Fetal cell carcinogenesis of the thyroid: a hypothesis for better understanding of gene expression profile and genomic alternation in thyroid carcinoma

Impact of Epithelial-Mesenchymal Immunophenotype on Local Aggressiveness in Papillary Thyroid Carcinoma Invading the Airway

Primary thyroid tumours show different levels of aggressiveness, from indolent to rapidly growing infiltrating malignancies. The most effective therapeutic option is surgery when radical resection is feasible. Biomarkers of aggressiveness may help in scheduling extended resections such as airway infiltration, avoiding a non-radical approach. The aim of the study is to evaluate the prognostic role of E-cadherin, N-cadherin, Aryl hydrocarbon receptor (AhR), and CD147 in different biological behaviours. Fifty-five samples from three groups of thyroid carcinomas were stained: papillary thyroid carcinomas (PTCs) infiltrating the airway (PTC-A), papillary intra-thyroid carcinomas (PTC-B) and poorly differentiated or anaplastic thyroid carcinomas (PDTC/ATC). High expressions of N-cadherin and AhR were associated with higher locoregional tumour aggressiveness (p = 0.005 and p < 0.001 respectively); PDTC/ATC more frequently showed a high expression of CD147 (p = 0.011), and a trend of lower expression of E-cadherin was registered in more aggressive neoplasms. Moreover, high levels of AhR were found with recurrent/persistent diseases (p = 0.031), particularly when tumours showed a concomitant high N-cadherin expression (p = 0.043). The study suggests that knowing in advance onco-biological factors with a potential role to discriminate between different subsets of patients could help the decision-making process, providing a more solid therapeutic indication and an increased expectation for radical surgery.

Thyroid Cancer and Circadian Clock Disruption

Thyroid cancer (TC) represents the most common malignancy of the endocrine system, with an increased incidence across continents attributable to both improvement of diagnostic procedures and environmental factors. Among the modifiable risk factors, insulin resistance might influence the development of TC. A relationship between circadian clock machinery disfunction and TC has recently been proposed. The circadian clock machinery comprises a set of rhythmically expressed genes responsible for circadian rhythms. Perturbation of this system contributes to the development of pathological states such as cancer. Several clock genes have been found deregulated upon thyroid nodule malignant transformation. The molecular mechanisms linking circadian clock disruption and TC are still unknown but could include insulin resistance. Circadian misalignment occurring during shift work, jet lag, high fat food intake, is associated with increased insulin resistance. This metabolic alteration, in turn, is associated with a well-known risk factor for TC i.e., hyperthyrotropinemia, which could also be induced by sleep disturbances. In this review, we describe the mechanisms controlling the circadian clock function and its involvement in the cell cycle, stemness and cancer. Moreover, we discuss the evidence supporting the link between circadian clockwork disruption and TC development/progression, highlighting its potential implications for TC prevention, diagnosis and therapy.

Expression of E-Cadherin/Beta-Catenin in Epithelial Carcinomas of the Thyroid Gland

BACKGROUND

The aberrant activation of Wnt signalling pathway may be a common denominator for the development of thyroid tumorigenesis. It was announced that the loss of E-cadherin rather than β-catenin mutation represents a crucial event in determining the degree of differentiation of thyroid carcinomas.

AIM

The aim of the study was to evaluate the expression of E-cadherin and β-catenin in the thyroid cancer tissue and to correlate these data with some histological and clinical parameters of the tumours.

MATERIAL AND METHODS

We investigated 112 patients, having thyroid tumours - papillary, follicular, anaplastic and oncocytic carcinomas immunohistochemically with antibodies against E-cadherin and β-catenin. Survival analyses were done.

RESULTS

E-cadherin expression was focally retained in the tumour cell membranes and the tumour cell cytoplasm of the papillary, follicular and oncocytic thyroid cancers, weather in anaplastic cancers it was almost lost (p = 0.0042, and p = 0.019, respectively, Fisher's Exact Test). The expression of β-catenin in tumour cytoplasm and membrane in papillary cancers was higher as compared to that in the other tumours (p = 0.111, and p = 0.0104, respectively).

CONCLUSION

Not surprisingly, the presence of aberrant expression of E-cadherin and β-catenin in thyroid cancer has been associated with better patients' prognosis and better differentiated tumour histology.

Activating BRAF Mutations Detected in Mixed Hürthle Cell Carcinoma and Multifocal Papillary Carcinoma of the Thyroid Gland

Despite the increase in the incidence of thyroid carcinomas, the occurrence of collision tumors in the thyroid remains a rare event. We present the case of a 69-year-old female who presented to the emergency department with a chief complaint of painful neck swelling. Imaging revealed a large right hemithyroid mass and a left hemithyroid nodule. Fine needle aspiration of the lesions and subsequent total thyroidectomy revealed a Hürthle cell carcinoma in the right lobe and bilateral multicentric papillary carcinoma foci, including 2 foci with a classical pattern and 1 encapsulated follicular variant in the isthmus. BRAF gene mutation analysis revealed V600E gene mutation in the classical variants of papillary carcinoma and in the Hürthle cell carcinoma. The focus of follicular variant of papillary carcinoma in the isthmus and a sample from normal thyroid tissue did not harbor BRAF mutations. This case is remarkable in being an unusual report of a follicular Hürthle cell carcinoma harboring the BRAF V600E mutation and occurring in collision with multifocal papillary carcinoma. Documentation of such cases is important as it helps better understand the pathogenesis, clinical behavior, and radiologic findings of such rare lesions and to determine the optimal treatment modalities.

Cancer Stem Cells in the Thyroid

The cancer stem cell (CSC) model posits that CSCs are a small, biologically distinct subpopulation of cancer cells in each tumor that have self-renewal and multi-lineage potential, and are critical for cancer initiation, metastasis, recurrence, and therapy-resistance. Numerous studies have linked CSCs to thyroid biology, but the candidate markers and signal transduction pathways that drive thyroid CSC growth are controversial, the origin(s) of thyroid CSCs remain elusive, and it is unclear whether thyroid CSC biology is consistent with the original hierarchical CSC model or the more recent dynamic CSC model. Here, we critically review the thyroid CSC literature with an emphasis on research that confirmed the presence of thyroid CSCs by in vitro sphere formation or in vivo tumor formation assays with dispersed cells from thyroid cancer tissues or bona fide thyroid cancer cell lines. Future perspectives of thyroid CSC research are also discussed.

Fetal cell carcinogenesis of the thyroid: a modified theory based on recent evidence

Thyroid cancer cells were believed to be generated by multi-step carcinogenesis, in which cancer cells are derived from thyrocytes, via multiple incidences of damage to their genome, especially in oncogenes or anti-oncogenes that accelerate proliferation or foster malignant phenotypes, such as the ability to invade the surrounding tissue or metastasize to distant organs, until a new hypothesis, fetal cell carcinogenesis, was presented. In fetal cell carcinogenesis, thyroid tumor cells are assumed to be derived from three types of fetal thyroid cell which only exist in fetuses or young children, namely, thyroid stem cells (TSCs), thyroblasts and prothyrocytes, by proliferation without differentiation. Genomic alternations, such as RET/PTC and PAX8-PPARγ1 rearrangements and a mutation in the BRAF gene, play an oncogenic role by preventing thyroid fetal cells from differentiating. Fetal cell carcinogenesis effectively explains recent molecular and clinical evidence regarding thyroid cancer, including thyroid cancer initiating cells (TCICs), and it underscores the importance of identifying a stem cells and clarifying the molecular mechanism of organ development in cancer research. It introduces three important concepts, the reverse approach, stem cell crisis and mature and immature cancers. Further, it implies that analysis of a small population of cells in a cancer tissue will be a key technique in establishing future laboratory tests. In the contrary, mass analysis such as gene expression profiling, whole genomic scan, and proteomics analysis may have definite limitations since they can only provide information based on many cells.

Preparation of thyroid follicular cells for mRNA quantification after fluorescence-activated cell sorting

We established a novel method to analyze cells collected by fluorescence-activated cell sorting (FACS) named mRNA quantification after FACS (FACS-mQ) in which cells are labeled with a fluorescence dye in a manner that minimizes RNA degradation, and then cells sorted by FACS are examined by analyzing their gene expression profile. In order to analyze cells using FACS-mQ, it is essential to prepare single-cell suspensions without RNA degradation. We found that a new tissue preservation medium, ThelioKeep™, which contains epigallocatechin-3-gallate (EGCG), was suitable for preservation of thyroid tissues. The aim of this study was to establish a cell dispersion method of thyroid follicular cells using ThelioKeep™. We compared the efficiency of cell dispersion between the two methods, the conventional cold pre-incubation method and the ThelioKeep™ method; then we determined if cells obtained by the ThelioKeep™ method were suitable for FACS-mQ analysis. We found that a larger number of cells were recovered using ThelioKeep™ than using the conventional cold pre-incubation method. Furthermore, cell viability was higher with the ThelioKeep™ method than with the cold pre-incubation method. Thyroid cells collected by this method were analyzed by FACS-mQ. A clear shift in flow cytometry analysis was observed when cells were stained with an anti-thyroglobulin or anti-thyroid transcription factor-1 antibody. After sorting, the same copy number of ACTB mRNA was detected in thyroid cells as in an anaplastic carcinoma cell line, 8305C. These findings imply that preparation of thyroid cells using the present method is suitable for FACS-mQ analysis.

Cytopathological review of patients that underwent thyroidectomies based on the diagnosis of papillary thyroid carcinoma by fine needle aspiration cytology but were later found to have benign tumors by histopathology

PURPOSE

The aim of this study is to evaluate the specificity of diagnosing PTC by fine needle aspiration (FNA) cytology.

METHODS

This study retrospectively reviewed the cytopathological reports of 1066 patients that underwent thyroidectomy based on a diagnosis of PTC by FNA between January 1993 and December 2008. This study re-evaluated the cytology and histopathology of the patients that received false positive diagnoses of PTC by FNA.

RESULTS

Ten patients (0.9 %) received false positive diagnoses of PTC by FNA. Three patients were overdiagnosed as having PTC by FNA cytology. In contrast, the nuclear features of PTC in the other seven cases were confirmed by the retrospective reviews of the patients' FNA cytology. Three of the seven patients showed follicular structures in their resection specimens, thus resulting in a diagnosis of either adenomatous goiter or follicular adenoma. However, PTC could not be diagnosed by histopathology in the remaining four patients, even though the histopathology showed the nuclear features of PTC.

CONCLUSIONS

Most cases of PTC can be easily diagnosed by cytological and morphological atypia with certain limitations. The difficulty in diagnosing PTC by cytology is because the pathological features of PTC also occur in some benign thyroid tumors. Therefore, immunohistochemical or molecular biological approaches must be combined with current cytological diagnostic techniques for the diagnosis of PTC.

Identifying thyroid stem/progenitor cells: advances and limitations

Continuing advances in stem cell science have prompted researchers to envisage the potential application of stem cells for the management of several debilitating disorders, thus raising the expectations of transplant clinicians. In particular, in order to find a source of adult stem cells alternative to embryonic stem cells (ESCs) for the exploration of novel strategies in regenerative medicine, researchers have attempted to identify and characterise adult stem/progenitor cells resident in compact organs, since these populations appear to be responsible for physiological tissue renewal and regeneration after injury. In particular, recent studies have also reported evidence for the existence of adult stem/progenitor cell populations in both mouse and human thyroids. Here, I provide a review of published findings about ESC lines capable of generating thyroid follicular cells, thyroid somatic stem cells and cancer stem cells within the thyroid. The three subjects are analysed by also considering the criticism recently raised against their existence and potential utility. I comment specifically on the significance of resident thyroid stem cells in the developmental biology of the gland and their putative role in the pathogenesis of thyroid disorders and on the protocols employed for their identification. I finally provide my opinion on whether from basic science results obtained to date it is possible to extrapolate any convincing basic for future treatment of thyroid disorders.

Molecular pathogenesis of follicular cell derived thyroid cancers

Thyroid cancers are the most common endocrine malignancy. Radiation exposure, family history of thyroid cancer and some inherited conditions are the most important predisposing factors for the development of thyroid cancer. Three mitogenic signalling pathways have been described in the thyroid cell, which are influenced by various stimulatory and inhibitory hormones, growth factors and neurotransmitters. Various proto-oncogenes and oncogenes like ras, braf, trk, met and RET also play a role in the signal transduction systems. Two theories have been described in thyroid cancer pathogenesis, the foetal cell carcinogenesis theory and the more common, multistep carcinogenesis theory. The multistep carcinogenesis theory is now the accepted model in many human cancers, including thyroid cancer. The early events of tumour formation are the consequence of activation of either various growth factors or the proto-oncogenes like ras, met or ret. This results in the formation of differentiated thyroid cancers like the papillary, follicular or Hurthle cell cancers. The later stages of tumour formation involve further activation of proto-oncogenes and loss or inactivation of tumour suppressor genes like p53. Based on this theory, follicular carcinomas are generated from follicular adenomas and papillary carcinomas from precursor cells generated from thyrocytes. Anaplastic carcinoma may develop from papillary or follicular carcinoma by dedifferentiation. In this review article, we highlight the molecular pathogenesis of thyroid tumours.

Thyroid stem cells and cancer

BACKGROUND

Thyroid gland development and function are essential for life, and recent findings indicate the presence of stem/progenitor cells within the thyroid gland as a potential source of tissue regeneration and cancer formation.

SUMMARY

This review summarizes the current knowledge on early differentiation of thyroid cells from embryonic stem cells and highlights exciting concepts and recent novel findings on adult thyroid stem/progenitor cells in the normal thyroid gland and in thyroid cancer. Other potential sources and markers of stem/progenitor cells in the thyroid include bone marrow, microchimerism, and embryological remnant-derived multifocal solid cell nests. Finally, we discuss new therapeutic strategies that target thyroid cancer stem cells.

CONCLUSIONS

Thyroid stem/progenitor cell populations are present in the normal and diseased thyroid gland. Advances in normal and cancer thyroid stem cell biology will be essential for future targeted therapies.

TSH signalling and cancer

Thyroid cancers are the most frequent endocrine neoplasms and mutations in the thyrotropin receptor (TSHR) are unusually frequent. Here we present the state-of-the-art concerning the role of TSHR in thyroid cancer and discuss it in light of the cancer stem cell theory or the classical view. We briefly review the gene and protein structure updating the cancer related TSHR mutations database. Intriguingly, hyperfunctioning TSHR mutants characterise differentiated cancers in contrast to undifferentiated thyroid cancers which very often bear silenced TSHR. It remains unclear whether TSHR alterations in thyroid cancers play a role in the onset or they appear as a consequence of genetic instability during evolution, but the presence of functional TSHR is exploited in therapy. We outline the signalling network build up in the thyrocyte between TSHR/PKA and other proliferative pathways such as Wnt, PI3K and MAPK. This networks integrity surely plays a role in the onset/evolution of thyroid cancer and needs further research. Lastly, future investigation of epigenetic events occurring at the TSHR and other loci may give better clues for molecular based therapy of undifferentiated thyroid carcinomas. Targeted demethylating agents, histone deacetylase inhibitors combined with retinoids and specific RNAis may help treatment in the future.

BRAF V600E mutation in anaplastic thyroid carcinomas and their accompanying differentiated carcinomas

Frequency of a BRAF^V600E mutation in anaplastic thyroid carcinoma, which is thought to be derived mainly from papillary carcinoma by multi-step carcinogenesis, is much lower than that in papillary carcinomas. To clarify this phenomenon, we analysed BRAF^V600E mutation in 20 cases of anaplastic carcinoma and 13 accompanying differentiated carcinomas. Among twenty cases of anaplastic carcinomas, nine and four accompanied papillary and follicular carcinomas, respectively. BRAF^V600E mutation was found in four (20%) cases. BRAF^V600E mutation was found in three of nine (33.3%), none of four and one of seven (14.3%) anaplastic carcinomas with papillary carcinoma, follicular carcinoma and without differentiated components, respectively. All three papillary carcinomas accompanied by anaplastic carcinoma with a BRAF^V600E mutation were also shown to have a BRAF^V600E mutation. In summary, BRAF^V600E mutation was occasionally observed in anaplastic carcinomas with papillary carcinoma, and the low frequency of BRAF^V600E mutation in anaplastic carcinoma was thought to be due to the low frequency of anaplastic carcinomas with papillary carcinoma. These findings raise a question about the classical model of anaplastic transformation and suggest some roles of thyroid cancer stem cells in the generation of anaplastic carcinoma.

Thrombospondin 1 mRNA as a candidate for a marker to detect thyroid-derived fibroblasts in fine needle aspiration biopsy of the thyroid

Possible interference of fibroblasts is suggested in aspiration biopsy nucleic acid diagnosis (ABND). However, detection of fibroblasts in the aspirates is difficult, because the gene expression profiles of thyroid malignancies and fibroblasts are much alike in many aspects. To identify a specific marker for thyroid-derived fibroblasts, the data of the serial analysis of gene expression (SAGE) were compared to screen differentially expressed genes between fibroblasts and thyroid normal and tumor tissues. In the SAGE data, 5 genes were identified to be differentially expressed. Among these, thrombospondin 1 (TSP-1, THBS1) mRNA was the most differentially expressed. Further, the overexpression of TSP-1 mRNA in fibroblasts was confirmed by real-time RT-PCR analysis using 73 thyroid normal and tumor tissues and 7 cultures of thyroid-derived fibroblasts. These results suggest that TSP-1 mRNA is a possible marker for contamination of thyroid-derived fibroblasts.

Fetal cell carcinogenesis of the thyroid: theory and practice

A novel hypothesis of thyroid carcinogenesis, the "fetal cell carcinogenesis" hypothesis, in which cancer cells are derived from the remnants of three types of fetal thyroid cells, instead of normal thyroid follicular cells, is proposed. In this hypothesis, thyroid cancer cells are generated from fetal cells by proliferation without differentiation and oncogenes play an oncogenic role by preventing fetal cells from differentiating. This hypothesis explains well the clinical and biological features and recent molecular evidence of thyroid carcinoma. It underscores the importance of clarifying the molecular mechanism of thyroid development and the identification of fetal thyroid cells, especially thyroid stem cells (TSCs), since such data will lead to better understanding of thyroid carcinoma and other thyroid diseases.

Anaplastic thyroid carcinoma associated with Graves' disease

This report concerns a 79-year-old woman with coexisting anaplastic thyroid carcinoma (ATC) and Graves' disease (GD). The patient was referred to our clinic because of palpitation and a palpable mass on the left side of her neck. Thyroid function tests showed hyperthyroidism with elevated thyroid-stimulating antibodies. Ultrasonography of the thyroid demonstrated an adenomatous nodule-like marcated nodule (27.6 x 26.5 x 36.4 mm) with cystic degeneration inside the left lobe. (123)I thyroid scintigraphic imaging showed a cold area corresponding to the nodule with continuous uptake in the remaining thyroid tissue despite suppressed TSH levels. These findings led to a diagnosis of GD. On the other hand, the thyroid nodule could not be definitely diagnosed even after fine needle aspiration biopsy (FNAB) which produced findings suggestive of both papillary thyroid carcinoma and ATC. Open biopsy of the nodule showed an ATC. Regional lymph node metastases as well as multiple lung metastases, which could not be found at the initial visit, had been already developed by that time. Our case is pathophysiologically interesting because it suggests that GD or thyroid-stimulating antibodies (TSAb) may stimulate malignant transformation of differentiated carcinoma. It is also clinically important because it indicates that all thyroid nodules, particularly palpable cold nodules, associated with GD require careful management to detect malignancy because they are at higher risk of harboring malignancy.