The ret/ptc1 oncogene is activated in familial adenomatous polyposis-associated thyroid papillary carcinomas

Genetic susceptibility to hereditary non-medullary thyroid cancer

Non-medullary thyroid cancer (NMTC) is the most common type of thyroid cancer. With the increasing incidence of NMTC in recent years, the familial form of the disease has also become more common than previously reported, accounting for 5-15% of NMTC cases. Familial NMTC is further classified as non-syndromic and the less common syndromic FNMTC. Although syndromic NMTC has well-known genetic risk factors, the gene(s) responsible for the vast majority of non-syndromic FNMTC cases are yet to be identified. To date, several candidate genes have been identified as susceptibility genes in hereditary NMTC. This review summarizes genetic predisposition to non-medullary thyroid cancer and expands on the role of genetic variants in thyroid cancer tumorigenesis and the level of penetrance of NMTC-susceptibility genes.

Inherited thyroid tumours

Inherited thyroid tumours are an important group which need clarification. This is partly because of the common use of the term Familial Non-Medullary Thyroid Cancer when some of the specific entities included under this heading really represent inherited benign tumours with a risk of progression to malignancy. The subject is briefly reviewed, and one syndromic and one non-syndromic type of inherited thyroid tumours of follicular cell origin discussed in more detail to emphasise the point that each of these groups need to be treated as separate entities.

Thyroid Carcinomas That Occur in Familial Adenomatous Polyposis Patients Recurrently Harbor Somatic Variants in APC, BRAF, and KTM2D

Background: Familial adenomatous polyposis (FAP) is a condition typically caused by pathogenic germline mutations in the APC gene. In addition to colon polyps, individuals with FAP have a substantially increased risk of developing papillary thyroid cancer (PTC). Little is known about the events underlying this association, and the prevalence of somatic "second-hit" mutations in APC is controversial. Methods: Whole-genome sequencing was performed on paired thyroid tumor and normal DNA from 12 FAP patients who developed PTC. Somatic mutation profiles were compared with clinical characteristics and previously sequenced sporadic PTC cases. Germline variant profiling was performed to assess the prevalence of variants in genes previously shown to have a role in PTC predisposition. Results: All 12 patients harbored germline mutations in APC, consistent with FAP. Seven patients also had somatic mutations in APC, and seven patients harbored somatic mutations in KMT2D, which encodes a lysine methyl transferase. Mutation of these genes is extremely rare in sporadic PTCs. Notably, only two of the tumors harbored the somatic BRAF p.V600E mutation, which is the most common driver mutation found in sporadic PTCs. Six tumors displayed a cribriform-morular variant of PTC (PTC-CMV) histology, and all six had somatic mutations in APC. Additionally, nine FAP-PTC patients had rare germline variants in genes that were previously associated with thyroid carcinoma. Conclusions: Our data indicate that FAP-associated PTCs typically have distinct mutations compared with sporadic PTCs. Roughly half of the thyroid cancers that arise in FAP patients have somatic "second-hits" in APC, which is associated with PTC-CMV histology. Somatic BRAF p.V600E variants also occur in some FAP patients, a novel finding. We speculate that in carriers of heterozygous pathogenic mutations of tumor suppressor genes such as APC, a cooperating second-hit somatic variant may occur in a different gene such as KTM2D or BRAF, leading to differences in phenotypes. The role of germline variance in genes other than APC (9 of the 12 patients in this series) needs further research.

Current Knowledge of Germline Genetic Risk Factors for the Development of Non-Medullary Thyroid Cancer

The thyroid is the most common site of endocrine cancer. One type of thyroid cancer, non-medullary thyroid cancer (NMTC), develops from follicular cells and represents approximately 90% of all thyroid cancers. Approximately 5%–15% of NMTC cases are thought to be of familial origin (FNMTC), which is defined as the occurrence of the disease in three or more first-degree relatives of the patient. It is often divided into two groups: Syndrome-associated and non-syndromic. The associated syndromes include Cowden syndrome, familial adenomatous polyposis, Gardner syndrome, Carney complex and Werner syndrome. The hereditary factors contributing to the unfavorable course of FNMTC remain poorly understood; therefore, considerable effort is being expended to identify contributing loci. Research carried out to date identifies fourteen genes (DICER1, FOXE1, PTCSC2, MYH9, SRGAP1, HABP2, BRCA1, CHEK2, ATM, RASAL1, SRRM2, XRCC1, TITF-1/NKX2.1, PTCSC3) associated with vulnerability to FNMTC that are not related to hereditary syndromes. In this review, we summarize FNMTC studies to date, and provide information on genes involved in the development of non-syndromic familial non-medullary thyroid cancers, and the significance of mutations in these genes as risk factors. Moreover, we discuss whether the genetic polymorphism rs966423 in DIRC3 has any potential as a prognostic factor of papillary thyroid cancer.

Prevalence of thyroid diseases in familial adenomatous polyposis: a systematic review and meta-analysis

Thyroid cancer (TC) is a known extra-intestinal manifestation and contributes to the mortality and morbidity in patients with familial adenomatous polyposis (FAP). Its exact prevalence is not well established and recent studies have shown an increasing number of TC in this patient population. The prevalence of benign thyroid masses and endocrinologic thyroid disorders are also poorly described. We conducted a systematic review and meta-analysis by using a random-effects model to characterize TC and estimated the prevalence of thyroid diseases in FAP patients. Twelve studies (n = 9821) were included. Pooled prevalence of TC, benign thyroid masses, and endocrinologic thyroid disorders in FAP were 2.6% [95% confidence interval (CI) 1.3-4.8], 48.8% [95% CI 33.8-64.0], and 6.9% [95% CI 4.5-10.3] respectively. Subgroup analyses revealed higher prevalence of TC in studies with fewer participants, studies that used screening ultrasound to diagnose TC, and studies that were published after 2002. TC diagnosis preceded the diagnosis of FAP in 34% of the patients. The means age at diagnosis of FAP and TC were 29 and 31 years, respectively. 95% of the patients were female and the most common pathology was of papillary subtype (83.3%). Most mutations (79.2%) were located at the 5' end of APC gene. In summary, benign thyroid disorders are common in FAP, yet, TC is an uncommon phenomenon. Certain patient subset, such as young female with APC mutation at the 5' end, might benefit from routine surveillance ultrasound.

Wnt Signaling in Thyroid Homeostasis and Carcinogenesis

The Wnt pathway is essential for stem cell maintenance, but little is known about its role in thyroid hormone signaling and thyroid stem cell survival and maintenance. In addition, the role of Wnt signaling in thyroid cancer progenitor cells is also unclear. Here, we present emerging evidence for the role of Wnt signaling in somatic thyroid stem cell and thyroid cancer stem cell function. An improved understanding of the role of Wnt signaling in thyroid physiology and carcinogenesis is essential for improving both thyroid disease diagnostics and therapeutics.

FAP Associated Papillary Thyroid Carcinoma: A Peculiar Subtype of Familial Nonmedullary Thyroid Cancer

Familial Nonmedullary Thyroid Carcinoma (FNMTC) makes up to 5–10% of all thyroid cancers, also including those FNMTC occurring as a minor component of familial cancer syndromes, such as Familial Adenomatous Polyposis (FAP). We give evidence that this extracolonic manifestation of FAP is determined by the same germline mutation of the APC gene responsible for colonic polyps and cancer but also shows some unusual features (F : M ratio = 80 : 1, absence of LOH for APC in the thyroid tumoral tissue, and indolent biological behaviour, despite frequent multicentricity and lymph nodal involvement), suggesting that the APC gene confers only a generic susceptibility to thyroid cancer, but perhaps other factors, namely, modifier genes, sex-related factors, or environmental factors, are also required for its phenotypic expression. This great variability is against the possibility of classifying all FNMTC as a single entity, not only with a unique or prevalent causative genetic factor, but also with a unique or common biological behavior and a commonly dismal prognosis. A new paradigm is also suggested that could be useful (1) for a proper classification of FAP associated PTC within the larger group of FNMTC and (2) for making inferences to sporadic carcinogenesis, based on the lesson from FAP.

Germline and somatic mutations of the APC gene in papillary thyroid carcinoma associated with familial adenomatous polyposis: Analysis of three cases and a review of the literature

Patients with familial adenomatous polyposis (FAP), which is caused by the dysfunction of the adenomatous polyposis coli (APC) protein, have the possibility of developing extracolonic manifestations, including thyroid cancer (TC), congenital hypertrophy of the retinal pigment epithelium, desmoid tumors, and gastric and duodenal adenomas. The pathogenesis of these disorders associated with FAP is considered to be affected by the site of the germline mutation on the APC gene as a genotype-phenotype correlation. Moreover, β-catenin binding sites consist of 20-amino acid repeats (20-AARs) in the APC protein, and they are essential for the development of colorectal adenomas and certain other extracolonic manifestations. The present study retrospectively analyzed the germline and somatic mutations of the APC gene in three papillary TC patients with FAP to analyze the association between the remaining number of 20-AARs and the development of TC. The mutation sites of two TCs did not include 20-AARs in each allele. In one patient, the remaining number of 20-AARs was two in the germline mutation and zero in the somatic mutation. Together with the data on 13 FAP-associated thyroid cancerous lesions in 3 FAP patients reported previously, the majority of the remaining numbers of 20-AARs was zero in the TC patients with FAP (13/16; 81.3%). Consequently, the APC/β-catenin signaling pathway may be strongly involved with the pathogenesis of TC with FAP. Further accumulation of FAP patients with TC will be required to confirm the molecular pathogenesis of TC.

Role of the wnt pathway in thyroid cancer

Aberrant activation of Wnt signaling is involved in the development of several epithelial tumors. Wnt signaling includes two major types of pathways: (i) the canonical or Wnt/β-catenin pathway; and (ii) the non-canonical pathways, which do not involve β-catenin stabilization. Among these pathways, the Wnt/β-catenin pathway has received most attention during the past years for its critical role in cancer. A number of publications emphasize the role of the Wnt/β-catenin pathway in thyroid cancer. This pathway plays a crucial role in development and epithelial renewal, and components such as β-catenin and Axin are often mutated in thyroid cancer. Although it is accepted that altered Wnt signaling is a late event in thyroid cell transformation that affects anaplastic thyroid tumors, recent data suggest that it is also altered in papillary thyroid carcinoma (PTC) with RET/PTC mutations. Therefore, the purpose of this review is to summarize the main relevant data of Wnt signaling in thyroid cancer, with special emphasis on the Wnt/β-catenin pathway.

Intracellular signal transduction and modification of the tumor microenvironment induced by RET/PTCs in papillary thyroid carcinoma

RET gene rearrangements (RET/PTCs) represent together with BRAF point mutations the two major groups of mutations involved in papillary thyroid carcinoma (PTC) initiation and progression. In this review, we will examine the mechanisms involved in RET/PTC-induced thyroid cell transformation. In detail, we will summarize the data on the molecular mechanisms involved in RET/PTC formation and in its function as a dominant oncogene, on the activated signal transduction pathways and on the induced gene expression modifications. Moreover, we will report on the effects of RET/PTCs on the tumor microenvironment. Finally, a short review of the literature on RET/PTC prognostic significance will be presented.

The beta-catenin axis integrates multiple signals downstream from RET/papillary thyroid carcinoma leading to cell proliferation

RET/papillary thyroid carcinoma (RET/PTC) oncoproteins result from the in-frame fusion of the RET receptor tyrosine kinase domain with protein dimerization motifs encoded by heterologous genes. Here, we show that RET/PTC stimulates the beta-catenin pathway. By stimulating PI3K/AKT and Ras/extracellular signal-regulated kinase (ERK), RET/PTC promotes glycogen synthase kinase 3beta (GSK3beta) phosphorylation, thereby reducing GSK3beta-mediated NH(2)-terminal beta-catenin (Ser33/Ser37/Thr41) phosphorylation. In addition, RET/PTC physically interacts with beta-catenin and increases its phosphotyrosine content. The increased free pool of S/T(nonphospho)/Y(phospho)beta-catenin is stabilized as a result of the reduced binding affinity for the Axin/GSK3beta complex and activates the transcription factor T-cell factor/lymphoid enhancer factor. Moreover, through the ERK pathway, RET/PTC stimulates cyclic AMP-responsive element binding protein (CREB) phosphorylation and promotes the formation of a beta-catenin-CREB-CREB-binding protein/p300 transcriptional complex. Transcriptional complexes containing beta-catenin are recruited to the cyclin D1 promoter and a cyclin D1 gene promoter reporter is active in RET/PTC-expressing cells. Silencing of beta-catenin by small interfering RNA inhibits proliferation of RET/PTC-transformed PC Cl3 thyrocytes, whereas a constitutively active form of beta-catenin stimulates autonomous proliferation of thyroid cells. Thus, multiple signaling events downstream from RET/PTC converge on beta-catenin to stimulate cell proliferation.

FAP associated thyroid carcinoma in mother and her daughter

A 21 year-old Japanese female was referred to the hospital for evaluation of a mass in her neck. Cytologic samples obtained through fine needle aspiration (FNA) material from the mass showed pseudopapillary or sheet-like clusters. The cells had oval nuclei and columnar cytoplasms. Nuclear groove and intranuclear inclusions were scarcely seen. The cells had a cribriform or solid pattern, unlike cells in papillary thyroid carcinoma. This distinct cytological appearance is thought to belong to FAP (familial adenomatous polyposis)-associated thyroid cancer. The patient was diagnosed with FAP associated papillary thyroid carcinoma. FAP was confirmed by colonoscopy. Her mother, 48 years old, also detected an anterior neck swelling at the time of her daughter's admission. At the age of ten, the mother had undergone total colectomy because of FAP. FNA of the mass demonstrated the same cytological appearance as from her daughter's tumor. Total thyroidectomy was performed. Gross and microscopic appearances of the tumor was similar in mother and daughter. We believe it is possible to detect FAP through FNA cytology of thyroid tumors if pathologists are aware of the unique cytohistological features of thyroid tumor cells in FAP.

Papillary thyroid carcinoma: 6 cases from 2 families with associated lymphocytic thyroiditis harbouring RET/PTC rearrangements

Familial papillary thyroid carcinoma (PTC) is a well recognized disease. However, genetic predisposition to familial PTC is rare and the molecular alterations at the origin of the pathology are unknown. The association between PTC and lymphocytic thyroiditis (LT) has been reported recently. We communicate here 6 cases of PTC associated with LT in 2 unrelated families. PTC was diagnosed on classical nuclear and architectural criteria. It was bilateral in 5 cases. Architecture was equally distributed between typical PTC and its follicular variant. LT was present in variable degrees, including in 4 cases, oncocytic metaplasia. Using the RT-PCR technique, we observed a RET/PTC rearrangement in the carcinomatous areas of patients of both families: PTC1 in family 1 and PTC3 in family 2 and a RET/PTC rearrangement in non-malignant thyroid tissue with LT in family 2. The RET/PTC band was weaker or absent in pure LT areas. Furthermore, using a polyclonal ret antibody, an apical or a diffuse cytoplasmic ret onc protein immunolabelling was observed in the three patients with RET/PTC1 rearrangement and in the three patients with RET/PTC3 rearrangement. In conclusion our data: (1) show the presence of a RET/PTC 1 or 3 rearrangement (depending on the family) together with a variable expression of ret protein in all the PTCs; (2) suggest that the molecular event at the origin of the PTCs seems to be particular to each one of the studied families; and (3) confirm that the ret proto-oncogene activating rearrangement(s) is an early event in the thyroid tumorigenic process and that it can be observed in association with LT.

Familial adenomatous polyposis-associated thyroid cancer: a clinical, pathological, and molecular genetics study

We report two familial adenomatous polyposis (FAP) kindreds with thyroid cancer, harboring two apparently novel germlineAPC mutations. The clinical phenotype in the first kindred was typical of classical adenomatous polyposis, whereas the second kindred exhibited an attenuated adenomatous polyposis phenotype. There was a female predominance with a mean age of 34 years (range, 23-49) at cancer diagnosis. Multiple sections of four thyroid tumors from three FAP patients were analyzed in detail. Histological examination of thyroid tumors showed a range of morphological features. Some tumors exhibited typical papillary architecture and were associated with multifocal carcinoma; in others, there were unusual areas of cribriform morphology, and spindle-cell components with whorled architecture. Immunoreactivity for thyroglobulin and high molecular weight keratins was strong. Somatic APC mutation analysis revealed an insertion of a novel long interspersed nuclear element-1-like sequence in one tumor sample, suggesting disruption of APC. In three FAP patients, ret/PTC-1 and ret/PTC-3 were expressed in thyroid cancers. No positivity was observed for ret/ PTC-2. p53 immunohistochemistry was positive in only one section of a recurrent thyroid tumor sample. Our data suggest that genetic alterations in FAP-associated thyroid cancer involve loss of function of APC along with the gain of function of ret/PTC, while alterations of p53 do not appear to be an early event in thyroid tumorigenesis.