Absence of RET gene point mutations in sporadic thyroid C-cell hyperplasia

Medullary thyroid carcinoma: a narrative historical review

INTRODUCTION

Sporadic or hereditary medullary thyroid carcinoma (MTC) is an uncommon thyroid malignancy arising from calcitonin secreting parafollicular C cells. Interestingly, MTC and calcitonin were distinct entities that were discovered independently yet concurrently, and their association was unknown.

AREAS COVERED

This review aims to present a historical review of the evolution of our understanding of MTC and its tumor marker calcitonin to highlight the prominent individuals that influenced and shaped our knowledge of this uncommon thyroid cancer type up to the dawn of the 21^st century. An overview of all published reports of novel research and work summarizing important findings for MTC and calcitonin was carried out.

EXPERT OPINION

Surgery remains the cornerstone of treatment for localized MTC. However, several new treatment options are either available or in development for advanced or metastatic MTC, including several novel small molecules targeting oncogenic RET and peptide receptor radionuclide therapy, immunotherapy, radioimmunotherapy, and radiofrequency ablation. In the near future, these novel treatments hold promise for therapy of this very distinct thyroid cancer type.

Age-Related Changes in Calcitonin-Producing Thyroid C-Cells of Male Wistar Rats

Thyroid C-cells secrete the hormone calcitonin (CT) which acts as an inhibitor of bone resorption. Our aim was to examine the age-related changes in the structure and function of CT-producing C-cells, using histomorphometric, ultrastructural, and biochemical analyses. We used young adult (3-months-old), middle-aged (16-months-old), and old (24-months-old) male rats. The peroxidase-antiperoxidase method was applied for localization of CT. Stereological analysis was performed using the newCAST stereological software package. Serum samples were analyzed for the determination of CT, testosterone (T), calcium (Ca2+), and phosphorus (P). We found a significant increase in the volume density (Vv) of C-cells in both older groups (p < 0.05). The percentage of smaller volume range C-cells increased (p < 0.0001), while the proportion of greater volume range C-cells decreased (p < 0.05) with ageing. Ultrastructural analysis revealed a larger number of secretory granules in older rats. Serum CT increased (p < 0.001), while serum T and P were reduced (p < 0.01) in older rats. Serum Ca2+ was lower (p < 0.0001) in middle-aged rats compared to young adults. We revealed a 20% incidence of C-cell hyperplasia in older rats and one case of medullary thyroid carcinoma in an old rat. Our findings indicate that the ageing process causes significant histomorphometric changes at the thyroid C-cell level.

Reactive C cell hyperplasia as an incidental finding after thyroidectomy for papillary carcinoma

The biologic and clinical significance of reactive C cell hyperplasia (CCH), adjacent to differentiated thyroid cancers, remains unknown. Our aim was to investigate the presence of CCH in thyroidectomy specimens with papillary thyroid carcinomas (PTC) and discuss its epidemiology and histology. In total, 413 patients were prospectively included in the study (189 benign goiters, 224 PTC). Reactive CCH was observed in 9.8% of PTC cases (32% males, 68% females, mean age 48.3 ± 16.4 years) and usually ipsilateral to the primary tumor (91%). Histologically, CCH was either focal (91%) or diffuse (9%) and almost always (92%) found in the middle or upper thirds of the thyroid lobes. Patients with PTC/CCH were generally younger than patients with benign goiters (0.027). On the other hand, patients with PTC and with PTC/CCH did not differ in terms of age, gender, basal calcitonin levels, primary tumor size, multifocality, extrathyroidal invasion, or lymph node metastasis. Thyroiditis, however, was more frequent in cases with PTC/CCH compared to PTC alone. Reactive CCH is considered a physiological response of the C cells to various stimuli, differentiated thyroid cancer among others. It bears no malignant potential and requires no additional treatment, following thyroidectomy.

Revisiting the Significance of Prominent C Cells in the Thyroid

C cell hyperplasia is considered a precursor lesion for hereditary forms of medullary thyroid carcinoma. It has therefore been suggested as a morphological marker to distinguish hereditary from sporadic medullary thyroid carcinoma and to triage genetic testing in resource poor settings. However, numerous definitions for C cell hyperplasia have been suggested, and there is surprisingly little data regarding the number of C cells present in thyroid glands removed for conditions other than medullary carcinoma. We therefore sought to investigate the specificity of different criteria for C cell hyperplasia. We examined the number of C cells and solid cell nests (ultimobranchial body remnants) present in 118 completion thyroidectomy specimens from patients without medullary carcinoma and with no risk factors for MEN2. Morphological review was performed on all H&E-stained slides, and immunohistochemistry for calcitonin was performed on one block from each case. Solid cell nests were found in 4 (3.3%) of thyroids. Increased numbers of C cells sufficient to fulfil criteria for C cell hyperplasia were found in 5 (4.2%) to 36 (30.5%) cases depending on the criteria used. We conclude that large numbers of C cells are commonly found in thyroids not associated with medullary carcinoma. Therefore, regardless of which criteria are used, the presence of C cell hyperplasia is not a specific marker for hereditary medullary thyroid carcinoma.

Update on: proteome analysis in thyroid pathology - part II: overview of technical and clinical enhancement of proteomic investigation of the thyroid lesions

INTRODUCTION

An accurate diagnostic classification of thyroid lesions remains an important clinical aspect that needs to be addressed in order to avoid 'diagnostic' thyroidectomies. Among the several 'omics' techniques, proteomics is playing a pivotal role in the search for diagnostic markers. In recent years, different approaches have been used, taking advantage of the technical improvements related to mass spectrometry that have occurred. Areas covered: The review provides an update of the recent findings in diagnostic classification, in genetic definition and in the investigation of thyroid lesions based on different proteomics approaches and on different type of specimens: cytological, surgical and biofluid samples. A brief section will discuss how these findings can be integrated with those obtained by metabolomics investigations. Expert commentary: Among the several proteomics approaches able to deepen our knowledge of the molecular alterations of the different thyroid lesions, MALDI-MSI is strongly emerging above all. In fact, MS-imaging has also been demonstrated to be capable of distinguishing thyroid lesions, based on their different molecular signatures, using cytological specimens. The possibility to use the material obtained by the fine needle aspiration makes MALDI-MSI a highly promising technology that could be implemented into the clinical and pathological units.

Molecular signatures of medullary thyroid carcinoma by matrix-assisted laser desorption/ionisation mass spectrometry imaging

The main aim of the study was to assess the feasibility of matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) in the pathological investigation of Medullary Thyroid Carcinoma (MTC). Formalin-fixed paraffin-embedded (FFPE) samples from seven MTC patients were analysed by MALDI-MSI in order to detect proteomic alterations within tumour lesions and to define the molecular profiles of specific findings, such as amyloid deposition and C cell hyperplasia (CCH). nLC-ESI MS/MS was employed for the identification of amyloid components and to select alternative proteomic markers of MTC pathogenesis. Results highlighted the potential of MALDI-MSI to confirm the classic immunohistochemical methods employed for the diagnosis of MTC, with good sensitivity and specificity. Intratumoural amyloid components were also detected and identified, and were characterised by calcitonin, apolipoprotein E, apolipoprotein IV, and vitronectin. The tryptic peptide profiles representative of MTC and CCH were distinctly different, with four alternative markers for MTC being detected; K1C18, and three histones (H2A, H3C, and H4). Finally, a further 115 proteins were identified through the nLC-ESI-MS/MS analysis alone, with moesin, veriscan, and lumican being selected due to their potential involvement in MTC pathogenesis. This approach represents a complimentary strategy that could be employed to detect new proteomic markers of MTC. STATEMENT OF SIGNIFICANCE: Medullary thyroid carcinoma (MTC) is a rare endocrine malignancy that originates from the parafollicular C-cells of the thyroid. The diagnosis is typically established using a combination of fine-needle aspiration biopsy (FNAB) of a suspicious nodule along with the demonstrable elevation of serum biomarkers, such as calcitonin and carcinoembryonic antigen (CEA). Unfortunately, this combination is often associated with a high degree of false-positive results and this can lead to misdiagnosis and avoidable total thyroidectomy. The current study presents the potential role of MALDI-MSI in the search for new proteomic markers of MTC with diagnostic and prognostic significance. MALDI-MSI was capable of detecting the classic immunohistochemical markers employed for the diagnosis of MTC, with good sensitivity and specificity. Furthermore, the complementary combination of MALDI-MSI and nLC-ESI-MS/MS analysis, using a single tissue section, enabled further potential markers to be identified and their spatial localisation visualised within tumoural regions. Such findings could be a valuable starting point for further studies focused on confirming the data presented here using thyroid FNABs, with the final objective being to provide complimentary assistance for the detection of MTC during the pre-operative phase.

C Cell and Follicular Epithelial Cell Precursor Lesions of the Thyroid

CONTEXT

- The identification of precursor or dysplastic lesions in the thyroid is difficult. Pathology of the C cell has been extensively studied, and the preneoplastic nature of C-cell hyperplasia in the setting of familial medullary thyroid carcinomas is well established. However, the distinction between neoplastic and physiologic/reactive C-cell hyperplasia remains a challenge. Unlike C cells, the existence of a precursor lesion of follicular cell-derived tumors is less well established, and a dysplastic or preneoplastic follicular lesion has not been well defined.

OBJECTIVE

- To discuss putative precursor lesions in the thyroid arising from C cells and follicular epithelial cells.

DATA SOURCES

- Data were obtained from a review of the pertinent peer-reviewed literature.

CONCLUSIONS

- Although the preneoplastic nature of C-cell hyperplasia in the setting of familial medullary thyroid carcinoma is well recognized, the preneoplastic nature/malignant potential of reactive/physiologic C-cell hyperplasia and its role in the development of sporadic, medullary thyroid carcinoma is still unclear. Current data suggest that benign follicular lesions may have malignant potential, and there may be a multifocal progression from benign to malignant. Atypical follicular lesions in the background of chronic lymphocytic thyroiditis may represent dysplastic or premalignant lesions.

[Thyroid C cells and their pathology: Part 1: normal C cells, - C cell hyperplasia, - precursor of familial medullary thyroid carcinoma]

The C cells (parafollicular) of the human thyroid gland are predominantly located within the thyroid follicles, are of neuroendocrine origin and produce and secrete the peptide hormone calcitonin. Calcitonin is clinically utilized as a screening marker to detect occult medullary thyroid carcinoma (MTC) as well as in the follow-up of patients with MTC. An increase in the number of C cells is designated as C cell hyperplasia (CCH). Neoplastic CCH is caused by an autosomal dominant inherited mutation of the RET protooncogene, which develops into invasive familial MTC in the setting of multiple endocrine neoplasia (MEN) type 2 depending on the location of the mutation in the RET gene with a high variation in latency. According to the current state of knowledge CCH without a germline mutation in the RET protooncogene, designated as non-MEN2-associated CCH, seems to be unrelated to the development of sporadic MTC.

C-cell hyperplasia as an incidental finding in a patient with papillary thyroid microcarcinoma

C-cell hyperplasia (CCH) is considered as a preneoplastic lesion associated with various endocrinopathies. Traditionally it is subdivided into reactive (benign) CCH and neoplastic. We report here a case of a young male, where CCH was an incidental finding after total thyroidectomy for papillary thyroid cancer.

Incidental thyroid C cell hyperplasia: clinical significance and implications in practice

Incidental C cell hyperplasia (CCH) following thyroidectomy for other indications may rarely be encountered, which may raise concerns about its clinical significance and proper management. CCH can be classified as physiological (reactive) or neoplastic. Reactive CCH has no malignant potential and can be observed in association with many other thyroid diseases (including differentiated thyroid cancer); in contrast, neoplastic CCH should be considered as a preneoplastic stage in the spectrum of C cell disease, ultimately leading to the development of medullary thyroid cancer (MTC). Neoplastic CCH is commonly observed in patients with germ-line mutations in the RET oncogene (commonly in families with a history of hereditary MTC, i.e. familial MTC or multiple endocrine neoplasia type 2 (MEN2)). CCH should be considered in patients with hypercalcitoninemia without nodular thyroidopathy. Total thyroidectomy, which is commonly performed for the majority of thyroid diseases, is an adequate treatment and achieves cure, even in patients with neoplastic CCH. There is no role for cervical lymph node dissection in patients with pure CCH. In conclusion, reactive CCH has no malignant potential, in contrast to neoplastic CCH. Total thyroidectomy achieves cure of patients with CCH.

Histopathology of C Cells and Medullary Thyroid Carcinoma

The human thyroid gland contains less than 0.01-0.1% calcitonin producing and secreting C cells, which in men are almost exclusively situated in an intrafollicular location; the vast majority of C cells are embryologically derived of remnants of the ultimobranchial body and ultimately of the neural crest, a small subset, however, is presumed to originate from endodermal stem cells. Thyroid tumours with C cell differentiation have been named medullary thyroid carcinoma (MTC); calcitonin is also produced and secreted by MTC which makes this peptide hormone a very useful serum marker both for early detection and clinical follow-up of patients with MTC. About 70-80% of MTC are sporadic tumours, whereas 20-30% are familial MTC which are autosomal-dominant inherited and caused by germline mutations of the RET proto-oncogene located on chromosome 10. This article summarizes the histological, immunhistochemical and molecular genetic features of C cells, C-cell hyperplasia (CCH) and MTC, emphasizing the role of diagnostic pathology.

Predominant RET Germline Mutations in Exons 10, 11, and 16 in Iranian Patients with Hereditary Medullary Thyroid Carcinoma

Medullary thyroid carcinoma occurs in both sporadic (75%) and hereditary (25%) forms. The missense mutations of RET proto-oncogene in MTC development have been well demonstrated. To investigate the spectrum of predominant RET germline mutations in exons 10, 11, and 16 in hereditary MTC in Iranian population, 217 participants were included. Genomic DNAs were extracted from the leukocytes using the standard Salting Out/Proteinase K method. Mutation detection was performed through PCR-RFLP and DNA sequencing. In 217 participants, 43 missense mutations were identified in exons 10 (6%), 11 (13%), and 16 (0.9%). Moreover, a novel germline mutation was detected in exon 11 (S686N). Also four different polymorphisms were found in intron 16 in eight patients. The obtained data showed the frequency profile of RET mutations in Iranian individuals with MTC (19.8%). The most frequent mutation in our population was C634G whereas in most population it was C634R. Altogether, these results underline the importance of the genetic background of family members of any patient with MTC.

[Molecular pathology of thyroid tumors]

Molecular genetic analysis is gaining in significance for the differential diagnosis of thyroid tumours. Identifying specific mutations and/or rearrangements offers not only the possibility to distinguish benign from malignant tumours, but also to classify thyroid malignancies more precisely, which can have a substantial influence on the clinical management of patients. In recent years expression analysis of micro-RNA (miRNA) has become an additional tool to improve diagnostic accuracy in thyroid tumours. In addition to its diagnostic contribution, molecular genetic evaluation of thyroid tumours has significantly deepened our understanding of the development, progression and therapy of these tumours.

[Multiple endocrine neoplasia type 2]

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant inherited cancer syndrome with the major components medullary thyroid carcinoma, pheochromocytoma and hyperparathyroidism. Due to the clinical course three distinct subtypes are distinguished, MEN 2A, MEN 2B and familial medullary thyroid carcinoma. The disease is caused by germ-line mutations of the RET proto-oncogene and the localization of these mutations correlates with the onset of the development of medullary thyroid carcinoma, which is crucial for the clinical course and outcome of the disease. It therefore has a substantial influence on the clinical management of the affected patients and their relatives. This review summarizes the morphology and clinic of MEN 2-associated tumors and their respective precursor lesions.

Multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant cancer syndrome with major components of medullary thyroid carcinoma (MTC), pheochromocytoma and hyperparathyroidism. The disease is caused by germline mutations of the RET proto-oncogene. Subtypes of MEN 2 include MEN 2A, MEN 2B and familial MTC (FMTC) which differ in pattern of additional lesions or--in FMTC--lack of pheochromocytoma. In 2009, after extensive review of the literature, the guidelines of the American Thyroid Association made several recommendations regarding clinical and genetic diagnostic testing and treatment options. In this article, the recently published literature is reviewed and concerns regarding future perspectives are added. In particular, a critical handling of rare DNA variants and double mutations is necessary. Up to now, mutation-specific risk profiles and mutation-associated treatment recommendations are unavailable. We emphasise the need for approved centres for treatment of patients affected by MEN 2, not only adults but young children as well. As a high level of skill is required for endoscopic adrenal-sparing surgery, surgeons should declare their expertise before operating such patients. Registry-based follow-up should be mandatory including documentation of short- and long-term outcome in order to provide valid data for future counselling of patients with MEN 2.

Tenascin C in medullary thyroid microcarcinoma and C-cell hyperplasia

Tenascin C (Tn-C) is an extracellular matrix glycoprotein that is expressed early in carcinogenesis including intraepithelial neoplastic lesions of different organs. In this study, we analyze whether stroma reaction seen by Tn-C expression is detected early in tumorigenesis of medullary thyroid carcinoma (MTC) including medullary microcarcinoma and C-cell hyperplasia (CCH), which is accepted to be a precursor lesion of MTC in the setting of RET oncogene germ-line mutation. Tn-C was expressed in the stroma of all medullary microcarcinoma and in the stroma next to CCH. Stromal Tn-C expression was significantly more often seen in CCH with concomitant MTC than in isolated CCH of hereditary as well as nonhereditary cases (p = 0.001 and p = 0.016, respectively). We conclude that Tn-C expression and thus early stroma remodeling is seen in medullary microcarcinoma and CCH. Stromal Tn-C expression seems to be an indicator of a further step in carcinogenesis of MTC irrespective of a RET oncogene germ-line mutation.

Molecular alterations in hereditary and sporadic thyroid and parathyroid diseases

Thyroid and parathyroid diseases are fairly common and can be either hereditary or sporadic in nature. Tumors and tumor-like processes account for the majority of surgical pathology specimens in both of these endocrine organs. Molecular alterations are well known to occur in both the hereditary and the sporadic settings, and include alterations in tumor suppressor genes and oncogenes. The genetic pathways of tumors of parathyroid and thyroid are beginning to be well understood and are proving to be useful diagnostic, prognostic, and potential therapeutic targets. The molecular alterations in parathyroid and thyroid tumors and tumor-like processes are reviewed, with a focus on the potentially clinically useful diagnostic markers.