% (37/46), which was lower than that of SYP (100%, 46/46), but comparable to that of CHGA (67.4%, 31/46) or CD56 (73.9%, 34/46). The overall specificity of INSM1 was 91.3% (42/46), which was greater than that of SYP (63.0%, 29/46) and CD56 (69.6, 32/46), but was not significantly different from that of CHGA (82.6%, 38/46). The proportion of 3 + staining for SYP (100%, 46/46) was greater than that of INSM1 (71.7, 33/46), while the proportion of 3 + staining for CHGA (10.9, 5/46) or CD56 (21.7, 10/46) was lower than that of INSM1. In conclusion, INSM1 exhibited high sensitivity and specificity in the diagnosis of gastrointestinal and pancreatic MiNENs.

INSM1 is a useful neuroendocrine marker to differentiate pancreatic serous cystadenoma from pancreatic well-differentiated neuroendocrine tumors in cytology and surgical specimens

INTRODUCTION

Differentiating pancreatic serous cystadenoma (SCA) from well-differentiated neuroendocrine tumors (WDNETs) based on histomorphology is critical yet challenging, particularly in small biopsy samples. Our study aimed to examine the expression profile of INSM1 in cytologic and surgical resection specimens from pancreatic SCA to evaluate its potential as a discriminative marker against pancreatic WDNET.

METHODS

We characterized INSM1 immunohistochemistry in 34 patients with pancreatic SCA, comprising 23 surgical resections and 11 cytology specimens. As a control, we used 28 cytology specimens from pancreatic WDNET. Clinical information was retrieved through a review of electronic medical records.

RESULTS

All 11 pancreatic SCA cytology specimens and 15 of 23 pancreatic SCA surgical resections exhibited absent INSM1 immunostaining. Each of the remaining eight surgical resection specimens demonstrated 1 % immunoreactivity. In contrast, 27 out of 28 (96 %) pancreatic WDNET cytology specimens were positive for INSM1 immunostaining, with a median immunoreactivity of 90 % and a range of 30-90 %. Overall, INSM1 immunostains perform similarly to chromogranin and synaptophysin in pancreatic SCA.

CONCLUSIONS

The results indicate that INSM1 immunohistochemistry staining may serve as a useful neuroendocrine marker to differentiate pancreatic SCA from pancreatic WDNET in clinical practice. To our knowledge, this represents the first large-scale study to evaluate INSM1 immunostaining in surgical and cytology specimens from pancreatic SCA.

Merkel cell carcinoma: updates in tumor biology, emerging therapies, and preclinical models

Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma thought to arise via either viral (Merkel cell polyomavirus) or ultraviolet-associated pathways. Surgery and radiotherapy have historically been mainstays of management, and immunotherapy has improved outcomes for advanced disease. However, there remains a lack of effective therapy for those patients who fail to respond to these established approaches, underscoring a critical need to better understand MCC biology for more effective prognosis and treatment. Here, we review the fundamental aspects of MCC biology and the recent advances which have had profound impact on management. The first genetically-engineered mouse models for MCC tumorigenesis provide opportunities to understand the potential MCC cell of origin and may prove useful for preclinical investigation of novel therapeutics. The MCC cell of origin debate has also been advanced by recent observations of MCC arising in association with a clonally related hair follicle tumor or squamous cell carcinoma in situ. These studies also suggested a role for epigenetics in the origin of MCC, highlighting a potential utility for this therapeutic avenue in MCC. These and other therapeutic targets form the basis for a wealth of ongoing clinical trials to improve MCC management. Here, we review these recent advances in the context of the existing literature and implications for future investigations.

INSM1 expression in neuroendocrine tumors in a tertiary care hospital

AIM

Neuroendocrine tumors are heterogenous group of neoplasms that includes benign and malignant tumors that originate from neuroendocrine or nonneuroendocrine organs. Insulinoma-associated protein 1 (INSM1) is a zinc finger transcription factor originally isolated from subtraction library of human insulinoma. The main aim was to study the INSM1 expression in a spectrum of neuroendocrine tumors and a limited spectrum of nonneuroendocrine tumors.

MATERIALS AND METHODS

A total of 100 cases of which 57 neuroendocrine neoplasms and 43 nonneuroendocrine neoplasms were included in the study. Immunohistochemistry (IHC) was done and expression patterns of INSM1 were analyzed. Pituitary adenoma, medullary carcinoma of thyroid, pheochromocytoma lung, gastrointestinal, and pancreatic neuroendocrine tumors were the neuroendocrine tumors that were included in the study. Papillary carcinoma of thyroid, gastrointestinal adenocarcinoma, lung adenocarcinoma, and squamous cell carcinoma were the nonneuroendocrine tumors that were included in the study. Depending upon the tissue availability, comparison of INSM1 with synaptophysin and chromogranin was also done in few neuroendocrine tumors.

RESULTS

All the 57 neuroendocrine tumors showed positive expression for INSM1 and all the nonneuroendocrine tumors were negative for INSM1. This study is statistically significant.

CONCLUSION

Our study suggests that INSM1 is a diagnostic marker for neuroendocrine tumors with high degree of sensitivity and specificity. The study is significant and suggests that INSM1- IHC shows nuclear positivity in a spectrum of neuroendocrine tumors. Being a nuclear marker, interpretation is easy and more reliable than the cytoplasmic markers. INSM1 has a stronger positivity than synaptophysin and chromogranin in the present study especially for small cell carcinoma lung. Hence, INSM1 may be included in the routine panel for neuroendocrine tumors along with synaptophysin and chromogranin.

Immunohistochemistry Update in Dermatopathology and Bone and Soft Tissue Pathology

CONTEXT.—

Immunohistochemistry plays an important role in dermatopathology, particularly for melanocytic lesions and poorly differentiated malignancies. In the field of bone and soft tissue pathology, molecular methods remain the gold standard for diagnosis; however, immunohistochemistry targeting underlying molecular alterations represents a valuable screening tool, especially in areas with limited access to molecular testing.

OBJECTIVE.—

To describe the utility and limitations of new and emerging immunohistochemical stains in the diagnosis of skin, soft tissue, and bone tumors.

DATA SOURCES.—

A literature review of recently described immunohistochemical stains in the fields of dermatopathology and bone and soft tissue pathology was performed.

CONCLUSIONS.—

Immunohistochemistry is an important adjunctive tool for select entities in dermatopathology and bone and soft tissue pathology, and it provides pathologists with valuable evidence of their behavior, underlying molecular alterations, and line of differentiation. Furthermore, immunostains targeting molecular abnormalities have the potential to replace current molecular methods. Many of these recently described stains demonstrate higher sensitivity and specificity; however, limitations and pitfalls still exist, and correlation with morphologic and clinical findings remains essential for diagnosis.

INSM1 expression in primary and metastatic neuroendocrine neoplasms at distinct locations

BACKGROUND

Insulinoma-associated protein 1 (INSM1) has been reported as a valuable marker for neuroendocrine neoplasms (NENs). The aims of this study were to evaluate any change in INSM1 expression between primary and metastatic NENs in distinct locations, as well as the expression of INSM1 at different differentiation levels. Furthermore, we would also investigate the significance of INSM1 expression in non-neuroendocrine neoplasms (non-NENs).

METHODS

We collected 78 cases with primary NENs and 16 cases with metastatic NENs. An addition 7 cases of non-NENs with neuroendocrine (NE) differentiation and 84 cases of other non-NENs, respectively, were included as controls.

RESULTS

In our cohort, 82% of primary NENs and 88% of metastatic NENs expressed INSM1 with no difference between them. There was no difference in the expression of INSM1 in the lung and digestive system, and its staining pattern was independent of tumor differentiation or location. The proportion of INSM1 -positive in non-NENs with NE differentiation was significantly higher than that in other non-NENs. INSM1 sensitivity for primary NENs (82%) was comparable to Chromogranin A (82%), less than that of Synaptophysin (96%) and CD56 (94%); specificity was higher (96% vs 94%, 82%, and 89%, respectively). The sensitivity of INSM1 for well differentiated NENs was significantly higher than that of poorly differentiated NENs (100% vs 79%).

CONCLUSIONS

INSM1 is a useful neuroendocrine marker in primary and metastatic NENs, helping to identify primary NENs with different degrees of differentiation. The expression of INSM1 was independent of tumor location. It should be with caution to interpret the expression of INSM1 in non-NENs that morphologically resemble NENs.

The role of insulinoma-associated protein 1 in predicting the progression and prognosis of human olfactory neuroblastoma in China

OBJECTIVE

Recent studies have suggested that insulinoma-associated protein 1 (INSM1) is a useful marker for pathological diagnosis of neuroendocrine tumors. In the present study, we investigated the association between INSM1 expression and prognosis in patients with olfactory neuroblastoma (ONB) and assessed the usefulness of INSM1 as a prognostic biomarker in these patients.

METHOD

Immunohistochemistry was performed on 109 ONB patients who underwent endoscopic surgery at Beijing Tong Ren Hospital (Beijing, China) between June 2006 and November 2021 Patient age at the time of surgery ranged from 10 months to 72 years (mean age, 43.55 ± 13.47 years). In total, 63 (57.8%) and 46 (42.2%) tumors occurred in male and female patients, respectively. The percentages of grade I-IV cases were 13.8% (15/109), 36.7% (40/109), 29.4% (32/109) and 20.2% (22/109), respectively.

RESULTS

The expression rate (moderately/strongly positive) of INSM1 was significantly higher in high-grade (Ⅲ/Ⅳ; 83%; 45/54) than low-grade (Ⅰ/Ⅱ; 27%; 15/55) ONB cases. High expression levels of INSM1 were significantly positively associated with high pathological stage (p < 0.001), local recurrence, and death. Kaplan‑Meier analysis revealed that patients with high INSM1 expression had significantly shorter disease‑free survival (DFS) and mean survival (75.01 ± 10.71 vs. 158.56 ± 10.32) times, and shorter overall survival (OS). Multivariate Cox regression analysis revealed that INSM1 was an independent prognostic factor for DFS (HR: 4.963, 95%CI [2.11-10.84] p < 0.001) and OS (HR: 4.791, 95%CI [2.117-10.485], p < 0.001) after adjusting for sex, age, and tumor grade. In addition, INSM1 was an independent prognostic factor for DFS in patients treated with surgery (HR: 3.714, 95%CI [1.267-10.889], p = 0.017) and chemotherapy (HR: 5.574, 95%CI [1.584-19.612], p = 0.007).

CONCLUSION

INSM1 expression had a positive association with the prognosis of patients with ONB and could serve as a prognostic biomarker in these patients.

Merkel Cell Polyomavirus T Antigen-Mediated Reprogramming in Adult Merkel Cell Progenitors

Whether Merkel cells regenerate in adult skin and from which progenitor cells they regenerate are a subject of debate. Understanding Merkel cell regeneration is of interest to the study of Merkel cell carcinoma, a rare neuroendocrine skin cancer hypothesized to originate in a Merkel cell progenitor transformed by Merkel cell polyomavirus small and large T antigens. We sought to understand what the adult Merkel cell progenitors are and whether they can give rise to Merkel cell carcinoma. We used lineage tracing to identify SOX9-expressing cells (SOX9+ cells) as Merkel cell progenitors in postnatal murine skin. Merkel cell regeneration from SOX9+ progenitors occurs rarely in mature skin unless in response to minor mechanical injury. Merkel cell polyomavirus small T antigen and functional imitation of large T antigen in SOX9+ cells enforced neuroendocrine and Merkel cell lineage reprogramming in a subset of cells. These results identify SOX9+ cells as postnatal Merkel cell progenitors that can be reprogrammed by Merkel cell polyomavirus T antigens to express neuroendocrine markers.

[Whipple's triad with high and low insulin levels]

A 69-year-old female patient and a 70-year-old male patient were admitted to hospital with recurrent, severe hypoglycemic episodes and a typical manifestation of Whipple's triad. In the female, elevated levels of insulin, C‑peptide and pro-insulin together with pathological findings during a fasting test proved the presence of an insulinoma, which could be detected by Ga-68-DOTATOC-PET-CT in the pancreas. There was a very rare co-existence of a neuroendocrine Merkel cell carcinoma. In the male, levels of insulin and C‑peptide were suppressed and a diagnosis of paraneoplastic hypoglycemia by IGF‑2 secretion was made with increased glucose disposal in skeletal muscle proven by ¹⁸F‑FDG-PET-CT.

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.

Investigation of the RB1-SOX2 axis constitutes a tool for viral status determination and diagnosis in Merkel cell carcinoma

MCC (Merkel cell carcinoma) is an aggressive neuroendocrine cutaneous neoplasm. Integration of the Merkel cell polyomavirus (MCPyV) is observed in about 80% of the cases, while the remaining 20% are related to UV exposure. Both MCPyV-positive and -negative MCCs-albeit by different mechanisms-are associated with RB1 inactivation leading to overexpression of SOX2, a major contributor to MCC biology. Moreover, although controversial, loss of RB1 expression seems to be restricted to MCPyV-negative cases.The aim of the present study was to assess the performances of RB1 loss and SOX2 expression detected by immunohistochemistry to determine MCPyV status and to diagnose MCC, respectively.Overall, 196 MCC tumors, 233 non-neuroendocrine skin neoplasms and 70 extra-cutaneous neuroendocrine carcinomas (NEC) were included. SOX2 and RB1 expressions were assessed by immunohistochemistry in a tissue micro-array. Diagnostic performances were determined using the likelihood ratio (LHR).RB1 expression loss was evidenced in 27% of the MCC cases, 12% of non-neuroendocrine skin tumors and 63% of extra-cutaneous NEC. Importantly, among MCC cases, RB1 loss was detected in all MCPyV(-) MCCs, while MCPyV( +) cases were consistently RB1-positive (p < 0.001). SOX2 diffuse expression was observed in 92% of the MCC cases and almost never observed in non-neuroendocrine skin epithelial neoplasms (2%, p < 0.0001, LHR +  = 59). Furthermore, SOX2 diffuse staining was more frequently observed in MCCs than in extra-cutaneous NECs (30%, p < 0.001, LHR +  = 3.1).These results confirm RB1 as a robust predictor of MCC viral status and further suggest SOX2 to be a relevant diagnostic marker of MCC.

Reproducible Histopathologic Features in Cases of Basal Cell Carcinoma With Neuroendocrine Expression: A Clinicopathologic Study of 24 Cases With a Potential Diagnostic Pitfall

ABSTRACT

Basal cell carcinomas (BCCs) are common malignancies that usually show clear histomorphologic features, but in certain instances, it can display different patterns of differentiation leading to potential diagnostic confusion. BCCs with neuroendocrine differentiation/expression have been mentioned only briefly in the literature. In this study, we present cases of BCCs with neuroendocrine differentiation/expression that demonstrate reproducible histopathological features. Twenty-four cases were included in the study. All tumors showed conventional histopathologic features that are seen in BCCs, but in addition, all the tumors showed large, hyperchromatic, pleomorphic, mononuclear, and multinucleate cells with intracytoplasmic inclusions and intranuclear cytoplasmic invaginations, with rare cases showing stippled nuclei (salt-and-pepper appearance). These histologic features were somewhat concerning for a neuroendocrine carcinoma; thus, immunohistochemistry studies were performed in all cases at the time of diagnosis. By immunohistochemistry, all tumors showed expression of neuroendocrine markers. CD56 was expressed in all cases 24/24, chromogranin was positive in 17/24 cases, and synaptophysin 8/24 was positive in cases. This study confirms a subset of histopathologic features that are present in cases of BCC that are associated with neuroendocrine expression that can potentially be interpreted differently and can create a diagnostic pitfall. Neuroendocrine expression in BCCs is yet uncertain, and further studies are required to fully understand this phenomenon. To avoid diagnostic pitfalls, dermatopathologists must be aware of these unusual histopathologic features and aberrant immunostaining in such tumors; hence, it is advised to perform a thorough histologic inspection.

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).

Insulinoma-associated Protein 1 (INSM1) Expression in Small Cell Neuroendocrine Carcinoma of the Urinary Tract

Clinical guidelines state that neoadjuvant chemotherapy should be administered before surgery in muscle invasive urinary bladder small cell neuroendocrine carcinoma. Recently described marker insulinoma-associated protein 1 (INSM1) has been reported to be sensitive and specific for neuroendocrine differentiation, however, its efficacy in urinary tract small cell carcinoma is not well established. This study examines immunohistochemical expression of INSM1 on whole tissue sections of urinary tract small cell neuroendocrine carcinoma and compares INSM1 expression with established neuroendocrine markers. Immunohistochemical stains for CD56, INSM1, synaptophysin, and chromogranin were performed on 32 cases of small cell neuroendocrine carcinoma of the bladder. Staining was scored for intensity (0: no staining; 1: weak; 2: moderate; 3: strong) and proportion of cells stained (0: 0%; 1: >0% to ≤25%; 2: >25% to ≤50%; 3: >50% to ≤75%; 4: >75% to 100%). INSM1 was positive (intensity 1 to 3 or proportion 1 to 4) in 87% (28/32) of cases (20 with intensity 2 to 3, 17 with proportion 3 to 4). CD56, synaptophysin, and chromogranin were positive in 75% (24/32), 60% (19/32), and 44% (14/32) of cases, respectively. INSM1 was negative (n=4) or only showed weak intensity staining (n=7) in 34% (11/32) of cases. INSM1 is a sensitive marker of small cell neuroendocrine differentiation of the urinary tract. However, this study suggests that optimal utilization of INSM1 would be inclusion in a limited panel of stains rather than as a stand-alone screening marker given that it is negative or only shows weak intensity staining in a significant proportion of cases.

Expression of insulinoma-associated protein 1 in non-small cell lung cancers: a diagnostic pitfall for neuroendocrine tumors

Insulinoma-associated protein 1 (INSM1) has been reported as a highly sensitive and specific marker of neuroendocrine tumors. INSM1 expression has also been reported, although uncommonly, in non-neuroendocrine tumors. This study aimed to elucidate potential nonspecific INSM1 expression in non-small cell non-neuroendocrine lung cancers (NSCNELCs), especially in squamous cell carcinomas (SqCCs) with basaloid features to avoid diagnostic pitfalls. Tissue microarrays (TMAs) were constructed for 324 NSCNELCs, including 196 adenocarcinomas (AdCs), 86 SqCCs, and 42 other NSCNELCs. In addition, 38 whole-tissue sections of SqCCs with basaloid features were examined. INSM1 immunostain was semiquantitively evaluated based on the percentage of nuclear staining in tumor cells, categorized as negative, focal (<10% tumor cells), and positive (>10% tumor cells). Among 324 TMAs, 6.2% (20/324) were positive for INSM1, 4.9% (16/324) were focal, and 88.9% (289/34) were negative. Of 196 AdCs, 5.1% (10/196) were positive for INSM1, 4.7% (9/196) were focal, and 90.3% (177/196) were negative. Of 86 SqCCs, 9.3% (8/86) were positive for INSM1, 5.8% (5/86) were focal, and 84.9% (73/86) were negative. Of the remaining 42 NSCNELCs, 4.8% (2/42) were positive for INSM1, 4.8% (2/42) were focal, and 90.4% (38/44) were negative. Among 38 cases of whole-tissue sections of SqCCs with basaloid features, 15.8% (6/38) were positive for INSM1, 18.4% (7/38) were focal, and 65.8% (25/38) were negative. Our study demonstrates that INSM1 is expressed in a significant subset of NSCNELCs, suggesting caution in interpreting INSM1 staining, especially with limited samples. INSM1 should not be used as a stand-alone neuroendocrine marker in differentiating primary lung tumors.

Utility of Insulinoma-Associated Protein 1 (INSM1) and Mucin 2 (MUC2) Immunohistochemistry in the Distinction of Endocrine Mucin-Producing Sweat Gland Carcinoma From Morphologic Mimics

ABSTRACT

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare low-grade adnexal malignancy with a predilection for the eyelids of elderly White women, which is associated with invasive mucinous carcinoma with endocrine features in one-third of cases. EMPSGC is characterized by the presence of neuroendocrine differentiation and mucin production. However, EMPSGC displays a variety of architectural patterns including solid, cribriform, papillary, and cystic growth. In addition, EMPSGC may also display nonendocrine cytologic features, such as apocrine change. Because of their variable appearance, EMPSGC can show significant morphologic overlap with certain histologic mimics, namely basal cell carcinoma, hidrocystoma, apocrine hidradenoma, and tubular adenoma. In addition, the often limited sampling of this anatomically delicate area can make the diagnosis of EMPSGC challenging. EMPSGC expresses neuroendocrine markers, including synaptophysin and chromogranin, often in a focal distribution. However, insulinoma-associated protein 1 (INSM1) has been found to be a more sensitive marker for EMPSGC. Recent studies have also demonstrated the expression of the gel-forming mucin 2 (MUC2) in EMPSGC, possibly signifying a lacrimal or conjunctival origin of these neoplasms. In this article, we discuss EMPSGC in the context of its histologic mimics (BCC, hidrocystoma, apocrine hidradenoma, and tubular adenoma) and we investigate the utility of the immunohistochemical expression of INSM1 and MUC2 in the distinction of EMPSGC from them. We demonstrate that INSM1 and MUC2 can reliably distinguish EMPSGC from these histologic mimics.

Insulinoma-associated Protein 1 (INSM1) in Thoracic Tumors is Less Sensitive but More Specific Compared With Synaptophysin, Chromogranin A, and CD56

OBJECTIVE

Recognition of neuroendocrine differentiation is important for tumor classification and treatment stratification. To detect and confirm neuroendocrine differentiation, a combination of morphology and immunohistochemistry is often required. In this regard, synaptophysin, chromogranin A, and CD56 are established immunohistochemical markers. Insulinoma-associated protein 1 (INSM1) has been suggested as a novel stand-alone marker with the potential to replace the current standard panel. In this study, we compared the sensitivity and specificity of INSM1 and established markers.

MATERIALS AND METHODS

A cohort of 493 lung tumors including 112 typical, 39 atypical carcinoids, 77 large cell neuroendocrine carcinomas, 144 small cell lung cancers, 30 thoracic paragangliomas, 47 adenocarcinomas, and 44 squamous cell carcinomas were selected and tissue microarrays were constructed. Synaptophysin, chromogranin A, CD56, and INSM1 were stained on all cases and evaluated manually as well as with an analysis software. Positivity was defined as ≥1% stained tumor cells in at least 1 of 2 cores per patient.

RESULTS

INSM1 was positive in 305 of 402 tumors with expected neuroendocrine differentiation (typical and atypical carcinoids, large cell neuroendocrine carcinomas, small cell lung cancers, and paraganglioma; sensitivity: 76%). INSM1 was negative in all but 1 of 91 analyzed non-neuroendocrine tumors (adenocarcinomas, squamous cell carcinomas; specificity: 99%). All conventional markers, as well as their combination, had a higher sensitivity (97%) and a lower specificity (78%) for neuroendocrine differentiation compared with INSM1.

CONCLUSIONS

Although INSM1 might be a meaningful adjunct in the differential diagnosis of neuroendocrine neoplasias, a general uncritical vote for replacing the traditional markers by INSM1 may not be justified.

A limited panel of INSM1 and LEF1 immunostains accurately distinguishes between pancreatic neuroendocrine tumor and solid pseudopapillary neoplasm

Solid pseudopapillary neoplasm (SPN) and well differentiated pancreatic neuroendocrine tumor (PNET) can show significant cytomorphological overlap. In this study, we evaluated the role of INSM1 and LEF1 immunohistochemical stains in distinguishing between these two tumors. 22 SPN and 25 PNET surgically resected cases were stained for both INSM1 and LEF1. All the 22 cases of SPN showed strong and diffuse nuclear staining for LEF1 (in >95 % of tumor cells), while all 25 PNET were negative for LEF1. All 25 PNET cases were positive for INSM1 (moderate to strong intensity nuclear staining in >50 % of the tumor cells), while all 22 cases of SPN were negative for INSM1. The results of our study show that a limited panel comprising of INSM1 and LEF1 immunostains accurately distinguishes between SPN and PNET.

INSM1 Expression in Angiosarcoma

OBJECTIVES

Aberrant expression of neuroendocrine markers has been reported in angiosarcomas and can occasionally result in diagnostic confusion. The aim of this study was to evaluate the expression of insulinoma-associated protein 1 (INSM1), a marker for neuroendocrine differentiation, in angiosarcomas as well as other sarcomas.

METHODS

Tissue microarrays, including angiosarcoma, Ewing sarcoma, desmoplastic small round cell tumor (DSRCT), clear cell sarcoma, synovial sarcoma, leiomyosarcoma, alveolar soft part sarcoma, epithelioid sarcoma, and undifferentiated pleomorphic sarcoma, were evaluated for expression of INSM1. The extent of immunoreactivity was graded according to the percentage of positive tumor cell nuclei (0, no staining; 1+, <5%; 2+, 5%-25%; 3+, 26%-50%; 4+, 51%-75%; and 5+, 76%-100%), and the intensity of staining was graded as weak, moderate, or strong.

RESULTS

INSM1 expression was found in a subset of angiosarcomas (n = 24/94, 26%; majority 5+, weak to moderate), as well as DSRCTs (n = 7/62, 11%; 2+, weak to strong) and rarely synovial sarcomas (n = 3/76, 4%; 2+, moderate to strong). No INSM1 expression was detected in the other sarcomas.

CONCLUSIONS

Aberrant expression of INSM1 can be seen in a subset of angiosarcomas often with diffuse labeling. Other sarcomas that can rarely demonstrate small cell morphology and focal INSM1 expression include DSRCT and synovial sarcoma.

INSM1 Is Less Sensitive But More Specific Than Synaptophysin in Gynecologic High-grade Neuroendocrine Carcinomas: An Immunohistochemical Study of 75 Cases With Specificity Test and Literature Review

Insulinoma-associated protein 1 (INSM1) has emerged as a promising diagnostic marker for high-grade neuroendocrine carcinomas (HGNECs); however, it is controversial whether INSM1 is more sensitive than conventional markers chromogranin, synaptophysin, and CD56. Here, we investigated immunohistochemical expression of INSM1 in 75 gynecologic HGNECs using full tissue sections (30 small-cell carcinomas [SmCCs], 34 large-cell neuroendocrine carcinomas [LCNECs], and 11 mixed SmCC and LCNEC), with specificity analysis in 422 gynecologic non-neuroendocrine tumors (410 in tissue microarrays and 12 full sections) and comparison with conventional neuroendocrine markers for their sensitivity and specificity. Positive INSM1 staining was seen in 69 (92%) HGNECs, whereas chromogranin, synaptophysin, and CD56 staining was seen in 61 (81%), 72 (96%), and 44 (69%) tumors, respectively (INSM1 vs. chromogranin, P=0.09; INSM1 vs. synaptophysin, P=0.4942; and INSM1 vs. CD56, P<0.001). The mean percentage of INSM1-positive tumor cells was 54% (median: 60%, range: 0% to 100%), similar to chromogranin (58%, P=0.2903) and higher than CD56 (30%, P=0.00001) but significantly lower than synaptophysin (89%, P<0.00001). INSM1 showed no staining difference among SmCCs, LCNECs, and mixed SmCC-LCNECs. Among the 422 non-neuroendocrine tumors, positive staining was seen in 5% tumors for INSM1, 18% for chromogranin, 19% for synaptophysin, and 25% for CD56. Our study indicates that INSM1 is a highly specific marker (95% specificity) for gynecologic HGNECs with high sensitivity (92%), but it is less sensitive than synaptophysin (96% sensitivity). INSM1 is more specific than chromogranin, synaptophysin, and CD56 for gynecologic HGNECs. Our literature review reveals that INSM1 has consistently (the same antibody clone A8 used for all reported studies) shown higher or similar sensitivity to chromogranin (for all 3 chromogranin antibody clones LK2H10, DAK-A3, DAKO polyclonal); however, whether INSM1 is more or less sensitive than synaptophysin or CD56 for HGNECs is highly dependent on the antibody clones used for synaptophysin (clones MRQ-40 and SNP88 showing higher sensitivity than clones 27G12 and DAK-SYNAP) or CD56 (clones CD564, MRQ-42, and MRQ-54 showing higher sensitivity than clones 123C3D5, 1B6, and Leu243).

LSD1 inhibition induces differentiation and cell death in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly aggressive, neuroendocrine skin cancer that lacks actionable mutations, which could be utilized for targeted therapies. Epigenetic regulators governing cell identity may represent unexplored therapeutic entry points. Here, we targeted epigenetic regulators in a pharmacological screen and discovered that the lysine‐specific histone demethylase 1A (LSD1/KDM1A) is required for MCC growth in vitro and in vivo. We show that LSD1 inhibition in MCC disrupts the LSD1‐CoREST complex leading to displacement and degradation of HMG20B (BRAF35), a poorly characterized complex member that is essential for MCC proliferation. Inhibition of LSD1 causes derepression of transcriptional master regulators of the neuronal lineage, activates a gene expression signature resembling normal Merkel cells, and induces cell cycle arrest and cell death. Our study unveils the importance of LSD1 for maintaining cellular plasticity and proliferation in MCC. There is also growing evidence that cancer cells exploit cellular plasticity and dedifferentiation programs to evade destruction by the immune system. The combination of LSD1 inhibitors with checkpoint inhibitors may thus represent a promising treatment strategy for MCC patients.

A promoter-driven assay for INSM1-associated signaling pathway in neuroblastoma

Aggressive form of neuroblastoma (NB) is a malignant childhood cancer derived from granule neuron precursors and sympatho-adrenal lineage with N-MYC amplification. An insulinoma associated-1 (INSM1) transcription factor has emerged as a NB biomarker that plays critical role in facilitating tumor cell growth and transformation. N-myc activates INSM1 in NB was discovered. In order to elucidate the signaling pathways associated with INSM1 expression and NB tumor cell growth, we developed an INSM1 promoter-driven luciferase assay for new drug discovery. Promoter-driven luciferase assay demonstrated high Z' factor (>0.7). Performance measures using signal-to-noise ratio, signal window, and Z' factor confirmed this assay is a robust screening method. A panel of FDA-approved oncology drugs set (147 compounds) was subjected to the INSM1 promoter-driven luciferase assay. The positive-hit compounds were validated for effects on cell viability and INSM1 expression. Screening a FDA-approved oncology drugs set revealed multiple inhibitors against various signaling pathways via suppression of INSM1 promoter activity. The positive-hit compounds consist of 9 signaling pathway inhibitors negatively regulates INSM1 expression and cell viability in NB. These inhibitors target DNA/RNA/protein synthesis, tubulin assembly, and histone deacetylase signaling pathways. The outcome of this assay indicates that the newly identified pathways could be critical for NB growth and transformation. This technology and the positive-hits of multiple pathways represent a promising option of identifying re-purposed FDA-approved drugs valuable for NB treatment in the context of a NB-specific marker, INSM1.

Comparative performance of insulinoma-associated protein 1 (INSM1) and routine immunohistochemical markers of neuroendocrine differentiation in the diagnosis of endocrine mucin-producing sweat gland carcinoma

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is a rare cutaneous adnexal malignancy with predilection for the eyelids of older adults. It must be distinguished from metastatic adenocarcinomas of extracutaneous origin and from benign adnexal proliferations on partial samples when a solid growth component and mucin production are not evident. Thus, demonstration of neuroendocrine differentiation can help to ensure a correct diagnosis. Insulinoma-associated protein 1 (INSM1) is a novel neuroendocrine marker that has recently shown greater sensitivity than synaptophysin (SYN) and chromogranin (CHR) in the diagnosis of various neuroendocrine neoplasms. We compared the performance of these three markers across 10 examples of EMPSGC. All EMPSGCs expressed INSM1. Eight of ten were also immunoreactive for SYN; however, INSM1 staining was generally more intense and stained a greater proportion of the tumor cells. CHR staining was weak and focal in most cases. INSM1 staining was present in hidrocystoma-like components of cystic EMPSGC. These findings suggest that INSM1 may be more sensitive than SYN and CHR and thus valuable for establishing a diagnosis of EMPSGC.

Long Non-coding RNAs in Pulmonary Neuroendocrine Neoplasms

Pulmonary neuroendocrine neoplasms (NENs) are classified into low-grade neuroendocrine tumors and high-grade neuroendocrine carcinomas (NECs). There are significant differences in therapeutic strategies of the different NEN subtypes, and therefore, precise classification of pulmonary NENs is critical. However, challenges in pulmonary NEN classification include overlap of diagnostic histological features among the subtypes and reduced or negative expression of neuroendocrine markers in poorly differentiated pulmonary NECs. Recently, transcription factor insulinoma-associated protein 1 (INSM1) was identified as a sensitive marker of neuroendocrine and neuroepithelial differentiation. In this study, INSM1 expression was detected by immunohistochemistry in greater than 94% of pulmonary NENs, indicating that it is a highly sensitive marker of pulmonary NENs and is useful to detect poorly differentiated pulmonary NECs. Although there are well-established morphological and immunohistologic criteria to diagnose pulmonary NENs, there is no universal consensus regarding prognostic markers of pulmonary NENs. Studies have shown that non-small cell lung cancers express long non-coding RNAs (lncRNAs), which regulate gene expression, epithelial-to-mesenchymal transition, and carcinogenesis. We characterized expression and function of lncRNAs, including HOX transcript antisense RNA (HOTAIR), maternally expressed 3 (MEG3), and prostate cancer antigen 3 (PCA3) in pulmonary NENs, including typical carcinoid tumors, atypical carcinoid tumors, small cell lung carcinoma (SCLC/NEC), and large cell neuroendocrine carcinoma (LCNEC/NEC). In situ hybridization and real-time polymerase chain reaction studies showed higher expression (p < 0.01) of all lncRNAs in SCLC/NEC. Small interfering RNA studies indicated a role for MEG3 and PCA3 in tumor proliferation. Therefore, these lncRNAs may serve as prognostic indicators of pulmonary NEN aggressiveness and as possible therapeutic targets.

Well-differentiated rectal neuroendocrine tumors: analysis of histology, including insulinoma-associated protein 1 expression, and biologic behavior, involving a large cohort of 94 cases

Well-differentiated rectal neuroendocrine tumors (R-NETs) are increasingly being detected by screening colonoscopy, commonly manifesting as polyps. Chromogranin A is frequently negative in R-NETs. Insulinoma-associated protein 1 (INSM1) is a novel transcription factor that has recently shown excellent sensitivity and specificity for neuroendocrine (NE) differentiation in various anatomic sites but has not been systematically evaluated in R-NET. A retrospective histologic review of all available R-NETs was performed and stained for INSM1 immunohistochemistry, as well as for Ki-67 and chromogranin A, if not already available. Clinical and follow-up information was obtained from the medical chart. A total of 94 R-NETs were included in our cohort. Of these, 82 (87%) were <10 mm in greatest dimension, and submucosal involvement was noted in 70 patients (74%). The tumors displayed a variety of histologic patterns, and the majority of the cases had intratumoral fibrosis (61%). Synaptophysin and INSM1 were reactive in 100% cases, whereas chromogranin A was reactive in 45% cases. The mean Ki-67 proliferative index was 1.6% (range: 0.5-5%). The median follow-up of the cohort was 30 months (80 cases, range: 3-226 months). Only three patients were identified with regional lymph node metastasis, all of which showed a tumor size ≥10 mm and had lymphovascular invasion (LVI). R-NETs in our fairly large cohort display an indolent biologic behavior without distant metastasis. Metastatic disease in lymph nodes was associated with tumor size and the presence of LVI, but not with the Ki-67 proliferative index. This is also the first systematic study documenting INSM1 as a highly sensitive NE marker in R-NET.

Neuroendocrine Tumors of the Gastrointestinal Tract and Pancreas

Neuroendocrine neoplasms (NENs) of the gastrointestinal (GI) tract and pancreas are a rare and heterogeneous group of neoplasms characterized by common cellular features as well as unique site-specific traits. GI and pancreatic NENs are much rarer than the more common adenocarcinomas arising at these sites. However, the incidences of GI and pancreatic NENs have increased significantly, particularly in the stomach and common site, followed by rectum, appendix, colon, and stomach. Pancreatic NENs are also uncommon, with fewer than 1 per 100,000, accounting for 1% to 2% of all pancreatic neoplasms.

Eyelid basal cell carcinoma with neuroendocrine differentiation: a case report and literature review

Basal cell carcinoma (BCC) is the most common type of malignant tumor in the periocular region. BCCs with neuroendocrine differentiation in the periocular region, however, have not been described in the literature.We present a retrospective case review of a patient with an eyelid BCC with neuroendocrine differentiation. Demographical, clinical, radiological, surgical, histological, and follow-up data are presented.The patient presented with a slow-growing lesion of the eyelid with associated epiphora and dull ache. Initial incisional biopsy of the lesion revealed an infiltrating carcinoma composed of epithelial cells. Immunohistochemistry showed that the tumor was positive for p40, Ber-Ep4, neuron specific enolase (NSE), chromogranin A, CD56 (NCAM), and synaptophysin. The pathology from the margin-controlled excision showed basosquamous cell carcinoma with neuroendocrine differentiation. Tumor recurrence was not detected clinically at the post-operative six-month review.BCC with neuroendocrine marker positivity represents an important diagnostic differential for rare eyelid carcinomas such as primary cutaneous neuroendocrine carcinoma and metastatic small cell carcinoma that have a poor prognosis. The prognostic importance of neuroendocrine marker positivity in BCCs is uncertain. The present case provides further evidence for neuroendocrine differentiation in BCCs.

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.

INSM1 Is a Highly Specific Marker of Neuroendocrine Differentiation in Primary Neoplasms of the Gastrointestinal Tract, Appendix, and Pancreas

OBJECTIVES

INSM1 has been described as a sensitive and specific neuroendocrine marker. This study aims to compare INSM1 with traditional neuroendocrine markers in gastrointestinal neuroendocrine neoplasms.

METHODS

Retrospective review (2008-2018) was used to retrieve paraffin-embedded tissue from 110 gastrointestinal neuroendocrine neoplasms and controls that was subsequently stained with INSM1, synaptophysin, chromogranin, CD56, and Ki-67.

RESULTS

INSM1 was positive in 16 of 17 (94.1%) gastric, 17 of 18 (94.4%) pancreatic, 13 of 18 (72.2%) small bowel, 17 of 21 (81.0%) colonic, and 26 of 36 (72.2%) appendiceal tumors. INSM1 was positive in 58 of 70 (82.9%) well-differentiated neuroendocrine tumors, 17 of 20 (85.0%) poorly differentiated neuroendocrine carcinomas, 8 of 11 (72.7%) low-grade goblet cell adenocarcinomas (grade 1), and 6 of 9 (66.7%) high-grade goblet cell adenocarcinomas (grade 2/3). INSM1 sensitivity for neuroendocrine neoplasms (80.9%) was less than that of synaptophysin (99.1%), chromogranin (88%), and CD56 (95.3%); specificity was higher (95.7% vs 86.0%, 87.3%, and 86.0%, respectively).

CONCLUSIONS

INSM1 is a useful marker of neuroendocrine differentiation in gastrointestinal neuroendocrine and mixed neuroendocrine neoplasms. Compared with traditional neuroendocrine markers, INSM1 is less sensitive but more specific.

An Algorithmic Immunohistochemical Approach to Define Tumor Type and Assign Site of Origin

Immunohistochemistry represents an indispensable complement to an epidemiology and morphology-driven approach to tumor diagnosis and site of origin assignment. This review reflects the state of my current practice, based on 15-years' experience in Pathology and a deep-dive into the literature, always striving to be better equipped to answer the age old questions, "What is it, and where is it from?" The tables and figures in this manuscript are the ones I "pull up on the computer" when I am teaching at the microscope and turn to myself when I am (frequently) stuck. This field is so exciting because I firmly believe that, through the application of next-generation immunohistochemistry, we can provide better answers than ever before. Specific topics covered in this review include (1) broad tumor classification and associated screening markers; (2) the role of cancer epidemiology in determining pretest probability; (3) broad-spectrum epithelial markers; (4) noncanonical expression of broad tumor class screening markers; (5) a morphologic pattern-based approach to poorly to undifferentiated malignant neoplasms; (6) a morphologic and immunohistochemical approach to define 4 main carcinoma types; (7) CK7/CK20 coordinate expression; (8) added value of semiquantitative immunohistochemical stain assessment; algorithmic immunohistochemical approaches to (9) "garden variety" adenocarcinomas presenting in the liver, (10) large polygonal cell adenocarcinomas, (11) the distinction of primary surface ovarian epithelial tumors with mucinous features from metastasis, (12) tumors presenting at alternative anatomic sites, (13) squamous cell carcinoma versus urothelial carcinoma, and neuroendocrine neoplasms, including (14) the distinction of pheochromocytoma/paraganglioma from well-differentiated neuroendocrine tumor, site of origin assignment in (15) well-differentiated neuroendocrine tumor and (16) poorly differentiated neuroendocrine carcinoma, and (17) the distinction of well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma; it concludes with (18) a discussion of diagnostic considerations in the broad-spectrum keratin/CD45/S-100-"triple-negative" neoplasm.

Merkel cell polyomavirus activates LSD1-mediated blockade of non-canonical BAF to regulate transformation and tumorigenesis

Merkel cell carcinoma (MCC), a neuroendocrine cancer of the skin, is caused by integration of Merkel cell polyomavirus (MCV) and persistent expression of Large T antigen (LT) and Small T antigen (ST). We report that ST in complex with MYCL and the EP400 complex activates expression of LSD1 (KDM1A), RCOR2, and INSM1 to repress gene expression by the lineage transcription factor ATOH1. LSD1 inhibition reduces growth of MCC in vitro and in vivo. Through a forward-genetics CRISPR-Cas9 screen, we identified an antagonistic relationship between LSD1 and the non-canonical BAF (ncBAF) chromatin remodeling complex. Changes in gene expression and chromatin accessibility caused by LSD1 inhibition could be partially rescued by BRD9 inhibition, revealing that LSD1 and ncBAF antagonistically regulate an overlapping set of genes. Our work provides mechanistic insight into the dependence of MCC on LSD1 and a tumor suppressor role for ncBAF in cancer.

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.

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 is a sensitive and specific marker for lung neuroendocrine tumors in cytologic and surgical specimens

INTRODUCTION

Insulinoma-associated protein 1 (INSM1) is an immunohistochemical marker for neuroendocrine differentiation with potentially superior sensitivity and specificity. INSM1 performance in pulmonary cytology cell block material (CB) has not been well established, and large series demonstrating its performance have been few.

MATERIALS AND METHODS

Typical and atypical carcinoid, small cell lung carcinoma, and large cell neuroendocrine carcinoma, squamous cell carcinoma, and adenocarcinoma CBs and 563 surgical specimens comprising 17 typical carcinoid, 14 atypical carcinoid, 8 small cell lung carcinoma, 10 large cell neuroendocrine carcinoma, 58 squamous cell carcinoma, 415 adenocarcinoma, and 17 large cell carcinoma cases and 24 other tumor types were immunostained with INSM1, CD56, synaptophysin, and chromogranin A.

RESULTS

The INSM1 sensitivity, specificity, positive predictive value, and negative predictive value were 92.3%, 100%, 78.9%, and 99% in the CBs and 89.8%, 98.1%, 81.5%, and 99% in the surgical specimens, respectively, with 86.2% concordance. The sensitivity, specificity, positive predictive value, and negative predictive value for the other neuroendocrine markers were 97.4%, 93.3%, 97.4%, and 93.3% in the CBs and 93.9%, 93.6%, 58.2%, and 99.4% in the surgical specimens for CD56; 89.7%, 100%, 100%, and 75% in the CBs and 93.4%, 91.2%, 50.5%, and 99.4% in the surgical specimens for synaptophysin; 66.7%, 100%, 100%, and 53.6% in the CBs and 75.5%, 98.6%, 84.1%, and 97.7% in the surgical specimens for chromogranin A, respectively. Finally, INSM1, together with CD56, maximized the sensitivity to 100% with 93.3% specificity in the CBs.

CONCLUSIONS

The results from our study have further established the high sensitivity and specificity of INSM1 in the largest pulmonary cytologic and surgical cohorts to date. INSM1 either matched or outperformed the performance of existing neuroendocrine markers, and its combination with CD56 appeared to maximize test performance.

INSM1 Expression in Peripheral Neuroblastic Tumors and Other Embryonal Neoplasms

Insulinoma-associated protein 1 (INSM1) is a transcription factor that functions in neuroepithelial tissue development and shows expression in neuroendocrine neoplasms. Given the role of INSM1 in controlling differentiation of the sympatho-adrenal lineage, we hypothesized that INSM1 expression would define a subset of neuroblastic tumors. This study aimed to characterize the immunohistochemical profile of INSM1 in a cohort of peripheral neuroblastic tumors and compare INSM1 expression in these tumors to that seen in other embryonal neoplasms, using both tissue microarrays and whole-slide histologic sections. INSM1 showed nuclear expression in 39/50 (78%) peripheral neuroblastic tumors, including 27/32 (84%) neuroblastomas, 9/9 (100%) ganglioneuroblastomas, and 3/9 (33%) ganglioneuromas. Altogether, 70% of peripheral neuroblastic tumors showed anti-INSM1 immunoreactivity in more than 20% of tumor nuclei. Although no non-neuroblastic tumors in this study exhibited INSM1 expression in more than 20% of nuclei, focal or patchy staining was identified in 7/14 (50%) rhabdomyosarcomas, 7/22 (32%) nephroblastomas, and 4/20 (20%) Ewing sarcomas. The absence of INSM1 expression in peripheral neuroblastic tumors was restricted to undifferentiated and poorly differentiated neuroblastomas, as well as mature ganglioneuromas, mimicking the transient INSM1 expression seen in sympatho-adrenal differentiation during normal development. No significant association between MYCN amplification status and INSM1 expression was observed. We found that all 3 INSM1-negative neuroblastoma patients with available follow-up were alive at a median of 15 years, in comparison to 9 of 13 INSM1-positive neuroblastoma patients living at a median of 5 years. Additional studies are needed to determine whether INSM1 expression is indicative of a clinically significant differentiation state in neuroblastoma.

INSM1 Is More Sensitive and Interpretable than Conventional Immunohistochemical Stains Used to Diagnose Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an extremely aggressive skin cancer that must be distinguished from other basaloid cutaneous neoplasms that have different treatments and prognoses. This is sometimes challenging in small shave specimens, crushed samples, lymph nodes, and core needle biopsies. Insulinoma-associated protein 1 (INSM1) immunohistochemistry is a sensitive nuclear marker of neuroendocrine differentiation. INSM1 staining was performed on 56 MCC (47 primary tumors, 9 nodal metastases), 50 skin control cases that included basal cell carcinomas, basaloid squamous cell carcinomas, Bowen disease, sebaceous neoplasms, melanoma, and B-cell lymphomas, and 28 lymph node control cases that included metastatic neuroendocrine neoplasms, melanomas, squamous cell carcinomas, lymphomas, and adenocarcinomas. Percent of staining nuclei (0, <25%, 25% to 50%, 50% to 75%, >75%) and intensity (weak, moderate, strong) were recorded for each sample. All 56 MCC expressed INSM1. By comparison, synaptophysin, CK20, and chromogranin were expressed in 96%, 92%, and 32% of MCC, respectively. While the 3 conventional markers showed significant variability in staining intensity and distribution, INSM1 stained >75% tumor nuclei in 89% of MCC and 50% to 75% of tumor nuclei in 11%. Staining intensity was strong in 85% and moderate in 15%. None of the 50 cutaneous basaloid non-MCC neoplasms in the control group stained with INSM1, and among the lymph node controls 5 of 5 neuroendocrine neoplasms expressed INSM1, confirming that INSM1 staining cannot distinguish MCC from metastatic extracutaneous neuroendocrine carcinoma. INSM1 holds promise as a neuroendocrine marker that can distinguish MCC from its mimickers in the skin and improve detection of sentinel lymph node metastases.

Parathyroid Neoplasms: Immunohistochemical Characterization and Long Noncoding RNA (lncRNA) Expression

Parathyroid adenomas are slow growing benign neoplasms associated with hypercalcemia, while atypical parathyroid adenomas and parathyroid carcinomas are uncommon tumors and their histologic features may overlap with parathyroid adenomas. LncRNAs participate in transcription and in epigenetic or post-transcriptional regulation of gene expression, and probably contribute to carcinogenesis. We analyzed a group of normal, hyperplastic, and neoplastic parathyroid lesions to determine the best immunohistochemical markers to characterize these lesions and to determine the role of selected lncRNAs in tumor progression. A tissue microarray consisting of 111 cases of normal parathyroid (n = 14), primary hyperplasia (n = 15), secondary hyperplasia (n = 10), tertiary hyperplasia (n = 11), adenomas (n = 50), atypical adenomas (n = 7), and carcinomas (n = 4) was used. Immunohistochemical staining with antibodies against chromogranin A, synaptophysin, parathyroid hormone, and insulinoma-associated protein 1(INSM1) was used. Expression of lncRNAs including metastasis-associated lung adenocarcinoma transcript one (MALAT1), HOX transcript antisense intergenic RNA (HOTAIR), and long intergenic non-protein coding regulator of reprograming (Linc-ROR or ROR) was also analyzed by in situ hybridization and RT-PCR. All of the parathyroid tissues were positive for parathyroid hormone, while most cases were positive for chromogranin A (98%). Synaptophysin was expressed in only 12 cases (11%) and INMS1 was negative in all cases. ROR was significantly downregulated during progression from normal, hyperplastic, and adenomatous parathyroid to parathyroid carcinomas. These results show that parathyroid hormone and chromogranin A are useful markers for parathyroid neoplasms, while synaptophysin and INSM1 are not very sensitive broad-spectrum markers for these neoplasms. LincRNA ROR may function as a tumor suppressor during parathyroid tumor progression.

Insulinoma-Associated-1: From Neuroendocrine Tumor Marker to Cancer Therapeutics

Insulinoma-associated-1 (IA-1 or INSM1) encodes a zinc-finger transcription factor, which was isolated from a human insulinoma subtraction library, with specific expression patterns, predominantly in developing neuroendocrine tissues and tumors. INSM1 is key in early pancreatic endocrine, sympatho-adrenal lineage, and pan-neurogenic precursor development. Insm1 gene ablation results in impairment of pancreatic β cells, catecholamine biosynthesis, and basal progenitor development during mammalian neocortex maturation. Recently, INSM1 has emerged as a superior, sensitive, and specific biomarker for neuroendocrine tumors. INSM1 regulates downstream target genes and exhibits extranuclear activities associated with multiple signaling pathways, including Sonic Hedgehog, PI3K/AKT, MEK/ERK^1/2, ADK, p53, Wnt, histone acetylation, LSD1, cyclin D1, Ascl1, and N-myc. Novel strategies targeting INSM1-associated signaling pathways facilitate the suppression of neuroendocrine tumor growth. In addition, INSM1 promoter-driven reporter assay and/or suicide gene therapy are promising effective therapeutic approaches for targeted specific neuroendocrine tumor therapy. In this review, the current knowledge of the biological role of INSM1 as a neuroendocrine tumor biomarker is summarized, and novel strategies targeting multiple signaling pathways in the context of INSM1 expression in neuroendocrine tumors are further explored. IMPLICATIONS: Neuroendocrine transcription factor (INSM1) may serve as a neuroendocrine biomarker for the development of novel cancer therapeutics against neuroendocrine tumors.

Diagnostic accuracy of a panel of immunohistochemical and molecular markers to distinguish Merkel cell carcinoma from other neuroendocrine carcinomas

Merkel cell carcinoma is a rare neuroendocrine carcinoma of the skin mostly induced by Merkel cell polyomavirus integration. Cytokeratin 20 (CK20) positivity is currently used to distinguish Merkel cell carcinomas from other neuroendocrine carcinomas. However, this distinction may be challenging in CK20-negative cases and in cases without a primary skin tumor. The objectives of this study were first to evaluate the diagnostic accuracy of previously described markers for the diagnosis of Merkel cell carcinoma and second to validate these markers in the setting of difficult-to-diagnose Merkel cell carcinoma variants. In a preliminary set (n = 30), we assessed optimal immunohistochemical patterns (CK20, thyroid transcription factor 1 [TTF-1], atonal homolog 1 [ATOH1], neurofilament [NF], special AT-rich sequence-binding protein 2 [SATB2], paired box protein 5, terminal desoxynucleotidyl transferase, CD99, mucin 1, and Merkel cell polyomavirus-large T antigen) and Merkel cell polyomavirus load thresholds (real-time PCR). The diagnostic accuracy of each marker was then assessed in a validation set of 103 Merkel cell carcinomas (9 CK20-negative cases and 15 cases without a primary skin tumor) and 70 extracutaneous neuroendocrine carcinoma cases. The most discriminant markers for a diagnosis of Merkel cell carcinoma were SATB2, NF expression, and Merkel cell polyomavirus DNA detection (positive likelihood ratios: 36.6, 44.4, and 28.2, respectively). Regarding Merkel cell carcinoma variants, cases without a primary skin tumor retained a similar immunohistochemical  profile and CK20-negative tumors displayed a different profile (decrease frequency of NF and SATB2 expression), but Merkel cell polyomavirus DNA remained detected (78% of cases by qPCR). Moreover, 8/9 (89%) CK20-negative Merkel cell carcinoma cases but only 3/61 (5%) CK20-negative extracutaneous neuroendocrine cases were positive for at least one of these markers. In conclusion, detection of SATB2 and NF expression and Merkel cell polyomavirus DNA helps distinguish between Merkel cell carcinoma classical and variant cases and extracutaneous neuroendocrine carcinomas.

Insulinoma-associated protein 1 (INSM1) is a sensitive and highly specific marker of neuroendocrine differentiation in primary lung neoplasms: an immunohistochemical study of 345 cases, including 292 whole-tissue sections

Recent evidence suggests a role for the nuclear marker INSM1 in the diagnosis of neuroendocrine lung neoplasms. The aim of this study was to determine the utility of INSM1 as a marker of neuroendocrine differentiation using a large series of whole-tissue sections of primary lung neoplasms. We stained 345 primary lung neoplasms with INSM1, including 292 whole-tissue sections. Most cases were also stained with synaptophysin, chromogranin, and CD56. The tumors included 64 small cell lung carcinomas, 24 large cell neuroendocrine carcinomas, 64 carcinoid tumors (48 typical, 16 atypical), 130 adenocarcinomas, and 33 squamous cell carcinomas. For small cell lung carcinoma, the sensitivity of INSM1 (98%) was similar to synaptophysin (100%) and CD56 (95%) but considerably higher than chromogranin (83%). For large cell neuroendocrine carcinoma, CD56 (92%) and synaptophysin (88%) were more sensitive than INSM1 (75%), while chromogranin was less sensitive (46%). All markers stained 100% of carcinoid tumors, except one atypical carcinoid tumor, which was negative for INSM1. The sensitivity of INSM1 for neuroendocrine lung neoplasms as a group (95%) was similar to synaptophysin (98%) and CD56 (97%), but higher than chromogranin (84%). The specificity of INSM1 for neuroendocrine lung neoplasms (97%) was similar to chromogranin (98%) but higher than synaptophysin (90%) and CD56 (87%). INSM1 staining was concordant in primary tumors and matched metastases. In conclusion, INSM1 is a reliable marker of neuroendocrine differentiation in primary lung neoplasms, with sensitivity similar to synaptophysin and CD56, and specificity similar to chromogranin.

CD10, TDAG51, CK20, AR, INSM1, and Nestin Expression in the Differential Diagnosis of Trichoblastoma and Basal Cell Carcinoma

BACKGROUND

Trichoblastoma (TB) and basal cell carcinoma (BCC) are 2 different neoplasms composed of basaloid cells and have overlapping histopathological features. We compared the immunoexpression of CD10, T-cell death-associated gene 51 (TDAG51), cytokeratin 20 (CK20), androgen receptor (AR), insulinoma-associated protein 1 (INSM1), and nestin for the differential diagnosis of these tumors.

MATERIALS AND METHODS

We assessed a total of 27 BCC and 27 TB cases, including 4 TB lesions in nevus sebaceous and 3 malignant TB lesions for CD10, TDAG51, CK20, AR, INSM1, and nestin expression.

RESULTS

Staining for CK20, TDAG51, INSM1, and stromal CD10 was significantly more common in TB cases than in BCC cases ( P < .001). Epithelial CD10 and AR staining was significantly more common in BCC cases than in TB cases ( P < .001). The difference between the groups for nestin staining was not significant ( P > .05). Stromal CD10 staining was the most sensitive marker (96.3%) and INSM1 the least sensitive (55.6%) marker for TB. TDAG51 showed 100% specificity for TB. A larger number of CK20 positive cells was found in the cases associated with nevus sebaceous than in the other TBs.

CONCLUSION

All the selected markers except nestin were useful for the differential diagnosis between TB and BCC. CD10 and TDAG51 were more useful than the other markers. The use of CK20 could be preferred in nevus sebaceous lesions. INSM1 was less effective in highlighting Merkel cells within the lesion than CK20.