Diagnostic Utility of INSM1 in Medullary Thyroid Carcinoma

Non-papillary thyroid carcinoma diagnoses in The Bethesda System for Reporting Thyroid Cytopathology categories V and VI: An institutional experience

BACKGROUND

The non-papillary thyroid carcinoma (PTC) subgroups of The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) categories V (Suspicious for malignancy) and VI (Malignant) are rare, and specific tumor typing is difficult. We aimed to analyze histologic outcomes and to investigate the points of caution.

METHODS

We reviewed the electronic database and identified 12,215 cases of thyroid fine-needle aspiration cytology between 2013 and 2022. In total, 2783 patients were diagnosed with TBSRTC V or VI. Of these, 51 patients with non-PTC diagnosis were identified. Histological outcomes were analyzed with the cytologic findings.

RESULTS

The subgroups of non-PTC diagnoses in TBSRTC category V or VI consisted of medullary thyroid carcinoma (MTC) (13/51, 25.5 %), anaplastic thyroid carcinoma (3/51, 5.9 %), lymphoma (2/51, 3.9 %), metastatic tumor (4/51, 7.8 %), and malignant, not otherwise specified (NOS) (29/51, 56.9 %). The concordance rate of the histological outcomes was 30 % (12/40), predominantly comprising MTC cases. The obscuring factors for specific tumor typing in the suspicious for malignancy/malignant NOS cytology diagnosis group was mixed pattern of well differentiated thyroid carcinoma and less differentiated carcinoma cells (9/24, 37.5 %), low cellularity (7/24, 29.2 %) and a history of non-thyroid organ malignancy (6/24, 25 %). The less differentiated carcinoma component in mixed pattern consisted of 2 poorly differentiated thyroid carcinomas, 2 anaplastic thyroid carcinomas, 4 high-grade PTCs and 1 high-grade MTC.

CONCLUSION

The high-grade feature of PTC or MTC cytology is a noteworthy obscuring factor in specific tumor typing of non-PTC cytology diagnosis.

Comparison of INSM1 immunostaining with established neuroendocrine markers synaptophysin and chromogranin A in over 14,000 neuroendocrine and non-neuroendocrine tumors

INSM1 is a transcription factor protein which is increasingly used as an immunohistochemical marker for neuroendocrine differentiation. To determine the prevalence of INSM1 expression in tumors and its expression pattern in normal tissues, tissue microarrays containing 14,908 samples from 117 different tumor types/subtypes as well as 76 different normal tissues were analyzed by immunohistochemistry. INSM1 was positive in 89.2% of 471 neuroendocrine neoplasms (NEN) and in 3.5% of 11,815 non-neuroendocrine neoplasms that were successfully analyzed. At least an occasional weak INSM1 positivity was observed in 59 different non-neuroendocrine tumor entities, of which 15 entities contained at least one case with strong INSM1 staining. A comparison with synaptophysin and chromogranin A staining revealed that in NEN, synaptophysin showed the highest sensitivity (93.3%), followed by INSM1 (89.2%) and chromogranin A (87.5%). In neuroendocrine carcinomas (NEC), sensitivity was highest for INSM1 (88.0%), followed by synaptophysin (86.5%) and chromogranin A (66.4%). If INSM1 was used as an additional marker, the sensitivity for detecting neuroendocrine differentiation in NEN increased from 96.6% (synaptophysin and chromogranin A) to 97.2% (synaptophysin, chromogranin A and INSM1). Our study shows that INSM1 is a useful additional marker for neuroendocrine differentiation with high sensitivity, particularly in NEC.

Immunohistochemistry in the pathologic diagnosis and management of thyroid neoplasms

The use of immunohistochemistry cannot be underestimated in the everyday practice of thyroid pathology. It has evolved over the years beyond the traditional confirmation of thyroid origin to molecular profiling and the prediction of clinical behavior. In addition, immunohistochemistry has served to implement changes in the current thyroid tumor classification scheme. It is prudent to perform a panel of immunostains, and the immunoprofile should be interpreted in light of the cytologic and architectural features. Immunohistochemistry can also be easily performed in the limited cellularity specimen preparation generated from thyroid fine-needle aspiration and core biopsy; however, it will require laboratory validation of immunostains specific to these preparations to avoid diagnostic pitfalls. This review discusses the application of immunohistochemistry in thyroid pathology with a focus on limited cellularity preparations.

The Complex Histopathological and Immunohistochemical Spectrum of Neuroendocrine Tumors-An Overview of the Latest Classifications

Neuroendocrine neoplasms (NENs) originate from the neuroendocrine cell system, which may either take the shape of organoid cell aggregations or be composed of dispersed cells across various organs. Therefore, these tumors are heterogenous regarding the site of origin, functional status, degree of aggressiveness, and prognosis. When treating patients with neuroendocrine tumors, one of the most significant challenges for physicians is determining the correct tumor grade and thus classifying patients into risk categories. Over the years, the classification of these tumors has changed significantly, often causing confusion due to clinical, molecular, and immunohistochemical variability. This review aims to outline the latest NENs classifications regardless of their site of origin. Thus, an overview of the key histopathological and immunohistochemical characteristics of NENs could pave the way to validate possible predictive and prognostic markers and also guide the therapeutic conduct.

Immunohistochemical analyses of the expression profiles of INSM1, ATRX, DAXX and DLL3 in solid papillary carcinomas of the breast

Solid papillary carcinoma (SPC) is a rare but distinct clinicopathological feature of breast cancer characterised by frequent neuroendocrine differentiation. Insulinoma-associated protein 1 (INSM1) is a useful neuroendocrine marker for various neuroendocrine tumours. α-thalassemia/mental retardation syndrome X-linked protein (ATRX) and death domain-associated protein (DAXX) are useful prognostic markers for patients with pancreatic neuroendocrine tumours. However, to the best of our knowledge, few studies have addressed INSM1 expression in SPCs. Although ATRX, DAXX and δ-like canonical notch ligand 3 (DLL3) are frequently expressed in neuroendocrine lung carcinomas, there are no reports on their expression in SPCs. Therefore, the present study aimed to analyse the expression profiles of INSM1, ATRX, DAXX and DLL3 in the largest series of patients with SPC that has been, to the best of our knowledge, studied until now. Immunohistochemical analyses were performed to determine chromogranin A, synaptophysin, INSM1, ATRX, DAXX and DLL3 expression in 39 specimens surgically resected from patients with SPC (18 SPC in situ and 21 SPC invasive). The associations between the expression of these markers and the clinicopathological factors were investigated. Chromogranin A, synaptophysin and INSM1 were expressed in 64.1, 100 and 92.3% of the patients, respectively. Both ATRX and DAXX expression was observed in 28.2% of the patients. No patient expressed DLL3. Lack of INSM1 or chromogranin A expression was significantly associated with advanced pathological stages in patients with SPC (P=0.033) and in patients with invasive SPC (P=0.012), showing a tendency for a high Ki-67 labelling index (LI) and advanced histological grade in patients with invasive SPC. Loss of ATRX or DAXX expression was significantly associated with lymphatic invasion, but not with histological grade, Ki-67 LI or presence of invasive tumours. Thus, INSM1 was demonstrated to be a useful diagnostic marker for SPCs. Overall, detecting the lack of INSM1 or chromogranin A expression may be useful for analysing the characteristics of tumour cells in SPCs.

Emerging Biomarkers in Thyroid Practice and Research

Simple Summary

Tumor biomarkers are molecules at genetic or protein level, or certain evaluable characteristics. These help in perfecting patient management. Over the past decade, advanced and more sensitive techniques have led to the identification of many new biomarkers in the field of oncology. A knowledge of the recent developments is essential for their application to clinical practice, and furthering research. This review provides a comprehensive account of such various markers identified in thyroid carcinoma, the most common endocrine malignancy. While some of these have been brought into use in routine patient management, others are novel and need more research before clinical application.

Abstract

Thyroid cancer is the most common endocrine malignancy. Recent developments in molecular biological techniques have led to a better understanding of the pathogenesis and clinical behavior of thyroid neoplasms. This has culminated in the updating of thyroid tumor classification, including the re-categorization of existing and introduction of new entities. In this review, we discuss various molecular biomarkers possessing diagnostic, prognostic, predictive and therapeutic roles in thyroid cancer. A comprehensive account of epigenetic dysregulation, including DNA methylation, the function of various microRNAs and long non-coding RNAs, germline mutations determining familial occurrence of medullary and non-medullary thyroid carcinoma, and single nucleotide polymorphisms predisposed to thyroid tumorigenesis has been provided. In addition to novel immunohistochemical markers, including those for neuroendocrine differentiation, and next-generation immunohistochemistry (BRAF V600E, RAS, TRK, and ALK), the relevance of well-established markers, such as Ki-67, in current clinical practice has also been discussed. A tumor microenvironment (PD-L1, CD markers) and its influence in predicting responses to immunotherapy in thyroid cancer and the expanding arena of techniques, including liquid biopsy based on circulating nucleic acids and plasma-derived exosomes as a non-invasive technique for patient management, are also summarized.

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).