PAX8 immunostaining of anaplastic thyroid carcinoma: a reliable means of discerning thyroid origin for undifferentiated tumors of the head and neck

Progress in diagnosing and treating thyroid squamous cell carcinoma under the 5th edition of WHO classification

Squamous cell carcinoma of the thyroid (SCCT) is a rare thyroid gland malignancy, with only a few hundred cases reported in the literature, mostly as case reports or small sample studies. In the previous WHO classification, squamous cell carcinoma of the thyroid was defined as a carcinoma composed entirely of squamous cells without differentiated carcinoma components. It was once included in the WHO tumor classification separately. However, the 2022 WHO classification of squamous cell carcinoma of the thyroid was reclassified as a morphologic subtype of anaplastic thyroid carcinoma (ATC). The squamous cell carcinoma pattern is similar to the other histologic types of ATC, but the phenotype associated has a poorer prognosis. The typical clinical manifestation of this condition is a cervical mass, accompanied by indications and symptoms of compression on adjacent structures such as the esophagus and trachea in advanced stages. Secondary squamous cell carcinoma of the thyroid may occur due to the spread of squamous carcinoma of the larynx or esophagus or distant metastases from other sites. Diagnosis of squamous cell carcinoma of the thyroid includes neck Ultrasound (US), Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), puncture tissue biopsy, and full endoscopy to identify metastatic lesions from the nasopharynx, oropharynx, hypopharynx, larynx, esophagus, or bronchi and to help with the initial staging of the tumor. Current treatment modalities include surgery, radiotherapy, chemotherapy, or a combination. Because of the poor prognosis of patients with this disease, the short survival period, usually less than one year, and the difficulty of preoperative diagnosis, this article reviews the epidemiological features, origin, clinical features, pathological features, and differential diagnosis to improve the diagnosis and treatment of this disease by clinicians.

Excess dietary sodium partially restores salt and water homeostasis caused by loss of the endoplasmic reticulum molecular chaperone, GRP170, in the mouse nephron

The maintenance of fluid and electrolyte homeostasis by the kidney requires proper folding and trafficking of ion channels and transporters in kidney epithelia. Each of these processes requires a specific subset of a diverse class of proteins termed molecular chaperones. One such chaperone is GRP170, which is an Hsp70-like, endoplasmic reticulum (ER)-localized chaperone that plays roles in protein quality control and protein folding in the ER. We previously determined that loss of GRP170 in the mouse nephron leads to hypovolemia, electrolyte imbalance, and rapid weight loss. In addition, GRP170-deficient mice develop an AKI-like phenotype, typified by tubular injury, elevation of clinical kidney injury markers, and induction of the unfolded protein response (UPR). By using an inducible GRP170 knockout cellular model, we confirmed that GRP170 depletion induces the UPR, triggers an apoptotic response, and disrupts protein homeostasis. Based on these data, we hypothesized that UPR induction underlies hyponatremia and volume depletion in rodents, but that these and other phenotypes might be rectified by supplementation with high salt. To test this hypothesis, control and GRP170 tubule-specific knockout mice were provided with a diet containing 8% sodium chloride. We discovered that sodium supplementation improved electrolyte imbalance and reduced clinical kidney injury markers, but was unable to restore weight or tubule integrity. These results are consistent with UPR induction contributing to the kidney injury phenotype in the nephron-specific GR170 knockout model, and that the role of GRP170 in kidney epithelia is essential to both maintain electrolyte balance and cellular protein homeostasis.

Concurrent Anaplastic and Papillary Thyroid Carcinoma Manifesting as a Thyrocutaneous Fistula

Anaplastic thyroid carcinoma (ATC) is a highly aggressive form of thyroid cancer with poor prognosis. Differentiated thyroid carcinoma (DTC) including papillary thyroid carcinoma (PTC) is more common and known to have a favorable outcome after treatment. Here, we report a case of a 59-year-old lady with a long-standing goiter presenting with a discharging anterior neck mass. Fine-needle aspiration cytology (FTAC) of the mass resulted with malignant cells. She underwent surgery, and histopathological examination revealed both ATC and PTC features. Mutation analysis was also performed, and results were positive for BRAF 600VE mutation. She received radiotherapy and also chemotherapy post-surgery. Treatment was well tolerated. The relatively favorable survival of this patient may suggest that synchronous ATC and DTC may have better prognosis than ATC alone. The objective of this article is to report the unique clinical presentation and favorable prognosis with combined treatment modalities.

Glomangiosarcoma-like Anaplastic Transformation in Papillary Thyroid Carcinoma: A Novel Form of Heterologous Differentiation and a Systematic Review of Heterologous Element Prevalence

Anaplastic thyroid carcinoma (ATC) demonstrates a wide variety of morphologies and is characteristically associated with a differentiated thyroid carcinoma component. Heterologous differentiation is a rare, potentially challenging phenomenon in ATC, mostly observed as osteosarcomatous or chondrosarcomatous differentiation. We now describe a novel 'glomangiosarcoma-like' differentiation, review our archival experience from two institutions (UPMC, CC), and perform a systematic review for the prevalence of heterologous elements in ATC. The patient is a 57-year-old female who presented with 4.5 cm left thyroid, and 3.4 cm neck masses. Histologically, the thyroid demonstrated a differentiated high grade papillary thyroid carcinoma, tall cell and hobnail/micropapillary subtypes transitioning into an anaplastic component with spindled to ovoid cells with hemangiopericytoma-like vasculature showing CD34 positivity, variable muscle marker expression and pericellular lace-like type IV collagen deposition. The neck mass consisted solely of the latter morphology. Targeted next-generation sequencing was performed on high grade DTC and adjacent ATC from the thyroid as well as ATC from the neck metastasis. All three components shared BRAFV600E, TERT promoter, and PIK3CA mutations confirming a clonal origin. Archival (UPMC: n = 150, CC: n = 74) and literature review showed no prior examples. Systematic review and meta-analysis of prevalence showed a baseline pooled prevalence (generalized linear mixed model) of heterologous elements of any type to be 1.6% (95% confidence interval: 1.0-2.6%) for studies where this was specifically addressed. ATC with glomangiosarcoma-like heterologous differentiation is a rarity among an already rare morphologic category with unique diagnostic pitfalls.

Adamantinoma-like ewing sarcoma arising in the pancreatic tail: a case report of a rare entity and review of the literature

ALES is a rare subtype that demonstrates the EWSR1-FLI1 translocation characteristic of ES and demonstrates complex epithelial differentiation including diffuse cytokeratin and p40 expression. It has predominantly recognized in the head and neck and is common in middle-aged population. This case is the first case of ALES reported in the pancreatic tail, sharing some morphological characteristics with ALES in the head and neck, including monotonous cytology, infiltrative growth pattern, and complex epithelioid differentiation, but ALES in the head and neck often has high-grade histological features (e.g., necrosis, high mitotic rate, etc.), and sudden keratinization can also occur, but these features were not reflected in this primary pancreatic tail ALES. Although ALES arising in the pancreatic tail and in the head and neck sites share the immunohistochemical and molecular profile, our case can provide new ideas in differential diagnosis of ALES arising in pancreatic tail and promote increased recognition and understanding of ALES.

Modeling the tumor microenvironment of anaplastic thyroid cancer: an orthotopic tumor model in C57BL/6 mice

Introduction

Securing a well-established mouse model is important in identifying and validating new therapeutic targets for immuno-oncology. The C57BL/6 mouse is one of the most fully characterised immune system of any animal and provides powerful platform for immuno-oncology discovery. An orthotopic tumor model has been established using TBP3743 (murine anaplastic thyroid cancer [ATC]) cells in B6129SF1 hybrid mice, this model has limited data on tumor immunology than C57BL/6 inbred mice. This study aimed to establish a novel orthotopic ATC model in C57BL/6 mice and characterize the tumor microenvironment focusing immunity in the model.

Methods

Adapted TBP3743 cells were generated via in vivo serial passaging in C57BL/6 mice. Subsequently, the following orthotopic tumor models were established via intrathyroidal injection: B6129SF1 mice injected with original TBP3743 cells (original/129), B6129SF1 mice injected with adapted cells (adapted/129), and C57BL/6 mice injected with adapted cells (adapted/B6).

Results

The adapted TBP3743 cells de-differentiated but exhibited cell morphology, viability, and migration/invasion potential comparable with those of original cells in vitro. The adapted/129 contained a higher Ki-67+ cell fraction than the original/129. RNA sequencing data of orthotopic tumors revealed enhanced oncogenic properties in the adapted/129 compared with those in the original/129. In contrast, the orthotopic tumors grown in the adapted/B6 were smaller, with a lower Ki-67+ cell fraction than those in the adapted/129. However, the oncogenic properties of the tumors within the adapted/B6 and adapted/129 were similar. Immune-related pathways were enriched in the adapted/B6 compared with those in the adapted/129. Flow cytometric analysis of the orthotopic tumors revealed higher cytotoxic CD8+ T cell and monocytic-myeloid-derived suppressor cell fractions in the adapted/B6 compared with the adapted/129. The estimated CD8+ and CD4+ cell fractions in the adapted/B6 were similar to those in human ATCs but negligible in the original/B6.

Conclusion

A novel orthotopic tumor model of ATC was established in C57BL/6 mice. Compared with the original B6129SF1 murine model, the novel model exhibited more aggressive tumor cell behaviours and strong immune responses. We expect that this novel model contributes to the understanding tumor microenvironment and provides the platform for drug development.

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.

Advances in Thyroid Pathology: High Grade Follicular Cell-derived Thyroid Carcinoma and Anaplastic Thyroid Carcinoma

In the upcoming World Health Organization fifth edition classification of endocrine tumors, there were several major changes related to high grade follicular-derived thyroid carcinoma (HGFCTC) and anaplastic thyroid carcinoma (ATC) based on emerging evidence about the diagnostic criteria clinical behavior, prognostic factors, and molecular signatures of these tumors. In this review, we aim to summarize the major evolutions of HGFCTC and ATC. HGFCTC is a nonanaplastic carcinoma with high grade features (High mitotic count, tumor necrosis). It is subdivided into poorly differentiated thyroid carcinoma diagnosed using the Turin proposal and differentiated high grade thyroid carcinoma. The latter is defined by the presence of the cytoarchitectutal features of well-differentiated thyroid carcinoma (eg, papillae) but harbors elevated mitotic activity and/or tumor necrosis. Poorly differentiated thyroid carcinoma is predominantly RAS -driven and associated with RAI avidity and high propensity for distant metastasis, whereas differentiated high grade thyroid carcinoma is mostly BRAFV600E -driven. ATC may show a wide range of histologic features. Carcinoma of pure squamous phenotype is associated with a high frequency of BRAF V600E mutations and is now considered as a subtype of ATC. There is a stepwise molecular progression from well-differentiated carcinoma to HGFCTC to ATC manifested by 1) early and persistent driver alteration in the MAPK pathway, particularly BRAF V600E and RAS mutations, and 2) gain of secondary aggressive molecular signatures (such as TERT promoter and TP53 mutations) when tumors progress from well-differentiated to high grade to anaplastic carcinoma.

Identifying SOX17 as a Sensitive and Specific Marker for Ovarian and Endometrial Carcinomas

Similar to PAX8, SOX17 was recently identified as a master transcription factor of ovarian cancer based on RNA sequencing data. We explored SOX17 utility in diagnosing ovarian tumors and other gynecologic tumors. We systematically evaluated SOX17 expression on tissue microarrays of 398 ovarian tumors of various types, 93 endometrial carcinomas, 80 cervical carcinomas, and 1371 nongynecologic carcinomas, such as those of kidney, thyroid, breast, colon, bladder, liver, bile duct, adrenal gland, pancreas, brain, and lung and malignant melanoma. In addition, we evaluated SOX17 expression in whole tissue sections from 60 gynecologic carcinomas and 10 angiosarcomas. The results demonstrated that SOX17 was highly expressed in most ovarian and endometrial tumors with strong intensity. However, unlike PAX8, it was predominately negative in other tested tumor types, including kidney and thyroid tumors. In particular, SOX17 was highly expressed in the following pathologic subtypes of ovarian tumors: serous carcinoma, clear cell carcinoma, endometrioid carcinoma, and germ cell tumors. SOX17 was mostly negative in mucinous carcinoma and sex cord stromal tumors. In addition, SOX17 was expressed in vascular endothelial cells and was positive in all tested angiosarcomas. In summary, our results demonstrate that SOX17 is a sensitive and specific marker for ovarian nonmucinous carcinomas and endometrial carcinomas. For ovarian germ cell tumors and angiosarcomas, SOX17 demonstrates higher specificity than PAX8, with comparable sensitivity. Furthermore, SOX17 positivity in endothelial cells serves as an internal positive control, making it an excellent marker.

PAX8 as a Potential Target for Ovarian Cancer: What We Know so Far

The Fallopian tube epithelium harbors the origin cells for the majority of high-grade serous ovarian carcinomas (HGSCs), the most lethal form of gynecologic malignancies. PAX8 belongs to the paired-box gene family of transcription factors and it is a marker of the FTE secretory cell lineage. Its role has been investigated in migration, invasion, proliferation, cell survival, stem cell maintenance, angiogenesis and tumor growth. In this review, we focus on the pro-tumorigenic role of PAX8 in ovarian cancer; in this context, PAX8 possibly continues to exert its transcriptional activity on its physiological targets but may also function on newly available targets after the tumorigenic hits. Acquiring new insights into the different PAX8 mechanism(s) of action in the tumor microenvironment could uncover new viable therapeutic targets and thus improve the current treatment regimen.

The new endocrine WHO classification: What does this mean for thyroid cytology?

The new World Health Organization classification of endocrine tumors will include many updates on thyroid pathology. This summary highlights the changes that are most relevant for cytopathologists.

PAX8 in the Junction between Development and Tumorigenesis

Normal processes of embryonic development and abnormal transformation to cancer have many parallels, and in fact many aberrant cancer cell capabilities are embryonic traits restored in a distorted, unorganized way. Some of these capabilities are cell autonomous, such as proliferation and resisting apoptosis, while others involve a complex interplay with other cells that drives significant changes in neighboring cells. The correlation between embryonic development and cancer is driven by shared proteins. Some embryonic proteins disappear after embryogenesis in adult differentiated cells and are restored in cancer, while others are retained in adult cells, acquiring new functions upon transformation to cancer. Many embryonic factors embraced by cancer cells are transcription factors; some are master regulators that play a major role in determining cell fate. The paired box (PAX) domain family of developmental transcription factors includes nine members involved in differentiation of various organs. All paired box domain proteins are involved in different cancer types carrying pro-tumorigenic or anti-tumorigenic roles. This review focuses on PAX8, a master regulator of transcription in embryonic development of the thyroid, kidney, and male and female genital tracts. We detail the role of PAX8 in each of these organ systems, describe its role during development and in the adult if known, and highlight its pro-tumorigenic role in cancers that emerge from PAX8 expressing organs.

The use of diagnostic patterns for interventional cytopathology during rapid on-site evaluation and final classification

Pathologist-performed fine-needle aspiration, or interventional cytopathology, is a minimally invasive, highly accurate technique for sampling and diagnosing palpable lesions. Utilizing cytomorphologic patterns during rapid onsite evaluation (ROSE) and final classification is one of many strategies that an interventional cytopathologist can employ to simplify the diagnostic approach. Herein, we provide an overview of the salient cytomorphologic patterns encountered in common specimens obtained by the interventional cytopathologist, including major salivary glands, the thyroid gland, and superficial lymph nodes. The topics covered should provide a primer for those interested in utilizing a site-specific, pattern-based approach to cytopathologic evaluation. In summary, cytomorphologic patterns can be used during ROSE to establish adequacy, build a differential diagnosis, and to appropriately triage the specimen for additional investigation, such as microbiology cultures, a liquid-based preparation, a cell block preparation, flow cytometry, chemical analysis, or molecular diagnostic tests. Finally, this approach can be applied at the time of diagnosis to suggest additional ancillary studies, such as immunohistochemistry, and to inform accurate and definitive classification.

Anaplastic Thyroid Carcinoma: Cytomorphologic Features on Fine-Needle Aspiration and Associated Diagnostic Challenges

OBJECTIVES

Anaplastic thyroid carcinoma (ATC) is an aggressive malignancy, and early diagnosis, often aided by fine-needle aspiration (FNA), is key to improving patient prognosis. While the current literature describes some of the cytologic features (CFs) of this entity, a comprehensive examination of the CFs has not yet been performed.

METHODS

We retrospectively searched our electronic database for ATC cases with available slides between January 2008 and December 2019. Cases were examined for 22 CFs and compared with a control group of differentiated thyroid carcinoma.

RESULTS

A total of 18 ATC cases meeting our inclusion criteria were identified. Most cases showed moderate to high cellularity (83%) and epithelioid cytomorphology (83%). Architecture included either predominantly groups/clusters of tumor cells (56%) or single tumor cells (44%). The other CFs were as follows: nuclear enlargement (100%), nuclear crowding (89%), nuclear membrane irregularities (100%), multinucleated tumor cells (33%), and background acute inflammatory cells (50%). Of the CFs examined, statistically significant differences between ATC and the control groups were found in the following: nuclear pleomorphism, coarse/clumped chromatin, macronucleoli, apoptosis, and necrosis.

CONCLUSIONS

Identification of key CFs in FNA coupled with the clinical history aids in the diagnosis of ATC and helps distinguish it from other mimickers.

Clinicopathological and Molecular Features of Secondary Cancer (Metastasis) to the Thyroid and Advances in Management

Secondary tumours to the thyroid gland are uncommon and often incidentally discovered on imaging. Symptomatic patients often present with a neck mass. Collision tumours of secondary tumours and primary thyroid neoplasms do occur. Ultrasound-guided fine-needle aspiration, core-needle biopsy, and surgical resection with histological and immunohistochemical analysis are employed to confirm diagnosis as well as for applying molecular studies to identify candidates for targeted therapy. Biopsy at the metastatic site can identify mutations (such as EGFR, K-Ras, VHL) and translocations (such as EML4-ALK fusion) important in planning target therapies. Patients with advanced-stage primary cancers, widespread dissemination, or unknown primary origin often have a poor prognosis. Those with isolated metastasis to the thyroid have better survival outcomes and are more likely to undergo thyroid resection. Systemic therapies, such as chemotherapy and hormonal therapy, are often used as adjuvant treatment post-operatively or in patients with disseminated disease. New targeted therapies, such as tyrosine kinase inhibitors and immune checkpoint inhibitors, have shown success in reported cases. A tailored treatment plan based on primary tumour features, overall cancer burden, and co-morbidities is imperative. To conclude, secondary cancer to the thyroid is uncommon, and awareness of the updates on diagnosis and management is needed.

Anaplastic Thyroid Carcinoma: An Update

Anaplastic thyroid carcinoma (ATC) is a rare and undifferentiated form of thyroid cancer. Its prognosis is poor: the median overall survival (OS) of patients varies from 4 to 10 months after diagnosis. However, a doubling of the OS time may be possible owing to a more systematic use of molecular tests for targeted therapies and integration of fast-track dedicated care pathways for these patients in tertiary centers. The diagnostic confirmation, if needed, requires an urgent biopsy reread by an expert pathologist with additional immunohistochemical and molecular analyses. Therapeutic management, defined in multidisciplinary meetings, respecting the patient's choice, must start within days following diagnosis. For localized disease diagnosed after primary surgical treatment, adjuvant chemo-radiotherapy is recommended. In the event of locally advanced or metastatic disease, the prognosis is very poor. Treatment should then involve chemotherapy or targeted therapy and decompressive cervical radiotherapy. Here we will review current knowledge on ATC and provide perspectives to improve the management of this deadly disease.

Paired-Box Gene 8 (PAX8) and Its Association With Epithelial Carcinomas

Cancer is the second most common culprit of mortality in the United States and epithelial carcinomas are considered as one of the most predominant types of cancer. The association between epithelial cancers and paired-box gene 8 (PAX8) has been studied significantly before. PAX8 belongs to the paired-box gene family, which plays an important role in the organogenesis of different body organ systems, especially the thyroid gland, the renal system, and the Müllerian system. Immunohistochemical staining is being used to detect PAX8 expression in different epithelial cancers and differentiate them from PAX8-negative tumors. In follicular, papillary, and anaplastic thyroid carcinomas, targeting the PAX8/peroxisome proliferator-activated receptors (PPARs) fusion protein is being considered as a potential mechanism for therapy. Moreover, because of its high expression in primary ovarian cancers, PAX8 is being considered as a target for ovarian cancer treatment as well. More studies are needed to test the possibility of using PAX8 as a possible target for managing endometrial carcinomas. In this article, we review the functions of the PAX8 gene, how its mutations lead to the development of certain epithelial carcinomas, how it can be used as a diagnostic or a prognostic marker, and its potential as a therapeutic target for these cancers.

Evaluation of E-Cadherin and β-Catenin Immunoreactivity for Determining Undifferentiated Cells in Anaplastic Thyroid Carcinoma

INTRODUCTION

An immunohistochemical study has occasionally been performed to diagnose anaplastic thyroid carcinoma (ATC). However, antibodies to confirm the undifferentiated nature of ATC have not yet been evaluated. The aim of this study was to evaluate E-cadherin and β-catenin expressions in immunoreactivity to determine undifferentiated carcinoma cells in the diagnosis of ATC.

METHODS

We immunohistochemically examined 29 ATCs, 30 poorly differentiated thyroid carcinomas (PDTCs), 22 well-differentiated thyroid carcinomas (WDTCs), and 3 squamous cell carcinomas. Antibodies for thyroid transcription factor-1 (TTF-1), paired-box gene 8 (PAX8), β-catenin, and E-cadherin were used.

RESULTS

All WDTCs tested positive for TTF-1, PAX8, and E-cadherin. The positive rates of TTF-1, PAX8, and E-cadherin were 93.3, 93.3, and 100%, respectively, in PDTCs and 17.2, 51.7, and 10.3%, respectively, in ATCs. WDTC expressed the lateral cell membrane staining for β-catenin and E-cadherin, whereas PDTC showed circumferential cell membranous expression (fishnet pattern). β-catenin cell membrane expression in ATCs is lost or discontinuous. Carcinoma cells with β-catenin nuclear expression without cell membranous expression were scattered in 72.4% of ATCs but were not observed in the other carcinomas.

CONCLUSION

We propose 3 immunohistochemical findings to determine undifferentiated carcinoma cells in the diagnosis of ATC: (1) β-catenin nuclear expression with no or reduced cell membranous expression, (2) the loss or discontinuous pattern of E-cadherin expression, and (3) the loss of PAX8 nuclear expression.

Primary squamous cell carcinoma of the thyroid: a case report

Primary squamous cell carcinoma of the thyroid (PSCCT) is a rare and rapidly progressive malignancy that carries a poor prognosis. PSCCT is easily misdiagnosed as acute thyroiditis or as another thyroid malignancy. We have reported a 76-year-old woman who presented with progressive neck pain for 1 month. Thyroid function tests revealed subclinical thyrotoxicosis. Ultrasound disclosed a solid nodule with calcification in the right thyroid lobe. Laboratory findings included neutrophilic leukocytosis and an elevated erythrocyte sedimentation rate. The patient's condition was diagnosed as subacute thyroiditis, and she was treated with cefixime and ibuprofen. However, her treatment response was poor. She was then treated with oral prednisone. Her neck pain gradually resolved. The patient subsequently developed dysphagia, choking, dyspnea, and dysphonia with an insidious onset. Further examinations including computed tomography and painless gastroscopy revealed that the volume of the thyroid gland had increased significantly, extending to the anterior superior mediastinum. The trachea and esophagus were stenotic because of external compression. Partial thyroidectomy and tracheotomy were performed under extracorporeal membrane oxygenation. The diagnosis of PSCCT was established via histopathology and immunohistochemistry.

Small bowel perforation and death caused by anaplastic thyroid carcinoma metastasis in a patient with concomitant colonic and bilateral breast carcinoma

Undifferentiated or anaplastic thyroid carcinoma (ATC) is rare and one of the most aggressive human malignancies. The tumor is usually voluminous and fast-growing and mostly affects older women. The most common sites of distant metastases are the lungs, brain, and bones. Herein, we describe the case of a 66-year-old woman with a history of bilateral breast carcinoma and ATC, who presented with an acute abdomen and subsequently died. At autopsy, an isolated metastasis of ATC in the small intestine leading to bowel perforation was found. Moreover, there was adenocarcinoma in the descending colon. The review of extra-abdominal malignancies metastasizing to bowel and coincidence of breast and thyroid carcinoma is included.

Primary squamous cell carcinoma of the thyroid gland successfully treated with surgical resection and adjuvant chemoradiotherapy

A 57-year-old woman presented with a 3-month history of an enlarging thyroid mass causing breathlessness and dysphagia. Cross-sectional imaging showed a thyroid tumour infiltrating the trachea and abutting the oesophagus. She underwent panendoscopy, total thyroidectomy and planned tracheal resection, but due to intraoperative findings, a staged procedure was planned instead. Histological analysis revealed a poorly differentiated squamous cell carcinoma (SCC) which was positive on paired box gene 8 (PAX8) immunostaining, suggesting a diagnosis of primary thyroid SCC. She subsequently underwent total laryngectomy and bilateral neck dissections followed by radiotherapy with concurrent cisplatin chemotherapy. The patient remains disease-free 22 months after treatment. Median overall survival is 10 months for macroscopically completely resected tumours. PAX8 immunostaining is a novel technique which helps with the diagnostic challenge of distinguishing between primary thyroid SCC and SCC metastatic to the thyroid from extrathyroidal sites. Complete surgical resection with adjuvant chemoradiotherapy may result in a favourable outcome despite conflicting reports in the literature.

2021 American Thyroid Association Guidelines for Management of Patients with Anaplastic Thyroid Cancer

Background: Anaplastic thyroid cancer (ATC) is a rare but highly lethal form of thyroid cancer. Since the guidelines for the management of ATC by the American Thyroid Association were first published in 2012, significant clinical and scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, and researchers on published evidence relating to the diagnosis and management of ATC. Methods: The specific clinical questions and topics addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of the Task Force members (authors of the guideline). Relevant literature was reviewed, including serial PubMed searches supplemented with additional articles. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations. Results: The guidelines include the diagnosis, initial evaluation, establishment of treatment goals, approaches to locoregional disease (surgery, radiotherapy, targeted/systemic therapy, supportive care during active therapy), approaches to advanced/metastatic disease, palliative care options, surveillance and long-term monitoring, and ethical issues, including end of life. The guidelines include 31 recommendations and 16 good practice statements. Conclusions: We have developed evidence-based recommendations to inform clinical decision-making in the management of ATC. While all care must be individualized, such recommendations provide, in our opinion, optimal care paradigms for patients with ATC.

IGF2BP1 is the first positive marker for anaplastic thyroid carcinoma diagnosis

Anaplastic thyroid carcinomas (ATC) are rare, but represent the most lethal malignancy of the thyroid. Selective molecular markers and drivers distinguishing ATC from other thyroid carcinomas of follicular origin remain largely unknown, limiting advances in diagnosis and treatment. In a retrospective study, we analyzed gene expression in 36 ATC, 18 poorly differentiated, 132 papillary, and 55 follicular thyroid carcinoma, as well as 124 paired and unpaired normal thyroid tissues in three independent cohorts by RNA-sequencing and immunohistochemistry. RNA-sequencing data in the test cohort suggested selective ATC protein biomarkers. Evaluation of these revealed that ATCs are characterized by the de novo expression of various testis antigens, including melanoma-associated antigen A3 (MAGEA3), but most importantly the oncofetal IGF2 mRNA binding protein 1 (IGF2BP1). Shallow whole genome sequencing essentially excluded that IGF2BP1 upregulation results from gene copy number alterations. Immunohistochemical analyses in all three tumor cohorts confirmed the selective de novo expression of IGF2BP1 protein in ATC. In sum, 75% (27/36) of all tested ATC and 0.5% (1/204) of poorly and well-differentiated thyroid carcinoma tissue samples were positive for IGF2BP1 protein. This indicates that IGF2BP1 protein expression identifies ATC with a diagnostic odds ratio of 612 (95% CI: 74.6-5021). In addition, we found that MAGEA3 is exclusively, although less consistently upregulated in ATC, presenting with an odds ratio of 411 (95% CI: 23.8-7098.7). Importantly, we provide confirmatory evidence that IGF2BP1 and MAGEA3 expression distinguishes ATC from poorly differentiated thyroid carcinoma. IGF2BP1 furthermore identified ATC foci within low-grade follicular thyroid carcinoma. In conclusion, IGF2BP1 represents the most promising single-gene marker available for ATC, followed by MAGEA3, improving on current techniques. Robust markers are essential to help distinguish this high-grade malignancy from other thyroid carcinomas, to guide surgical decision making, therapy and post-resection/therapy monitoring strategies.

Updates in the Pathologic Classification of Thyroid Neoplasms: A Review of the World Health Organization Classification

Advances in medical sciences and evidence-based medicine have led to momentous changes in classification and management of thyroid neoplasms. Much progress has been made toward avoiding overdiagnosis and overtreatment of thyroid cancers. The new 2017 World Health Organization (WHO) classification of thyroid neoplasms updated the diagnostic criteria and molecular and genetic characteristics reflecting the biology and behavior of the tumors, and newly introduced the category of borderline malignancy or uncertain malignant potential. Some neoplasms were subclassified, renamed, or redefined as a specific entity. This review introduces changes in the fourth edition WHO classification of thyroid tumors and updates the contemporary diagnosis and classification of thyroid tumors. We also discuss several challenges with the proposal of new diagnostic entities, since they have unique histopathologic and molecular features and clinical relevance.

Anaplastic thyroid carcinoma: Updates on WHO classification, clinicopathological features and staging

Anaplastic thyroid carcinoma is an uncommon carcinoma representing 1 to 4% of all thyroid cancers. The carcinoma is most common in females of the eight decades. It is a locally advanced cancer with frequent infiltration of surrounding organs, blood vessels and skin of neck. Paraneoplastic manifestations could occur. Approximately half of the patients with anaplastic thyroid carcinoma had distant metastasis with lung and brain as the most frequent sites of metastasis. The median survival of patients with anaplastic thyroid carcinoma reported was from 1 to 6 months. The terminology of the cancer in World Health Organization is "anaplastic thyroid carcinoma" rather than "undifferentiated thyroid carcinoma". In the latest American Joint Committee on Cancer (AJCC) TNM staging system for anaplastic thyroid carcinoma, there are updates on T and N categories. To conclude, updated knowledge of clinicopathological features, classification, pathological staging will improve our understanding of the cancer and will help in the management of the patients with this aggressive cancer.

Metastasis to the thyroid gland: a single-institution 16-year experience

AIMS

Metastasis to the thyroid gland is a rare occurrence that may pose a diagnostic challenge. In this study, we aimed to report the clinicopathological features, immunoprofile, molecular alterations and outcome of 30 patients treated at our centre from 2003 to 2019.

METHODS AND RESULTS

The most common site of the primary tumour was the kidney, followed by the lung, lower gastrointestinal tract and breast. In seven (23%) patients, the thyroid metastases were resected prior to the diagnosis of the primary tumours. Six patients (20%) had thyroid as the sole metastatic site. Three (10%) patients harboured tumour-to-tumour metastasis; 71% had a unilateral unifocal thyroid mass, which might be mistaken for a primary thyroid tumour. Among the 13 cases that were initially diagnosed at an outside hospital, four (31%) were misinterpreted as a thyroid primary. An immunohistochemical panel of thyroid follicular cell markers was most useful to differentiate primary thyroid tumours from metastasis. Molecularly, the metastasis showed alterations characteristic of the primary tumour, which may be helpful in establishing the diagnosis and primary site. Although the prognosis was poor, with a 5-year disease specific survival of 58%, a long-term cure was possible in cases with oligometastasis successfully treated with surgery.

CONCLUSIONS

Metastasis to the thyroid gland is an uncommon phenomenon, with an incidence of 0.36% in all thyroid malignancies. It may present as a solitary thyroid mass before the discovery of the primary tumour, posing a diagnostic challenge. Although the overall prognosis is poor, a subset of patients with oligometastasis can be managed surgically.

Contemporary Management of Anaplastic Thyroid Cancer

OPINION STATEMENT

Anaplastic thyroid cancer (ATC) is a rare but very aggressive form of undifferentiated thyroid cancer. Due to its rapid rate of progression and invasive nature, ATC poses significant risks of morbidity and mortality. The cornerstone in the management of ATC remains a prompt diagnosis of the disease and timely management of complications depending on the stage of disease. Surgery continues to offer a higher chance of a cure, although not all patients are candidates for surgical management. Patients with advanced disease may be considered for palliative surgery to reduce morbidity and complications from advanced disease. With the advent of new molecular testing and improved methods of diagnosis, novel therapeutic targets have been identified. Systemic therapy (chemotherapy and radiation therapy) as well as novel immunotherapy have shown some promise in patients with targetable genetic mutations. Patients should therefore have molecular testing of their tumor-if it is unresectable-and be tested for mutations that are targetable. Mutation-targeted therapy may be effective and may result in a significant response to allow surgical intervention for exceptional responders. Overall, patients who receive all three modalities of therapy (surgery, chemotherapy, and radiation therapy) have the highest overall survival.

Anaplastic transformation of thyroid cancer in mesentery metastases presenting as intestinal perforation: a case report

Background

Anaplastic thyroid carcinoma is a highly aggressive form of thyroid cancer associated with a very poor prognosis. Anaplastic transformation most commonly occurs in the thyroid itself or within regional lymph nodes. Here we report the case of a patient with papillary thyroid cancer, presenting with colon perforation as a result of anaplastic transformation of metastases in the mesentery tissue. There have been no previous reports of this form of anaplastic transformation.

Case presentation

A 74-year-old man was admitted to our hospital, presenting with abdominal pain that he had been experiencing for 1 week prior to admission. The patient had a history of papillary thyroid carcinoma, for which he underwent a total thyroidectomy and mediastinal lymph node dissection 6 years earlier, and subsequently received radioactive iodine therapy for postoperative recurrence in the lung 2 years later. During the present reported admission, a computed tomography scan revealed a large intra-abdominal mass infiltrating into the colon and retroperitoneum and also highlighted the pneumoperitoneum. The patient was diagnosed with generalized peritonitis as a result of colon perforation, as such, we conducted an emergency laparotomy. Intraoperative findings showed a mass affecting the ascending colon and kidney, following which, an ileostomy and biopsy were completed. Poorly differentiated spindle cells were identified in the biopsy specimens, and histopathological and immunohistochemical findings revealed the absence of thyroid carcinoma cells. The tumor was therefore believed to be a primary sarcoma. Following surgery, the patient recovered from sepsis that had arisen as a result of colon perforation, however, rapidly developed systemic metastases and died 1 month post-operation. An autopsy was performed, and the patient was diagnosed with anaplastic papillary thyroid cancer at the mesentery site of metastasis. This conclusion was reached owing to the presence of the squamous differentiation of lymph node cells, and because tumor cells were positive results for paired-box gene 8 expressions.

Conclusions

Anaplastic transformation of papillary thyroid carcinoma should be considered in the diagnosis of a large mesentery mass in patients with a history of papillary carcinoma. An appropriate biopsy and paired-box gene 8 immunostaining can be useful in confirming such a diagnosis.

Anaplastic thyroid carcinoma

Anaplastic thyroid carcinoma (ATC) is a rare but significant malignancy due to its high mortality rate. Rendering an accurate diagnosis is crucial given the prognostic implications and treatment ramifications. Based on the prognostic significance of the extent of invasion of the primary tumor, T staging for ATC changed in the most recent edition of the American Joint Committee on Cancer (AJCC) staging manual. In the past 5 years there has been a rapid increase in our understanding of the molecular basis of ATC which has provided the basis for targeted therapy for some ATC patients. In this review, ATC prognostic factors, histologic and immunotypic features, staging updates, and molecular alterations, with an emphasis on those that may impact treatment, will be discussed.

Oncogenic properties and signaling basis of the PAX8-GLIS3 fusion gene

Hyalinizing trabecular tumors of the thyroid are rare and mostly benign epithelial neoplasms of follicular cell origin, which have recently been shown to be underpinned by the PAX8-GLIS3 fusion gene. In our study, we sought to investigate the potential oncogenic mechanisms of the PAX8-GLIS3 fusion gene. Forced expression of PAX8-GLIS3 was found to increase proliferation, clonogenic potential and migration of human nonmalignant thyroid (Nthy-ori 3-1) and embryonic kidney (HEK-293) cells. Moreover, in xenografts, Nthy-ori 3-1 PAX8-GLIS3 expressing cells generated significantly larger and more proliferative tumors compared to controls. These oncogenic effects were found to be mediated through activation of the Sonic Hedgehog (SHH) pathway. Targeting of smoothened (SMO), a key protein in the SHH pathway, using the small molecule inhibitor Cyclopamine partially reversed the increased proliferation, colony formation and migration in PAX8-GLIS3 expressing cells. Our data demonstrate that the oncogenic effects of the PAX8-GLIS3 fusion gene are, at least in part, due to an increased activation of the SHH pathway.

Metastatic rectal cancer to papillary thyroid carcinoma: a case report and review of literature

BACKGROUND

Tumor-to-tumor metastasis is a rare event. Rectal cancer to primary thyroid neoplasm metastasis is extremely rare. Herein, we reported a case of metastatic rectal adenocarcinoma to a papillary thyroid carcinoma. The incidence and clinicopathological characteristics of metastatic colorectal cancer to a thyroid gland neoplasm were described, and the pertinent literature was reviewed.

CASE PRESENTATION

A 34-year-old female patient had curative treatment of initial rectal adenocarcinoma in 2012, and was found to have lung metastases by follow-up CT scan 3 years later. In 2018, she was found to have thyroid metastasis by imaging due to left neck pain and hoarseness. A fine-needle aspiration biopsy (FNAB) result suggested suspicious papillary thyroid carcinoma (PTC). The patient underwent a total thyroidectomy and bilateral cervical lymph nodes dissection. The histopathology of thyroidectomy specimen revealed a rectal adenocarcinoma metastatic to the thyroid concomitant with the papillary carcinoma in metastatic adenocarcinoma. The patient received levothyroxine supplementation therapy and palliative chemotherapy with irinotecan and anti-angiogenesis for the metastatic rectal adenocarcinoma. After 1 year of thyroidectomy, no newly developed lesion evidence of recurrent PTC was observed. The patient remains still alive.

CONCLUSION

The possibility of metastases should be considered in patients with a history of rectal cancer and with a thyroid lesion, particularly in those with ageing, hereditary nonpolyposis colorectal cancer (HNPCC) or long-term survival. The diagnosis should be histologically confirmed for the presence of both primary thyroid lesions and secondary thyroid neoplasms. Thyroidectomy may be a feasible treatment for symptomatic thyroid metastasis or thyroid cancer. we need to gain more available evidence from large or multi-center clinical data to help clinicians to diagnose rectal cancer to thyroid neoplasm metastases and evaluate treatment.

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.

BRAFV600E Transduction of an SV40-Immortalized Normal Human Thyroid Cell Line Induces Dedifferentiated Thyroid Carcinogenesis in a Mouse Xenograft Model

Background: Despite active studies of the clinical importance of BRAF^V600E, suitable research models to investigate the role of this mutation in the etiopathogenesis of human thyroid cancers are limited. Thus, we generated cell lines by transducing the simian virus (SV)-40 immortalized human thyroid cell line Nthy-ori 3-1 (Nthy) with lentiviral vectors expressing either BRAF^WT (Nthy/WT) or BRAF^V600E. Nthy/WT and Nthy/V600E cells were then xenografted into mice to evaluate the carcinogenic role of BRAF^V600E. Methods: Each cell line was subcutaneously injected into NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ mice, and a pathological analysis was performed. The effects of the mutation were further verified by using a BRAF^V600E-selective inhibitor (PLX-4032, vemurafenib). The transcriptome was analyzed by RNA sequencing and compared with data from The Cancer Cell Line Encyclopedia and Gene Expression Omnibus. Results: While Nthy/WT was not tumorigenic in vivo, Nthy/V600E formed tumors reaching 2784.343 mm³ in 4 weeks, on average. A pathological analysis indicated that Nthy/V600E tumors were dedifferentiated thyroid cancer. We found metastases in the lung, liver, and relevant lymph nodes. A transcriptomic analysis revealed 5512 differentially expressed genes (DEGs) between the mutant and wild-type cell lines, and more DEGs were shared with anaplastic thyroid cancer than with papillary thyroid cancer. BRAF^V600E activated the cell cycle mainly by regulating G1/S phases. PLX-4032 treatment significantly inhibited tumor growth and metastasis. Conclusions: Our data show that BRAF^V600E plays a pivotal role in the carcinogenic transformation of an SV40-transfected immortalized normal human thyroid cell line. This xenograft model is expected to contribute to studies of the etiopathogenesis and treatment of highly malignant thyroid cancers.

Solid variant of papillary thyroid carcinoma: an under-recognized entity

Solid variant of papillary thyroid carcinoma (SVPTC) is a rare morphological variant of papillary thyroid carcinoma (PTC). SVPTC is histologically characterized by predominant solid, trabecular and insular nests of tumor cells while cytological features of PTC such as nuclear grooves and nuclear inclusions are preserved. In fine needle aspiration cytology smears, tumor cells of SVPTC may be presented in cohesive, syncytial or trabecular clusters accompanied by some discohesiveness in the absence of necrosis. Although SVPTC and poorly differentiated thyroid carcinoma (PDTC) share similar histological findings of solid nests, SVPTC can be differentiated from PDTC in the lack of tumor necrosis, severe nuclear atypia, and a higher mitotic index. Immunohistochemical expression of CK19 and HBME-1, common markers of PTC, is decreased in solid nests of SVPTC. In pediatric patients exposed to radiation after the Chernobyl nuclear accident, there was a higher prevalence of SVPTC with RET/PTC3 type rearrangement. BRAF mutations are also reported in a small number of adult patients with SVPTC without any prior radiation exposure. Patients with SVPTC may have a slightly higher incidence of metastasis and recurrence of the tumor compared to conventional PTC, although overall survival rate is comparable. In this article, the current knowledge of SVPTC will be reviewed and discussed with an emphasis on the histopathological feature.

Do You Know the Details of Your PAX8 Antibody? Monoclonal PAX8 (MRQ-50) Is Not Expressed in a Series of 45 Medullary Thyroid Carcinomas

Medullary thyroid carcinomas display cytologic and architectural features that can simulate various primary and metastatic neoplasms. PAX8 immunoexpression in neuroendocrine neoplasms yielded antibody-dependent findings. Since the data regarding the expression profile of monoclonal PAX8 (MRQ-50) antibody is limited in large series of medullary thyroid carcinomas, this study investigated the expression profile of PAX8 (MRQ-50) in a series of 45 medullary thyroid carcinomas. PAX8 (MRQ-50) expression was noted in the thyroid follicular epithelial cells surrounding the tumor and was negative in all medullary thyroid carcinomas. In addition, twenty medullary thyroid carcinomas showed scattered entrapped thyroid follicular epithelial cells at the periphery of the tumor. Entrapped follicular epithelial cells were positive for PAX8 and thyroglobulin, and were negative for monoclonal CEA and calcitonin. A panel approach combining monoclonal antibodies to transcription factors, hormones and cell-specific peptides often assist diagnosticians in the workup of the cellular origin of a neuroendocrine neoplasm. Since PAX8 immunostaining is dependent on the antibody characteristics in neuroendocrine neoplasms, pathologists should be aware of the details of the PAX8 antibody used in a particular case.

Clear cell change in follicular adenoma of the thyroid. A diagnostic challenge

Clear cells in thyroid neoplasms can take two main forms: balloon-shaped and signet-ring cells. Balloon-shaped cell change in follicular adenoma is rare. A review of the literature has revealed only 20 previously published cases. We report herein a new case in the right thyroid lobe of a 45-year-old man. The clinicopathological data of the 21 cases including our paper have revealed that the ages of the patients ranged from 22-70 years, with a mean of 41.6 years. There was a clear predominance in women (M:F, 1:6). The most frequent location was in either of both lobes (81.8%), rarely affecting the isthmus. One case was observed in an ectopic thyroid in the submandibular region. The size ranged from 0.7-5.5 cm (mean 2.9 cm). The type of surgical intervention where this data was reported it was lobectomy for 10 (55.5%) cases, thyroidectomy for six (33.3%) cases, and simple excision for two (11.1%) cases. In one patient, the lobectomy was accompanied by cervical lymph node dissection. No cases recurred or extended outside the thyroid. The main differential diagnoses include intrathyroidal clear cell tumor of parathyroid origin, clear cell carcinoma of follicular, oncocytic, papillary, medullary or undifferentiated (anaplastic) origin, paraganglioma, metastatic clear cell carcinoma, especially of renal origin, metastatic balloon cell melanoma, and clear large-cell lymphoma. A thyroid lesion showing clear cell change constitutes a diagnostic challenge in cytological and biopsy diagnosis. Careful observation of the routine techniques along with the aid of an adequate immunohistochemical panel is essential to reach a correct biopsy diagnosis.

Multi-omics Signatures and Translational Potential to Improve Thyroid Cancer Patient Outcome

Recent advances in high-throughput molecular and multi-omics technologies have improved our understanding of the molecular changes associated with thyroid cancer initiation and progression. The translation into clinical use based on molecular profiling of thyroid tumors has allowed a significant improvement in patient risk stratification and in the identification of targeted therapies, and thereby better personalized disease management and outcome. This review compiles the following: (1) the major molecular alterations of the genome, epigenome, transcriptome, proteome, and metabolome found in all subtypes of thyroid cancer, thus demonstrating the complexity of these tumors and (2) the great translational potential of multi-omics studies to improve patient outcome.

Thyroid Tumors You Don't Want to Miss

This article examines more uncommon thyroid entities, including anaplastic thyroid carcinoma, poorly differentiated thyroid carcinoma, rare papillary thyroid carcinoma variants, medullary thyroid carcinoma, non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), and multiple adenomatous nodules in the setting of Cowden syndrome. These entities were chosen based on their clinical significance and because they can be diagnostically challenging due to their morphologic diversity and overlap with other thyroid tumors. This article addresses the diagnostic features of each entity, focusing on how to avoid potential pitfalls and mimics while also highlighting the clinical implications of each diagnosis.

Salutary Response to Targeted Therapy in Anaplastic Thyroid Cancer

Context. Anaplastic thyroid cancer (ATC) is an aggressive tumor with a median survival of 3 to 9 months, a 1-year survival of less than 10% and without definitive therapies. Recently, in BRAF V600E mutated ATCs, new targeted therapy using a combination of a BRAF inhibitor, dabrafenib (Dab), with a mitogen-activated extracellular protein kinase (MEK) inhibitor, trametinib (Tram), has shown significant promise. Case Description. We report a case of aggressive ATC with 5 sequence mutations: BRAF V600E (mutation fraction [MF] 34%), TERT E441del (MF 37%), RET N579K (MF 55%), EZH2 D154E (MF 60%), and CDK4 S259L (MF 48%). The patient had a dramatic response to the Dab/Tram combination with near complete resolution of his lung, bone, hepatic, and splenic lesions soon after starting therapy. Unfortunately, intolerable side effects (grade 2-3) on this regimen required tapering and discontinuation of the treatment. He had a quick resurgence of disease after stopping the combination therapy. The patient died approximately 3 months after discontinuing Dab/Tram. Autopsy revealed an atrophic thyroid gland with microscopic subcapsular focus of well-differentiated papillary thyroid carcinoma. There was extensive lymphatic spread of the tumor throughout bilateral lungs with fibrosis. No other metastatic site was identified. Conclusion. We report a unique case of ATC with 2 new mutations of EZH2 D154E and CDK S529L. This case exemplifies the significant promise Dab/Tram therapy holds, the potential side effects that limit their use, and autopsy findings status post use of this combination therapy.

PAX8 expression in anaplastic thyroid carcinoma is less than those reported in early studies: a multi-institutional study of 182 cases using the monoclonal antibody MRQ-50

Anaplastic thyroid carcinoma (ATC) is an aggressive malignant tumor composed of undifferentiated thyroid follicular cells. Pathological diagnosis of ATC can be challenging as the tumor may show morphological overlap with other neoplasms with anaplastic morphology. Immunohistochemical demonstration of thyroid origin facilitates the diagnosis of ATC. Previous studies using the polyclonal anti-PAX8 antibody 10336-1-AP suggested that PAX8 was the most sensitive marker, expressed in up to 80% of ATC. According to a 2018 NordiQC report, the monoclonal anti-PAX8 antibody MRQ-50 has become the most commonly used anti-PAX8 antibody worldwide. However, validation of this antibody in ATC is lacking. In this study, we recruited 182 ATC cases from seven institutions. Pathology slides were subjected to histology review. PAX8 immunohistochemistry using the MRQ-50 antibody was performed in whole tissue slides (n = 147) or tissue microarray sections (n = 35). We found PAX8 expression in 54.4% of the cases, which was significantly lower than those reported in prior studies with the polyclonal antibody. PAX8 expression was positively correlated with the presence of an epithelial pattern (63.6% vs 37.5%, p = 0.0008) and a coexisting differentiated thyroid carcinoma component (71.6% vs 44.3%, p = 0.0004), but was not associated with age, gender, specimen type, or presence of giant cell and sarcomatoid patterns. In conclusion, we demonstrated PAX8 expression using the monoclonal antibody MRQ-50 in only half of the cases in a large ATC series. Pathologists should be aware that PAX8 expression in ATC is less than those reported in early studies to avoid misdiagnosis.

Anaplastic thyroid carcinoma mimicking a malignant pleural mesothelioma: Clues for diagnosis

Pleural metastasis of thyroid carcinoma is very rarely encountered in the evaluation of pleural effusion and diagnosis may be challenging. However, an anaplastic transformation of papillary thyroid carcinoma (PTC), although a rare condition, should be considered even after a prolonged period of patient follow-up. Here we report a case of anaplastic thyroid carcinoma mimicking malignant pleural mesothelioma diagnosed nine years after the initial diagnosis of PTC and detail the clues used to orient and confirm the diagnosis.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

Two cases of thyroid gland invasion by upper mediastinal carcinoma

Summary

The objective this study is to report two cases of thyroid gland invasion by upper mediastinal carcinoma. Mediastinal tumors are uncommon and represent 3% of the tumors seen within the chest. In reports on mediastinal masses, the incidence of malignant lesions ranged from 25 to 49%. The thyroid gland can be directly invaded by surrounding organ cancers. We report these cases contrasting them to the case of a thyroid cancer with mediastinal lesions. Case 1 was a 73-year-old woman who was diagnosed with papillary thyroid carcinoma, and she underwent surgery and postoperative radioactive iodine. Case 2 was a 74-year-old man who was diagnosed with non-small-cell lung carcinoma, favor squamous cell carcinoma, and he underwent chemoradiotherapy. Case 3 was a 77-year-old man who was diagnosed a thymic carcinoma based on pathological findings and referred the patient to thoracic surgeons for surgical management. The images of the three cases were similar, and the differential diagnoses were difficult and required pathological examination. Primary thyroid carcinoma and invading carcinoma originating from the adjacent organs need to be distinguished because their prognoses and treatment strategies are different. It is important to properly diagnose them by images and pathological findings.

The thyroid gland in the anterior neck can be directly invaded by surrounding organ cancers. Primary thyroid carcinoma and invading carcinoma originating from the adjacent organs need to be distinguished because their prognoses and treatment strategies are different. It is important to properly diagnose by images and pathological findings.

Metastasis of squamous cell carcinoma of the head and neck to the thyroid: a single institution's experience with a review of relevant publications

The thyroid gland is a rare site of metastasis, and in particular of those of squamous cell carcinoma (SCC) from the head and neck region. We have reviewed the aetiology, pathogenesis, clinical characteristics, radiological features, immunohistochemical profile, prognosis, and management of metastatic SCC from the head and neck region to the thyroid, and searched current publications on the Medline, Embase, and Cochrane databases using the following keywords: "SCC of thyroid", "secondary SCC of thyroid", and "metastasis to the thyroid", for papers published during the last 33 years (April 1984 to October 2017).We found a total of 19 papers that reported a total of 32 cases that were relevant. Four further cases were discovered as an incidental finding on follow-up positron emission tomographic/computed tomographic scans with magnetic resonance imaging of the head and neck at our hospital, which were confirmed with an ultrasound-guided core needle biopsy followed by immunohistochemical examination. For patients who are doing well, whose disease is controlled at the primary site, and who have no evidence of distant metastatic disease, total thyroidectomy could be considered followed by adjuvant radiation or chemoradiotherapy, depending on the presence of intermediate or high-risk features on pathological examination and previous history of radiation. This may help to control the disease and avoid local morbidity.

Targeting Super-Enhancer-Driven Oncogenic Transcription by CDK7 Inhibition in Anaplastic Thyroid Carcinoma

Background: Anaplastic thyroid carcinoma (ATC) is one of the most aggressive malignancies, with no effective treatment currently available. The molecular mechanisms of ATC carcinogenesis remain poorly understood. The objective of this study was to investigate the mechanisms and functions of super-enhancer (SE)-driven oncogenic transcriptional addiction in the progression of ATC and identify new drug targets for ATC treatments. Methods: High-throughput chemical screening was performed to identify new drugs inhibiting ATC cell growth. Cell viability assay, colony formation analysis, cell-cycle analysis, and animal study were used to examine the effects of drug treatments on ATC progression. Chromatin immunoprecipitation sequencing was conducted to establish a SE landscape of ATC. Integrative analysis of RNA sequencing, chromatin immunoprecipitation sequencing, and CRISPR/Cas9-mediated gene editing was used to identify THZ1 target genes. Drug combination analysis was performed to assess drug synergy. Patient samples were analyzed to evaluate candidate biomarkers of prognosis in ATC. Results: THZ1, a covalent inhibitor of cyclin-dependent kinase 7 (CDK7), was identified as a potent anti-ATC compound by high-throughput chemical screening. ATC cells, but not papillary thyroid carcinoma cells, are exceptionally sensitive to CDK7 inhibition. An integrative analysis of both gene expression profiles and SE features revealed that the SE-mediated oncogenic transcriptional amplification mediates the vulnerability of ATC cells to THZ1 treatment. Combining this integrative analysis with functional assays led to the discovery of a number of novel cancer genes of ATC, including PPP1R15A, SMG9, and KLF2. Inhibition of PPP1R15A with Guanabenz or Sephin1 greatly suppresses ATC growth. Significantly, the expression level of PPP1R15A is correlated with CDK7 expression in ATC tissue samples. Elevated expression of PPP1R15A and CDK7 are both associated with poor clinical prognosis in ATC patients. Importantly, CDK7 or PPP1R15A inhibition sensitizes ATC cells to conventional chemotherapy. Conclusions: Taken together, these findings demonstrate transcriptional addiction in ATC pathobiology and identify CDK7 and PPP1R15A as potential biomarkers and therapeutic targets for ATC.

Primary Squamous Cell Carcinoma of the Thyroid

Background: Primary squamous cell carcinoma of the thyroid (PSCCT) is a rare malignancy of the head and neck, with fewer than 60 cases reported in the literature. We report a case of PSCCT and provide a brief review of the literature. Case Report: A 66-year-old female with a history of a hemithyroidectomy for a benign thyroid lesion presented with 3 months of progressively worsening compressive symptoms and shortness of breath. Physical examination revealed right-sided thyromegaly and right-sided true vocal fold immobility. Preoperative imaging with ultrasound and computed tomography scan confirmed an enlarged right thyroid, as well as right anterior cervical lymphadenopathy, subglottic stenosis, and bilateral pulmonary nodules. Fine needle aspiration of the thyroid was suggestive of carcinoma. Intraoperative findings of gross tracheal invasion during a planned completion thyroidectomy prompted limited resection and impromptu tracheotomy. Histopathologic and immunohistochemical evaluation confirmed a squamous cell carcinoma of thyroid origin. Further oncologic workup with core lung biopsy and positron emission tomography scan demonstrated metastasis to the lung and cervical spine. Palliative chemotherapy was begun, but the patient died 1 week into therapy. Conclusion: PSCCT is a rare but aggressive malignancy of the head and neck. Histopathologic and immunohistochemical evaluations are essential for diagnosis. While locoregional surgery and radiation therapy may improve the length of survival, the prognosis of patients with PSCCT is poor. Physicians should be mindful of this unique but deadly disease process, as early diagnosis and rapid treatment initiation are essential to optimize treatment outcomes.

Clinically Relevant Prognostic Parameters in Differentiated Thyroid Carcinoma

Although differentiated thyroid carcinomas typically pursue an indolent clinical course, it is important to identify the subset of tumors that are most likely to behave aggressively so that patients with these tumors are counseled and treated appropriately. Extent of disease is fundamental to the prognostication for differentiated thyroid carcinoma; however, there are additional histologic features of the tumor separate from extent of disease that have been shown to affect clinical course. This review will start with a discussion of aggressive variants of papillary thyroid carcinoma, move to the prognostic significance of vascular invasion in follicular thyroid carcinoma, and finish with a discussion of Hürthle cell carcinoma, with an emphasis on why it is not considered a subtype of follicular thyroid carcinoma in the 2017 WHO Classification of Tumors of Endocrine Organs.

Metastases to the Thyroid: Potential Cytologic Mimics of Primary Thyroid Neoplasms

Secondary tumors of the thyroid gland, although uncommon, can sometimes pose as diagnostic dilemmas on fine-needle aspiration cytology, frequently mimicking primary thyroid neoplasms. An accurate diagnosis of such lesions, however, is critical for patient management and prognosis. The present study reviews the cytologic aspects of secondary involvement of the thyroid, listing the most common primary malignancies that metastasize to this gland. Knowledge of such morphologic aspects, combined with prompt clinical correlation, is essential for the cytopathologist to achieve a proper, definite diagnosis.