Prevalences of Gs alpha, ras, p53 mutations and ret/PTC rearrangement in differentiated thyroid tumours in a Korean population

Ubiquitin-modifying enzymes in thyroid cancer：Mechanisms and functions

Thyroid cancer is the most common malignant tumor of the endocrine system, and evidence suggests that post-translational modifications (PTMs) and epigenetic alterations play an important role in its development. Recently, there has been increasing evidence linking dysregulation of ubiquitinating enzymes and deubiquitinases with thyroid cancer. This review aims to summarize our current understanding of the role of ubiquitination-modifying enzymes in thyroid cancer, including their regulation of oncogenic pathways and oncogenic proteins. The role of ubiquitination-modifying enzymes in thyroid cancer development and progression requires further study, which will provide new insights into thyroid cancer prevention, treatment and the development of novel agents.

Looking at Thyroid Cancer from the Tumor-Suppressor Genes Point of View

Thyroid cancer is the most frequent endocrine malignancy and accounts for approximately 1% of all diagnosed cancers. A variety of mechanisms are involved in the transformation of a normal tissue into a malignant one. Loss of tumor-suppressor gene (TSG) function is one of these mechanisms. The normal functions of TSGs include cell proliferation and differentiation control, genomic integrity maintenance, DNA damage repair, and signaling pathway regulation. TSGs are generally classified into three subclasses: (i) gatekeepers that encode proteins involved in cell cycle and apoptosis control; (ii) caretakers that produce proteins implicated in the genomic stability maintenance; and (iii) landscapers that, when mutated, create a suitable environment for malignant cell growth. Several possible mechanisms have been implicated in TSG inactivation. Reviewing the various TSG alteration types detected in thyroid cancers may help researchers to better understand the TSG defects implicated in the development/progression of this cancer type and to find potential targets for prognostic, predictive, diagnostic, and therapeutic purposes. Hence, the main purposes of this review article are to describe the various TSG inactivation mechanisms and alterations in human thyroid cancer, and the current therapeutic options for targeting TSGs in thyroid cancer.

Clinical utility of the imunohistochemical co-expression of p53 and MDM2 in thyroid follicular lesions

In order to investigate the possible correlation between p53 and MDM2 co-expression with clinicopathological features of differentiated thyroid cancer (DTC) and its use as diagnostic and/or prognostic markers, we used immunohistochemistry to evaluate 317 thyroid samples including 208 DTC and 94 benign nodules, in addition to 15 normal tissues. MDM2 and p53 expression were highly associated (r = 0.7161; p < 0.0001). The co-expression of p53-MDM2 was observed more frequently in malignant lesions (p < 0.0001) and helped characterize follicular patterned lesions distinguishing FVPTC from FA (p < 0.0001) and FVPTC from FTC (p < 0.0001). In addition, p53-MDM2 co-expression was associated with characteristics of less aggressiveness. It was more frequent in patients ≤45 years old (p = 0.0035), with unique tumors (p = 0.0095), tumors <2 cm (p < 0.0001), tumors without extrathyroid invasion (p = 0.0425), without metastasis at evolution (p = 0.0179), and in patients evolving free of disease after treatment (p = 0.0485). We suggest that p53-MDM2 co-expression profile analysis might help establishing diagnostic and determining prognostic of DTC patients.

Diagnostic Limitation of Fine-Needle Aspiration (FNA) on Indeterminate Thyroid Nodules Can Be Partially Overcome by Preoperative Molecular Analysis: Assessment of RET/PTC1 Rearrangement in BRAF and RAS Wild-Type Routine Air-Dried FNA Specimens

Molecular markers are helpful diagnostic tools, particularly for cytologically indeterminate thyroid nodules. Preoperative RET/PTC1 rearrangement analysis in BRAF and RAS wild-type indeterminate thyroid nodules would permit the formulation of an unambiguous surgical plan. Cycle threshold values according to the cell count for detection of the RET/PTC1 rearrangement by real-time reverse transcription-polymerase chain reaction (RT-PCR) using fresh and routine air-dried TPC1 cells were evaluated. The correlation of RET/PTC1 rearrangement between fine-needle aspiration (FNA) and paired formalin-fixed paraffin-embedded (FFPE) specimens was analyzed. RET/PTC1 rearrangements of 76 resected BRAF and RAS wild-type classical PTCs were also analyzed. Results of RT-PCR and the Nanostring were compared. When 100 fresh and air-dried TPC1 cells were used, expression of RET/PTC1 rearrangement was detectable after 35 and 33 PCR cycles, respectively. The results of RET/PTC1 rearrangement in 10 FNA and paired FFPE papillary thyroid carcinoma (PTC) specimens showed complete correlation. Twenty-nine (38.2%) of 76 BRAF and RAS wild-type classical PTCs had RET/PTC1 rearrangement. Comparison of RET/PTC1 rearrangement analysis between RT-PCR and the Nanostring showed moderate agreement with a κ value of 0.56 (p = 0.002). The RET/PTC1 rearrangement analysis by RT-PCR using routine air-dried FNA specimen was confirmed to be technically applicable. A significant proportion (38.2%) of the BRAF and RAS wild-type PTCs harbored RET/PTC1 rearrangements.

ENDOCRINE TUMOURS: Genetic predictors of thyroid cancer outcome

Genetic predictors of outcome are reviewed in the context of a disease--cancer--that can be (too) simplistically described as a 'successful, invasive clone of our own tissues'. Context has many faces that determine a thyroid cancer patient's outcome beyond the influence of genetic markers. There is also plenty of evidence on the prognostic meaning of the interplay between genetics and context/microenvironment factors (encapsulation, degree of invasion, staging, etc.). This review addresses only genetic alterations detected by molecular methods in surgically resected specimens, thus ruling out immunohistochemistry and (F)ISH, despite their crucial relevance as topographically oriented methods. For the sake of the discussion, well-differentiated carcinomas were divided into two main morphologic types: papillary carcinoma (classic and most variants) displaying BRAFV600E mutations and RET/papillary thyroid carcinoma rearrangements and the group of follicular patterned carcinomas that encompasses follicular carcinoma and the encapsulated form of follicular variant of papillary carcinoma, displaying RAS mutations and PAX8/PPARγ rearrangement. TERT promoter mutations have been recently described (and associated with distant metastases and reduced survival) in papillary and follicular carcinomas, as well as in poorly differentiated and undifferentiated carcinoma. TP53 mutations, previously thought to be restricted to less differentiated carcinomas, were also detected in papillary and follicular carcinoma and found to carry a guarded prognosis. Besides their putative importance for targeted therapies, the prognostic meaning of such mutations is discussed per se and in the setting of concurrent BRAF mutation.

Associations of the BRAF (V600E) mutation and p53 protein expression with clinicopathological features of papillary thyroid carcinomas patients

The BRAF (V600E) mutation is the most prevalent type of genetic alteration that has been identified in papillary thyroid carcinoma (PTC); in addition, previous immunohistochemical studies have revealed the overexpression of p53 protein in PTC. The aim of the present study was to investigate the prevalence of the BRAF (V600E) mutation and the expression of p53 in PTC, as well as to determine any associations between these two factors and the clinicopathological features of PTC. The study was performed on 66 PTC patients who underwent surgical tumor resection between January and December 2012. Polymerase chain reaction-based DNA amplification was used to analyze extracted DNA from the tumor specimens in order to determine the prevalence of the BRAF (V600E) mutation. In addition, immunohistochemical analysis was employed in order to evaluate the protein expression of p53 in sections of tumor tissue. Furthermore, statistical analysis was performed in order to determine any associations among the BRAF (V600E) mutation prevalence, p53 overexpression and the clinicopathological features of PTC patients, including age, gender, tumor size, multiplicity, lymph node metastasis and extrathyroidal extension. The results revealed that the BRAF (V600E) mutation was observed in 50 (75.8%) of the 66 PTC patients and overexpression of p53 was found in 52 (78.8%) of 66 cases. No significant correlations were observed between the BRAF (V600E) mutation or p53 protein overexpression and the clinicopathological features of patients. However, the BRAF (V600E) mutation demonstrated noteworthy, but non-significant, correlations with the overexpression of p53 (P=0.0854) and extrathyroidal extension (P=0.0661). In addition, a significant correlation was observed between lymph node metastasis and bilaterality (P=0.0280). In conclusion, the present study demonstrated that the BRAF (V600E) mutation and overexpression of p53 were not significantly correlated with clinicopathological features of PTC, although notable associations were identified between BRAF (V600E) mutation and overexpression of p53 as well as extrathyroidal extension. In addition, lymph node metastasis was significantly associated with bilaterality.

Mutation Profile of Well-Differentiated Thyroid Cancer in Asians

Recent advances in molecular diagnostics have led to significant insights into the genetic basis of thyroid tumorigenesis. Among the mutations commonly seen in thyroid cancers, the vast majority are associated with the mitogen-activated protein kinase pathway. B-Raf proto-oncogene (BRAF) mutations are the most common mutations observed in papillary thyroid cancers (PTCs), followed by RET/PTC rearrangements and RAS mutations, while follicular thyroid cancers are more likely to harbor RAS mutations or PAX8/peroxisome proliferator-activated receptor γ (PPARγ) rearrangements. Beyond these more common mutations, alterations in the telomerase reverse transcriptase (TERT) promoter have recently been associated with clinicopathologic features, disease prognosis, and tumorigenesis in thyroid cancer. While the mutations underlying thyroid tumorigenesis are well known, the frequency of these mutations is strongly associated with geography, with clear differences reported between Asian and Western countries. Of particular interest is the prevalence of BRAF mutations, with Korean patients exhibiting the highest rate of BRAF-associated thyroid cancers in the world. Here, we review the prevalence of each of the most common mutations in Asian and Western countries, and identify the characteristics of well-differentiated thyroid cancer in Asians.

Analysis of RAS mutation and PAX8/PPARγ rearrangements in follicular-derived thyroid neoplasms in a Korean population: frequency and ultrasound findings

OBJECTIVE

To investigate the frequency and ultrasonography (US) findings of RAS mutations and PAX8/PPARγ rearrangements between follicular thyroid adenomas (FTAs) and follicular thyroid carcinomas (FTCs) in a Korean population.

METHODS

RAS mutations and PAX8/PPARγ rearrangements in 56 FTAs and 35 FTCs were analyzed. We also analyzed the US findings of FTCs and FTAs.

RESULTS

16 nodules of 35 FTCs (45.7 %) and 19 nodules of 56 FTAs (33.9 %) harbored RAS mutations. Three FTCs and three FTAs showed two point mutations simultaneously. K-RAS codon 12-13 (n = 6, 31.6 %), N-RAS codon 61 (n = 5, 26.3 %), H-RAS codon 61 (n = 4, 21.1 %), K-RAS codon 61 (n = 3, 15.8 %), and N-RAS codon 12-13 (n = 1, 5.3 %) were found in FTCs, and N-RAS codon 61 (n = 10, 45 %), K-RAS codon 12-13 (n = 5, 22.7 %), H-RAS codon 61 (n = 5, 22.7 %), K-RAS codon 61 (n = 1, 4.5 %), and N-RAS codon 12-13 (n = 1, 4.5 %) were observed in FTAs. 4 of 56 (7.1 %) FTAs and 1 of 35 (2.9 %) FTCs represented PAX8/PPARγ rearrangements, respectively (P = 0.645). The absence of a hypoechoic rim (P = 0.021) and presence of calcifications (P = 0.049) were significantly associated with FTCs compared with FTAs.

CONCLUSIONS

RAS mutation frequency targeting the Korean population showed a 45.7 % in FTCs and 35.7 % in FTAs, and PAX8/PPARγ rearrangements were more frequently showed in FTAs. K-RAS codon 12-13 was the most common RAS mutation in FTCs, whereas N-RAS codon 61 was more frequent in FTAs. The presence of calcifications and absence of a hypoechoic rim showed more frequently in FTCs.

Clinicopathologic and diagnostic significance of p53 protein expression in papillary thyroid carcinoma

BACKGROUND

P53 protein expression has been detected immunohistochemically in papillary thyroid carcinoma(PTC). We investigated the relations between its expression and clinicopathologic features and its significance as a diagnostic marker.

MATERIALS AND METHODS

We compared and evaluated 93 patients in whom thyroidectomy with lymph node dissection had been performed to treat PTC for clinicopathologic significance and 102 patients with 23 papillary thyroid overt carcinomas (POC), 57 papillary thyroid microcarcinomas(PMC), 5 follicular adenomas (FA), 5 Hashimoto's thyroiditis (HT) and 12 nodular hyperplasias (NH) for significance as a diagnostic marker. Expression of p53 protein was evaluated immunohistochemically in sections of paraffin- embedded tissue.

RESULTS

Statistical analysis showed significantly different expression of p53 in PTC versus other benign thyroid lesions (BTL).The diagnostic sensitivity and specificity were 85.0% and 72.7%, respectively. Overexpression of p53 protein was observed in 44 of the 93 PTC cases (47.3%), but no significant correlation between p53 protein overexpression and clinicopathologic features (age, size, multiplicity, lymph node metastasis, extrathyroidal extension and vascular invasion) was noted.

CONCLUSIONS

p53 is valuable to distinguish PTC from other BTL, but there is no correlation between p53 protein overexpression and clinicopathologic features.

Does papillary thyroid carcinoma have a better prognosis with or without Hashimoto thyroiditis?

BACKGROUND

It has been reported that the BRAF (V600E) mutation is related to a low frequency of background Hashimoto thyroiditis (HT); however, there are not many factors known to be related to the development of HT. The aim of this study was to determine whether patients with both papillary thyroid carcinoma (PTC) and HT show aggressive features, by investigating the clinicopathological features of HT in patients with PTC.

METHODS

A database of patients with PTC who underwent thyroidectomy between October 2008 and August 2012 was collected and reviewed. All 2464 patients were offered a thyroidectomy, and DNA was extracted from the atypical cells in the surgical specimens for detection of the BRAF (V600E) mutation. Clinical and pathological characteristics were also investigated.

RESULTS

Four hundred and fifty-two of 1945 (23.2%) patients were diagnosed with HT, and of these, 119 (72.1%) had a BRAF (V600E) mutation. HT was not significantly associated with the BRAF (V600E) mutation (P < 0.001) and extrathyroidal extensions (P = 0.005) but was associated with a low stage (P = 0.011) and female predominance (P < 0.001). In a subgroup analysis for gender, HT was associated with a low probability of BRAF (V600E) mutations in both genders (P < 0.001 for both females and males). Also, recurrence was significantly associated with HT (OR 0.297, CI 0.099-0.890, P = 0.030), lymph node ratio (OR 2.545, CI 1.092-5.931, P = 0.030), and BRAF (V600E) mutation (OR 2.075, CI 1.021-4.217, P = 0.044). However, there was no relationship with clinicopathological factors or with death.

CONCLUSIONS

Our results show that HT in patients with PTC is associated with a low probability of BRAF (V600E) mutations. Moreover, HT was correlated with some factors that were associated with less aggressive clinical features and inversely related to recurrence. Therefore, these results may be useful to predict whether PTC concurrent with HT exhibits a better prognosis than PTC alone.

Impact of molecular testing in the diagnosis of thyroid fine needle aspiration cytology: data from mainland China

Background. The molecular work-up of thyroid nodules from fine needle aspiration samples has given clinicians a new level of diagnostic information. The aim of the present study was to evaluate the utility of molecular analysis in thyroid fine needle aspiration samples from a Chinese population. Methods. Specimens were collected from thyroid nodules by fine needle aspiration. Cytology diagnosis and genes analysis were performed and correlated with histology outcome. Results. A total of 83 patients with thyroid nodules were enrolled, including 20 benign lesions and 63 papillary carcinomas. BRAF and RAS mutations and RET/PTC gene rearrangements were found in 65.1%, 0%, and 1.6% of papillary carcinomas, respectively. No gene alterations were found in benign lesions. The combination of BRAF testing and cytology improved the accuracy of cytology from 69.9% to 89.2% (P < 0.05). Moreover, BRAF testing confirmed 82.4% of papillary carcinomas with suspicious cytology and identified 33.3% of papillary carcinomas with atypia cytology. Conclusions. Of the three candidate markers, BRAF testing showed diagnostic utility in fine needle aspiration. Combining BRAF testing with cytology improves the accuracy of fine needle biopsy. Those who have positive BRAF and malignant or suspicious malignant cytology can undergo thyroidectomy without a frozen section.

P53 and expression of immunological markers may identify early stage thyroid tumors

Background. Besides its major role in cell proliferation, DNA repair, and apoptosis, functional p53 protein is involved in the induction of antitumor cytotoxic-T-cell activity against carcinoma cells. We aimed to investigate p53 and immune cell markers utility as diagnostic and prognostic markers of differentiated thyroid cancer (DTC). Methods. ACIS-III system was used to evaluate p53 and immune cell markers including tumor-associated macrophages (TAM); CD68 and tumor-infiltrating lymphocytes (TIL) subsets such as CD3, CD4, CD8, and CD20 in 206 thyroid carcinomas, 105 benign nodules, and 18 normal tissues. Also, TP53 was sequenced in 78 out of 164 patients with papillary thyroid carcinoma. Results. P53 expression was observed more frequently in malignant than in benign lesions (P < 0.0001) and helped discriminate follicular patterned lesions. In addition, p53 was more frequent in smaller (P = 0.0015), unique tumors (P = 0.0286), with thyroiditis (P = 0.0486) and without metastasis at diagnosis (P = 0.0201). TAM was more frequent in P53 negative tumors (P = 0.002). Infiltration of CD8+ TIL was found in 61.7% of P53 positive and 25.6% of P53 negative DTC (P < 0.001). Conclusions. We suggest that p53 and CD8+ TIL immune profile analysis might be useful in DTC.

Genetic alterations in poorly differentiated and undifferentiated thyroid carcinomas

Thyroid gland presents a wide spectrum of tumours derived from follicular cells that range from well differentiated, papillary and follicular carcinoma (PTC and FTC, respectively), usually carrying a good prognosis, to the clinically aggressive, poorly differentiated (PDTC) and undifferentiated thyroid carcinoma (UTC).It is usually accepted that PDTC and UTC occur either de novo or progress from a pre-existing well differentiated carcinoma through a multistep process of genetic and epigenetic changes that lead to clonal expansion and neoplastic development. Mutations and epigenetic alterations in PDTC and UTC are far from being totally clarified. Assuming that PDTC and UTC may derive from well differentiated thyroid carcinomas (WDTC), it is expected that some PDTC and UTC would harbour genetic alterations that are typical of PTC and FTC. This is the case for some molecular markers (BRAF and NRAS) that are present in WDTC, PDTC and UTC. Other genes, namely P53, are almost exclusively detected in less differentiated and undifferentiated thyroid tumours, supporting a diagnosis of PDTC or, much more often, UTC. Thyroid-specific rearrangements RET/PTC and PAX8/PPARγ, on the other hand, are rarely found in PDTC and UTC, suggesting that these genetic alterations do not predispose cells to dedifferentiation. In the present review we have summarized the molecular changes associated with the two most aggressive types of thyroid cancer.

The evolution of biomarkers in thyroid cancer-from mass screening to a personalized biosignature

Thyroid cancer is the most common malignancy of the endocrine system. The diagnosis of thyroid nodules, made by neck examination and ultrasonography, is a common event occurring in over 50% of the patient population over the age of 50. Yet, only 5% of these patients will be diagnosed with cancer. Fine needle aspiration biopsy is the gold standard for diagnosing thyroid nodules. However, 10–15% of these biopsies are inconclusive, ultimately requiring a diagnostic thyroid lobectomy. Consequently, research in thyroid biomarkers has become an area of active interest. In the 40 years since calcitonin was first described as the biomarker for medullary thyroid cancer, new biomarkers in thyroid cancer have been discovered. Advances in genomic and proteomic technologies have defined many of these novel thyroid biomarkers. The purpose of this article is to provide a comprehensive literature review of how these biomarkers have evolved from simple screening tests into a complex array of multiple markers to help predict the malignant potential and genetic signature of thyroid neoplasms.

The cytological, clinical, and pathological features of the cribriform-morular variant of papillary thyroid carcinoma and mutation analysis of CTNNB1 and BRAF genes

BACKGROUND

The cribriform-morular variant of papillary thyroid carcinoma (CMVPTC) is an unusual subtype of papillary thyroid carcinoma. The goal of this study was to determine the clinicopathological features of CMVPTC and whether the tumor can be diagnosed by fine-needle aspiration cytology.

METHODS

We retrospectively analyzed the clinical appearance and pathological findings in five patients with CMVPTC and sequenced exon 3 of CTNNB1 and exon 15 of BRAF in tumor tissue.

RESULTS

All patients were young women, 15-34 years of age at the time of the cancer diagnosis. Preoperative cytological examination showed scattered tall columnar cells, fascicular spindle cells, and cribriform and morular patterns in the fine-needle aspirates of the thyroid from the five patients. Grossly, all tumors were well-circumscribed, solid or cystic. Immunohistochemically, most tumor cells showed nuclear expression of thyroid transcription factor-1, estrogen and progesterone receptors, and p53; cytoplasmic expression of cytokeratins 7 and 19, vimentin, and bcl-2; and cytoplasmic and nuclear accumulation of beta-catenin and galectin-3. There was no expression of thyroglobulin, cytokeratin 5/6, or human mesothelial cell-1. However, among these markers, the morular cells showed only positive immunostaining for beta-catenin, galectin-3, p53, and bcl-2. A CTNNB1 mutation was identified in only one case and no BRAF mutation was found in any of the five cases.

CONCLUSIONS

Taken together, these data suggest that CMVPTC can be diagnosed preoperatively, based on careful cytology examination, and shows unique immunohistochemical findings.

Clinical significance of p53 protein expression in papillary thyroid carcinoma

BACKGROUND

Although mutations in the p53 suppressor gene in thyroid carcinoma have usually been detected in anaplastic carcinoma, P53 protein expression has been detected immunohistochemically in papillary thyroid carcinoma (PTC). In the present study, we examined the immunohistochemical expression of P53 protein in PTC to investigate the relations between its expression and the clinicopathologic features.

METHODS

The study was performed on 68 patients in whom thyroidectomy with lymph node dissection had been performed to treat PTC at Teikyo University Hospital. Expression of P53 protein was evaluated immunohistochemically in sections of paraffin-embedded tissue in 68 primary tumors and 196 lymph node metastases.

RESULTS

Overexpression of P53 protein in the primary tumor was observed in 29 cases (43%). Statistical analysis revealed significant correlation between P53 protein expression in the primary tumor and large tumor size (unpaired t-test: p < 0.01), the presence of lymph node metastasis (unpaired t-test: p < 0.05), and the mean number of lymph node metastases (unpaired t-test: p < 0.05). Although 29 (43%) of the primary tumors overexpressed P53 protein, 143 (73%) of the metastatic lymph nodes overexpressed P53 protein irrespective of whether there was P53 overexpression by the primary tumor.

CONCLUSIONS

The results of this study suggest that immunohistochemistry for P53 in the primary tumor could be useful in the clinical evaluation of patients with PTC. Moreover, P53 protein overexpression in lymph node metastasis may be useful as a treatment guide or target for lymph node recurrences.

Clinical and pathological features and the BRAF(V600E) mutation in patients with papillary thyroid carcinoma with and without concurrent Hashimoto thyroiditis

BACKGROUND

It has been reported that patients with papillary thyroid carcinoma (PTC) have a high incidence of background Hashimoto thyroiditis (HT); however, the linkage of HT to PTC is controversial. Recent studies have shown that the prevalence of activating point mutations in BRAFV600E is much higher (73-86%) in Korea than in Western countries (29-69%), and associated with a poor prognosis in PTC. The purpose of the present study was to investigate the frequency of the BRAFV600E mutation in PTC with and without HT, and to determine clinical and pathological features that were associated with concomitant HT and PTC.

METHODS

Fine-needle aspiration slides from 101 patients with surgically confirmed PTC were studied. The DNA was extracted from the atypical cells that were scraped from slides. It was then analyzed for the BRAFV600E mutation by pyrosequencing. In addition, the presence of background HT in surgical specimens and other clinical and pathological features of the patients were characterized.

RESULTS

HT was present in 37 (36.6%) of the patients. The BRAFV600E mutation was present in 27 (72.9%) of patients with HT but was present in 61 (95.3%) of patients without HT ( p#0.01). The inverse correlation of concurrent HT with the BRAFV600E mutation was significant for both males and females ( p < 0.01). The presence of background HT was not associated with tumor size, extrathyroidal invasion, lymph node (LN) metastasis, or tumor stage. The patients were younger in the group without background HT (44.1 +/- 13.2 vs. 49.8 +/- 13.9, p 1/40.05). The BRAFV600E mutation was present in 88 (87.1%) of the 101 patients with PTC. The presence of the BRAFV600E mutation was significantly associated with LN metastasis ( p < 0.02; odds ratio, 6.24; 95% confidence interval, 1.51-25.79).

CONCLUSION

In Korean patients with PTC, the BRAFV600E mutation is associated with a lower frequency of background HT and a high frequency of LN metastasis.

Intragenic mutations in thyroid cancer

The close genotype-phenotype relationship that characterizes thyroid oncology stimulated the authors to address this article by using a mixed, genetic and phenotypic approach. As such, this article addresses the following aspects of intragenic mutations in thyroid cancer: thyroid stimulating hormone receptor and guanine-nucleotide-binding proteins of the stimulatory family mutations in hyperfunctioning tumors; mutations in RAS and other genes and aneuploidy; PAX8-PPARgamma rearrangements; BRAF mutations; mutations in oxidative phosphorylation and Krebs cycle genes in Hürthle cell tumors; mutations in succinate dehydrogenase genes in medullary carcinoma and C-cell hyperplasia; and mutations in TP53 and other genes in poorly differentiated and anaplastic carcinomas.

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.

Detection of BRAFV600E mutation on fine needle aspiration specimens of thyroid nodule refines cyto-pathology diagnosis, especially in BRAF600E mutation-prevalent area

BACKGROUND

Between 10 and 30% of the fine needle aspiration biopsies (FNABs) of thyroid nodules are diagnosed as 'indeterminate'. A molecular diagnostic method is needed to reduce unnecessary surgery in this group. In Korea, most thyroid cancer is the classic papillary type and the BRAF(V600E) mutation is highly prevalent.

AIM

To evaluate the role of pre-operative detection of BRAF(V600E) mutation in the FNAB specimens of thyroid nodules in a BRAF(V600E) mutation-prevalent geographical area.

PATIENTS AND METHODS

In 137 specimens of FNAB (107 papillary thyroid carcinomas (PTC); 3 follicular thyroid carcinomas (FTC); 2 undifferentiated thyroid carcinomas; 25 benign lesions), both direct DNA sequencing and PCR-RFLP were used for detecting the BRAF(V600E) mutation. The sensitivity and specificity were calculated. We analysed the association between BRAF(V600E) mutation and the clinico-pathological parameters.

RESULTS

The BRAF(V600E) mutation was present in 93 (83%) of 112 thyroid cancers. Direct DNA sequencing showed a sensitivity of 83.0% and a specificity of 96.0%. The sensitivity and specificity of PCR-RFLP were 78.6% and 80.0%, respectively. Among 25 cases with indeterminate FNAB cytology, 8 patients had malignant lesions (5 PTC and 3 FTC). Three (60%) of 5 PTCs and 1 out of 17 benign lesions had BRAF(V600E) mutation (only one false positive case and the definitive pathology showed atypical nodular hyperplasia that could be a premalignant lesion). The diagnostic accuracy of this molecular method in only the 25 indeterminate nodules was 76% (19/25). No mutation was found in 3 FTCs. Among 107 PTCs, there was no significant association of the BRAF(V600E) mutation with the known risk factors.

CONCLUSION

Detection of the BRAF(V600E) mutation in FNAB specimens refines the FNAB-cytology diagnosis, especially in a BRAF(V600E) mutation-prevalent area. Direct DNA sequencing was a more reliable method than PCR-RFLP for detecting the BRAF(V600E) mutation with a high sensitivity and specificity.

Influence of the BRAF V600E mutation on expression of vascular endothelial growth factor in papillary thyroid cancer

CONTEXT

The BRAF mutation may influence the expression patterns of molecular markers that are related to the development and progression of thyroid cancer.

OBJECTIVE

The objective of the study was to investigate the effects of the BRAF V600E mutation on expression of galectin-3, cyclooxygenase-2, cyclin D1, p53, and vascular endothelial growth factor (VEGF) in papillary thyroid cancer (PTC).

DESIGN, SETTING, AND SUBJECTS

One hundred sixty-three PTC and 28 nodular hyperplasia patients were selected retrospectively. The presence of the BRAF V600E mutation and the level of expression of the molecular markers were determined.

RESULTS

Of 161 PTC patients, 102 patients (63.4%) were BRAF V600E(+), and these cases had significantly larger tumor sizes (P = 0.01), compared with V600E(-) cases (n = 59, 36.6%). Although PTC tissues had higher expression levels of the selected molecular markers than nodular hyperplasia tissues, expression levels of several molecular markers in BRAF V600E(+) PTC were not significantly different from those of BRAF V600E(-) PTC. But VEGF was significantly up-regulated in BRAF V600E(+) PTC, compared with BRAF V600E(-) PTC. VEGF expression levels were strongly positively correlated to tumor size (P < 0.001), extrathyroidal invasion (P = 0.02), and tumor stage (P = 0.04). Multivariate analysis clearly showed that VEGF expression was up-regulated in BRAF V600E(+) PTC (odds ratio 2.5, confidence interval 1.1-5.6; P = 0.03).

CONCLUSIONS

BRAF V600E(+) PTC tended to have larger tumor volumes and higher expression of VEGF. The level of VEGF expression was closely correlated with tumor size, extrathyroidal invasion, and stage. The relatively high levels of VEGF expression may be related to poorer clinical outcomes and recurrences in BRAF V600E(+) PTC.

Low prevalence of RET rearrangements (RET/PTC1, RET/PTC2, RET/PTC3, and ELKS-RET) in sporadic papillary thyroid carcinomas in Taiwan Chinese

Somatic rearrangement of the tyrosine kinase receptor RET is restricted to papillary thyroid carcinoma (PTC). The prevalence of RET/PTC1, RET/PTC2, and RET/PTC3 has been found to vary between 0% and 20% in most series of sporadic (nonradiation-induced) PTCs analyzed by type-specific reverse transcription-polymerase chain reaction (RT-PCR) alone. However, high prevalence reported from Taiwan (6 out of 11, 55%) indicates RET rearrangement is an important genetic lesion underlying the development of PTC in Taiwan. Because the high prevalence of RET rearrangements in Chinese patients was particularly striking, we were prompted to reexamine chimeric transcripts of RET/PTC1, RET/PTC2, and RET/PTC3 using the same experimental designs in a larger number of cases in the same population. RT-PCR was performed to amplify fusion products of RET/PTC1, RET/PTC2, RET/PTC3, and ELKS-RET from frozen tissue of 105 sporadic PTCs. RT-PCR was also performed with two different primer sets for RET/PTC1, RET/PTC2, and RET/PTC3 followed by Southern hybridization in the first 62 tumors. In our study, RET/PTC1, RET/PTC2, and RET/PTC3 oncogenes were found in only 7 of 105 (7%) sporadic PTCs. Of these tumors, 3 involved RET/PTC1 and 4 involved RET/PTC3. No RET/PTC2 rearrangements were observed. In the first 62 tumor samples, another two different primer sets for each rearrangement also gave concordant results. Furthermore, application of Southern hybridization in these 62 PTCs did not identify additional tumor harboring RET chimeric transcripts. We identified one tumor as having an ELKS-RET rearrangement (1 of 105, 1%). In conclusion, we detected RET rearrangements in 8 of 105 (8%) sporadic PTCs in Taiwan, a much lower prevalence than previously reported for this population but comparable to those reported in other nations using similar methodology. RET chimeric oncogenes only account for a small fraction of PTCs in Taiwan.

High prevalence of c-RET expression in papillary thyroid carcinomas from the Korean population

BACKGROUND

Activation of the RET proto-oncogene, located on the long arms of chromosome 10, contributes to the development of thyroid cancers in two different ways. First, somatic rearrangements of RET with variable activation genes are frequently found in papillary thyroid carcinomas. Second, germ-line point mutations are responsible for the development of medullary thyroid carcinomas and multiple endocrine neoplasia type 2 (MEN 2). There are several conflicting reports on the influences of RET expression and RET/PTC rearrangements on the clinical outcome of thyroid cancers. Therefore, the wild-type RET gene expression and RET/PTC-1, RET/PTC-2, RET/PTC-3 rearrangements were examined in thyroid carcinomas and other thyroid diseases.

MATERIALS AND METHODS

Thirty-six papillary thyroid carcinomas (PTCs), 8 follicular thyroid carcinomas (FTCs), 4 anaplastic thyroid carcinomas (ATC), 7 follicular adenomas (FAs), 23 hyperplasias, 6 normal thyroid tissues, and 39 normal portions from each tumor were included in this study. Reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical analyses were used to identify the RET gene and RET/PTC rearrangements.

RESULTS

From the RT-PCR analysis, 68.9% of the PTCs, a single case of FTC, and 22.2% of the hyperplasias expressed the RET gene. No RET gene expression was observed in ATCs, FAs, or normal thyroid tissues. One RET/PTC-1 and one RET/PTC-2 rearrangement were detected in the PTCs. No RET/PTC-3 rearrangement was detected in any specimen. The immunohistochemical results revealed that 66.7% of PTCs, 28.6% of FAs, and 18.2% of hyperplastic thyroid tissue specimens showed high levels of RET protein expression. Neither the normal thyroid tissues nor the FTCs and ATC, showed high levels of RET protein expression. The two methods are agreed in PTC and hyperplastic nodules, but not in FA and FTC.

CONCLUSION

PTCs among Koreans rarely showed RET/PTC rearrangements, but commonly showed increased RET gene expression. Compared to earlier reports indicating that the expression of the RET gene was limited to PTCs, the RET gene was also expressed in hyperplasias in this study.

RET/PTC and CK19 expression in papillary thyroid carcinoma and its clinicopathologic correlation

Recently, the rearrangement of RET proto-oncogene has been reported to be the most common genetic change in papillary thyroid carcinoma (PTC). However, its prevalence has been reported variably and its relation to clinical outcome has been controversial. The characteristic nuclear features of PTC usually render the diagnosis, but problem arises with equivocal cytologic features that are present focally. Although there remains some controversy, CK19 has been reported to be a useful ancillary tool for diagnosis of PTC. To evaluate the expression rate of RET/PTC rearrangement and CK19 in PTCs in a Korean population, we studied 115 papillary thyroid carcinomas in 3 mm-core tissue microarray based immunohistochemical analysis. The prevalence of Ret protein expression was 62.6% and the CK19 immunoreactivity was 80.9%. There was no statistically significant association between the Ret positivity and CK19 immunoreactivity, although the percent agreement of the two was relatively high. The clinicopathological variables did not correlate with the expression of Ret. In conclusion, the prevalence of Ret protein expression and its clinicopathological implications in a Korean population are not much different from those reported in previous studies. However, its detection via immunohistochemistry can be a useful diagnostic tool for diagnosing papillary thyroid carcinoma in conjunction with CK19.

Real-time quantitative RT-PCR identifies distinct c-RET, RET/PTC1 and RET/PTC3 expression patterns in papillary thyroid carcinoma

RET/PTC1 and RET/PTC3 are the markers for papillary thyroid carcinoma. Their reported prevalence varies broadly. Nonrearranged c-RET has also been detected in a variable proportion of papillary carcinomas. The published data suggest that a wide range in expression levels may contribute to the different frequency of c-RET and, particularly, of RET/PTC detection. However, quantitative expression analysis has never been systematically carried out. We have analyzed by real-time RT-PCR 25 papillary carcinoma and 12 normal thyroid samples for RET/PTC1, RET/PTC3 and for RET exons 10-11 and 12-13, which are adjacent to the rearrangement site. The variability in mRNA levels was marked and four carcinoma groups were identified: one lacking RET/PTC rearrangement with balanced RET exon levels similar to those of the normal samples (7/25 cases, 28%), the second (6/25 cases, 24%) with balanced RET expression and very low levels of RET/PTC1, the third with unbalanced RET exons 10-11 and 12-13 expression, high RET/PTC1 levels but no RET/PTC3 (7/25 cases, 28%), and the fourth with unbalanced RET expression, high RET/PTC1 levels and low levels of RET/PTC3 (5/25 cases, 20%). Papillary carcinomas with high RET/PTC1 expression showed an association trend for large tumor size (P=0.063). Our results indicate that the variability in c-RET and RET/PTC mRNA levels contributes to the apparent inconsistencies in their reported detection rates and should be taken into account not only for diagnostic purposes but also to better understand the role of c-RET activation in thyroid tumorigenesis.

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.

Immunohistochemical localisation of RET and p53 mutant protein of thyroid lesions in a North-Eastern Malaysian population and its prognostic implications

AIMS

To investigate RET and p53 expression in local thyroid lesions, in order to shed light on the pathogenesis of papillary carcinoma and explain the high prevalence of this condition among the nodular hyperplasia (multi-nodular goitre) cases.

METHODS

Archival thyroid tissue was retrieved from Hospital Universiti Sains Malaysia (HUSM) Pathology Department files and studied by immunohistochemistry for RET and p53 mutant protein. Normal tissues from 74 cases served as controls.

RESULTS

Fifty follicular adenoma, 66 nodular hyperplasia and 53 papillary carcinoma cases were studied. RET was expressed in 5.4% of normal thyroid tissue, 18% of follicular adenomas, 22.7% of nodular hyperplasia cases and 71.7% of papillary carcinomas. Its expression in papillary carcinoma was not associated with the coexistence of nodular hyperplasia lesions. p53 was expressed by 17% of papillary carcinomas. No association was found between p53 expression of nodular hyperplasia with or without co-existing papillary carcinoma. p53, rather than RET, was an excellent predictor of tumour lymph node metastasis and capsular invasion. p53 was also a significant prognosticator of survival outcome.

CONCLUSIONS

RET expression is highly prevalent in local papillary carcinoma, indicating a significant role in the pathogenesis of this tumour, with no apparent role in tumour behaviour and survival outcome. p53 on the other hand appears to be a significant factor in the latter events. The two genes appear to act in two different pathways: the former being an initiator, and the later a propagator of papillary carcinoma.

Where to set the threshold between well differentiated and poorly differentiated follicular carcinomas of the thyroid

A critical review of the literature reveals that different types of thyroid carcinomas have been interpreted as poorly differentiated, including the tall and columnar cell variants as well as carcinomas with insular, trabecular, and solid growth patterns. In some publications the growth patterns have been emphasized, while in others histologic patterns and cytologic features are considered important for identification. However, insular, trabecular, nodular, and solid growth patterns lack specificity because they can be observed in hyperplastic lesions and benign thyroid tumors. The cytologic features of the vast majority of poorly differentiated thyroid carcinomas are similar to or overlap with those of papillary or follicular carcinomas. Cytologic atypia, mitotic activity, and necrosis--believed by some investigators to be useful clues in the diagnosis of poorly differentiated carcinomas--do not reflect cell differentiation, especially in endocrine organs. It is therefore not surprising that the immunohistochemical profile and the molecular abnormalities described in this heterogeneous group of carcinomas lack specificity and are not useful diagnostic tools. Because poorly differentiated thyroid carcinomas have not been well defined, currently it is not possible to set the threshold between well-differentiated and poorly differentiated thyroid carcinomas with follicular phenotype. The authors believe that the vast majority of poorly differentiated thyroid carcinomas are in fact examples of papillary or follicular carcinomas with unusual growth patterns.

Feline hyperthyroidism: advances towards novel molecular therapeutics

Feline hyperthyroidism is the most common endocrine disorder of the elderly cat. Traditionally, the disease is treated by surgical thyroidectomy, medical management with antithyroid drugs or radiation therapy using iodine-131. However, none of these treatments is ideal and molecular therapeutics may offer novel methods of treating the disease. This article reviews the background of, and preliminary investigations into, the development of a transcriptionally targeted somatic gene therapy strategy for the treatment of this feline condition.

Screening of selected genomic areas potentially involved in thyroid neoplasms

Loss of heterozygosity (LOH) studies have been used to identify sites harbouring tumour suppressor genes (TSGs) involved in tumour initiation or progression. To further elucidate the genetic mechanisms for follicular and papillary thyroid tumours development, we studied the frequency of LOH in 36 thyroid tumours (21 follicular thyroid adenomas (FAs) and 15 papillary thyroid carcinomas (PTCs)) on 10 specific genomic areas: 3p22, 3p25, 7q21, 7q31, 10q23, 10q25-26, 11q13, 11q23, 13q13 and 17p13.3-13.2 using 20 polymorphic markers. We have selected these areas for two reasons: (a) Even though LOH in thyroid neoplasms has been described in some of these areas, results are controversial, and (b) we have also studied areas described as involved in other epithelial or endocrine tumour types, but not studied up to now in thyroid neoplasms. Two areas showed a high percentage of LOH: 7q31 and 11q23. A 62% LOH was found at 7q31 in the FAs, suggesting, as other authors have proposed, that at least one TSG must be present in the vicinity of the c-met locus. The second area in frequency was at the 11q23 locus, with a 45% LOH in the FAs. This area was studied because it has been described as being involved in the development of epithelial and endocrine cancers. This locus had not been studied before in thyroid neoplasms. This result is interesting because the LOH11CR2A gene is localised at this locus. We suggest that this gene and/or an other TSG nearby may be involved in the progression to FA. In our study, a low percentage of LOH was found in the PTC samples, indicating that TSGs present in the areas we have studied are not significantly involved in their progression. Our data also suggest that TSGs located in areas where no LOH was detected (PTEN, MEN1, Cyclin D1, BRCA2 and RFC3) are not involved or do not have an important role in tumour progression.

Ras mutations are rare in solitary cold and toxic thyroid nodules

OBJECTIVE

Activation of ras proto-oncogenes as a result of point mutations is detectable in a significant percentage of most types of tumour. Similar to neoplasms of other organs, mutations of all three ras genes can be found in thyroid tumours. H-, K- and N-ras mutations have been detected in up to 20% of follicular adenomas and adenomatous nodules which were not functionally characterized. This raises the question as to whether ras mutations are specific for hypofunctional nodules and TSH receptor mutations for hyperfunctioning nodules.

DESIGN

To investigate ras and TSH receptor mutations with respect to functional differentiation we studied 41 scintigraphically cold nodules and 47 toxic thyroid nodules. To address the likelihood of a somatic mutation we also studied the clonal origin of these tumours.

MEASUREMENTS

Genomic DNA was extracted from nodular and surrounding tissue. Mutational hot spots in exons 1 and 2 of the H- and K-ras gene were PCR amplified and sequenced using big dye terminator chemistry. Denaturing gradient gel electrophoresis (DGGE) was used to verify sequencing results for the H-ras gene and to analyse the N-ras gene because its greater sensitivity in detecting somatic mutations. Clonality of nodular thyroid tissue was evaluated using X-Chromosome inactivation based on PCR amplification of the human androgen receptor locus.

RESULTS

Monoclonal origin was detectable in 14 of 23 informative samples from cold thyroid nodules. In toxic thyroid nodules the frequency of clonal tissue was 20 in 30 informative cases. Only one point mutation could be found in the N-ras gene codon 61 (Gly to Arg) in a cold adenomatous nodule which was monoclonal. In toxic thyroid nodules no ras mutation was detectable.

CONCLUSION

Our study suggests that ras mutations are rare in solitary cold and toxic thyroid nodules and that the frequent monoclonal origin of these tumours implies somatic mutations in genes other than H-, K- and N-ras.

P53 mutations in thyroid carcinoma: tidings from an old foe

The underlying mechanism leading to carcinogenesis involves genomic instability, likely related to aneuploidy. While p53 as a "guardian of the genome" is an appealing candidate as an initiator of genomic instability, its mutations or deletions usually occur late in the course of tumor progression. P53 may, however, become a target of events initiated by genomic instability. P53 is a transcription factor with multifaceted regulatory functions in the cell cycle, DNA repair and apoptosis. Inactivating p53 mutations have been described in some 50% of human cancers. These mutations are not only important in tumor progression but apparently also in the response of some tumors to chemotherapy and radiation treatment, thus to clinical outcome. P53 mutations are found in 14% of malignant thyroid tumors and are more frequent in poorly differentiated and anaplastic tumors. We have examined the mutation rates of p53 as a measure of genomic instability (hypermutability) of malignant thyroid tumors. We also wondered whether radiation enhances this tendency to genomic instability. To those ends we extracted all available entries from the p53 mutations database (http://www.perso@curies.fr), verified, extended where applicable, and supplemented that information from the original published reports. We were able to locate 100 entries. The distribution of the types of p53 aberrations in thyroid cancer was similar to those in the database as a whole. The silent mutation rate of 20%, not different from the expected 25%, is consistent with a random occurrence of these mutations. This silent mutation rate is 130 times that expected and is 7 times that of the p53 database. Moreover the distribution of p53 mutations is compatible with Poisson's distribution, which, when considered in the context of the silent mutation rates, indicates that p53 is particularly hypermutable in thyroid cancer. Epigenetic deamination of CpG dinucleotides at highly transforming DNA-contact residues is a feature of poorly differentiated tumors and thus associated with tumor progression. The rates of p53 mutations in radiation-related thyroid cancers (15.4%) are similar to those in spontaneously arising tumors, although there was a highly significant heterogeneity (p<0.0005) in the residues mutated in the two tumor sets. None of the residues mutated in radiation-related thyroid cancer involved CpG deamination. Based on the evidence of p53 hypermutability, thyroid cancer appears to exhibit remarkable genomic instability. Spontaneous epigenetic mutational events are involved in tumor progression. While thyroid cancer related to radiation exposure does not increase the rates of p53 mutation, they exhibit mutation at residues not involved in p53/DNA interface.

Growth inhibition and chemosensitivity of poorly differentiated human thyroid cancer cell line (NPA) transfected with p53 gene

BACKGROUND

We investigated whether retroviral p53 transfection could enhance growth inhibition and chemosensitivity in a p53 mutant papillary thyroid cancer cell line (NPA).

METHODS

NPA cells were transfected with either LXSN/p53 or mock infection in the presence of Adriamycin. Gene expression was confirmed by western blotting. Nude mice were injected subcutaneously with NPA cells after transfection with either LXSN/p53 or mock infection on opposite sides, and the tumor growth was compared.

RESULTS

There was a dose-dependent inhibition of tumor growth with LXSN/p53 transfection. Tumor growth was inhibited more by p53 gene transfection relative to mock transfection in the presence of Adriamycin.

CONCLUSION

These treatment modalities could be beneficial in the treatment of p53 mutant positive thyroid cancers.

Thyroid carcinoma is characterized by genomic instability: evidence from p53 mutations

p53 is a transcription factor with multifaceted regulatory functions in cell cycle progression, DNA repair, and programmed cell death. Inactivating mutations have been described in 50% of human cancers. These mutations appear to be important in tumor progression and response to chemotherapy and radiation treatment and thus clinical outcome. p53 mutations are found in 14% of malignant thyroid tumors and are more frequent in poorly differentiated and anaplastic tumors. Given that p53 is a late event in the notional multistep pathogenesis of cancer, we examined its mutation rates as a measure of genomic instability (hypermutability) of malignant thyroid tumors and also wondered whether radiation enhances that proclivity to genomic instability. To that end we have extracted all available data from the p53 mutation database (http://www.perso@curie.fr), verified, extended, where applicable, and supplemented that information from published reports. We were able to identify 100 entries. The distribution of the p53 mutational events--deletions/insertions, transitions versus transversion mutations--was similar to that of the database as a whole. The silent mutation rate of 17.8%, not different from the expected 25%, is consistent with a random occurrence of these mutations. The silent mutation rate is 120 times that expected and is 6 times that of the database. Moreover, the distribution of p53 mutations is compatible with Poisson's distribution, which taken with silent mutation rates indicates that p53 is particularly hypermutable in thyroid carcinomas. Epigenetic deamination of CpG dinucleotide at highly oncogenic DNA-contact residues is a feature of poorly differentiated tumors and thus associated with tumor progression. The rates of p53 mutations (15.4%) in radiation-related cancers were very similar to those in apparently spontaneously arising tumors, although there was a highly significant heterogeneity (P < 0.0005) in the residues mutated. None involved CpG deamination. It is apparent that thyroid cancer exhibits remarkable genomic instability evidenced by p53 hypermutability. Spontaneous epigenetic mutational events are involved in tumor progression and while radiation increases the absolute prevalence of thyroid cancer in the susceptible it does not increase the rate of p53 mutation and seemingly targets different non-DNA-contact residues than those in spontaneously arising tumors.

Overexpression of p53 protein and MDM2 in papillary carcinomas of the thyroid: Correlations with clinicopathologic features

Expression of p53 protein and MDM2 was evaluated in paraffin-embedded tissue from 78 patients with papillary carcinomas of the thyroid (PCT), in order to elucidate the relationship between them and their correlations with some clinicopathologic features implicated in tumor progression. These proteins were expressed in nuclei of tumor cells, but not in non-tumor cells. Staining was defined as positive when 10% or more of tumor cells expressed these proteins. The number of cases positive for p53 protein was 21/78 (27%), and that positive for MDM2 was 26/78 (33%). Co-overexpression of p53 protein and MDM2 was observed in 12/78 cases (15%). A significant positive relationship was found between them (P < 0.01); p53-positive cases tended to be also positive for MDM2 and vice versa. Statistical analysis revealed that overexpression of p53 protein significantly correlated with large tumor size (P = 0.0271) and the presence of capsular invasion (P = 0.04). There were significant positive correlations between tumor size and intrathyroidal invasion and between tumor size and capsular invasion in PCT, suggesting that p53 protein overexpression is associated only with tumor progression (tumor size). However, we could not find any significant correlations between MDM2 expression and clinicopathologic features. Our findings suggest that overexpression of p53 protein and MDM2 in papillary carcinoma of the thyroid is associated with the progression of the tumors, and that p53 may be a marker of the progression of PCT.

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.

RET proto-oncogene mutations in thyroid carcinomas: clinical relevance

Different forms of RET mutations are found in papillary and medullary thyroid carcinomas. Rearrangements with other genes (RET/PTC oncogene) play a causative role in a significant proportion of papillary thyroid carcinomas. In this case, several factors influence the frequency and the type of RET/PTC, such as exposure to radiation, age and histological variant of the papillary tumor. On the other hand, the presence of the mutation does not seem to influence the biological behavior of the tumor or its response to conventional treatment modalities. In the setting of medullary thyroid cancer, germline RET point-mutations are implicated in the pathogenesis of virtually all hereditary forms and somatic point-mutations in nearly half of the sporadic forms. The clinical impact of this finding is that family members at-risk of hereditary MTC may be screened by genetic analysis, to distinguish those carrying or not-carrying the mutation. The last can be reassured on their status and relieved from further follow-up. Those with the mutation may be treated at a pre-clinical stage of the disease or even before the disease is started. The present review is focused on the clinical implication of RET gene mutations in thyroid cancer patients.

P53-independent down-regulation of Mdm2 in human cancer cells treated with adriamycin

Mdm2 is a nuclear phosphoprotein which functions as a negative feedback regulator of the p53 tumor suppressor gene. In this study, we investigated the alteration of Mdm2 and p53 in three human cancer cell lines containing either a wild-type or mutant p53 gene after treatment with Adriamycin (doxorubicin, ADR), a DNA damaging agent. We found that human breast cancer MCF-7 cells containing wild-type p53 were much more susceptible to ADR compared to human breast cancer MDA-MB-231 and human prostate cancer Du-145 cells which contain mutant p53. ADR resulted in a significant dose-dependent accumulation of p53 protein in MCF-7 cells, whereas little or no influence was observed on p53 protein of the two mutant p53 cell lines. However, a significant down-regulation of Mdm2 at protein and mRNA levels was observed in these three cell lines following ADR treatment. Moreover, the decrease of Mdm2 was in both a dose- and time-dependent manner. It is interestingly noted that 5 microM is a critical dose for significant down-regulation of the Mdm2 protein. Selected proteasome inhibitors did not rescue the ADR-caused decline in the expression of Mdm2 protein. Therefore, our present results reveal that ADR can induce a down-regulation of Mdm2 via a p53-independent pathway in human cancer cells and the ubiquitin-proteasome degradation mechanism may not be involved in the decreased expression of Mdm2 protein.

Molecular alterations involving p53 codons 167 and 183 in papillary thyroid carcinomas from chernobyl-contaminated regions of belarus

After the Chernobyl accident in 1986, there was a significant increase in the incidence of papillary thyroid carcinoma in fallout-exposed children from Belarus. We studied the p53 gene from 24 papillary thyroid carcinoma cases presenting in 1996. All subjects lived in contaminated regions of Belarus at the time of the accident and were under age 20 when exposed to fallout. Exons 5 through 9 of p53 were amplified from genomic tumor DNA using the polymerase chain reaction (PCR). The PCR products were analyzed by direct DNA sequencing using an automated sequencer. Five cases each exhibited two molecular alterations within exon 5. Alterations were confirmed by sequencing in both directions. One alteration, involving codon 167 (CAG-->CAT) in all five cases, resulted in the substitution of HIS for GLN. The second alteration, involving codon 183 (TCA-->TGA) in all five cases, resulted in a premature termination codon. Leukocyte DNA from each of the positive cases was analyzed and found to contain only wild-type p53 sequence. These results suggest that mutations involving codons 167 and 183 in the p53 locus are important in the pathogenesis of a subset (21%) of radiation-induced papillary thyroid carcinomas from Belarus.

Detection of RET/PTC oncogene rearrangements in Korean papillary thyroid carcinomas

The prevalence of RET/PTC rearrangement in papillary thyroid carcinomas has been found to vary widely in different populations. Recent studies, however, have reported no significant geographical difference between Asian and Western countries. In addition, there are some disagreements about the correlation of RET/PTC expression with clinical aggressiveness. We have performed this study in order to examine the prevalence of RET/PTC-1, RET/PTC-2, and RET/PTC-3 rearrangements in Korean papillary thyroid carcinomas, and to ascertain its clinical relevance. Thyroid tumors from 31 patients histologically confirmed to be papillary carcinomas were included in this study. To find rearrangements, we utilized reverse transcription-polymerase chain reaction (RT-PCR) and automated direct sequencing. Initial and follow-up clinical data were obtained from the patients' medical records. We identified two tumors containing RET/PTC-1 (2/31, 6.5%) and two containing RET/PTC-2 (2/31, 6.5%). However, we could not find RET/PTC-3 rearrangement in any patients (0/31). In conclusion, we report RET/PTC rearrangements in 4 of 31, (12.9%) Korean patients with papillary thyroid carcinomas, a higher prevalence than previously reported in this population.