A case of primary secretory carcinoma of the thyroid with high-grade features

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

Aggressive Primary Thyroid Mucoepidermoid Carcinoma with Extensive Pulmonary Involvement

Mucoepidermoid carcinomas (MECs) represent the most common malignant neoplasms of the salivary glands, but they have also been described in other unusual sites. Primary MECs originating in the thyroid gland are exceedingly rare, accounting for less than 0.5% of thyroid tumors. Owing to their low to medium grade, they are usually associated with an indolent evolution and a good long-term prognosis, generally being managed surgically based on the extent of the disease. However, this does not always apply, as primary thyroid MECs may present as metastatic or locally advanced diseases. While several treatment options have been explored in such cases, no consensus currently exists on their optimal treatment plan, and they should be managed in a multidisciplinary fashion. We report the case of a 67-year-old patient with primary MEC of the thyroid, which behaved aggressively, with extensive pulmonary metastasis, ultimately leading to the rapid clinical deterioration and death of the patient.

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.

Secretory Carcinoma of the Thyroid in a 49-Year-Old Man Treated with Larotrectinib: Protracted Clinical Course of Disease Despite the High-Grade Histologic Features

Secretory carcinoma of the thyroid gland is histologically and genetically similar to its mammary and salivary gland counterparts. Unlike differentiated thyroid carcinomas of follicular cell origin, thyroid SC is not a thyroglobulin-producing tumor and would not be amenable to radioactive iodine therapy. Instead, these carcinomas may respond to targeted therapy with TRK inhibitors, which further emphasizes the importance of their recognition among morphologically similar thyroid entities. Based on eleven cases reported to date, most primary thyroid SC tend to present as locally advanced malignancies and are characterized by frequent recurrences and long-term survival. High-grade histologic features, increased mitotic count and necrosis have been described but their impact on clinical course and outcome remains unclear. We hereby report the case of a primary SC with high-grade features arising in the thyroid of a 49-year-old man, who was treated with Larotrectinib for his second recurrence. The patient achieved a durable response that lasted for 18 months but then he continued to progress and died of disease 181 months after the diagnosis.

Molecular Pathology of Thyroid Tumors: Old Problems and New Concepts

The molecular signatures of many thyroid tumors have been uncovered. These discoveries have translated into clinical practice and are changing diagnostic and tumor classification paradigms. Here, the findings of recent studies are presented with special emphasis on how molecular insights are impacting the understating of RAS mutant thyroid nodules, Hürthel cell neoplasms, and unusual thyroid tumors, such as hyalinizing trabecular tumor, secretory carcinoma of the thyroid, and sclerosing mucoepidermoid carcinoma with eosinophilia. In addition, the utility of detecting actionable molecular alterations by immunohistochemistry in advanced and aggressive thyroid cancer is also discussed.

Mammary analog secretory carcinoma of the thyroid gland: A rare cancer harboring TRK fusion

Mammary analog secretory carcinoma (MASC), or secretory carcinoma of the thyroid is an extremely rare disease harboring ETV6-NTRK3 gene fusion with TRK activation. Here we report the twelfth case of MASC of the thyroid worldwide. A 36-year-old female was diagnosed with poor-differentiated thyroid carcinoma (PDTC). Pathology consultant and immunochemical workups showed the tumor cells were negative for TTF1, TG, PAX8, positive for S100, Vimentin, GATA-3, and focally positive for mammaglobin. Fluorescence in situ hybridization (FISH) assay using a dual-color break-apart probe showed ETV6 translocation t(12p13) (ETV6) was present and established the diagnosis of MASC. Next-generation sequencing (NGS) of a 47-gene panel identified exon 1-5 of ETV6 gene were fused with exons 15-19 of NTRK3 gene. The patient experienced three loco-regional recurrences within 12 months and eventually developed inoperable local disease as well as bilateral lung metastasis. She is currently receiving anti-TRK treatment with a follow-up time of 33 months. A literature review of MASC in the thyroid was also conducted.

Salivary-Like Tumors of the Thyroid: A Comprehensive Review of Three Rare Carcinomas

Thyroid carcinomas represent 3.2% of all new cases of cancer in the United States. Whereas most thyroid tumors arise from follicular cells or, less commonly, parafollicular cells, the derivation of some rare primary thyroid carcinoma subtypes is less clear and represents an area of evolving knowledge. Primary thyroid carcinomas that resemble neoplasms characteristic of the salivary glands ("salivary-like" primary thyroid carcinomas) arguably represent some of the most unusual primary thyroid tumors. Herein, we have undertaken a review of the literature in order to present a comprehensive overview of salivary-like primary thyroid carcinomas including: mucoepidermoid carcinoma, sclerosing mucoepidermoid carcinoma with eosinophilia, and secretory carcinoma. Awareness of these unusual, distinct primary tumors is important for timely diagnosis and optimal patient management. This review highlights these three salivary-like carcinomas, with special emphasis on developments since publication of the World Health Organization (WHO) 2017 Classification of Tumours of Endocrine Organs.

Ancillary testing in salivary gland cytology: A practical guide

Salivary gland cytology is challenging, and historically the role of ancillary testing has been limited. However, numerous molecular/genetic advances in the understanding of salivary gland neoplasms during the last decade have facilitated the development of many useful diagnostic markers, such as PLAG1 and HMGA2 immunohistochemistry for pleomorphic adenoma and ETV6 fluorescence in situ hybridization for secretory carcinoma. Numerous salivary gland neoplasms are characterized by specific molecular/genetic alterations, many of which can be identified on cytologic preparations by karyotype analysis, fluorescence in situ hybridization, or immunohistochemical surrogates. Next-generation sequencing also has potential diagnostic applications, although to the authors' knowledge it currently has no routine role in salivary cytology. The primary goal of salivary fine-needle aspiration (FNA) is to facilitate appropriate clinical management. Ancillary testing has greatly enhanced the ability for accurate classification as per The Milan System for Reporting Salivary Gland Cytopathology and allows for the definitive diagnosis of many salivary FNA specimens, and also may resolve diagnostic uncertainty for FNAs that may be classified in The Milan System for Reporting Salivary Gland Cytopathology categories of salivary gland neoplasm of uncertain malignant potential or suspicious for malignancy. This review provides an updated discussion of the molecular/genetic features of the more commonly encountered salivary neoplasms by FNA, and discusses the application of available diagnostic immunohistochemical and molecular tests in salivary gland cytology.

Immunohistochemistry with a pan-TRK antibody distinguishes secretory carcinoma of the salivary gland from acinic cell carcinoma

AIMS

Secretory carcinoma (previously known as mammary analogue secretory carcinoma) is characterised by ETV6 rearrangements, most often ETV6-NTRK3 fusion. Given its histological overlap with other salivary gland tumours, secretory carcinoma can be difficult to diagnose without genetic confirmation. A recently developed pan-TRK antibody shows promise for identifying tumours with NTRK fusions. The aim of this study was to evaluate the utility of pan-TRK immunohistochemistry in distinguishing secretory carcinoma from mimics.

METHODS AND RESULTS

We examined whole-tissue sections from 86 tumours, including 14 secretory carcinomas (12 parotid primaries and one buccal primary, and one metastasis; five with ETV6 rearrangement confirmed by fluorescence in-situ hybridisation, and one with ETV6-NTRK3 fusion and one with ETV6-RET fusion detected by targeted sequencing), 14 acinic cell carcinomas, 18 polymorphous adenocarcinomas, 20 low-grade mucoepidermoid carcinomas, and 20 pleomorphic adenomas. Immunohistochemistry was performed with a pan-TRK rabbit monoclonal antibody. Pan-TRK staining was detected in nine (64%) secretory carcinomas, all with a nuclear pattern and four with diffuse staining (>50% of cells). Among other tumour types, pan-TRK immunoreactivity was observed in all (100%) pleomorphic adenomas (particularly myoepithelial cell-rich, myxoid areas), 15 (83%) polymorphous adenocarcinomas, and four (20%) low-grade mucoepidermoid carcinomas, all with predominantly membranous/cytoplasmic immunoreactivity; only six cases showed focal (<10%) nuclear staining. All acinic cell carcinomas were entirely negative.

CONCLUSIONS

Although pan-TRK expression is not entirely sensitive or specific for secretory carcinoma, nuclear staining distinguishes secretory carcinoma from mimics. Acinic cell carcinomas are negative for pan-TRK, though membranous expression of TRK is common in other salivary gland neoplasms. The lack of pan-TRK immunoreactivity in a subset of secretory carcinomas may suggest non-NTRK fusion partners.

Secretory Carcinoma of the Thyroid Gland: Report of a Highly Aggressive Case Clinically Mimicking Undifferentiated Carcinoma and Review of the Literature

After being described in the salivary glands as a malignancy with features essentially identical to those of the breast, secretory carcinoma (SC) (formerly mammary analogue SC) has now been identified in other sites including the skin, lung, and thyroid gland. In the breast, SC has a relatively favorable prognosis. Likewise when arising in the salivary glands, it is generally considered to be a low to intermediate grade carcinoma; however, there is a range of clinical behavior with occasional patients dying of progressive disease. SCs of the thyroid gland are rare, and reports suggest a relatively aggressive behavior, at least relative to well differentiated carcinomas such as papillary carcinoma and minimally invasive follicular carcinoma. We present a patient with a highly aggressive thyroid gland SC that mimicked undifferentiated carcinoma clinically. The patient had widespread metastatic disease and died rapidly from airway compromise. We also review the literature for reported cases of thyroid gland SC in order to better establish the clinical features and expected clinical course of such tumors occurring at this site.

Applications of Immunohistochemistry to Endocrine Pathology

The role of immunohistochemistry (IHC) in endocrine pathology is similar to that in other organ systems in that it can aid in the subclassification of tumors within an organ, confirm site of primary in metastatic disease, provide prognostic information, identify underlying genetic alterations, and predict response to treatment. Although most endocrine tumors do not require IHC to render a diagnosis, there are certain scenarios in which IHC can be extremely helpful. For example, in thyroid, IHC can be used to support tumor dedifferentiation, in the adrenal it can aid in the diagnosis of low-grade adrenocortical carcinomas, and in paragangliomas it can help identify tumors arising as part of an inherited tumor syndrome. This review will focus on the applications of IHC in tumors of the thyroid, parathyroids, adrenals, and paraganglia in adults.

Salivary Secretory Carcinoma With a Novel ETV6-MET Fusion: Expanding the Molecular Spectrum of a Recently Described Entity

Secretory carcinoma of the salivary glands, also known as mammary analogue secretory carcinoma, is a recently described tumor characterized by generally indolent clinical behavior and recurrent ETV6-NTRK3 fusions. However, a small subset of recent cases with high-grade histology, aggressive behavior, or alternate molecular findings are expanding the spectrum of this entity. In this case, a 59-year-old female presented with an infiltrative submandibular gland tumor that was originally classified as a high-grade acinic cell carcinoma, papillary-cystic variant. She developed persistent local disease and, 11 years after initial presentation, was found to have widespread metastases. Rereview of her primary tumor highlighted microcystic, papillary, and solid architecture, eosinophilic cytoplasm, vesicular nuclei with prominent nucleoli, abundant mitotic figures, and necrosis. Immunostains showed the tumor cells to be positive for S100 and mammaglobin and negative for DOG-1, and fluorescence in situ hybridization highlighted an ETV6 rearrangement, supporting a diagnosis of high-grade secretory carcinoma. Finally, next-generation sequencing demonstrated a novel ETV6-MET fusion. To our knowledge, this is the first ETV6-MET fusion reported in secretory carcinoma. This finding further expands the definition of secretory carcinoma while carrying implications for selecting appropriate targeted therapy.