Analysis of adenomatous polyposis coli gene in thyroid tumours

Cribriform-morular variant of thyroid carcinoma: a neoplasm with distinctive phenotype associated with the activation of the WNT/β-catenin pathway

Cribriform-morular variant of thyroid carcinoma is classically associated with familial adenomatous polyposis but, it can also occur as a sporadic neoplasm. This neoplasm is much more frequently observed in women than in men (ratio of 61:1). In familial adenomatous polyposis patients, tumors are generally multifocal and/or bilateral (multinodular appearance), whereas in the sporadic cases tumors tend to occur as single nodules. The tumors are well delimited, and characteristically show a blending of follicular, cribriform, papillary, trabecular, solid, and morular patterns. Neoplastic cells are tall or cuboidal with the occasional nuclear features of classic papillary thyroid carcinoma. The morules include cells with peculiar nuclear clearing and show positivity for CDX2 and CD10. Angioinvasion and capsular invasion have been described in about 30 and 40% of cases, respectively, with lymph node metastases in less than 10% of patients and distant metastases in 6%. Although this tumor has good prognosis, neuroendocrine and/or poor differentiation have been associated with aggressive behavior. Tumor cells can be focally positive or negative for thyroglobulin, but are always positive for TTF-1, estrogen and progesterone receptors, and negative for calcitonin and cytokeratin 20. Nuclear and cytoplasmic staining for β-catenin is the hallmark of this tumor type; this feature plays a role in fine needle aspiration biopsy. Cribriform-morular variant of thyroid carcinoma has a peculiar endodermal (intestinal-like) type phenotype, activation of the WNT/β-catenin signaling pathway, and belongs to the non-BRAF-non-RAS subtype of the molecular classification of thyroid tumors. Elevated expression of estrogen and progesterone receptors and activation of the WNT/β-catenin pathway may prove useful as putative therapeutic targets in cases that do not respond to conventional therapy. Clinicians should be alerted to the possibility of familial adenomatous polyposis when a diagnosis of cribriform-morular variant of thyroid carcinoma is made. Instead of being considered as a variant of papillary thyroid carcinoma its designation as cribriform-morular thyroid carcinoma seems more appropriate.

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.

Cribriform-morular variant of papillary thyroid carcinoma displaying poorly differentiated features

Cribriform-morular variant of papillary thyroid carcinoma (CMVPTC) usually occurs in the setting of familial adenomatous polyposis (FAP) although it can rarely arise sporadically. Poorly differentiated thyroid carcinoma (PDTC) is a follicular cell-derived neoplasm with more aggressive behavior than well-differentiated carcinomas such as CMVPTC. We report the case of a 35-year-old woman without FAP history who presented a left neck mass and complained of back pain. Imagiological examinations revealed a nodule in the left lobe of thyroid and multiple nodular lesions in the bone and lungs suggestive of metastases. The patient was submitted to total thyroidectomy and radioactive iodine. The tumor was composed of CMVPTC and PDTC components that shared the same somatic APC gene mutation (p.Cys520Tyr_fsX534). Besides this mutation, no CTNNB1, BRAF, N-RAS, and H-RAS gene mutations were detected in any of the 2 components. To the best of our knowledge, this is the first report of a sporadic CMVPTC with transformation into PDTC. Although the majority of CMVPTCs carry an indolent clinical outcome, the coexistence of poorly differentiated areas may justify the aggressiveness of the CMVPTC reported here.

Frizzled-1 is down-regulated in follicular thyroid tumours and modulates growth and invasiveness

The mechanisms of follicular thyroid carcinoma (FTC) transformation and progression are not well understood. Previously, we detected LOH at 7q21 in all FTCs examined, indicating that loss of genetic material in that region is a common trait in these lesions. To analyse the effects of LOH on gene expression, we performed an analysis of the mRNA expression levels of six different genes, located at 7q21.1-7q21.3. A total of 23 lesions, including eight follicular hyperplasias (FHs), eight follicular adenomas (FAs), two FTCs and five papillary thyroid carcinomas (PTCs) were analysed. The Frizzled-1 (FZD-1) gene, located at 7q21.13, showed the lowest levels of mRNA expression. Down-regulation of FZD-1 expression was also confirmed in an independent series of 69 follicular neoplastic lesions compared to 25 PTCs, analysed by quantitative RT-PCR. In vitro studies showed that FZD-1 expression was also markedly reduced at both protein and mRNA levels in three FTC-derived cell lines (FRO, WRO and FTC-133), while it was normal in the three PTC-derived cell lines (Ca300, Ca301 and K1) examined. We demonstrated that over-expression of FZD-1 in 3 FTC-derived cells decreased invasiveness and proliferation rate, indicating a possible pathogenetic role. In addition, FZD-1 RNA interference in the PTC-derived cell line K1 increased invasiveness. Our data indicated that FZD-1 is involved in growth of follicular tumours and may be considered as a novel marker of this type of tumour.

Pathogenetic mechanisms in thyroid follicular-cell neoplasia

Thyroid cancer is one of the few malignancies that are increasing in incidence. Recent advances have improved our understanding of its pathogenesis; these include the identification of genetic alterations that activate a common effector pathway involving the RET-Ras-BRAF signalling cascade, and other unique chromosomal rearrangements. Some of these have been associated with radiation exposure as a pathogenetic mechanism. Defects in transcriptional and post-transcriptional regulation of adhesion molecules and cell-cycle control elements seem to affect tumour progression. This information can provide powerful ancillary diagnostic tools and can also be used to identify new therapeutic targets.

Immunohistochemical and sequencing analyses of the Wnt signaling components in Japanese anaplastic thyroid cancers

We investigated the status of the components and target genes of the Wnt signaling pathway in Japanese anaplastic thyroid cancers (ATCs) in the present study. Nuclear and cytoplasmic positive staining of beta-catenin, which might indicate the existence of alterations in the Wnt signaling pathway, were found in 40.9% and 63.6% of the 22 ATC samples, respectively. The beta-catenin, adenomatous polyposis coli (APC) and Axin 1 gene mutations were observed in 4.5%, 9.0%, and 81.8% of the 22 ATC samples, respectively. Overexpression of cyclin D1 and c-myc, which are the target genes of the Wnt signaling pathway, was observed in 27.3% and 59.1% of the ATC samples, respectively. There was no significant correlation between nuclear or cytoplasmic positive staining of beta-catenin and nuclear positive staining of cyclin D1 or c-myc. Taken together, the results of beta-catenin immunohistochemistry suggest that alterations in the Wnt signaling pathway are associated with carcinogenesis of ATC, but the frequency of beta-catenin gene mutation in our series is lower than that previously reported. Furthermore, cyclin D1 and c-myc frequently accumulated in ATC, independently of dysfunction in the Wnt signaling pathway.

Genotype and phenotype of patients with both familial adenomatous polyposis and thyroid carcinoma

The incidence of thyroid carcinoma in familial adenomatous polyposis (FAP) is thought to be 1%-2%, with the majority of cases being female. We have investigated the phenotype and genotype of 16 patients with FAP associated thyroid carcinoma. Among 1194 FAP patients studied in two high risk registries in North America (Familial Gastrointestinal Cancer Registry, Toronto and University California, San Francisco), 16 (1.3%) unrelated patients with FAP associated thyroid cancers were identified. Adenomatous polyposis coli (APC) gene testing was performed in 14 of the 16 cases. The average age of diagnosis for FAP and thyroid carcinoma was 29 years (range 17-52 years) and 33 years (range 17-55 years), respectively. All FAP patients except 1 had more than 100 colonic adenomas. Extracolonic manifestations, beside thyroid cancer, were presented in 81% (n = 13) of the patients, including gastric and duodenal polyps, desmoid tumor, osteoma, epidermoid cyst, sebaceous cyst and lipoma. Colorectal cancer was diagnosed in 38% (n = 6) of the patients. The pathology of the FAP associated thyroid cancer was predominantly papillary carcinoma. Germline mutations were identified in 12 of 14 patients tested. Mutations proximal to the mutation cluster region (1286-1513) were detected in 9 cases. Thyroid cancer in our FAP population was rare, predominantly in females and showed papillary carcinoma histology. Additionally, thyroid cancer in our patients occurred in the setting of classic FAP phenotype. Germline mutations were located predominantly outside the APC mutation cluster region.

Cribriform-morular variant of papillary thyroid carcinoma: a pathological and molecular genetic study with evidence of frequent somatic mutations in exon 3 of the beta-catenin gene

The cribriform-morular variant (C-MV), an unusual and peculiar subtype of papillary thyroid carcinoma (PTC), has been observed frequently in familial adenomatous polyposis (FAP)-associated thyroid carcinoma and also in sporadic thyroid carcinoma. In this paper, five young women with the C-MV of PTC, aged 22-34 years at cancer diagnosis, are reported; two of them had attenuated FAP. Grossly, one FAP-associated tumour and one sporadic tumour were multicentric and the others were solitary. Histologically, the tumours were encapsulated and exhibited a combination of cribriform, follicular, trabecular, solid, and papillary patterns of growth, with morular areas. Immunohistochemically, the tumour cells showed cytoplasmic expression of thyroglobulin, neuron-specific enolase, epithelial membrane antigen, high- and low-molecular-weight cytokeratins, vimentin, and bcl-2 protein; nuclear expression of oestrogen and progesterone receptors, and retinoblastoma protein; and cytoplasmic and nuclear accumulation of beta-catenin. Germline mutations of the adenomatous polyposis coli (APC) gene were investigated using the protein truncation test in four subjects, including two FAP individuals. Germline APC mutation was identified in only one FAP patient with the multicentric C-MV of PTC, who had a thymidine deletion at codon 512, resulting in a frameshift leading to a premature stop codon. No loss of heterozygosity of loci close to the APC gene was detected in tumour tissues from these four patients. Somatic mutation analysis of exon 3 of the beta-catenin gene (CTNNB1) revealed alterations in seven tumours from all five individuals: one at a serine residue (codon 29), three at amino acids adjacent to serine or threonine residues (codons 22, 39, and 44), and three at other amino acids (codons 49, 54, and 56). Moreover, each of two different tumours examined from two patients with the multicentric C-MV of PTC, had different somatic mutations of the CTNNB1 gene. Taken together, these data suggest that accumulation of mutant beta-catenin contributes to the development of the C-MV of PTC.

Molecular pathobiology of thyroid neoplasms

Tumors of thyroid follicular cells provide a very interesting model to understand the development of human cancer. It is becoming apparent that distinct molecular events are associated with specific stages in a multistep tumorigenic process with good genotype/ phenotype correlation. For instance, mutations of the gsp and thyroid-stimulating hormone receptor genes are associated with benign hyperfunctioning thyroid nodules and adenomas while alterations of other specific genes, such as oncogenic tyrosine kinase alterations (RET/PTC, TRK) in papillary carcinoma and the newly discovered PAX8/peroxisome proliferator-activated receptor gamma rearrangement, are distinctive features of cancer. Although activating RAS mutations occur at all stages of thyroid tumorigenesis, evidence is accumulating that they may also play an important role in tumor progression, a role that is well documented for p53. Environmental factors (iodine deficiency, ionizing radiations) have been shown to play a crucial role in promoting the development of thyroid cancer, influencing both its genotypic and phenotypic features. It is possible that the follicular thyroid cell has unique ways to respond to DNA damage. Similarly to leukemia or sarcomas (and unlike most epithelial cancers), numerous specific rearrangements are being discovered in thyroid cancer suggesting preferential activation of DNA repair instead of cell death programs after environmentally induced genetic alterations.

Increased risk for nonmedullary thyroid cancer in the first degree relatives of prevalent cases of nonmedullary thyroid cancer: a hospital-based study

The genetic basis for nonmedullary forms of thyroid cancer (NMTC) is less well established than that of medullary thyroid cancer. However, epidemiological and family studies suggest that a proportion of NMTC may be due to inherited predisposition. To estimate the familial risk of thyroid cancer, we conducted a hospital-based case-control study at the Princess Margaret Hospital in Toronto, Ontario, Canada, and at 2 university hospitals in Montréal, Québec, Canada. We obtained pedigrees from 339 unselected patients diagnosed with NMTC and from 319 unaffected ethnically matched controls. Family histories of cancer were obtained from the cases and controls for 3292 first degree relatives of cases and controls. Seventeen cases (5.0%) and 2 controls (0.6%) reported at least one first degree relative with thyroid cancer. In relatives of patients with thyroid cancer, the incidence of any type of cancer (including NMTC) was 38% higher than in relatives of controls (incidence rate ratio, 1.4; 95% confidence interval, 1.1-1.7). The relative risk for thyroid cancer was 10-fold higher in relatives of cancer patients than in controls (incidence rate ratio, 10.3; 95% confidence interval, 2.2-47.6). Our findings suggest that hereditary or other familial factors are important in a small proportion of NMTC. Molecular studies are needed to determine the genetic basis of cancer susceptibility in these families.

Absence of mutations in the beta-catenin and adenomatous polyposis coli genes in papillary and follicular thyroid carcinomas

beta-Catenin has multiple functions both in intercellular adhesion and in signal transduction. As a signaling molecule, mutations in exon 3 of the beta-catenin gene stabilize this protein in the cytoplasm. Subsequently, accumulated beta-catenin protein translocates to nuclei with T-cell factor-4, and upregulates transcriptional activity of the target genes involved in carcinogenesis. Mutations in exon 3 of the beta-catenin gene have been detected in various carcinomas. We examined immunolocalization of beta-catenin protein and mutations in the beta-catenin and adenomatous polyposis coli (APC) genes in papillary carcinoma (25 cases), follicular carcinoma (two cases), and benign thyroid tumor (29 cases). We detected no mutation in exon 3 of the beta-catenin gene in both malignant and benign thyroid tumors by polymerase chain reaction (PCR) and direct sequencing. No mutations in the mutation cluster region of APC were found in any tumor samples analyzed. Immunohistochemically, beta-catenin showed membranous localization in most specimens. These results suggest that mutations of the beta-catenin and APC genes are rare and that activation of the Wnt signaling pathway may not contribute to pathogenesis in human papillary and follicular thyroid carcinomas.

Beta-catenin dysregulation in thyroid neoplasms: down-regulation, aberrant nuclear expression, and CTNNB1 exon 3 mutations are markers for aggressive tumor phenotypes and poor prognosis

beta-catenin has a role in cell adhesion and Wnt signaling. It is mutated or otherwise dysregulated in a variety of human cancers. In this study we assess beta-catenin alteration in 145 thyroid tumors samples from 127 patients. beta-catenin was localized using immunofluorescence and mutational analysis was performed by single-strand conformational polymorphism. Membrane beta-catenin expression was decreased in eight of 12 (66%) adenomas and in all 115 carcinomas (P: < 0.0001). Among carcinomas, reduced membrane beta-catenin was associated with progressive loss of tumor differentiation (P: < 0.0001). CTNNB1 exon 3 mutations and nuclear beta-catenin localization were restricted to poorly differentiated [7 of 28 (25%) and 6 of 28 cases (21.4%), respectively] or undifferentiated carcinomas [19 of 29 (65.5%) and 14 of 29 (48.3%) cases, respectively]. Poorly differentiated tumors always featured mutations involving Ser and Thr residues and were characterized by Thr to Ile amino acid substitutions (P: = 0.0283). The association between CTNNB1 exon 3 mutations and aberrant nuclear immunoreactivity (P: = 0.0020) is consistent with Wnt activation because of stabilizing beta-catenin mutations. Low membrane beta-catenin expression as well as its nuclear localization or CTNNB1 exon 3 mutations are significantly associated with poor prognosis, independent of conventional prognostic indicators for thyroid cancer but not of tumor differentiation. Analysis of beta-catenin dysregulation may be useful to objectively subtype thyroid neoplasms and more accurately predict outcomes.

Familial nonmedullary thyroid neoplasia

Thyroid carcinoma accounts for less than 1% of all human malignancies and carries one of the highest overall familial relative risks as compared with cancers from other sites. This is particularly true for medullary carcinoma, as well as for carcinomas of follicular cell origin in general, where inheritance has been implicated in 2.5 to 6.3% of the cases. Familial nonmedullary thyroid tumors show a variety of genetic mechanisms implicated in thyroid tumorigenesis and occur in several tumor-prone traits (e.g., familial adenomatous polyposis [FAP] and Cowden's disease [CD]) or as the only or dominant inherited manifestation. The latter group includes the most common familial papillary carcinoma, in which environmental factors such as radiation exposure may also play an important etiological role. Familial follicular cell tumors show a variety of morphological features ranging from benign thyroid nodulation to carcinoma, usually develop in young individuals, and tend to be multicentric--an indication for total thyroidectomy to avoid tumor recurrence and potential risk of malignant transformation. The pathologist may play an important role in the histological interpretation of familial nonmedullary thyroid tumors, which may lead to further clinicogenetical investigations of the affected patient and family screening. Familial follicular cell thyroid neoplasms show a complex molecular biological pathway of tumorigenesis when compared between themselves and with their sporadic counterparts.

Molecular pathogenesis of thyroid nodules and cancer

Tumours derived from the thyroid follicular epithelium represent an informative model for understanding the molecular pathogenesis of multistage tumourigenesis, which is the prevailing theory on cancer development and progression nowadays. The early stages of thyroid tumour development appear to be the consequence of the activation or 'de novo' expression of several proto-oncogenes or growth factor receptors, such as ras, ret, NTRK, met, gsp and the thyrotropin (TSH) receptor. Alterations in the expression pattern of these genes are associated with the development of differentiated neoplasms, ranging from benign toxic adenomas (gsp and TSH receptor), to follicular (ras) and papillary (ret/PTC, NTRK, met) carcinomas. They may all be considered to be early events of thyroid cell transformation and, for some, experimental evidence derived from gene transfer studies supports this hypothesis. Alterations in tumour suppressor genes (p53, Rb) are associated instead with the most aggressive and poorly differentiated forms of thyroid cancer, indicating that, in the thyroid tumourigenic process, they represent late genetic events. Specific environmental factors (iodine deficiency, ionizing radiations) have been shown to play a crucial role in promoting the development of thyroid cancer, influencing both its genotypic and phenotypic features. Interestingly, a high percentage of genetic lesions causing thyroid cancer originate from gene rearrangements and chromosomal translocations (ret/PTC, NTRK, Pax-8/PPARgamma) a finding which, being a rare event in most epithelial tumours, makes the molecular pathogenesis of thyroid cancer unique. The uninterrupted flow of information on the molecular genetics of thyroid nodules and cancer will broaden the correlation between genotype and phenotype and will also provide important information for the development of more accurate preoperative diagnostic tools and more efficient treatment choices for the different forms of thyroid cancer.

Somatic mutation of the APC gene in thyroid carcinoma associated with familial adenomatous polyposis

We report the existence of both germline and somatic mutations of the APC gene in thyroid carcinomas from familial adenomatous polyposis (FAP) patients. One papillary thyroid carcinoma from a 210-year-old woman, with germline mutation of the APC gene (TCA to TGA at codon 1110), showed a somatic mutation of AAAAC deletion between codons 1060 and 1063. Another somatic mutation of CAG to TAG at codon 886 was also found in one of multiple thyroid carcinomas from a 26-year-old woman with attenuated FAP and germline mutation at codon 175 (C deletion). This is the first evidence that total absence of the normal function of the APC gene is involved in development of thyroid carcinomas in FAP.

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.

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

Familial adenomatous polyposis (FAP) is caused by germ-line mutations of the apc gene, and it is associated with an increased risk of developing papillary thyroid carcinomas. We have previously reported that a significant fraction of sporadic human papillary thyroid carcinomas is characterized by gene rearrangements affecting the ret protooncogene. These rearrangements generate chimeric transforming oncogenes designated ret/ptc. By a combined immunohistochemical and RT-PCR approach, we analyzed, for ret/ptc oncogene activation, papillary thyroid carcinomas occurred in two FAP kindreds, both showing typical apc gene mutations. Kindred 1 had seven members affected by FAP, and among these, three patients showed papillary thyroid carcinomas. Kindred 2 had two patients, mother and daughter, affected by colonic polyposis; the 20-yr-old daughter showed also a papillary carcinoma. Here we report that ret/ptc1 oncogene was activated in two of the three papillary carcinomas of FAP kindred 1 and in the papillary carcinoma of FAP kindred 2. These findings document that loss of function of apc coexists with gain of function of ret in some papillary thyroid carcinomas, suggesting that ret/ptc1 oncogene activation could be a progression step in the development of FAP-associated thyroid tumors.

High frequency deletion of the tumour suppressor gene P16INK4a (MTS1) in human thyroid cancer cell lines

p16INK4a (MTS1) is an important negative regulator of mammalian cell proliferation, acting via inhibition of CDK4/cyclin D-dependent phosphorylation of pRb to prevent progression through the G1 phase of the cell cycle. Loss of p16 activity by either gene deletion, mutation or transcriptional inactivation has now been found in a wide range of human cancers of both epithelial and mesenchymal origin, at a frequency rivalling that of p53 mutation. As a first step towards investigating its possible role as a tumour suppressor gene in thyroid tumorigenesis, we have carried out a Southern blot analysis of the p16 gene locus in a series of cell lines derived from differentiated human thyroid cancers. Homozygous deletion of the entire p16 coding sequence was observed in two of three follicular and two of four papillary cancer cell lines, but not in normal tissue or normal cells immortalised by SV40 T antigen. Given the co-existence of p16 abnormalities in primary tumours and cell lines observed in other tumour types, this high frequency of deletion suggests that p16 is a key tumour suppressor gene in the genesis of differentiated thyroid cancer.