Positivity for GATA3 and TTF-1 (SPT24), and Negativity for Monoclonal PAX8 Expand the Biomarker Profile of the Solid Cell Nests of the Thyroid Gland

Top 10 Nested Pattern Head and Neck Lesions to Notice

BACKGROUND

Nested is defined as "cellular clusters arranged in small groupings with intervening vascular or stromal networks, lacking lumens or glandular formation." Using this definition, multiple neoplastic and non-neoplastic lesions of the head and neck come into the differential. We have broadly organized the differential diagnosis of "nested" tumors into entities with neuroendocrine differentiation, squamous differentiation, thyroid follicular cell differentiation, and other lesions.

METHODS

Review.

RESULTS

Many different entities have a nested appearance and the morphologic, immunohistochemical, clinical, and radiographic features contribute to the differential diagnosis. The different tumors covered in this review include neuroendocrine neoplasms, paraganglioma, middle ear neuroendocrine tumor (formerly known as middle ear adenoma), medullary thyroid carcinoma, poorly differentiated thyroid carcinoma, olfactory neuroblastoma, ectopic pituitary neuroendocrine tumor, hyalinizing trabecular tumor, solid subtype of papillary thyroid carcinoma, solid cell nests/C-cell hyperplasia, necrotizing sialometaplasia, and meningioma.

CONCLUSION

In this review, we discuss the morphologic and immunohistochemical features of the covered entities as a guide to differential diagnosis when nested-patterned head and neck lesions are encountered.

Secondary thyroid malignancy - a rare clinical finding?

Metastases to the thyroid gland, while rarely seen in clinical practice, can pose a diagnostic and therapeutic challenge. Most commonly, they originate from lung, renal, and breast cancer, and are generally a sign of multiorgan metastatic disease. In most cases, metastases to the thyroid gland are diagnosed incidentally on imaging studies, since they are rarely symptomatic and often do not influence thyroid function tests. Thyroid ultrasonography and fine-needle aspiration biopsy play a pivotal role in their evaluation, as both classic immunocytochemical features, and more novel molecular markers can help in the differential diagnosis. Prognosis mainly depends on the biology of the primary tumor and its extension. Communication between clinicians is essential in such patients, in order to ensure that the treatment options are carefully balanced, thus raising the need for multidisciplinary teams in their management.

Role of GATA3 in tumor diagnosis: A review

GATA binding protein 3 (GATA3) belongs to a family of transcription factors comprising six members. These proteins identify G-A-T-A containing sequences in the target gene and bind to DNA target via two zinc-finger domains. The aim of this study was to evaluate the role of GATA3 in the diagnosis of tumors and its value as a prognostic marker. To perform this review, a comprehensive search was conducted through PubMed, Embase, Scopus, Cochrane and Google Scholar databases from 1985 to 2020. Articles were considered thoroughly by independent reviewers and data were extracted in predefined forms. Final synthesis was conducted by using appropriate data from included articles in each topic. Studies have shown that GATA3 has a critical role in the development of epithelial structures in both embryonic and adult tissues. The majority of studies regarding GATA3 expression in tumor evaluation focused on breast and urothelial neoplasms, whether primary or metastatic. Its sensitivity in these neoplasms has been reported to be high and made this marker more valuable than other available immunohistochemistry markers. However, GATA3 expression was not restricted to these tumors. Studies have shown that GATA3 immunostaining could be a useful tool in various tumors in kidney, salivary gland, endocrine system, hematopoietic system, and skin. GATA3 can also be used as a useful prognostic tool. Although GATA3 is a multi-specific immunohistochemical stain, it is a valuable marker in the panel for confirming many epithelial or mesenchymal neoplasms as both a diagnostic and prognostic tool.

GATA3 expression in the solid cell nest of thyroid

Solid cell nest (SCN) of thyroid is a benign histomorphological mimicker of papillary microcarcinoma. Previous studies have elucidated a few immunohistochemical markers of SCN that aid in its distinction from papillary microcarcinoma. The positivity of GATA3 in SCN has been demonstrated only recently. We also document GATA3 positivity in three cases of SCN.

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

Thyroid pathology encompasses a heterogenous group of clinicopathological entities including rare and diagnostically challenging neoplasms. The review is focused on morphological, immunohistochemical, and molecular features of rare thyroid neoplasms that can pose diagnostic problems. The tumors are organized based on growth patterns including thyroid neoplasms with predominantly papillary, follicular, solid, and spindle cell growth pattern, as well as neoplasms with distinct cytological characteristics. A special section is also dedicated to rare thyroid tumors with peculiar patterns including thyroid carcinoma with Ewing family tumor elements and intrathyroidal thymic-related neoplasms.

Thyroid Adenoma of Probable Ultimobranchial Body Origin: A Case Report

Solid cell nests are generally believed to represent remnants of the ultimobranchial body, which can be found in the normal thyroid gland, occasionally associated with other branchial pouch remnants such as salivary gland, cartilage, and adipose tissue. We describe the case of a 44-year-old man incidentally found to have a large tumor in the left lobe of the thyroid. The tumor was a circumscribed growth consisting of distinctly lobulated proliferation of solid to cystic epidermoid cell nests and thyroid follicles in a fibromatous stroma, which merged into abundant adipose tissue and focally myxoid matrix. The solid epidermoid cell nests resembled solid cell nests and exhibited a p63+, GATA3+, galectin-3+, TTF1-, PAX8-, thyroglobulin- phenotypes, while the follicles were p63-, GATA3-, galectin-3-, TTF1+, PAX8+, and thyroglobulin+. RAS mutations were not found. This thyroid tumor may represent a hitherto undescribed "ultimobranchial body adenoma" in human.

GATA3 immunoreactivity expands the transcription factor profile of pituitary neuroendocrine tumors

The modern classification of pituitary neuroendocrine tumors relies mainly on immunohistochemistry for pituitary transcription factors, hormones, and other biomarkers, including low molecular weight cytokeratins. The transcription factor GATA2 is required for development of gonadotrophs and thyrotrophs but has not been used for classification of pituitary tumors. Because of genomic paralogy of GATA2 and GATA3, we postulated that GATA3 immunohistochemistry may detect GATA2 in the adenohypophysis. We examined 151 tumors originating from Ondokuz Mayis University, Turkey (n = 83) and University Health Network, Canada (n = 68). Initially, 83 tumors (26 gonadotroph, 24 somatotroph, 17 corticotroph, 12 lactotroph, 2 poorly differentiated Pit-1 lineage tumors that expressed TSH and 2 null cell tumors) from Ondokuz Mayis University were investigated with the GATA3 monoclonal antibody L50-823. Retrospective review of the files of University Health Network identified 68 tumors (43 gonadotroph, 3 somatotroph, 2 lactotroph, 1 mammosomatotroph, 9 corticotroph, 7 poorly differentiated Pit-1 lineage tumors with TSH expression, 2 plurihormonal tumors with TSH expression and 1 null cell tumor) that were examined with the same GATA3 antibody and served as a validation cohort. All somatotroph, lactotroph and mammosomatotroph tumors and the null cell tumors were negative for GATA3. Sixty-eight (98.5%) gonadotroph tumors were positive for GATA3; 64 had diffuse reactivity. Two plurihormonal tumors with TSH expression and eight (88.8%) poorly differentiated Pit-1 lineage tumors with variable TSH expression were positive for GATA3. One of 26 (3.8%) corticotroph tumors was diffusely positive for GATA3. This study shows that GATA3 immunoreactivity is characteristic of pituitary gonadotroph and TSH-producing tumors. This finding expands the pattern of transcription factors that are used to classify adenohypophysial tumors and is important in the differential diagnosis of sellar tumors, as GATA3 expression is also a feature of primary sellar paragangliomas as well as carcinomas that may metastasize to the sella.

Solid Cell Nests Within a Parathyroid Gland-Report of an Exceptional Case

The ultimobranchial body (UBB) denotes the cellular mass originating from the fourth branchial pouch, which migrates from the neural crest and infolds within the middle and upper poles of the thyroid lobes, thereby establishing the presence of calcitonin-secreting parafollicular C cells. In various numbers, UBB remnants (entitled "solid cell nests", or SCNs) are found in thyroid glands examined histologically. However, despite the close embryological relation between the UBB and the superior parathyroid glands, intraparathyroidal SCNs have to our knowledge not been previously reported. Here, we describe a patient presenting with a papillary thyroid carcinoma with central and lateral lymph node metastases. Upon postoperative analysis, an unintentionally removed parathyroid gland was observed adjacent to the superior aspect of the right thyroid lobe. Within a 0.6 × 0.5-mm area of the parathyroid gland, solid nests composed of epithelial cells with oval and slightly elongated nuclei were seen. The cells were positive for p40, p63, and GATA3, but negative for PTH. The final diagnosis was a SCN entrapped within the parathyroid gland. Empirically, we have not previously observed SCNs within the parathyroid glands. To our knowledge, our finding thus constitutes a very unusual histological manifestation, and could indicate an underlying aberrancy during embryogenesis given the close anatomical relationship between the UBB and the superior parathyroid glands.

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.

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.

Immunohistochemical Biomarkers in Thyroid Pathology

The application of immunohistochemistry to the diagnosis of thyroid lesions has increased as new biomarkers have emerged. In this review, we discuss the biomarkers that are critical for accurate diagnosis, prognosis, and management. Immunohistochemical markers are used to confirm that an unusual tumor in the thyroid is indeed of thyroid origin, either of follicular epithelial or C-cell differentiation; the various mimics include nonthyroidal lesions such as parathyroid tumors, paragangliomas, thymic neoplasms, and metastatic malignancies. Tumors of thyroid follicular epithelial cells can be further subclassified using a number of immunohistochemical biomarkers that can distinguish follicular-derived from C-cell lesions and others that support malignancy in borderline cases. The use of mutation-specific antibodies can distinguish papillary carcinomas harboring a BRAF^V600E mutation from RAS-like neoplasms. Immunostains have been developed to further identify molecular alterations underlying tumor development, including some rearrangements. Altered expression of several biomarkers that are known to be epigenetically modified in thyroid cancer can be used to assist in predicting more aggressive behavior such as a propensity to develop locoregional lymphatic spread. Immunohistochemistry can assist in identifying lymphatic and vascular invasion. Biomarkers can be applied to determine dedifferentiation and to further classify poorly differentiated and anaplastic carcinomas. The rare tumors associated with genetic predisposition to endocrine neoplasia can also be identified using some immunohistochemical stains. The application of these ancillary tools allows more accurate diagnosis and better understanding of pathogenesis while improving prediction and prognosis for patients with thyroid neoplasms.