Genetic alterations in human epithelial thyroid tumours

KRAS-SOS-1 Inhibition as New Pharmacological Target to Counteract Anaplastic Thyroid Carcinoma (ATC)

Anaplastic thyroid carcinoma (ATC) is the most aggressive type of thyroid cancer. Tumor cells have been shown to activate alternative signaling pathways, making treatments less effective. One of the major proteins involved in the progression of ATC is the proto-oncogene KRAS that belongs to a group of small guanosine triphosphate (GTP)-binding proteins. Despite its recognized importance in cancer malignancy, KRAS is considered non-druggable and has never been studied in the field of ATC. In this context, a new synthetic molecule, BAY-293, has recently been developed that selectively inhibits the KRAS-SOS-1 interaction. Based on these findings, the aim of this study was to evaluate for the first time the antitumor effect of BAY-293 using in vitro and in vivo models of ATC. The in vitro model included different thyroid cancer (TC) cell lines used to study the effect of BAY-293 on the modulation of mitogen-activated protein kinase (MAPK) pathways, apoptosis, and cell migration. To confirm the in vitro findings and better mimic the complex tumor microenvironment, an in vivo orthotopic model of ATC was used. The results of the study indicate that BAY-293, both in vitro and in vivo, effectively blocked the KRAS/MAPK/ERK pathway and β-catenin, which act as downstream effectors essential for cell migration, and increased the apoptotic process by slowing the progression of ATC. In conclusion, this study demonstrated that KRAS/SOS-1 inhibition could be a promising therapeutic target for the treatment of ATC and highlighted BAY-293 as an innovative molecule that needs further research to fully evaluate its efficacy in the field of thyroid cancer.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Evaluation and management of the pediatric thyroid nodule

Thyroid nodules are commonly diagnosed in adults. Although rare in children, the risk for thyroid cancer is much higher in the pediatric population compared with adults. Presenting as either a solitary nodule or a multinodular goiter, thyroid nodular disease in children requires a thorough workup that includes a detailed clinical examination comprised of prior history of thyroid disease in the patient or in their family, history of radiation exposure, careful palpation of the thyroid and lymph nodes, blood tests, ultrasonography, and cytological assessment. Thyroid surgery is the gold-standard treatment for pediatric thyroid nodules; nonetheless, the extent of surgery remains controversial. Because surgery is not without risk, the decision matrix necessitates focus on the benefits of surgery for the child contingent upon all the preoperative exams. New diagnostic technology such as molecular testing with fine needle aspiration biopsy may help distinguish between benign and malignant lesions while potentially decreasing surgery for benign disease. The objective of this review is to summarize new concepts in clinical disease management of nodular thyroid disease in the pediatric population, including patient history, medical examination, and diagnosis workup.

Genetic alterations in thyroid tumors from patients irradiated in childhood for tinea capitis treatment

OBJECTIVE

Exposure to ionizing radiation at young age is the strongest risk factor for the occurrence of papillary thyroid carcinoma (PTC). RET/PTC rearrangements are the most frequent genetic alterations associated with radiation-induced PTC, whereas BRAF and RAS mutations and PAX8-PPARG rearrangement have been associated with sporadic PTC. We decided to search for such genetic alterations in PTCs of patients subjected in childhood to scalp irradiation.

DESIGN

We studied 67 thyroid tumors from 49 individuals irradiated in childhood for tinea capitis scalp epilation: 36 malignant (12 cases of conventional PTC (cPTC), two cPTC metastases, 20 cases of follicular variant PTC (FVPTC), one oncocytic variant of PTC and one follicular carcinoma) and 31 follicular thyroid adenomas.

METHODS

The lesions were screened for the BRAF(V600E) and NRAS mutations and for RET/PTC and PAX8-PPARG rearrangements.

RESULTS

BRAF(V600E) mutation was detected in seven of 14 (50%) cPTC and two of 20 FVPTC (10%) (P=0.019). NRAS mutation was present in one case of FVPTC (5%). RET/PTC1 rearrangement was found, by RT-PCR, in one of 17 cases (5.9%) and by fluorescence in situ hybridization in two of six cases (33%). PAX8-PPARG rearrangement was not detected in any carcinoma. None of the follicular adenomas presented any of the aforementioned genetic alterations.

CONCLUSIONS

The prevalence of BRAF(V600E) mutation in our series is the highest reported in series of PTCs arising in radiation-exposed individuals. The prevalence of RET/PTC1 rearrangement fits with the values recently described in a similar setting.

Essential genes in thyroid cancers: focus on fascin

Although thyroid cancers are not among common malignancies, they rank as the first prevalent endocrine cancers in human. According to the results of published studies it has been shown the gradual progress from normal to the neoplastic cell in the process of tumor formation is the result of sequential genetic events. Among them we may point the mutations and rearrangements occurred in a group of proto-oncogenes, transcription factors and metastasis elements such as P53, RAS,RET,BRAF, PPARγ and Fascin. In the present article,we reviewed the most important essential genes in thyroid cancers, the role of epithelial mesenchymal transition and Fascin has been highlighted in this paper.

Amplification of thymosin beta 10 and AKAP13 genes in metastatic and aggressive papillary thyroid carcinomas

Papillary thyroid carcinoma (PTC) is the most common well-differentiated thyroid cancer. Although the great majority of the cases exhibit an indolent clinical course, some of them develop local invasion with distant metastasis, and a few cases transform into undifferentiated/anaplastic thyroid carcinoma with a rapidly lethal course. To identify gene copy number alterations predictive of metastatic potential or aggressive transformation, array-based comparative genomic hybridization (CGH-array) was performed in 43 PTC cases. Formalin-fixed and paraffin-embedded samples from primary tumours of 16 cases without metastasis, 14 cases with only regional lymph node metastasis, and 13 cases with distant metastasis, recurrence or extrathyroid extension were analysed. The CGH-array and confirmatory quantitative real-time PCR results identified the deletion of the EIF4EBP3 and TRAK2 gene loci, while amplification of thymosin beta 10 (TB10) and Tre-2 oncogene regions were observed as general markers for PTC. Although there have been several studies implicating TB10 as a specific marker based on gene expression data, our study is the first to report on genomic amplification. Although no significant difference could be detected between the good and bad prognosis cases in the A-kinase anchor protein 13 (AKAP13) gene region, it was discriminative markers for metastasis. Amplification in the AKAP13 region was demonstrated in 42.9% and 15.4% of the cases with local or with distant metastasis, respectively, while no amplification was detected in non-metastatic cases. AKAP13 and TB10 regions may represent potential new genomic markers for PTC and cancer progression.

Recent advances in molecular diagnosis of thyroid cancer

Recent molecular studies have described a number of abnormalities associated with the progression and dedifferentiation of thyroid carcinoma. These distinct molecular events are often associated with specific stages of tumor development. In particular, remarkable advances have occurred in several major biological areas of thyroid cancer, including the molecular alterations for the loss of radioiodine avidity of thyroid cancer, the pathogenic role of the MAP kinase and PI3K/Akt pathways and their related genetic alterations, and the aberrant methylation of functionally important genes in thyroid tumorigenesis and pathogenesis. Recognition of these features is crucial to the management of patients with thyroid cancer. Novel treatments are being designed based on our enhanced understanding of this disease process.

RAS mutation-positive follicular variant of papillary thyroid carcinoma arising in a struma ovarii

Struma ovarii is an ovarian mature teratoma composed exclusively or predominantly of thyroid tissue. Malignant transformation of struma ovarii is rare and poorly understood, although this process is thought to be similar to carcinogenesis in malignant tumors of differentiated thyroid tissue originating in the thyroid gland. Genetic alterations in the mitogen-activated protein kinase pathway, including mutations of BRAF, RAS, and RET genes, have been implicated in the development of differentiated thyroid carcinoma arising in the thyroid gland. We report here a case with RAS mutation detected in a malignant struma ovarii. The patient is a 38-year-old female who had a 2.4 cm ovarian cyst noted incidentally on a first trimester ultrasound. She proceeded to ovarian cystectomy post-delivery, with pathologic examination detecting a papillary thyroid carcinoma, follicular variant, arising in a cystic teratoma. The tumor was tested for BRAF, RAS, and RET/PTC mutations. HRAS codon 61 mutation was identified. This is the first report of RAS mutation detected in the follicular variant of papillary carcinoma arising in a struma ovarii. It provides evidence that tumors developing in this setting involve molecular mechanisms similar to those implicated in tumors developing in the thyroid gland.

Improved method for analysis of RNA present in long-term preserved thyroid cancer tissue of atomic bomb survivors

BACKGROUND

Since many thyroid cancer tissue samples from atomic bomb (A-bomb) survivors have been preserved for several decades as unbuffered formalin-fixed, paraffin-embedded specimens, molecular oncological analysis of such archival specimens is indispensable for clarifying the mechanisms of thyroid carcinogenesis in A-bomb survivors. Although RET gene rearrangements are the most important targets, it is a difficult task to examine all of the 13 known types of RET gene rearrangements with the use of the limited quantity of RNA that has been extracted from invaluable paraffin-embedded tissue specimens of A-bomb survivors. In this study, we established an improved 5' rapid amplification of cDNA ends (RACE) method using a small amount of RNA extracted from archival thyroid cancer tissue specimens.

METHODS

Three archival thyroid cancer tissue specimens from three different patients were used as in-house controls to determine the conditions for an improved switching mechanism at 5' end of RNA transcript (SMART) RACE method; one tissue specimen with RET/PTC1 rearrangement and one with RET/PTC3 rearrangement were used as positive samples. One other specimen, used as a negative sample, revealed no detectable expression of the RET gene tyrosine kinase domain.

RESULTS

We established a 5' RACE method using an amount of RNA as small as 10 ng extracted from long-term preserved, unbuffered formalin-fixed, paraffin-embedded thyroid cancer tissue by application of SMART technology. This improved SMART RACE method not only identified common RET gene rearrangements, but also isolated a clone containing a 93-bp insert of rare RTE/PTC8 in RNA extracted from formalin-fixed, paraffin-embedded thyroid cancer specimens from one A-bomb survivor who had been exposed to a high radiation dose. In addition, in the papillary thyroid cancer of another high-dose A-bomb survivor, this method detected one novel type of RET gene rearrangement whose partner gene is acyl coenzyme A binding domain 5, located on chromosome 10p.

CONCLUSION

We conclude that our improved SMART RACE method is expected to prove useful in molecular analyses using archival formalin-fixed, paraffin-embedded tissue samples of limited quantity.

Fatal outcome of a young woman with papillary thyroid carcinoma and graves' disease: possible implication of "cross-signalling" mechanism

A 29 yrs-old patient was referred to our hospital due to generalized convulsions. She had hyperthyroidism treated with methimazole. Her MRI showed 4 metastatic lesions in the brain. She had a goiter with a "cold" nodule and a palpable ipsilateral lymph node. The FNAB disclosed a papillary thyroid carcinoma. Under 5 mg of MMI treatment, she had a subclinical hyperthyroidism and TRAb were 47.8% (n.v. < 10%). The CT scan also showed lung metastasis. She underwent a total thyroidectomy with a modified neck dissection and she received an accumulated radioiodine dose of 700 mCi during the following two years. She died from the consequences of multiple metastatic lesions. Studies were performed in DNA extracted from paraffin-embedded tissue from the tumor, the metastatic lymph node and the non-tumoral thyroid. The genetic analysis of tumoral DNA revealed point mutations in two different genes: the wild type CAA at codon 61 of N-RAS mutated to CAT, replacing glycine by histidine (G61H) and the normal GCC sequence at codon 623 of the TSHR gene was replaced by TCC, changing the alanine by serine (A623S). In the non-tumoral tissue no mutations were found. In vitro studies showed a constitutive activation of the TSHR. It is very probable that this activating mutation of the TSHR is unable to reach the end point of the PKA cascade in the tumoral tissue. One possibility that could explain this is the presence of a cross-signaling mechanism generating a deviation of the TSH receptor cascade to the more proliferative one involving the MAPKinase, giving perhaps a more aggressive behavior of this papillary thyroid cancer.

RET/PTC rearrangements preferentially occurred in papillary thyroid cancer among atomic bomb survivors exposed to high radiation dose

A major early event in papillary thyroid carcinogenesis is constitutive activation of the mitogen-activated protein kinase signaling pathway caused by alterations of a single gene, typically rearrangements of the RET and NTRK1 genes or point mutations in the BRAF and RAS genes. In childhood papillary thyroid cancer, regardless of history of radiation exposure, RET/PTC rearrangements are a major event. Conversely, in adult-onset papillary thyroid cancer among the general population, the most common molecular event is BRAF(V600E) point mutation, not RET/PTC rearrangements. To clarify which gene alteration, chromosome aberration, or point mutation preferentially occurs in radiation-associated adult-onset papillary thyroid cancer, we have performed molecular analyses on RET/PTC rearrangements and BRAF(V600E) mutation in 71 papillary thyroid cancer cases among atomic bomb survivors (including 21 cases not exposed to atomic bomb radiation), in relation to radiation dose as well as time elapsed since atomic bomb radiation exposure. RET/PTC rearrangements showed significantly increased frequency with increased radiation dose (P(trend) = 0.002). In contrast, BRAF(V600E) mutation was less frequent in cases exposed to higher radiation dose (P(trend) < 0.001). Papillary thyroid cancer subjects harboring RET/PTC rearrangements developed this cancer earlier than did cases with BRAF(V600E) mutation (P = 0.03). These findings were confirmed by multivariate logistic regression analysis. These results suggest that RET/PTC rearrangements play an important role in radiation-associated thyroid carcinogenesis.

A molecular expression signature distinguishing follicular lesions in thyroid carcinoma using preamplification RT-PCR in archival samples

Follicular variant of papillary thyroid carcinoma is a lesion that frequently causes difficulties from a diagnostic perspective in the laboratory. The purpose of this study was to interrogate a cohort of archival thyroid lesions using gene expression analysis of a panel of markers proposed to have utility as adjunctive markers in the diagnosis of thyroid neoplasia and follicular variant of papillary thyroid carcinoma in particular. Laser Capture Microdissection was used to procure pure cell populations for extraction. In addition a novel, multiplex preamplification technique was used to facilitate analysis of multiple targets. The panel comprised: HLA-DMA, HLA-DBQ1, CD74, CSNK1G2, IRF3, KRAS2, LYN, MT1K, MT1X, RAB23, TGFB1 and TOP2A, with CDKN1B as an endogenous control. Expression profiles for each target were generated using TaqMan Real-Time PCR. HLA-DMA, HLA-DQB1, MT1X, CSNK1G2 and RAB23 were found to be differentially expressed (P<0.05) when comparing follicular adenoma and follicular variant of papillary thyroid carcinoma. Comparison of follicular adenoma and follicular thyroid carcinoma groups showed significant differential expression for MT1K, MT1X and RAB23 (P<0.05). Comparison of the papillary thyroid carcinoma group (classic and follicular variants) and the follicular adenoma group showed differential expression for CSNK1G2, HLA-DQB1, MT1X and RAB23 (P<0.05). Finally, KRAS2 was found to be differentially expressed (P<0.05) when comparing the papillary thyroid carcinoma and follicular thyroid carcinoma groups. This panel of molecular targets discriminates between follicular adenoma, papillary thyroid carcinoma, follicular variant of papillary thyroid carcinoma and follicular thyroid carcinoma by their expression repertoires. It may have utility for broader use in the setting of fine-needle aspiration cytology and could improve the definitive diagnosis of certain categories of thyroid malignancy.

[Iodothyronine deiodinases expression in thyroid neoplasias]

The iodothyronine deiodinases constitute a family of selenoenzymes that catalyze the removal of iodine from the outer ring or inner ring of the thyroid hormones. The activating enzymes, deiodinases type I (D1) and type II (D2), are highly expressed in normal thyroid gland. Benign or malignant neoplastic transformation of the thyroid cells is associated with changes on the expression of these enzymes, suggesting that D1 or D2 can be markers of cellular differentiation. Abnormalities on the expression of both enzymes and also of the deiodinase type III (D3), that inactivates thyroid hormones, have been found in other human neoplasias. So far, the mechanism or implications of these findings on tumor pathogenesis are not well understood. Nevertheless, its noteworthy that abnormal expression of D2 can cause thyrotoxicosis in patients with metastasis of follicular thyroid carcinoma and that increased D3 expression in large hemangiomas causes severe hypothyroidism.

Differential expression of miRNAs in papillary thyroid carcinoma compared to multinodular goiter using formalin fixed paraffin embedded tissues

microRNAs (miRNAs) are approximately 22 nt RNAs that negatively regulate target gene expression. Their dysregulation has been implicated in the pathogenesis of a number of human cancers, including papillary thyroid carcinoma (PTC). Whereas previous studies using microarray technologies have largely relied on the ability to procure fresh tissue at the time of surgery to characterize miRNA signatures in PTC, we exploited the ability to procure sufficient miRNA from formalin-fixed paraffin-embedded (FFPE) tissue to describe a series of miRNAs whose expression is dysregulated in PTC compared to benign proliferative multinodular goiter (MNG). We identified 13 miRNAs upregulated and 26 miRNAs downregulated in PTC versus MNG. These include miRNA-21, miRNA-31, miRNA-221, and miRNA-222. Their dysregulation was further validated by real time RT-PCR analysis in an independent set of FFPE tissues. Many of these have previously been described in fresh tissue studies as altered in PTC, confirming the utility of this approach. These results further highlight the applicability of miRNA expression patterns as potential markers of human cancer, and our results suggest that FFPE tissues are suitable resources for such miRNA expression analyses. The ability to utilize FFPE tissue in the molecular characterization of human malignancy will unlock a rich resource for future cancer studies.

Clinical significance of RET/PTC and p53 protein expression in sporadic papillary thyroid carcinoma

AIMS

Rearranged during Transfection (RET)/papillary thyroid carcinoma (PTC) and p53 are two genes involved in the pathogenesis of PTC. It has been suggested that RET/PTC expression is associated with higher rates of local extension and lymph node involvement, whereas p53 mutations are more frequent in poorly differentiated and anaplastic carcinomas. In addition, experimental studies have shown that p53 activity can modify the behaviour of PTC carrying RET/PTC. The aim of this study was to investigate the expression of both RET/PTC and p53 in order to evaluate their usefulness as prognostic factors.

METHODS AND RESULTS

Resected specimens of 61 cases of PTC were studied immunohistochemically using a polyclonal antibody to RET and a monoclonal antibody to p53 protein. RET/PTC expression was associated with extrathyroid extension of PTC, at diagnosis (P < 0.05). In contrast, no relationship between p53 immunoreactivity and clinical status was found. In addition, p53 expression was more prevalent among RET/PTC+ patients, and significantly influenced the relationship observed between RET/PTC and extrathyroid extension of the disease.

CONCLUSION

Our results suggest that immunohistochemistry for both PTC/RET and p53 could be useful in the clinical evaluation of patients with PTC.

Down-regulation of an inhibitor of cell growth, transmembrane protein 34 (TMEM34), in anaplastic thyroid cancer

PURPOSE

Ansaplastic thyroid cancer (ATC) is one of the most lethal malignancies, but the carcinogenic mechanism of ATC has not been clarified. Recently, we performed a cDNA microarray analysis and identified transmembrane protein 34 (TMEM34) that down-regulated in anaplastic thyroid cancer cell lines (ACL)s as compared to normal thyroid tissues.

METHODS

To investigate the role of TMEM34 in ATC carcinogenesis, we examined expression levels of TMEM34 in ACLs as well as differentiated thyroid cancers (DTC)s and normal human tissues. To explore the effect of TMEM34 in ATC development, cell-growth assays with KTA2 cells were performed.

RESULTS

Expression of TMEM34 was down-regulated in all 11 ACLs, as compared to either normal thyroid tissues or cell lines derived from papillary or follicular thyroid cancers. TMEM34 was expressed ubiquitously in normal human tissues tested. Transfection of TMEM34 into KTA2 cells led to inhibition of cell growth.

CONCLUSIONS

Our findings suggest that TMEM34 might be a tumor suppressor gene, associated with the development of ATC from DTC.

Assessing the utility of a mutational assay for B-RAF as an adjunct to conventional fine needle aspiration of the thyroid gland

Thyroid carcinoma is the most common endocrine malignancy; it is typified by a number of classical genomic insults, which tend to cluster with the discrete histologic subtypes. The most common of these is a mutation in B-RAF, which is present in approximately 44% (29% to 83%) of cases. In this review we have assessed the potential utility of a molecular test for somatically acquired mutations in B-RAF using thyroid malignancy as a model system according to 3 fundamental questions: would a test enhance our ability to distinguish benign from malignant, would a test unveil a risk factor not otherwise known, and would detecting a mutation enable a therapeutic option specific to those patients who carry the mutation?

Follicular carcinoma presenting as autonomous functioning thyroid nodule and containing an activating mutation of the TSH receptor (T620I) and a mutation of the Ki-RAS (G12C) genes

Most autonomous functioning thyroid nodules (AFTN) are benign thyroid follicular neoplasms. There are rare reports of malignant hot nodules, in which activating mutations of the TSH receptor (TSHR) were found. We report a case of follicular carcinoma presenting as an AFTN causing subclinical hyperthyroidism in a 64-year-old woman who had a 6-cm hot nodule in the left thyroid lobe. Genomic DNA was extracted from paraffin-embedded tissues from the tumor and extratumoral thyroid tissue. Sequence analyses revealed point mutations in two different genes: the normal ACC sequence at codon 620 of the TSHR gene was replaced by ATC, changing the threonine by isoleucine (T620I); and the wild-type GGT at codon 12 of Ki-RAS mutated to TGT, replacing glycine by cysteine (G12C). In transfection experiments the T620I mutant showed constitutive activity in terms of cyclic adenosine monophosphate (cAMP) production when permanently transfected in 3T3 cells. Here, we describe for the first time an activating mutation in 3codon 620 of the TSHR. In addition, the cancerous AFTN also contained a G12C Ki-RAS mutation. We hypothesize that the combination of these two mutations might have played an important role in both the hyperfunction of the tumor and the carcinogenetic process.

Evidence that one subset of anaplastic thyroid carcinomas are derived from papillary carcinomas due to BRAF and p53 mutations

BACKGROUND

Anaplastic thyroid carcinoma (ATC) is the most lethal form of thyroid neoplasia and represents the end stage of thyroid tumor progression. In the current study, genetic alterations in a panel of ATC were profiled to determine the origins of ATC.

METHODS

Eight ATC were analyzed for BRAF mutation at codon 599 by using mutant-allele-specific polymerase chain reaction (PCR) and DNA sequencing of the PCR-amplified exon 15. RAS mutation (HRAS, KRAS, and NRAS) at codons 12, 13, and 61 was analyzed by direct sequencing of PCR-amplified exons 1 and 2 of the RAS gene. RET/PTC rearrangements and p53 mutation were monitored by immunohistochemical (IHC) staining by anti-RET antibodies and an anti-p53 mAb, respectively.

RESULTS

BRAF was mutated in 5 of the 8 ATCs tested. Histologic examination revealed that 4 of these 5 BRAF-mutated ATCs contained a PTC component, suggesting that they may be derived from BRAF-mutated PTC. Of the 3 ATCs with wild-type BRAF, 2 had spindle cell features; one had follicular neoplastic characteristics mixed with papillary structures. Analysis of RAS mutation revealed only an HRAS mutation at codon 11, due to the transversion of GCC to TCC in one ATC with wild-type BRAF. This leads to the substitution of valine to serine. IHC analysis of RET/PTC rearrangements revealed no positive staining of RET in any of 8 ATCs, suggesting that these ATCs are not derived from RET/PTC- rearranged PTC. In contrast, IHC analysis of p53 mutation revealed that p53 was detected in the nuclei of 5 of 5 BRAF-mutated ATCs and 2 of 3 ATCs with wild-type BRAF. p53 staining was present only in anaplastic thyroid tumor cells but not in neighboring papillary thyroid tumor cells.

CONCLUSIONS

These results suggest that many ATCs with papillary components are derived from BRAF-mutated PTC, because of the addition of p53 mutation.

Familial nonmedullary thyroid cancer

Familial nonmedullary thyroid cancer (FNMTC) is a syndrome of familial clustering of thyroid cancers of follicular cell origin. It is characterized by multifocality, early onset, more recurrences, and a higher degree of aggressiveness than nonfamilial thyroid cancers of follicular cell origin. An autosomal dominant inheritance pattern with reduced penetrance appears likely in most pedigrees. Although several candidate genes responsible for isolated clinical variants of FNMTC have been identified in single families, the gene(s) responsible for the vast majority of FNMTC cases has yet to be identified. Members of FNMTC cohorts should be followed longitudinally with physical examination and ultrasonography, and aggressively treated when cancer is diagnosed. When cancer is diagnosed, total thyroidectomy should be performed, and most patients should have a prophylactic central neck dissection and a therapeutic lateral functional neck dissection, postoperative radioiodine ablation and thyroid-stimulating hormone (TSH) suppressive therapy. Close follow-up with stimulated thyroglobulin levels, neck ultrasounds, and radioiodine scans are also central to the management strategy.

Current Strategies for Surgical Management and Adjuvant Treatment of Childhood Papillary Thyroid Carcinoma

Childhood papillary thyroid carcinoma is associated with more locally aggressive and more frequent distant disease than its adult counterpart. Recurrence rates tend to be higher in children, but cause-specific mortality remains low. Optimal initial treatment of childhood papillary thyroid carcinoma should include total or near-total thyroidectomy and central compartment node clearance. Modified neck dissections should be performed for biopsy-proven lateral neck disease. Every effort should be made to maintain parathyroid and laryngeal nerve function. Radical neck dissections are to be avoided. Radioiodine remnant ablation (RRA), appropriate thyroid hormone suppressive therapy (THST), and judicious use of therapeutic doses of (131)I are applied to achieve a disease-free status, which is most often confirmed by negative neck ultrasonography, negative whole-body scan (either withdrawal or recombinant human thyroid-stimulating hormone-stimulated), and extremely low levels of serum thyroglobulin. Appropriate utilization of (131)I, THST, repeat surgery, external beam radiotherapy, and rarely chemotherapy may provide long-term palliation and some cures in patients with recurrent/persistent disease. Follow-up should be lifelong, and the care of children after age 17 should subsequently be transferred to adult-care endocrinologists with expertise in managing thyroid neoplasia. Optimal surgical management can be achieved if adequate operations are routinely carried out by "high-volume" thyroid surgeons with expertise in the care of children. Nowhere is a multidisciplinary approach (endocrinologists, surgeons, nuclear medicine physicians, pediatricians, pathologists, oncologists) more critical than in the long-term management of papillary thyroid carcinoma that presents during childhood.

Selective occurrence of ras mutations in benign and malignant thyroid follicular neoplasms in Taiwan

Previous studies have demonstrated that point mutations in all three ras genes (H-ras, K-ras, and N-ras) may occur in thyroid neoplasia. However, the overall incidence of ras mutations in thyroid tumors and their frequency in specific histologic types varies widely in different series. Many earlier studies have chosen allele-specific oligonucleotide hybridization approaches to examine ras mutations without further confirmation of the positive samples by DNA sequencing. In this study, mutational hot spots in exon 1 (codons 12/13) and exon 2 (codon 61) of the H-ras, K-ras, and N-ras were polymerase chain reaction (PCR) amplified and sequenced with an automatic sequencer. ras mutations were detected in 4 of 89 (4.5%) benign and malignant thyroid tumors. Three of 8 follicular carcinomas exhibited mutations in codon 61 of H-ras, K-ras, and N-ras, respectively, and mutation at codon 61 of N-ras was found in 1 of 12 follicular adenomas. No mutations were observed in the other tumors, which included 20 nodular goiters, 5 Hürthle cell adenomas, 42 papillary carcinomas, and 2 undifferentiated carcinomas. Our results, obtained by the direct sequencing technique, indicate a lower overall prevalence of ras oncogenes in thyroid tumors than reports in earlier series. However, the frequency of ras mutations in specific histotype of thyroid tumors and their exclusive involvement of codon 61 in our series are similar to those studies utilizing DNA sequencing to detect or to confirm ras gene alterations. The selective occurrence of ras mutations in benign and malignant follicular neoplasms indicates that ras gene alterations have a specific and early role in the development of follicular type of thyroid tumors in Taiwan.

Galectin-3: presurgical marker of thyroid follicular epithelial cell-derived carcinomas

Preoperative follicular lesion characterisation represents an unsolved diagnostic problem in thyroid nodular disease. Although fine-needle aspiration biopsy is the most reliable preoperative diagnostic procedure, it shows inherent limitations in differentiating adenoma from follicular carcinoma and, sometimes, follicular variants of papillary carcinoma. Galectin-3 cytoplasmic neoexpression has been proposed as a peculiar feature of thyroid malignant cells, easily detectable in cytological and histological samples. The aim of this study was to re-evaluate the galectin-3 expression in a large sample of thyroid lesions using an immunohistocytochemical biotin-free detection system and a specific anti-human-galectin-3 monoclonal antibody in order to avoid the interference of technical factors, a cause of conflicting results recently reported by some authors. We analysed galectin-3 expression of 39 follicular carcinomas, 26 papillary carcinomas, and 105 adenomas in both cell-block samples and their histological counterparts. All cell-block and histological papillary carcinoma samples showed high levels of galectin-3 immunoreactivity. Thirty-four follicular carcinomas were positive, whereas 5 were negative in cell-blocks but positive in their histological counterparts. Twelve out of 105 adenomas expressed galectin-3 in cell-blocks and histological samples. The diagnostic accuracy of preoperative galectin-3 evaluation in adenomas vs follicular carcinomas was 90.0%. Galectin-3 expression was also investigated in 22 minimally-invasive follicular carcinomas. All of them showed galectin-3 immunoreactivity in both cytological and histological specimens with the exception of two cases, where galectin-3 positivity was observed only in the surgical material. The routine correct use of galectin-3, by increasing the diagnostic accuracy of conventional cytology, improves the management of thyroid nodules and can lead to a sensitive reduction of useless thyroid surgeries.

Early occurrence of RASSF1A hypermethylation and its mutual exclusion with BRAF mutation in thyroid tumorigenesis

Follicular epithelial cell-derived thyroid tumors are common neoplasms comprised mainly of benign thyroid adenomas, follicular thyroid cancers, and papillary thyroid cancers (PTCs). Hypermethylation of the tumor suppressor gene RASSF1A and activating mutation of BRAF gene have been reported recently in thyroid cancers. To additionally investigate the roles of these two epigenetic/genetic alterations in thyroid tumor progression, we examined their occurrences and relationship in both benign and malignant thyroid neoplasms. With real-time quantitative methylation-specific PCR, we found that 4 of 9 (44%) benign adenomas, 9 of 12 (75%) follicular thyroid cancers tumors, and 6 of 30 (20%) of PTC tumors harbored promoter methylation in > or = 25% of RASSF1A alleles. Additional quantitative analysis revealed RASSF1A methylation only in BRAF mutation-negative PTCs. A similar inverse correlation of RASSF1A methylation with BRAF mutation was seen in thyroid tumor cell lines. Our results, therefore, suggest that epigenetic inactivation of RASSF1A through aberrant methylation is an early step in thyroid tumorigenesis. Like the previously reported mutually exclusive relationship between BRAF mutation and other Ras pathway components such as RET/PTC rearrangement, a mutually exclusive relationship also exists between BRAF mutation and RASSF1A methylation in thyroid tumorigenesis.

Chromosomal imbalances associated with anaplastic transformation of follicular thyroid carcinomas

The genetic alterations that underlie the progression of follicular thyroid carcinoma towards anaplasia are still largely uncharacterised. We compared the Comparative Genomic Hybridization (CGH) profiles of 20 follicular (FTCs), 12 poorly differentiated (PDTCs) and seven anaplastic thyroid carcinomas (ATCs), in order to identify the chromosomal imbalances potentially associated with cancer progression. We found: (i) when considering that a ‘direct’ transformation of FTC towards anaplasia occurs, the defined significantly important alterations were the increase of gains at 3q (P<0.05) and 20q (P<0.01), and the increase of losses at 7q (P<0.05) and Xp (P<0.01); (ii) regarding poorly differentiated carcinomas as an intermediate independent entity in the anaplastic transformation of follicular cancers, evidenced as important alterations towards anaplasia, were the proportional decrease in copy sequences at 7p, 7q, 12q and 13q resulting from the significant decrease of DNA gains at 7p and 12q (P<0.05), and the significant increase of losses at 7q and 13q (P<0.05). These results unveil the chromosomal regions where genes of interest in thyroid anaplastic transformation are to be located, and demonstrate that different gene dosage copy sequence imbalances are associated to the ‘direct’ pathway of transformation of follicular into anaplastic cancers and to the progressive FTC → PDTC → ATC pathway.

Genes differentially expressed in thyroid carcinoma identified by comparison of SAGE expression profiles

To identify transcripts that distinguish malignant from benign thyroid disease serial analysis of gene expression (SAGE) profiles of papillary thyroid carcinoma and of normal thyroid are compared. Of the 21,000 tags analyzed, 204 tags are differentially expressed with statistical significance in the tumor. Thyroid tumor specificity of these transcripts is determined in silico using the tissue preferential expression (TPE) algorithm. TPE values demonstrate that 42 tags of the 204 are thyroid tumor specific. BC013035, a cDNA encoding a novel protein, is up-regulated from 0 to 24 tags in the thyroid tumor SAGE library. In a tissue panel of 30 thyroid tumors and 12 controls, it has an expression pattern similar to thyroid peroxidase, indicating possible involvement of BC013035 in thyroid differentiation. A tag coding for extracellular matrix protein 1 (ECM1) is absent in the normal thyroid SAGE library and present 55 times in the tumor. ECM1, a protein recently associated with angiogenesis and expressed in metastatic breast carcinoma, is up-regulated in 50% of all thyroid carcinoma and absent in normal controls and follicular adenoma. In conclusion, SAGE analysis and subsequent determination of TPE values facilitates the rapid distinction of genes specifically expressed in cancer tissues.

TSH-activated signaling pathways in thyroid tumorigenesis

Thyrotropin (TSH) is considered the main regulator of thyrocyte differentiation and proliferation. Thus, the characterization of the different signaling pathways triggered by TSH on these cells is of major interest in order to understand the mechanisms implicated in thyroid pathology. In this review we focus on the different signaling pathways involved in TSH-mediated proliferation and their role in thyroid transformation and tumorigenesis. TSH mitogenic activities are mediated largely by cAMP, which in turn may activate protein kinase (PKA)-dependent and independent processes. We analyze the effects of increased cAMP levels and PKA activity during cell cycle progression and the role of this signaling pathway in thyroid tumor initiation. Alternative pathways to PKA in the cAMP-mediated proliferation appear to involve the small GTPases Rap1 and Ras. We analyze the Ras effectors (PI3K, RalGDS and Raf) that are thought to mediate its oncogenic activity, as well as the ability of Ras to induce apoptosis in thyrocytes. Finally, we discuss the activation of the PLC/PKC cascade by TSH in thyroid cells and the role of this signaling pathway in the TSH-mediated proliferation and tumorigenesis.

Molecular pathogenesis of thyroid cancer

A number of molecular abnormalities have been described in association with the progression from normal thyroid tissue to benign adenomas to well-differentiated and finally anaplastic epithelial thyroid cancer. These include upregulation of proliferative factors, such as growth hormones and oncogenes, downregulation of apoptotic and cell-cycle inhibitory factors, such as tumor suppressors, disruption of normal cell-to-cell interactions, and cellular immortalization. The progression model for thyroid carcinoma has not been proven, but evidence suggests that an evolutionary molecular process is involved, especially in the development of follicular thyroid cancers for which there are distinct intermediate phenotypes. We present a comprehensive evaluation of factors involved in thyroid tumorigenesis and attempt to describe preliminary attributes of a progression model. The organization of this model should also provide a template for the incorporation of new information as it is derived from large-scale genomic studies.

Increased expression of genes encoding mitochondrial proteins in papillary thyroid carcinomas

To investigate differences in gene expression between normal thyroid tissue and papillary thyroid carcinomas, we performed differential display (DD) polymerase chain reaction (PCR) using total RNA from fresh-frozen surgically removed thyroid specimens. Four DD fragments that were overexpressed in tumor tissue were identified as parts of genes from the mitochondrial genome: nicotinamide adenine dinucleotide (NADH) dehydrogenase 5, adenosine triphosphate (ATP) synthase 6, cytochrome b, and cytochrome c oxidase I. The expression profiles of these genes were confirmed by hybridization using a DNA dot-blot array and radioactively labeled complex cDNA probes generated from tumor (30 biopsies) and nontumor (15 biopsies) total RNA. Cytochrome c oxidase III was also found to be overexpressed in papillary carcinomas, while the nuclear-encoded mitochondrial transcription factor A showed similar mRNA expression levels in tumor and nontumor tissue. Electron microscopy showed increased number and size of mitochondria in papillary carcinomas. Immunohistochemistry using a monoclonal antibody recognizing a nuclear-encoded mitochondrial protein showed positivity in all cases of papillary carcinoma (44 samples), while normal thyroid tissue (34 samples) was negative in all cases except 3, in which there was a weak, focal cytoplasmic staining. We conclude that papillary thyroid carcinomas show increased expression of mitochondrial mRNA and proteins, encoded by nuclear as well as mitochondrial genes.

Specific pattern of RAS oncogene mutations in follicular thyroid tumors

The prevalence of H-RAS, K-RAS, and N-RAS gene mutations in thyroid tumors according to malignancy and histology is controversial. Differences in methodology and histological classifications may explain discrepant results. To address this issue, we first performed a pooled analysis of 269 mutations garnered from 39 previous studies. Mutations proved significantly less frequent when detected with direct sequencing than without (12.3% vs. 17%). The rate of mutation involving N-RAS exon 1 (N1) and K-RAS exon 2 (K2) was less than 1%. Mutations of codon 61 of N-RAS (N2) were significantly more frequent in follicular tumors (19%) than in papillary cancers (5%) and significantly more frequent in malignant (25%) than in benign (14%) tumors. H-RAS mutations in codons 12/13 (H1) were found in 2-3% of all types of tumors, but H-RAS mutations in codon 61 (H2) were observed in only 1.4% of tumors, and almost all of them were malignant. K-RAS mutations in exon 1 were found more often in papillary than follicular cancers (2.7% vs. 1.6%) and were sometimes correlated with special epidemiological circumstances. The second part of this study involved analysis of 80 follicular tumors from patients living in Marseille (France) and Kiev (Ukraine). We used direct sequencing after PCR amplification of exons 1 and 2 of the three RAS genes. Common and atypical adenomas were separated using strict cytological criteria. Mutations of H1-RAS were found in 12.5% of common adenomas and one follicular carcinoma (2.9%). Mutations of N2-RAS occurred in 23.3% and 17.6% of atypical adenomas and follicular carcinomas, respectively. These results confirm the predominance of N2-RAS mutations in thyroid follicular tumors and their correlation with malignancy. They support the implication of N2-RAS mutations in the malignant progression of thyroid follicular tumors and the assumption that some atypical adenomas are precursors of follicular carcinomas.

Accumulation of Fra-1 in ras-transformed cells depends on both transcriptional autoregulation and MEK-dependent posttranslational stabilization

The AP-1 transcription factor plays an essential role in cell proliferation and tumorigenesis. It was previously shown that the fra-1 gene product is upregulated by various oncogenes and is involved in the in vitro and in vivo transformation of thyroid cells. Here we show that the ras oncogene-dependent accumulation of Fra-1 is mediated by a positive feedback mechanism which requires both transcriptional autoregulation and posttranslational stabilization of the protein. The oncogene-dependent transcriptional activation involves the cooperation between both Raf-dependent and Raf-independent pathways and is mediated by an AP-1 site within the fra-1 first intron, which becomes stably occupied by a transcriptionally active Fra-1-containing complex in ras-transformed cells. The posttranslational stabilization results in a drastic increase in the Fra-1 half-life in ras-transformed cells and is totally dependent on the activity of the MEK/ERK phosphorylation pathway. The analysis of the Fra-1 transactivation potential shows that the protein is able to stimulate a heterologous promoter in a ras-dependent manner, but the transactivating activity requires the recruitment of a heterodimeric partner. These data show that the alteration of multiple regulatory mechanisms is required for the constitutive activation of Fra-1 as a nuclear target of ras transformation.

Loss of heterozygosity in follicular and papillary thyroid carcinomas

In this study we aimed at investigating the incidence and the role of 3p deletions, particularly at the 3p25 approximately pter region, in follicle cell-derived thyroid neoplasms, by using loss of heterozygosity (LOH) analysis. We analyzed 12 follicular adenomas (FA), 13 follicular thyroid carcinomas (FTC), and 15 papillary thyroid carcinomas (PTC) with 11 microsatellite markers for chromosome 3. One additional marker on 3q25.2 was also investigated for assessment of deletion extent on 3q. Microsatellite instability was detected at one locus in 1 of 15 PTC (7%) and at four loci in 1 of 13 FTC (8%). Loss of heterozygosity was found in 8 of 12 cases of FTC (67%), in 6 of 15 cases of PTC (40%), and in 2 of 12 FA (17%). We identified three minimal common deleted regions (CDR) involving significant sites of LOH: two in FTC (a new terminal region, of approximately 8 cM distal to D3S1620 at 3p25.3 approximately pter and the D3S1573-D3S1595 region at 3p21.2 approximately p12) and one in PTC (D3S1304-D3S1263 region at 3p25.3 approximately p24.2). The newly identified 3p25.3 approximately pter CDR seems to be specific for FTC. Our results suggest the existence of at least three distinct regions on 3p that might harbor tumor suppressor genes involved in the carcinogenesis processes of FTC and PTC.

Spindle epithelial tumor with thymus-like differentiation of the thyroid: a case report with pathological and molecular genetics study

We report an unusual case of spindle epithelial tumor with thymus-like differentiation (SETTLE) of the thyroid present in a 6-year-old boy. The tumor, located at both the left lobe and isthmus, was a circumscribed mass with slightly gritty whorled appearance. Microscopically, the lobulated, highly cellular, spindle cell neoplasm was arranged in intersecting bundles and fascicles separated by fibrous bands. Benign-appearing glands entrapped within fibrous bands and foci of squamous differentiation within spindle cells were observed. Immunohistochemically, the spindle cells were diffusely positive for cytokeratins, vimentin, and alpha-smooth muscle actin and patchily reactive for muscle-specific actin and epithelial membrane antigen, exhibiting myoepithelial differentiation. The spindle cells were also patchily immunopositive for p53 protein. Molecular genetic analysis revealed Ki-ras gene mutations at codons 13 (GGC(gly) to AGC(ser)) and 15 (GGC(gly) to AGC(ser)) on the same allele. Mutation of the p53 gene was not detected. This is the first report on Ki-ras oncogene mutations in a case of SETTLE.

Association of RET codon 691 polymorphism in radiation-induced human thyroid tumours with C-cell hyperplasia in peritumoural tissue

The RET proto-oncogene encodes a protein structurally related to transmembrane receptors with an intracellular tyrosine kinase domain. In human thyroid gland, the RET proto-oncogene is normally expressed in parafollicular C-cells. Thyroid C-cell hyperplasia is associated with inherited medullary thyroid carcinomas and is considered as a pre-neoplastic stage of C-cells disease. It has also been observed in thyroid tissues adjacent to follicular and papillary carcinomas. In order to study the relationship between a misfunctioning of the RET proto-oncogene and the presence of C-cell hyperplasia, we compared a series of thyroid glands presenting sporadic or radiation-associated tumours, as well as samples of unrelated normal thyroid tissues, for alteration in exons 10 and 11 of the gene and for the presence or absence of C-cell hyperplasia. Here we report a significantly higher frequency of C-cell hyperplasia present in peritumoural thyroid tissues of radiation-induced epithelial thyroid tumours, than in peritumoural of sporadic thyroid tumours or in control normal thyroid tissues (P=0.001). A G691S RET polymorphism was present with a higher frequency in radiation-induced epithelial thyroid tumours (55%) than in sporadic tumours (20%) and in control normal thyroid tissues (15%). Interestingly, this polymorphism was associated in the majority (88%) of radiation-induced tumours with a C-cell hyperplasia in the peritumoural tissues. Several explanations for this association are discussed.

Novel germline RET mutation segregating with papillary thyroid carcinomas

The RET proto-oncogene is responsible for inherited medullary thyroid cancer syndromes. RET is also found mutated in sporadic medullary thyroid cancer (MTC) and rearranged in sporadic papillary thyroid carcinomas. Here, we describe a previously unreported germline RET mutation at codon 603 in exon 10 associated with both MTC and nonmedullary thyroid cancer (NMTC) in a kindred. RET may thus not be excluded as a potential candidate for predisposition to some forms of NMTC.

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.

Differentiated thyroid carcinoma: a polygenic disease

Differentiated thyroid cancer is a rare disease and until recently was considered to be sporadic. However, increasing evidence has been found for a genetic basis of this disease. In approximately 5% of patients the differentiated thyroid cancer is dominantly inherited. Several families with different syndromes, of which differentiated thyroid cancer is a feature, have already been described. However, until now, single genes explain only a minority of cases. We hypothesize that differentiated thyroid cancer is a polygenic disease. Data from epidemiologic studies, about occult and multifocal carcinomas and the different response to specific risk factors contribute to this hypothesis.

Karyotypic characterization of papillary thyroid carcinomas

BACKGROUND

Cytogenetic studies performed in papillary thyroid carcinoma (PTC) identified chromosome 10q rearrangements with breakpoints at 10q11.2 as the most frequent aberrations in these tumors. In the current study, the authors aimed to identify other chromosomal abnormalities nonrandomly associated with papillary thyroid carcinomas.

METHODS

Cytogenetic analysis was performed on 94 papillary thyroid carcinomas after short-term culture of the tumors sterile fragments.

RESULTS

Clonal chromosomal changes were found in 37 tumors (40%). Structural cytogenetic abnormalities were observed in 18 carcinomas. Chromosomes 1, 3, 7, and 10 were the most frequently involved in rearrangements. Pooled results of the breakpoints detected in these tumors, as well as those described in the literature, allowed the authors to verify as the most common breakpoint loci 1p32-36, 1p11-13, 1q, 3p25-26, 7q34-36, and 10q11.2. The correlation between the karyotype features of the 94 PTCs and the histologic data revealed that some PTC follicular variants were characterized by chromosomal aberrations commonly found in thyroid follicular adenomas: a del(11)(q13q13), a t(2;3)(q13;p35), and gains of chromosomes 3, 5, 7, 9, 12, 14, 17, and 20. In the tall cell PTC variant group, 4 of the 7 tumors presented clonal cytogenetic changes, 3 (75%) of which were characterized by anomalies of chromosome 2 that lead to a overrepresentation of the long arm of this chromosome. Noted also in these series was an association between complex karyotypes and tumors with poorly differentiated histiotypes.

CONCLUSIONS

In this study, the authors report chromosome 1p32-36, 1p11-13, 3p25-26, and 7q32-36 as novel breakpoint cluster regions in PTC, and they suggest that there are cytogenetic changes preferentially associated with the follicular and tall cell PTC variants.

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.

Hyperfunctioning malignant thyroid nodule in an 11-year-old girl: pathologic and molecular studies

We identified a papillary carcinoma in an 11-year-old girl with a hyperfunctioning thyroid nodule. A met453thr mutation in TSHR was found in the nodule but not in normal thyroid tissue or in leukocytes. This case documents that this activating mutation is associated with neoplasia.

No evidence of thyrotropin receptor and G(s alpha) gene mutation in high iodine uptake thyroid carcinoma

Usually, thyroid carcinoma presents as a cold nodule on radioiodine scintigraphy. High-uptake nodules on iodine thyroid scans are associated with an exceedingly low incidence of malignancy. Only 29 cases of carcinomas appearing as hot or warm nodules have as yet been reported. From 1993 to 1999, we have observed eight similar cases (4 hot and 4 warm thyroid nodules) suggesting that thyroid carcinomas may not be as rare as usually considered in these circumstances. Four tumors were available for molecular analysis on paraffin-embedded sections. Because no mutations were found in the whole coding portions of thyrotropin-receptor (TSH-R) gene and fragments encompassing the mutational hot spots of the G(s alpha) gene, it is unlikely that activating mutations of the TSH-R or G(s alpha) genes were involved in these carcinomas.

Loss of p53 promotes anaplasia and local invasion in ret/PTC1-induced thyroid carcinomas

Papillary thyroid carcinomas in humans are associated with the ret/PTC oncogene and, following loss of p53 function, may progress to anaplastic carcinomas. Mice with thyroid-targeted expression of ret/PTC1 developed papillary thyroid carcinomas that were minimally invasive and did not metastasize. These mice were crossed with p53-/- mice to investigate whether loss of p53 would promote anaplasia and metastasis of ret/PTC1-induced thyroid tumors. The majority of p53-/- mice died or were euthanized by 17 weeks of age due to the development of thymic lymphomas, soft tissue sarcomas, and testicular teratomas. All ret/PTC1 mice developed thyroid carcinomas, but tumors in p53-/- mice were more anaplastic, larger in diameter, more invasive, and had a higher mitotic index than tumors in p53+/+ and p53+/- mice. Thyroid tumors did not metastasize in any of the experimental p53+/+ and p53+/- mice </=28 weeks of age or p53-/- mice </= 17 weeks of age; however, an older (170-day-old) male p53-/- mouse used to maintain the colony developed anaplastic thyroid carcinoma with liver metastases. These findings demonstrate that the lack of functional p53 in ret/PTC1 mice promotes anaplasia and invasiveness of thyroid carcinomas.

Molecular basis of epithelial thyroid tumorigenesis

The results of experiments carried out in different laboratories (including ours) during the last 10 years have enabled us to propose the hypothesis that there are different initiators able to start the epithelial thyroid tumorigenic process via different pathways:--gsp and TSHR genes: at the origin of hyperfunctioning tumors (toxic nodules and adenomas);--ras and probably gsp genes (in a minority of samples): via a vesicular adenoma progressing eventually to a vesicular carcinoma. This could be also the case for ret but only in radiation-associated tumours;--ras, ret, trk and probably gsp and met: starting from small papillary lesions ('spontaneous' or radiation-induced) and progressing to a clinically evident papillary carcinoma;--the p53 gene playing a role only in the final dedifferentiation process. Simultaneous alteration in the same sample of combinations of ras, gsp, ret, trk and TSHR was found in only a minority of the approximately 150 tumours studied. These data suggest an interchangeable role for these genes in the initiation of 'spontaneous' or radiation-associated epithelial thyroid tumorigenesis. The requirement of one of the genes cited above to interact with other genes must not be neglected. Ras is the most frequently altered gene in 'spontaneous' thyroid tumours and ret in radiation-associated thyroid tumours.

Multiple ras downstream pathways mediate functional repression of the homeobox gene product TTF-1

Expression of oncogenic Ras in thyroid cells results in loss of expression of several thyroid-specific genes and inactivation of TTF-1, a homeodomain-containing transcription factor required for normal development of the thyroid gland. In an effort to understand how signal transduction pathways downstream of Ras may be involved in suppression of the differentiated phenotype, we have tested mutants of the Ras effector region for their ability to affect TTF-1 transcriptional activity in a transient-transfection assay. We find that V12S35 Ras, a mutant known to interact specifically with Raf but not with RalGDS or phosphatidylinositol 3-kinase (PI3 kinase) inhibits TTF-1 activity. Expression of an activated form of Raf (Raf-BXB) also inhibits TTF-1 function to a similar extent, while the MEK inhibitors U0126 and PD98059 partially relieve Ras-mediated inactivation of TTF-1, suggesting that the extracellular signal-regulated kinase (ERK) pathway is involved in this process. Indeed, ERK directly phosphorylates TTF-1 at three serine residues, and concomitant mutation of these serines to alanines completely abolishes ERK-mediated phosphorylation both in vitro and in vivo. Since activation of the Raf/MEK/ERK pathway accounts for only part of the activity elicited by oncogenic Ras on TTF-1, other downstream pathways are likely to be involved in this process. We find that activation of PI3 kinase, Rho, Rac, and RalGDS has no effect on TTF-1 transcriptional activity. However, a poorly characterized Ras mutant, V12N38 Ras, can partially repress TTF-1 transcriptional activity through an ERK-independent pathway. Importantly, concomitant expression of constitutive activated Raf and V12N38 Ras results in almost complete loss of TTF-1 activity. Our data indicate that the Raf/MEK/ERK cascade may act in concert with an as-yet-uncharacterized signaling pathway activated by V12N38 Ras to repress TTF-1 function and ultimately to inhibit thyroid cell differentiation.