Activin A and activin receptors in thyroid cancer

Serum Follistatin Is Increased in Thyroid Cancer and Is Associated With Adverse Tumor Characteristics in Humans

CONTEXT

Obesity and classical growth factors are associated with thyroid cancer (TC). However, less is known regarding novel hormones such as follistatins and activins. We hypothesized that serum follistatin but not activins would be increased in TC.

OBJECTIVE

This work aimed to assess circulating levels of follistatins, activins, and growth factors in patients with a history of TC vs patients with nonmalignant thyroid diseases.

METHODS

A hospital-based, unmatched case-control study was conducted with 170 thyroidectomized patients due to well-differentiated TC and 106 thyroidectomized patients without history of malignancy. Anthropometric, biochemical, and histological parameters were recorded. Serum samples were collected in the steady state 45 days after surgery. Multivariate models were used to adjust for baseline differences of the unmatched variables. Serum levels of follistatin (FST), follistatin like-3, activin A, activin B, bioactive insulin-like growth factor-1, and stanniocalcin-2 were assayed with novel, highly specific ELISA kits.

RESULTS

In unmatched univariate models, TC patients had higher FST serum levels compared to cancer-free individuals, independently of histological subtype. In multivariate models adjusting for covariates, individuals in the highest tertile of FST levels were associated with an increased risk for the presence of any type of TC or specific histological subtypes, including papillary, follicular and Hürthle-cell carcinoma, and medullary TC. Higher postoperative FST concentrations were found in patients with vascular invasion and distant metastases and associated with TNM staging at diagnosis.

CONCLUSION

FST serum levels are increased in TC patients and correlate with advanced tumor aggressiveness. Future longitudinal studies are needed to confirm and extend our observations.

Identification of candidate aberrantly methylated and differentially expressed genes in thyroid cancer

Aberrant methylation of DNA sequences plays a criticle role in finding novel aberrantly methylated genes and pathways in thyroid cancer (THCA). This study aimed to integrate three cohorts profile datasets to find novel aberrantly methylated genes and pathways in THCA. Data of gene expression profiling microarrays (GSE33630 and GSE65144) and gene methylation profiling microarrays (GSE51090) were downloaded from the Gene Expression Omnibus database. Aberrantly methylated and differentially expressed genes were sorted and pathways were analyzed. Functional and enrichment analyses of selected genes were performed using the String database. A protein‐protein interaction network was constructed using the Cytoscape software, and module analysis was performed using Molecular Complex detection. In total, we identified 12 hypomethylation/high‐expression genes and 30 hypermethylation/low‐expression genes at the screening step and, finally, found 6 mostly changed hub genes including PPARGC1A, CREBBP, EP300, CD44, SPP1, and MMP9. Pathway analysis showed that aberrantly methylated differentially expressed genes were mainly associated with the thyroid hormone signaling pathway, AMP‐activated protein kinase (AMPK) signaling pathway, and cell cycle process in THCA. After validation in the Cancer Genome Atlas database, the methylation and expression status of hub genes was significantly altered and the same with our results. Taken together, we identified novel aberrantly methylated genes and pathways in THCA, which could improve our understanding of the cause and underlying molecular events, and these candidate genes could serve as aberrant methylation‐based biomarkers for precise diagnosis and treatment of THCA.

miR-197: A novel biomarker for cancers

microRNAs (miRNAs) are small noncoding RNAs that could regulate post-transcription level through binding to 3' untranslated region (3'UTR) of target messenger RNAs (mRNAs), which were reported to be related with the incidence and development of diverse neoplasms. Among them, miR-197 was confirmed to play a vital role of oncogene or anti-oncogene in different cancers via targeting key tumorigenic or tumor-suppressive genes. Additionally, miR-197 had extensively been studied in carcinogenesis progression of cancers through various mechanisms, including apoptosis, proliferation, angiogenesis, metastasis, drug resistance and tumor suppressor, and also played a role in prognosis of cancers. In this review, we summarized the roles of miR-197 in cancers and considered it as a potentially novel biomarker for different cancers, offering an alternatively secure and effective tool in molecular targeting cancer treatment.

Epigenetic modifications in human thyroid cancer

Thyroid carcinoma is the most common endocrine malignancy of the endocrine organs, and its incidence rate has steadily increased over the last decade. Over 95% of thyroid carcinoma is derived from follicular cells that have a spectrum of differentiation to the most invasive malignancy. The molecular pathogenesis of thyroid cancer remains to be clarified, although activating the RET, RAS and BRAF oncogenes have been well characterized. Increasing evidence from previous studies demonstrates that acquired epigenetic abnormalities participating with genetic alteration results in altered patterns of gene expression/function. Aberrant DNA methylation has been established in the CpG regions and microRNAs (miRNAs) expression profile recognized in cancer development. In the present review, a literature review was performed using MEDLINE and PubMed with the terms 'epigenetic patterns in thyroid cancer [or papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), medullary thyroid cancer (MTC), anaplastic thyroid cancer (ATC)]', 'DNA methylation in thyroid cancer (or PTC, FTC, MTC, ATC)', 'miRNA expression in thyroid cancer (or PTC, FTC, MTC, ATC)', 'epigenetic patterns in cancer' and the current understanding of epigenetic patterns in thyroid cancer was discussed.

Molecular pathways associated with aggressiveness of papillary thyroid cancer

The most common thyroid malignancy is papillary thyroid cancer (PTC). Mortality rates from PTC mainly depend on its aggressiveness. Geno- and phenotyping of aggressive PTC has advanced our understanding of treatment failures and of potential future therapies. Unraveling molecular signaling pathways of PTC including its aggressive forms will hopefully pave the road to reduce mortality but also morbidity from this cancer. The mitogen-activated protein kinase and the phosphatidylinositol 3-kinase signaling pathway as well as the family of RAS oncogenes and BRAF as a member of the RAF protein family and the aberrant expression of microRNAs miR-221, miR-222, and miR-146b all play major roles in tumor initiation and progression of aggressive PTC. Small molecule tyrosine kinase inhibitors targeting BRAF-mediated events, vascular endothelial growth factor receptors, RET/PTC rearrangements, and other molecular targets, show promising results to improve treatment of radioiodine resistant, recurrent, and aggressive PTC.

Deregulation of microRNA expression in thyroid tumors

MicroRNAs (miRNAs or miRs) are endogenous non-coding RNAs that negatively regulate gene expression by binding to the 3' non-coding regions of target mRNAs, resulting in their cleavage or blocking their translation. miRNAs may have an impact on cell differentiation, proliferation, and survival, and their deregulation can be inclined to diseases and cancers, including thyroid tumors. The purpose of this review is to summarize the existing findings of deregulated miRNAs in different types of thyroid tumors and to exhibit their potential target genes, especially to demonstrate those involved in tumor invasion and metastasis. In addition, new findings of circulating miRNA expression profiles, single nucleotide polymorphism (SNP) in thyroid tumors, and the correlation of somatic mutations with deregulated miRNA expression in thyroid tumors were all included in this review.

microRNAs and thyroid cancer: biological and clinical significance (Review)

Despite recent advances in the management of thyroid cancer, the survival rate of this tumor may still be improved. Therefore, the identification of biological and molecular features of indolent and aggressive disease would be critical to define clinically useful predictors of high-risk lesions. microRNAs (miRNAs) are small RNA molecules with regulatory function and marked tissue specificity that modulate multiple targets belonging to several pathways. They are frequently deregulated in cancer and constitute a new class of blood-based biomarkers useful for cancer detection and prognosis definition, including thyroid cancer. In this review, the role of miRNAs in thyroid cancer development is described. The most common miRNAs detected in thyroid cancer along with their clinical significance are also discussed. Further studies aimed to detect plasma-based miRNA biomarkers in thyroid cancer patients may provide further insight into the management of thyroid cancer.

Pathogenic mechanisms of deregulated microRNA expression in thyroid carcinomas of follicular origin

Thyroid cancer is one of the most common malignancies of the endocrine system with increasing incidence. The vast majority of thyroid carcinomas derive from thyroid hormone producing follicular cells. Carcinomas of follicular origin are classified as follicular (FTCs), papillary (PTCs), partially differentiated (PDTCs) or anaplastic (ATCs) thyroid carcinomas. While FTCs and PTCs can be managed effectively, ATCs are considered one of the most lethal human cancers. Despite the identification of various genetic alterations, pathogenic mechanisms promoting the progression of thyroid carcinomas are still largely elusive. Over the recent years, aberrant microRNA expression was revealed in all as yet analyzed human cancers, including thyroid carcinomas. In view of the rapidly evolving perception that deregulated microRNA expression serves a pivotal role in tumor progression, microRNAs provide powerful tools for the diagnosis of thyroid carcinomas as well as the identification of potential therapeutic targets. Here, we summarize recent findings on microRNA signatures in thyroid carcinomas of follicular origin and discuss how deregulated microRNA expression could promote cancer progression.

MicroRNA Role in Thyroid Cancer Development

MicroRNAs (miRNAs) are endogenous noncoding RNAs that negatively regulate gene expression by binding the 3' noncoding region of the messenger RNA targets inducing their cleavage or blocking the protein translation. They play important roles in multiple biological and metabolic processes, including developmental timing, signal transduction, and cell maintenance and differentiation. Their deregulation can predispose to diseases and cancer. miRNA expression has been demonstrated to be deregulated in many types of human tumors, including thyroid cancers, and could be responsible for tumor initiation and progression. In this paper we reviewed the available data on miRNA deregulation in different thyroid tumors and describe the putative role of miRNA in thyroid cancer development.

Activin signaling: effects on body composition and mitochondrial energy metabolism

Activin-betaA and activin-betaB (encoded by Inhba and Inhbb genes, respectively) are closely related TGF-beta superfamily members that participate in a variety of biological processes. We previously generated mice with an insertion allele at the Inhba locus, Inhba(BK). In this allele, the sequence encoding the Inhba mature domain is replaced with that of Inhbb, rendering the gene product functionally hypomorphic. Homozygous (Inhba(BK/BK)) and hemizygous (Inhba(BK/-)) mice are smaller and leaner than their wild-type littermates, and many tissues are disproportionately small relative to total body weight. To determine the mechanisms that contribute to these phenomena, we investigated the metabolic consequences of the mutation. Although the growth of Inhba(BK) mice is improved by providing a calorie-rich diet, diet-induced obesity, fatty liver, and insulin resistance (hallmarks of chronic caloric excess) do not develop, despite greater caloric intake than wild-type controls. Physiological, molecular, and biochemical analyses all revealed characteristics that are commonly associated with increased mitochondrial energy metabolism, with a corresponding up-regulation of several genes that reflect enhanced mitochondrial biogenesis and function. Oxygen consumption, an indirect measure of the metabolic rate, was markedly increased in Inhba(BK/BK) mice, and polarographic analysis of liver mitochondria revealed an increase in ADP-independent oxygen consumption, consistent with constitutive uncoupling of the inner mitochondrial membrane. These findings establish a functional relationship between activin signaling and mitochondrial energy metabolism and further support the rationale to target this signaling pathway for the medical treatment of cachexia, obesity, and diabetes.

Role of transforming growth factor beta in the regulation of thyroid function and growth

Transforming growth factor beta (TGF-beta) exists in nature as three isoforms. They exert their effects by binding to a type II receptor located at the cell membrane. The TGF-beta-type II receptor complex then recruits type I receptor, and this new complex stimulates the phosphorylation of Smads 2 and 3, which are subsequently transferred to the nucleus, where they regulate gene transcription. The thyroid gland expresses the TGF-beta1 gene mRNA and synthesizes the protein, which under physiologic conditions regulates thyroid growth and function. Different studies have demonstrated that TGF-beta1 inhibits cell proliferation and a number of functional parameters. These include cyclic adenosine monophosphate (AMP) formation, iodine uptake and organification, hormone secretion, and the expression of thyroglobulin, thyroid peroxidase, and Na(+)/I(-) symporter. The expression of the TGF-beta1 gene and protein may be stimulated by iodine under normal conditions. Since TGF-beta1 mimics some of the inhibitory actions of iodine, its participation in thyroid autoregulation has been proposed; however, this concept is still debated. In thyroid tumors, the inhibitory action of TGF-beta1 on cell proliferation is progressively lost as the tumor becomes more undifferentiated. The alterations in the signaling pathway of TGF-beta1 are not the same in tumors from different species. Even within the same species, such as the pig thyroid, the results may be different depending on whether monolayers or follicular suspensions are employed. The data suggest that it is not entirely possible to apply the results obtained in animal studies to normal or pathological human thyroid tissue. More studies are required to provide the information needed to develop treatments, based on targeting the signaling pathway of TGF-beta1, for undifferentiated thyroid cancer and other thyroid diseases.

TGFbeta, activina e sinalização SMAD em câncer de tiróide

TGFbeta e activina são membros da superfamília TGFbeta e desempenham um amplo papel no desenvolvimento, proliferação e apoptose. Estes fatores de crescimento exercem seus efeitos biológicos ligando-se a receptores de membrana do tipo I e do tipo II que transduzem a sinalização até o núcleo através da fosforilação das proteínas R-SMADs (SMAD 2/3) e co-SMADs (SMAD4). O controle apropriado da via de TGFbeta/activina ainda depende da regulação negativa exercida pelo SMAD inibitório (SMAD7) e pelas enzimas E3 de ubiquitinação (Smurfs). Fisiologicamente, TGFbeta e activina atuam como potentes inibidores da proliferação na célula folicular tiroidiana. Desta forma, alterações de receptores e componentes da via de sinalização SMAD estão associadas a diferentes tipos de tumores. Desde que TGFbeta e activina geram sua sinalização intracelular utilizando os mesmos componentes da via SMAD, o desequilíbrio desta via prejudica dois processos anti-mitogênicos da célula. Nesta revisão, enfocamos aspectos que indicam o mecanismo de resistência ao efeito inibitório de TGFbeta e activina ocasionado pelo desequilíbrio da via de sinalização SMAD nas neoplasias da tiróide.

A limited set of human MicroRNA is deregulated in follicular thyroid carcinoma

CONTEXT

Although the pathogenesis of follicular thyroid carcinoma (FTC) and its relation to follicular adenoma (FA) remains unclear, detailed understanding of FTC carcinogenesis would facilitate addressing the scientific and clinical challenges, given that there are morphological and molecular similarities between FTC and the frequently occurring FA. Micro-RNAs (miRNAs) are a new class of small, noncoding RNAs implicated in development and cancer and may lend novel clues to FTC genesis. For the latter process, a deregulated miRNA can orchestrate the aberrant expression of several hundred target genes.

OBJECTIVE

The objective of the study was to identify deregulated miRNAs in FTC.

DESIGN

We used two high-density expression arrays to identify miRNAs and their target genes that are differentially expressed between FTC and FA. Validation was done by quantitative RT-PCR. We further functionally characterized the effect of deregulated miRNAs in vitro using HEK293T, FTC133, and K5 cell lines.

PATIENTS

In total, 45 primary thyroid samples (23 FTC, 20 FA, four normal control thyroid) were analyzed.

RESULTS

Two specific miRNAs, miR-197 and miR-346, were significantly overexpressed in FTC. In vitro overexpression of either miRNA induced proliferation, whereas inhibition led to growth arrest. Overexpression of miR-197 and miR-346 repressed the expression of their predicted target genes in vitro and in vivo.

CONCLUSIONS

Our observations show that miR-197 and miR-346 contribute to FTC carcinogenesis. Both miRNAs and their target genes might potentially provide for novel molecular markers and act as novel targets for treatment by interference, which could potentially normalize the deregulated profile of many downstream target genes.

Activin A circulating levels in patients with bone metastasis from breast or prostate cancer

Recent studies have highlighted that Activin A, a member of the transforming growth factor-beta (TGF-beta) superfamily, may be involved in the regulation of osteoblastic activity and in osteoclast differentiation. Therefore, we have investigated the clinical significance of its circulating levels in patients with bone metastasis. Activin A serum concentrations were determined, by a commercially available enzyme-linked immunosorbent assay kit, in 72 patients with breast cancer (BC) or prostatic cancer (PC) with (BM+) or without (BM-) bone metastases, in 15 female patients with age-related osteoporosis (OP), in 20 patients with benign prostatic hypertrophy (BPH) and in 48 registered healthy blood donors (HS) of both sex (25 female and 23 male). Activin A serum concentrations were significantly increased in BC or PC patients as compared to OP (P < 0.0001) or BPH (P = 0.045), respectively, or to sex matched HS (P < 0.0001). Additionally, these levels resulted more elevated in PC patients as compared to BC patients (P = 0.032). Interestingly, Activin A was significantly higher in BM+ patients than in BM- patients (BC, P = 0.047; PC, P = 0.016). In BC patients, a significant correlation was observed only between Activin A and number of bone metastases (P = 0.0065) while, in PC patients, Activin A levels were strongly correlated with the Gleason score (P = 0.011) or PSA levels (P = 0.0001) and, to a lessen extent, with the number of bone metastases (P = 0.056). Receiver operating characteristic curve (ROC) analysis showed a fair diagnostic accuracy of Activin A to discriminate between BM+ and BM- patients (BC: AUC = 0.71 +/- 0.09, P = 0.03; PC: AUC = 0.73 +/- 0.081, P = 0.005). These findings indicate that Activin A may be implicated in the pathogenesis of bone metastasis. Therefore, this cytokine may be considered a novel potential target for a more selective therapeutic approach in the treatment of skeletal metastasis and may be also useful as additional biochemical marker of metastatic bone disease.

The functional interaction between the paired domain transcription factor Pax8 and Smad3 is involved in transforming growth factor-beta repression of the sodium/iodide symporter gene

Transforming growth factor-beta (TGF-beta) is a secreted protein that regulates proliferation, differentiation, and death in various cell types, including thyroid cells, although few details are known about its mechanisms of action in this cell type. Here, we studied the role of TGF-beta on the regulation of sodium/iodide symporter (NIS) gene expression in PC Cl3 thyroid cells. TGF-beta inhibits thyroid-stimulated hormone (TSH)-induced NIS mRNA and protein levels in a dose-dependent manner. This effect takes place at the transcriptional level, as TGF-beta inhibits TSH-induced transcription of a luciferase reporter construct containing a 2.8-kb DNA fragment of the rat NIS promoter. The inhibitory effect of TGF-beta was partially overcome by inhibitory Smad7 and mimicked by overexpression of either Smad3 or a constitutively activated mutant of TGF-beta receptor I (acALK-5). Using internal deletions of the promoter, we defined a region between -2,841 to -1,941, which includes the NIS upstream enhancer (NUE), as responsible for the TGF-beta/Smad inhibitory effect. NUE contains two binding sites for the paired domain transcription factor Pax8, the main factor controlling NIS transcription. The physical interaction observed between Pax8 and Smad3 appears to be responsible for the decrease in Pax8 binding to DNA. Expression of Pax8 mRNA and protein was also decreased by TGF-beta treatment. The results suggest that, through activation of Smad3, TGF-beta decreases Pax8 DNA binding activity as well as Pax8 mRNA and protein levels, which are at least partially involved in TGF-beta-induced down-regulation of NIS gene expression in thyroid follicular cells. Our results thus demonstrate a novel mechanism of Smad3 function in regulating thyroid cell differentiation by functionally antagonizing the action of the paired domain transcription factor Pax8.

Activin betaB expression in rat experimental goiter and human thyroid tumors

Activins are dimeric proteins of the transforming growth factor beta superfamily, which exhibit multiple functions in gonadal and extragonadal tissues. Expression of activin A, composed of two betaA subunits, has been shown in the thyroid, whereas there has been no study regarding activin B (betaBbetaB) in this gland. In other tissues, such as the gonads, pancreas, and adrenal cortex, expression of both activin betaA and activin betaB has been described. In this study, we detected activin betaB mRNA and protein expression using reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry in rat experimental goiter and in human thyroid, including multinodular goiter, follicular adenoma, papillary carcinoma, and follicular carcinoma. Activin betaA mRNA and protein expression was also investigated in rat and human thyroid tissue. The expression of both activin betaB and activin betaA was highest in rat methimazole-induced goiter and in human follicular adenoma, and papillary and follicular carcinomas when compared with multinodular goiter and normal thyroid tissue. The increased expression of activin betaB as well as activin betaA, observed in this study, suggests that activin B and activin A may be involved in the proliferative and neoplastic processes of the thyroid.

Serum activin A levels in different thyroid disorders

Activin A belongs to the transforming growth factor-beta superfamily that exerts a wide range of biologic activities on cellular proliferation and differentiation. Although it was suggested that gonadal tissue is the primary site of activin production, several extragonadal sources have subsequently been identified, including human thyrocytes. The goal of the present study was to evaluate serum activin A levels in a series of patients with different thyroid disorders during the active state of the diseases and after recovery. Serum activin A levels were evaluated in 60 healthy subjects (controls), 8 with multinodular nontoxic goiter (MNG), 30 hyperthyroid (15 with Graves' disease (GD), 12 with autonomous hyperfunctioning adenoma (ATA), and 3 with thyrotropin (TSH)-secreting pituitary adenoma, 16 hypothyroid (11 with Hashimoto's thyroiditis and 5 after total thyroidectomy), and 9 patients with resistance to thyroid hormone (RTH) by commercial enzyme-linked immunosorbent assay (ELISA) kit. Patients with GD and ATA showed activin A levels higher than those found in controls and similar to those observed in MNG (GD, 0.74 +/- 0.3 ng/mL; ATA, 0.86 +/- 0.4; and MNG; 1.0 +/- 0.2 vs. controls: 0.39 +/- 0.5, p < 0.001), while in patients with Hashimoto's thyroiditis, total thyroidectomy or RTH activin A levels were similar to those of controls. In conclusion, this study demonstrates that thyroid hyperplasia and hyperfunction result in increased levels of activin A, although the normal levels observed in thyroidectomized patients clearly demonstrate that the thyroid gland is not the predominant source of activin A in normal conditions. Because activin A may exert negative action on thyrocyte proliferation, it is conceivable that activin A hypersecretion in thyroid disorders might represent a counteracting mechanism.

Overexpression of wild-type activin receptor alk4-1 restores activin antiproliferative effects in human pituitary tumor cells

Activin is a member of the TGF beta family of cytokines involved in the control of cell proliferation. We have previously shown that the majority of clinically nonfunctioning pituitary tumors do not respond to activin-induced growth suppression. Human pituitary tumors specifically express alternatively spliced activin type I receptor Alk4 mRNAs, producing C-terminus truncated isoforms designated Alk4-2, 4-3, and 4-4. However, it is not known whether these truncated activin receptors suppress activin effects on cell proliferation in human pituitary cells. Therefore, we investigated activin signaling in a human pituitary tumor cell line, HP75, derived from a clinically nonfunctioning pituitary tumor. HP75 cells express activin A mRNA and secrete activin A, as measured by ELISA and a functional bioassay. TGF beta administration decreases the proliferation of HP75 cells, suggesting that the signaling pathway shared by TGF beta and activin is functional in this cell line. However, activin neither inhibits cell proliferation nor stimulates reporter gene expression in HP75 cells, indicating that activin signaling is specifically blocked at the receptor level. HP75 cells express all truncated activin type I receptor Alk4 isoforms, as determined by RT-PCR. Because truncated Alk4 receptor isoforms inhibit activin signaling by competing with the wild-type receptor for binding to activin type II receptors, we hypothesized that overexpression of wild-type activin type I receptor will restore activin signaling. In HP75 cells, cotransfection of the wild-type activin type I receptor Alk4-1 expression vector increases activin-responsive reporter activity. Furthermore, transfection with wild-type activin receptor type I results in activin-mediated suppression of cell proliferation. These data indicate that truncated Alk4 isoforms interfere with activin signaling pathways and thereby may contribute to uncontrolled cell growth. Overexpression of the wild-type Alk4-1 receptor restores responsiveness to activin in human pituitary tumor-derived cells.

Apoptosis: life through planned cellular death regulating mechanisms, control systems, and relations with thyroid diseases

Apoptosis is an active biologic process that represents a form of programmed cellular suicide, activated either by genetic factors or by cellular lesions caused by various extracellular traumatic agents. The alterations of its functional mechanisms control cellular homeostasis are involved in the genesis of many illnesses. There are different control systems that can both stimulate and inhibit apoptosis, such as the p53 and Bcl-2 proteins. Different injuries may cause a rapid increase in the levels of p53 and the activation of the complex mechanism which leads either to damage repair or cellular apoptosis. The concept of tumor growth as a dynamic balance between cellular development and death is well applicable to differentiated thyroid carcinomas, which are generally not highly invasive and present excellent prognosis. On the contrary, in aggressive anaplastic thyroid carcinoma there is an increase in p53, whereas in normal thyroid cells there is a high expression of Bcl-2, so as to interfere with apoptosis when physiologic hormone levels are normal. However, only some of the biomolecular mechanisms behind the genesis of thyroid tumors have been explained, and the role of apoptosis in thyroid diseases has not been well defined. This review provides information about relationship between apoptosis and thyroid diseases.