Pitfalls in Challenging Thyroid Tumors: Emphasis on Differential Diagnosis and Ancillary Biomarkers

Spindle epithelial tumor with thymus-like element (SETTLE)-Report of a rare thyroid carcinoma

Spindle epithelial tumor with thymus-like element should be included in the differential diagnosis of thyroid gland cancers, particularly in medullary carcinoma, younger patients and indolent clinical presentation, because it may influence treatment and prognosis.

Poorly differentiated thyroid carcinomas: conceptual controversy and clinical impact

Poorly differentiated thyroid carcinomas (PDTC) are rare diseases; nevertheless, they account for the majority of deaths from non-anaplastic follicular cell-derived thyroid carcinomas. Establishing the diagnosis and treatment of PDTC is challenging given the low incidence and the lack of standardization of diagnostic criteria. These limitations hamper the ability to compare therapeutic modalities and outcomes between recent and older studies. Recently, the 5th edition of the classification of endocrine tumors has been published, which includes changes in nomenclature and the addition of the disease entity of "differentiated high-grade follicular cell-derived carcinomas". On the other hand, the recently witnessed advances in molecular diagnostics have enriched therapeutic options and improved prognosis for patients. We herein review the various historical variations and evolution in the diagnostic criteria for PDTC. This systematic review attempts to clarify the evolution of the histological and molecular characteristics of this disease, its prognosis, as well as its treatment options.

Primary Mucinous Carcinoma of the Thyroid: A Case Report, Literature Review, and Immunohistochemistry Summary

Introduction

Primary mucinous carcinoma of the thyroid is an exceedingly rare malignancy that is histologically similar to mucinous carcinoma of other sites. Accurate diagnosis is a challenging yet crucial component of clinical management for both patients and our understanding of this rare disease.

Case Presentation

We report the case of a 69-year-old male patient with primary mucinous carcinoma of the thyroid. Microscopic examination of a biopsy specimen showed fibrous tissue, which was extensively and irregularly infiltrated by a cytologically malignant epithelial neoplasm showing glandular differentiation with mucin production. Immunohistochemistry demonstrated that tumor cells were positive for TTF1, thyroglobulin, CK7, and PAX8. Co-expression of TTF1 and PAX8 is most commonly seen in thyroid tumors. These findings support our diagnosis of mucinous carcinoma of thyroid origin, which is rare and highly aggressive.

Conclusion

In this report, we present the only documented case of primary mucinous carcinoma of the thyroid reported in the United States in the last decade. The diagnosis of primary mucinous carcinoma of the thyroid can be challenging. Therefore, we discuss and detail the clinicopathologic tumor profile and provide more current, detailed histological criteria to assist in the diagnosis of this rare disease.

Diagnostic utility of RAS mutation testing for refining cytologically indeterminate thyroid nodules

RAS mutations are prevalent in indeterminate thyroid nodules, but their association with malignancy risk and utility for diagnosis remains unclear. We performed a systematic review and meta-analysis to establish the clinical value of RAS mutation testing for cytologically indeterminate thyroid nodules. PubMed and Embase were systematically searched for relevant studies. Thirty studies comprising 13,328 nodules met the inclusion criteria. Random effects meta-analysis synthesized pooled estimates of RAS mutation rates, risk of malignancy with RAS positivity, and histologic subtype outcomes. The pooled mutation rate was 31 % (95 % CI 19-44 %) among 5,307 indeterminate nodules. NRAS mutations predominated at 67 % compared to HRAS (24 %) and KRAS (12 %). The malignancy rate with RAS mutations was 58 % (95 %CI=48-68 %). RAS positivity increased malignancy risk 1.7-fold (RR 1.68, 95 %CI=1.21-2.34, p=0.002), with significant between-study heterogeneity (I2=89 %). Excluding one outlier study increased the relative risk to 1.75 (95 %CI=1.54-1.98) and I2 to 14 %. Funnel plot asymmetry and Egger's test (p=0.03) indicated potential publication bias. Among RAS-positive malignant nodules, 38.6 % were follicular variant papillary carcinoma, 34.1 % classical variant, and 23.2 % follicular carcinoma. No statistically significant difference in the odds of harboring RAS mutation was found between subtypes. In conclusion, RAS mutation testing demonstrates clinical utility for refining the diagnosis of cytologically indeterminate thyroid nodules. Positivity confers a 1.7-fold increased malignancy risk, supporting use for personalized decision-making regarding surgery vs. monitoring. Follicular variant papillary carcinoma constitutes the most common RAS-positive malignant histological subtype. See also the graphical abstract(Fig. 1).

Canine thyroid carcinomas: A review with emphasis on comparing the compact subtype of follicular thyroid carcinomas and medullary thyroid carcinomas

Canine thyroid carcinomas are relatively common malignant endocrine neoplasms in dogs derived from either thyroid follicular cells (forming follicular thyroid carcinomas) or medullary cells (parafollicular, C-cells; forming medullary thyroid carcinomas). Older and recent clinical studies often fail to discriminate between compact cellular (solid) follicular thyroid carcinomas and medullary thyroid carcinomas, which may skew conclusions. The compact subtype of follicular thyroid carcinomas appears to be the least differentiated subtype of follicular thyroid carcinomas and needs to be differentiated from medullary thyroid carcinomas. This review includes information on the signalment, presentation, etiopathogenesis, classification, histologic and immunohistochemical diagnosis, clinical management, and biochemical and genetic derangements of canine follicular and medullary carcinomas, and their correlates with human medicine.

Intrathyroidal thymic carcinoma not so indolent a neoplasm?

ABSTRACT

Intrathyroidal thymic carcinoma (ITC) is a very rare malignant epithelial tumor of the thyroid gland with thymic epithelial differentiation. Here, we are reporting the case of an eighty-year-old man who at presentation had extrathyroidal spread to the larynx and metastasis to regional lymph nodes. Though the tumor had a relatively low-grade morphology, there were areas of high mitotic activity with areas of necrosis. The classically described ivory-white gross appearance of the tumor, histomorphology of thick bands dividing the tumor into lobules, squamous cell differentiation, tight whorls of cells resembling Hassall's corpuscle, and areas showing dense lymphocytic infiltration, together with an immunoprofile of CD5, Ckit, Tumor protein 63 (p63), and B-cell lymphoma 2 gene (bcl2) positivity, helped in diagnosing this rare entity. Though classically ITC is said to have a good prognosis, cases with spread to adjacent organs and lymph node metastasis may not have an indolent course.

Spindle Epithelial Tumor With Thymus-Like Differentiation of Thyroid (SETTLE): A Case Report and Literature Review

Spindle epithelial tumor with thymus-like differentiation of thyroid (SETTLE) is very rare neoplasm with 2 cellular forms, epithelial cell and spindle cell, and most reported cases have been in young people. An 11-year-old boy presented with painless swelling of the right neck lasting for more than 2 months. A tumor size measuring approximately 3 × 3 cm was resected, and intraoperative frozen pathology suggested a spindle cell tumor, which was confirmed as SETTLE by immunohistochemical staining and external hospital consultation. The immunohistochemical staining profile of the resected tumor tissue was as follows: cytokeratin (CK) (+), smooth muscle actin (weak+), vimentin (+), CK7 (focal+), B-cell lymphoma 2 (partial+), CD99 (-), calcitonin (+), galectin-3 (+), CK19 (+), and Ki-67 (10%+). Ultrasound at 1-year postoperative follow-up revealed no local recurrence of the lesion or lymph node metastasis in the thyroid gland. We summarized the disease characteristics of SETTLE among 6 cases reported to date and found that SETTLE is associated with a good prognosis and low postoperative recurrence rate. Thus, for this type of malignant thyroid tumor, diagnosis depends mainly on postoperative pathology and immunohistochemical staining and simple surgical resection is recommended.

Preoperative, Intraoperative, and Postoperative Parathyroid Pathology: Clinical Pathologic Collaboration for Optimal Patient Management

Parathyroid disease typically presents with parathyroid hyperfunction as result of neoplasia or a consequence of non-neoplastic systemic disease. Given the parathyroid gland is a hormonally active organ with broad physiologic implications and serologically accessible markers for monitoring, the diagnosis of parathyroid disease is predominantly a clinical pathologic correlation. We provide the current pathological correlates of parathyroid disease and discuss preoperative, intraoperative, and postoperative pathology consultative practice for optimal patient care.

MiR-203a-3p, miR-204-3p, miR-222-3p as useful diagnostic and prognostic tool for thyroid neoplasia spectrum

PURPOSE

The challenge in the diagnosis and treatment of thyroid carcinoma is to correctly classify neoplasias with overlapping features and to identify the high-risk patients among those with a less aggressive form, in order to personalize the treatment of thyroid carcinoma patients accordingly.

METHODS

MiR-203a-3p, miR-204-3p, and miR-222-3p levels were determined in 99 cases of thyroid neoplasias (77 papillary thyroid carcinomas (PTC) of diverse variants, 12 follicular thyroid adenomas (FTA) and 10 nodular goiters (NG)) along with 99 adjacent non-malignant thyroid tissues using quantitative RT-PCR. The results were evaluated in comparison with the clinicopathological features of the patients and available TCGA data.

RESULTS

Down-regulated miR-203a-3p indicates the presence of thyroid tumor (PTC or FTA) with high sensitivity (75%) and specificity (73%), while its up-regulation indicates NG. If miR-203a-3p is down-regulated, up-regulated miR-204-3p with high sensitivity (83.3%) and specificity (74.4%) indicates FTA presence, while up-regulated miR-222-3p, with high sensitivity (76.6%) and specificity (75.0%), points to PTC. The expression of miR-204-3p and miR-222-3p depends on the PTC subtype (P < 0.05). While the deregulated expression of tested miRs is associated with a long-range of unfavorable clinicopathological parameters of PTC, only abundant expression of miR-222-3p may be used as an independent predictive factor for the presence of extrathyroid invasion and advanced pTNM stage of PTC (P < 0.05).

CONCLUSION

Successive evaluation of miR-203a-3p, miR-204-3p, and miR-222-3p expression can help in the differential diagnosis of thyroid neoplasias. A high relative value of miR-222-3p expression is an independent predictive factor for the presence of extrathyroid invasion and advanced pTNM stage of PTC. The panel consisting of miR-203a-3p, miR-204-3p, and miR-222-3p could be used as a diagnostic and prognostic tool for personalizing the treatment of thyroid cancer patients.

Update from the 2022 World Health Organization Classification of Thyroid Tumors: A Standardized Diagnostic Approach

The fifth edition of the World Health Organization (WHO) histologic classification of thyroid neoplasms released in 2022 includes newly recognized tumor types, subtypes, and a grading system. Follicular cell-derived neoplasms are categorized into three families (classes): benign tumors, low-risk neoplasms, and malignant neoplasms. The terms "follicular nodular disease" and "differentiated high-grade thyroid carcinoma" are introduced to account for multifocal hyperplastic/neoplastic lesions and differentiated thyroid carcinomas with high-grade features, respectively. The term "Hürthle cells" is replaced with "oncocytic cells." Invasive encapsulated follicular and cribriform morular variants of papillary thyroid carcinoma (PTC) are now redefined as distinct tumor types, given their different genetic alterations and clinicopathologic characteristics from other PTC subtypes. The term "variant" to describe a subclass of tumor has been replaced with the term "subtype." Instead, the term "variant" is reserved to describe genetic alterations. A histologic grading system based on the mitotic count, necrosis, and/or the Ki67 index is used to identify high-grade follicular-cell derived carcinomas and medullary thyroid carcinomas. The 2022 WHO classification introduces the following new categories: "salivary gland-type carcinomas of the thyroid" and "thyroid tumors of uncertain histogenesis." This review summarizes the major changes in the 2022 WHO classification and their clinical relevance.

Medullary thyroid carcinoma diagnosed with liquid-based cytology and immunocytochemistry

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine malignancy that arises from the parafollicular cells (C cells) secreting calcitonin. This study summarizes our experience in the diagnosis of MTC with ultrasound-guided thyroid FNA, subsequently processed with liquid-based cytology (LBC) and immunocytochemistry (ICC). We searched our laboratory archives for thyroid FNA cases with an interpretation of positive or suspicious for MTC, during the period 2004-2018. A total of 20 cases (18 thyroid FNAs; two lymph node FNAs) were selected and included in this study. These displayed high cellularity and a discohesive pattern, with a few loose syncytial groups. There was some variation in the cell size and shape both across and within our cases. Most MTCs (n = 15) exhibited a predominant plasmacytoid/epithelioid cell morphology, whereas five of our cases showed a spindle cell pattern. Of interest, none of eight MTC microcarcinomas (≤1 cm) showed a spindle cell morphology. Amyloid was found in 11/20 cases (55%), while binucleation/multinucleation in 17/20 (85%), and nuclear pseudoinclusions in 3/20 MTC cases (15%). Nuclei exhibited a granular, "salt and pepper" chromatin in all cases. ICC was performed in 18/20 cases (90%). Calcitonin, CEA, TTF1, and Chromogranin were positive wherever applied, whereas thyroglobulin and CK19 were negative. In conclusion, ultrasound-guided thyroid FNA - processed with LBC and ICC - is a reliable modality to detect MTC preoperatively, facilitating the management of such patients.

Overview of the 2022 WHO Classification of Thyroid Neoplasms

This review summarizes the changes in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors that relate to the thyroid gland. The new classification has divided thyroid tumors into several new categories that allow for a clearer understanding of the cell of origin, pathologic features (cytopathology and histopathology), molecular classification, and biological behavior. Follicular cell-derived tumors constitute the majority of thyroid neoplasms. In this new classification, they are divided into benign, low-risk, and malignant neoplasms. Benign tumors include not only follicular adenoma but also variants of adenoma that are of diagnostic and clinical significance, including the ones with papillary architecture, which are often hyperfunctional and oncocytic adenomas. For the first time, there is a detailed account of the multifocal hyperplastic/neoplastic lesions that commonly occur in the clinical setting of multinodular goiter; the term thyroid follicular nodular disease (FND) achieved consensus as the best to describe this enigmatic entity. Low-risk follicular cell-derived neoplasms include non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), thyroid tumors of uncertain malignant potential, and hyalinizing trabecular tumor. Malignant follicular cell-derived neoplasms are stratified based on molecular profiles and aggressiveness. Papillary thyroid carcinomas (PTCs), with many morphological subtypes, represent the BRAF-like malignancies, whereas invasive encapsulated follicular variant PTC and follicular thyroid carcinoma represent the RAS-like malignancies. This new classification requires detailed subtyping of papillary microcarcinomas similar to their counterparts that exceed 1.0 cm and recommends not designating them as a subtype of PTC. The criteria of the tall cell subtype of PTC have been revisited. Cribriform-morular thyroid carcinoma is no longer classified as a subtype of PTC. The term "Hürthle cell" is discouraged, since it is a misnomer. Oncocytic carcinoma is discussed as a distinct entity with the clear recognition that it refers to oncocytic follicular cell-derived neoplasms (composed of > 75% oncocytic cells) that lack characteristic nuclear features of PTC (those would be oncocytic PTCs) and high-grade features (necrosis and ≥ 5 mitoses per 2 mm²). High-grade follicular cell-derived malignancies now include both the traditional poorly differentiated carcinoma as well as high-grade differentiated thyroid carcinomas, since both are characterized by increased mitotic activity and tumor necrosis without anaplastic histology and clinically behave in a similar manner. Anaplastic thyroid carcinoma remains the most undifferentiated form; squamous cell carcinoma of the thyroid is now considered as a subtype of anaplastic carcinoma. Medullary thyroid carcinomas derived from thyroid C cells retain their distinct section, and there is a separate section for mixed tumors composed of both C cells and any follicular cell-derived malignancy. A grading system for medullary thyroid carcinomas is also introduced based on mitotic count, tumor necrosis, and Ki67 labeling index. A number of unusual neoplasms that occur in the thyroid have been placed into new sections based on their cytogenesis. Mucoepidermoid carcinoma and secretory carcinoma of the salivary gland type are now included in one section classified as "salivary gland-type carcinomas of the thyroid." Thymomas, thymic carcinomas and spindle epithelial tumor with thymus-like elements are classified as "thymic tumors within the thyroid." There remain several tumors whose cell lineage is unclear, and they are listed as such; these include sclerosing mucoepidermoid carcinoma with eosinophilia and cribriform-morular thyroid carcinoma. Another important addition is thyroblastoma, an unusual embryonal tumor associated with DICER1 mutations. As in all the WHO books in the 5th edition, mesenchymal and stromal tumors, hematolymphoid neoplasms, germ cell tumors, and metastatic malignancies are discussed separately. The current classification also emphasizes the value of biomarkers that may aid diagnosis and provide prognostic information.

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.

Ultrasound-guided fine-needle aspiration biopsy of thyroid neoplasms with lipomatous stroma: Report of two cases

Thyroid tumors with abundant adipose tissue component are rare, reportedly accounting for 0.98-2.8% of all thyroid nodules, and include entities such as thyroid lipoadenoma and thyroid carcinoma with lipomatous stroma (TCLS). They may be encountered on fine-needle aspiration biopsy (FNAB), which is widely used in evaluation of thyroid nodules. However, due to their relative rarity, adipose elements rarely are recognized preoperatively in these tumors. Herein, we report two cases of thyroid tumors with abundant adipose tissue, along with cytologic, histologic, and ultrasonographic features. Although an intermixture of adipose tissue and thyroid follicular cells is the key cytologic feature of thyroid tumors with adipose stroma, other cytologic findings, such as abundant fat droplets or isolated fragments of adipose tissue, also should raise the possibility of a fat-containing tumor, particularly when a biopsy is performed by a cytopathologist under ultrasonographic guidance and adequate radiologic-pathologic correlation. Cytopathologists should be aware that overlooking lesional adipose tissue within a thyroid neoplasm might give the false impression of a non-diagnostic or sparsely cellular FNAB specimen.

Intratumoral Heterogeneity in Differentiated Thyroid Tumors: An Intriguing Reappraisal in the Era of Personalized Medicine

Differentiated thyroid tumors (DTTs) are characterized by significant molecular variability in both spatial and temporal intra-tumoral heterogeneity (ITH), that could influence the therapeutic management. ITH phenomenon appears to have a relevant role in tumor growth, aggressive behavior and drug resistance. Accordingly, characteristics and consequences of ITH in DTTs should be better analyzed and understood in order to guide clinical practice, improving survival. Consequently, in the present review, we investigated morphological and molecular ITH of DTTs in benign, borderline neoplasms and in malignant entities, summarizing the most significant data. Molecular testing in DTTs documents a high risk for recurrence of cancer associated with BRAF^V600E, RET/PTC 1/3, ALK and NTRK fusions, while the intermediate risk may be related to BRAF^K601E, H/K/N RAS and PAX8/PPARγ. In addition, it may be suggested that tumor genotype is associated with peculiar phenotype.

Inherited Follicular Epithelial-Derived Thyroid Carcinomas: From Molecular Biology to Histological Correlates

Cancer derived from thyroid follicular epithelial cells is common; it represents the most common endocrine malignancy. The molecular features of sporadic tumors have been clarified in the past decade. However the incidence of familial disease has not been emphasized and is often overlooked in routine practice. A careful clinical documentation of family history or familial syndromes that can be associated with thyroid disease can help identify germline susceptibility-driven thyroid neoplasia. In this review, we summarize a large body of information about both syndromic and non-syndromic familial thyroid carcinomas. A significant number of patients with inherited non-medullary thyroid carcinomas manifest disease that appears to be sporadic disease even in some syndromic cases. The cytomorphology of the tumor(s), molecular immunohistochemistry, the findings in the non-tumorous thyroid parenchyma and other associated lesions may provide insight into the underlying syndromic disorder. However, the increasing evidence of familial predisposition to non-syndromic thyroid cancers is raising questions about the importance of genetics and epigenetics. What appears to be "sporadic" is becoming less often truly so and more often an opportunity to identify and understand novel genetic variants that underlie tumorigenesis. Pathologists must be aware of the unusual morphologic features that should prompt germline screening. Therefore, recognition of harbingers of specific germline susceptibility syndromes can assist in providing information to facilitate early detection to prevent aggressive disease.