Ras oncogene mutations in thyroid tumors: polymerase chain reaction-restriction-fragment-length polymorphism analysis from paraffin-embedded tissues

Genetic differences in follicular thyroid carcinoma between Asian and Western countries: a systematic review

Thyroid cancer is the most common endocrine malignancy, and follicular thyroid carcinoma (FTC) is the second most common thyroid cancer following papillary thyroid carcinoma (PTC). RAS mutation and PAX8/PPARγ rearrangement are the two representative genetic alterations in FTC, and there are studies from various countries on their regional frequencies. In this study, we systematically reviewed all available literature aiming to create a complete global map showing the frequencies of these common oncogenic drivers in FTC and to highlight the trends in Asian and Western countries. We performed a search in two electronic databases and identified 71 studies that fit our criteria from 1,329 studies found with our database search terms. There were 54 articles with 1,143 FTC patients and 39 articles with 764 FTC patients available for calculating the frequency of RAS mutation and PAX8/PPARγ rearrangement, respectively. NRAS mutation was the most frequent RAS mutation in all regions, followed by HRAS and KRAS mutation. The frequency of RAS mutation in Asian countries was higher than Western countries (34% vs. 27%, P=0.006) when the mutation detection method was not taken into account. In contrast, this difference in RAS mutation incidence between Asian and Western countries (28% vs. 25%, P=0.47) did not show up in our subgroup analysis incorporating only studies using direct sequencing method. The reported difference of RAS mutation frequency in the previous literature might not be due to the true prevalence of RAS mutation. They could be attributed to the difference in the detection method. As to PAX8/PPARγ rearrangement, Western countries overall had a much higher prevalence than Asian countries (23% vs. 4%, P<0.001), but some European countries had a low incidence, implying regional heterogeneity of PAX8/PPARγ rearrangement. A substantial lack of mutation data in FTC was found in several regions of the world such as Central Asia, Middle East, Africa, and Central and South America. Our results provide the most comprehensive global status of representative genetic alterations in FTC and highlight the similarities and differences between Asian and Western countries.

GLIS rearrangements in thyroid nodules: A key to preoperative diagnosis of hyalinizing trabecular tumor

Hyalinizing trabecular tumor (HTT) is a rare thyroid neoplasm with peculiar morphologic features that overlap with those of papillary thyroid carcinoma (PTC). Specifically, the presence of enlarged oval nuclei, nuclear grooves, and intranuclear pseudoinclusions makes precise cytopathologic diagnosis challenging. If the cytopathologic diagnosis is suspicious for malignancy (Bethesda V) or is malignant (Bethesda VI), a total thyroidectomy, which would be considered an overtreatment, may follow. The recent discovery of the strong association between GLIS fusions and HTT sheds light on its pathogenesis and offers a pathway for its presurgical identification. Although the number of cases analyzed is limited, the recent landmark study shows that GLIS fusions are highly specific for HTT and that lobectomy is the likely appropriate surgical treatment, because these neoplasms, which lack invasion, are benign. For overall success, cytopathologic recognition of the subtle features is important to avoid false-positive diagnoses and directing potential HTT cases toward indeterminate cytopathologic diagnoses, which would trigger further molecular testing. Additional studies are needed to determine whether a malignant counterpart of GLIS fusion-positive HTT exists and if more conservative approaches may be taken.

Are BRAF V600E and K-Ras Mutations Associated With Tumor Aggressiveness in Well-Differentiated Thyroid Cancer?

Aim:

Many clinical studies have shown an association between B-type rapidly growing fibrosarcoma kinase [BRAF(V600E)] mutation and aggressive clinicopathologic features, although some results from others are controversial. Besides, Kirsten rat sarcoma (K-Ras) mutations are more common in endemic iodine deficiency regions, as our country is. However, use of the biologic markers are questioned in clinical practice; they are beginning to be used for the management of patients with thyroid nodules and cancers. The aim of the present study was to evaluate the prevalence of the BRAF(V600E) mutation in tumor samples and its relationship to high-risk clinicopathologic features.

Methods:

From 2000 to 2007, 82 patients with well-differentiated thyroid cancer (WDTC) who underwent surgery in Ege University were enrolled retrospectively in the study. Univariate and multivariate analyses were performed to analyze associations between BRAF(V600E) and K-Ras mutations and clinicopathologic features. We identified 82 patients with WDTC (male:female = 1:3.2).

Results:

The median follow-up was 96 months. The mean age was 46.4 (16–80). None of the all analyzed prognostic factors—age; sex; lymph node metastasis; multifocality; multicentricity; invasion; tumor diameter; and tumor, node, metastasis staging—were correlated with BRAF(V600E) mutation status in the univariate analysis. Meanwhile, none of the analyzed prognostic factors were correlated with K-Ras mutation status.

Discussion:

Although many studies suggest BRAF(V600E) and K-Ras mutations as prognostic factors in WDTC, our results are controversial. BRAF(V600E) and K-Ras mutations have no significant effects on tumor aggressiveness in Turkish patients with WDTC. Our results underline that it is too early to reach a conclusion that BRAF(V600E) and K-Ras mutations are involved with poor clinical outcomes.

GLIS Rearrangement is a Genomic Hallmark of Hyalinizing Trabecular Tumor of the Thyroid Gland

BACKGROUND

Hyalinizing trabecular tumor (HTT) is a rare thyroid neoplasm with a characteristic trabecular growth pattern and hyalinization. This lesion has been the subject of long-term controversy surrounding its genetic mechanisms, relationship to papillary thyroid carcinoma (PTC), and malignant potential. Due to the presence of nuclear features shared with PTC, HTT frequently contributes to a false-positive cytology, which hampers patient management. The goal of this study was to apply genome-wide sequencing analyses to elucidate the genetic mechanisms of HTT and its relationship to PTC.

METHODS

Whole-exome, RNA-Seq, and targeted next-generation sequencing analyses were performed to discover and characterize driver mutations in HTT. RNA-Seq results were used for pathway analysis. Tissue expression of GLIS3 and other proteins was detected by immunohistochemistry. The prevalence of GLIS fusions was studied in 17 tumors initially diagnosed as HTT, 220 PTC, and 10,165 thyroid fine-needle aspiration samples.

RESULTS

Using whole-exome and RNA-Seq analyses of the initial three HTT, no known thyroid tumor mutations were identified, while in-frame gene fusion between PAX8 exon 2 and GLIS3 exon 3 was detected in all tumors. Further analysis identified PAX8-GLIS3 in 13/14 (93%) and PAX8-GLIS1 in 1/14 (7%) of HTT confirmed after blind pathology review. The fusions were validated by Sanger sequencing and FISH. The fusions resulted in overexpression of the 3'-portion of GLIS3 and GLIS1 mRNA containing intact DNA-binding domains of these transcription factors and upregulation of extracellular matrix genes including collagen IV. Immunohistochemistry confirmed upregulation and deposition of collagen IV and pan-collagen in HTT. The analysis of 220 PTC revealed no PAX8-GLIS3 and one PAX8-GLIS1 fusion. PAX8-GLIS3 was prospectively identified in 8/10,165 (0.1%) indeterminate cytology fine-needle aspiration samples; 5/5 resected fusion-positive nodules were HTT on surgical pathology.

CONCLUSIONS

This study demonstrates that GLIS rearrangements, particularly PAX8-GLIS3, are highly prevalent in HTT but not in PTC. The fusions lead to overexpression of GLIS, upregulation of extracellular matrix genes, and deposition of collagens, which is a characteristic histopathologic feature of HTT. Due to unique genetic mechanisms and an indolent behavior, it is proposed to rename this tumor as "GLIS-rearranged hyalinizing trabecular adenoma."

Recent Advances in the Classification of Low-grade Papillary-like Thyroid Neoplasms and Aggressive Papillary Thyroid Carcinomas: Evolution of Diagnostic Criteria

Papillary thyroid carcinomas account for ∼80% of well-differentiated thyroid tumors. During the past decade, several new variants of papillary-like thyroid neoplasms and papillary thyroid carcinomas have been recognized. Some of these neoplasms that were previously classified as malignant have been reclassified as low-grade neoplasms, as the diagnostic criteria have evolved. Similarly, some of the papillary thyroid carcinomas that were previously classified as conventional or classic papillary thyroid carcinomas have now been recognized as more aggressive variants of papillary thyroid carcinomas. Recognizing these differences becomes more important for the proper medical, surgical, and radiotherapeutic management of patients with these neoplasms.

Key genes and pathways predicted in papillary thyroid carcinoma based on bioinformatics analysis

PURPOSE

The aim of this study was to predict the key genes and pathways associated with papillary thyroid carcinoma (PTC).

METHODS

Based on the microarray data of GSE3467 from Gene Expression Omnibus database, we identified the differentially expressed genes (DEGs) between 9 PTC samples and 9 normal controls. With the identified DEGs, functional enrichment analyses were performed. Additionally, a protein-protein interaction network was constructed to screened out some key gene nodes. These key nodes were then performed clustering analysis and pathway enrichment analysis. Furthermore, human PTC-associated network was constructed based on these key genes to investigate the potential relationships between genes and PTC.

RESULTS

A total of 651 up-regulated and 692 down-regulated DEGs were identified in PTC samples compared with controls. The up-regulated DEGs, such as complement component 3 (C3), were mainly enriched in hsa04610:Complement and coagulation cascades. The down-regulated DEGs, including paired box 8 (PAX8), peroxisome proliferator-activated receptor gamma (PPARG), and cadherin 1, type 1 were found enriched in hsa05216:Thyroid cancer. Total 33 DEGs were considered as key genes, such as PAX8, PPARG and Jun proto-oncogene (JUN). Disease-associated network analysis found that 15 key genes such as JUN, PPARG and matrix metallopeptidase 9 (MMP9) were involved in this network.

CONCLUSIONS

DEGs of C3, PPARG, PAX8, JUN and MMP9 were differentially expressed in PTC samples and may be used as potential biomarkers in the diagnosis and treatment of PTC. Additionally, pathways of complement and coagulation cascades and thyroid cancer may also play important roles in the development of PTC.

Pathologic diagnosis of papillary thyroid carcinoma: today and tomorrow

Papillary thyroid carcinoma is the most common malignancy of the thyroid. It is a well-differentiated tumor and the majority behaves in an indolent fashion. The pathologic diagnosis of papillary carcinoma in both cytology and histologic specimens is based upon demonstration of typical nuclear morphology. Using these morphologic criteria, most papillary cancers can be diagnosed with ease, except cases in which there is a paucity of diagnostic nuclear features. Despite advances in the treatment of thyroid cancer, disease recurrences and metastasis can be observed in 20% of cases. Recently, many advances have been made in the pathogenesis of papillary thyroid carcinoma. The notable genetic events include Ret/PTC rearrangements, Ras and BRAF gene mutations. The identification of these has also led to their use in diagnosis and predicting prognosis of papillary thyroid carcinoma. In addition, these involved genes may also serve as targets for cancer chemotherapy in patients where standard thyroid cancer treatment is not effective.

Unusual thyroid tumors: a review of pathologic and molecular diagnosis

The most common thyroid neoplasms are either follicular derived (papillary, follicular and Hürthle cell lesions) or C-cell derived (medullary carcinoma). The diagnosis of these tumors can usually be made at the histologic level, with immunohistochemical stains necessary in some circumstances. Specific molecular mutations have been described that can be diagnostically useful or explain, in part, their pathogenesis, including the well-known Ret/PTC and PPARgamma-PAX8 translocations, point mutations in the Ret, Ras and BRAF genes, and loss of heterozygosity of multiple different tumor suppressor genes. Some unusual tumors of the thyroid gland are more difficult to diagnose. In examining these lesions, the pathologist may use the hematoxylin and eosin-stained morphology, coupled with an analysis of the immunohistochemical staining profiles and possibly analysis of the underlying molecular mutational patterns. These less common thyroid tumors include tall cell and cribriform-morular variants of papillary carcinoma, hyalinizing trabecular tumor, mucoepidermoid and sclerosing mucoepidermoid carcinoma with eosinophilia, poorly differentiated (insular) carcinoma, and undifferentiated (anaplastic) carcinoma. The diagnostic features of these rare tumors, including the histology, immunohistochemical expression profiles and the known molecular mutational profiles of each, are reviewed.

Recent progress of genome study for anaplastic thyroid cancer

Anaplastic thyroid cancer (ATC) belongs to the most malignant and rapidly progressive human thyroid cancers and its prognosis is very poor. Also, it shows high resistance to cancer treatments, so that effective treatment for ATC has not been found to date, and virtually all patients terminate their life rapidly after diagnosis. Although targeted treatment of genetic alterations has emerged as an extremely promising approach to human cancers, such as BRAF in metastatic melanoma, it remains unclear that how commonly genomic alterations are influenced in ATC tumorigenesis. In recent years, genome wide approaches have been exploited to find genetic alterations associated with complex diseases, including cancer. Here, we reviewed the comprehensive genetic alterations in ATC and recent approaches in the context of identifying genomic alterations associated with ATC. Since surprisingly few reports have been published on the genome wide study of ATC, this review puts emphasis on the urgent needs of genomic research for the prevention and treatment of ATC.

Do benign thyroid nodules have malignant potential? An evidence-based review

BACKGROUND

Benign thyroid tumors account for most nodular thyroid disease. Determination of whether a thyroid nodule is benign or malignant is a major clinical dilemma and underlies the decision to proceed to surgery in many patients. Although the accuracy of thyroid nodule fine-needle aspiration (FNA) has reduced the need for surgery over the years, questions regarding how to follow FNA-designated benign nodules remain unresolved. This is true at least in part because of uncertainty over whether some benign nodules harbor malignant potential.

METHODS

An evidence-based review of recent clinical, pathologic, and molecular data is presented. A summary of data and observations from our own experience is also provided.

RESULTS

Review of our recent 10-year experience indicates that 2% of thyroid malignancies arise within a preexisting benign thyroid nodule. In addition, both cytologic and molecular tumor markers, including Gal-3, CITED1, HBME-1, Ras, RET/PTC, and PAX8/PPAR gamma, have been identified in some histopathologically classified benign nodules. Gene expression profiling suggests that follicular adenomas and Hürthle cell adenomas have similarities to both benign and malignant tumors, suggesting that some of these tumors are premalignant. In addition, 10% of surgically excised follicular tumors are encapsulated follicular lesions with nuclear atypia, which have been termed "well-differentiated tumors of uncertain malignant potential." The data available suggest that these tumors could be precursors to carcinoma.

CONCLUSION

Some benign thyroid nodules have malignant potential. Further molecular testing of these tumors can shed light on the pathogenesis of early malignant transformation.

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.

Anaplastic carcinoma of the thyroid arising more often from follicular carcinoma than papillary carcinoma

BACKGROUND

Anaplastic thyroid carcinoma (ATC), a rare and highly malignant tumor, has long been thought to arise from well-differentiated carcinoma (WDC) such as follicular thyroid carcinoma (FTC) and papillary thyroid carcinoma (PTC). The purpose of this study was to test this notion by examining whether and, if so, how often ATC harbors the oncogenes that are commonly associated with WDC, such as RAS in FTC and BRAF in PTC.

METHODS

We analyzed the mutation hotspots of BRAF (codon 600) and N-, K-, and H-RAS (codons 12, 13, and 61) in 16 ATCs. We also examined two genes, PIK3CA (exons 9 and 20) and TP53 (exons 5-9), both of which have been reported in ATCs.

RESULTS

The results showed that approximately 31% (5 of 16) of ATCs harbored N-RAS mutation, 6% (1 of 16) had mutated BRAF, and approximately 56% (9 of 16) had mutated TP53. As to the three ATCs that had coexisted PTCs, mutated BRAF was detected in all PTC components but only in one ATC, while mutated PIK3CA was found in only one PTC component but not in the ATC.

CONCLUSION

A number of ATCs arise from WDCs, more often from RAS-mutant tumors than from BRAF-mutant tumors, implying that particular attention should be paid to the WDC harboring RAS mutation.

Pathology and genetics of thyroid carcinoma

Carcinomas of the thyroid comprise a heterogeneous group of neoplasms with distinctive clinical and pathological characteristics. Over the past 15 years, the application of molecular technologies to the study of these neoplasms has elucidated critical genetic pathways associated with the development of specific thyroid tumor types. In papillary thyroid carcinoma (PTC), genetic events involve RET and TRK (rearrangements) and BRAF and RAS (mutations), although RAS mutations are uncommon except in the follicular variant of PTC. These genetic alterations, which rarely overlap in the same tumor, result in signaling abnormalities in the mitogen-activated protein kinase pathway. In contrast, genetic alterations in follicular carcinomas include PAX8-PPARgamma translocations and RAS mutations while mutations of CTNNB1 and p53 have been implicated in the development and progression of poorly differentiated and undifferentiated (anaplastic) thyroid carcinomas. Germline mutations of RET are responsible for the development of heritable forms of medullary thyroid carcinoma (MTC) while somatic mutations of this oncogene are found in a significant proportion of sporadic MTCs. The results of these studies not only have provided additional approaches to thyroid tumor classification, but also have stimulated the development of novel approaches to tumor diagnosis and additional parameters for prognostic assessment and potential biologic therapeutic strategies.

The status of CDKN2A alpha (p16INK4A) and beta (p14ARF) transcripts in thyroid tumour progression

CDKN2A locus on chromosome 9p21 encodes two tumour suppressor proteins pl6^INK4A, which is a regulator of the retinoblastoma (RB) protein, and p14^ARF, which is involved in the ARF–Mdm2–p53 pathway. The aim of this study was to determine if CDKN2A gene products are implicated in differentiated thyroid carcinogenesis and progression. We used real-time quantitative RT–PCR and immunohistochemistry to assess both transcripts and proteins levels in 60 tumours specimens. Overexpression of p14^ARF and pl6^INK4A was observed in follicular adenomas, follicular carcinomas and papillary carcinomas, while downregulation was found in oncocytic adenomas compared to nontumoral paired thyroid tissues. These deregulations were statistically significant for pl6^INK4a (P=0.006) in follicular adenomas and close to statistical significance for p14^ARF in follicular adenomas (P=0.06) and in papillary carcinomas (P=0.05). In all histological types, except papillary carcinomas, we observed a statistically significant relationship between p14^ARF and E2F1 (r=0.64 to 1, P<0.05). Our data are consistent with involvement of CDKN2A transcript upregulation in thyroid follicular tumorigenesis as an early event. However, these deregulations do not appear to be correlated to the clinical outcome and they could not be used as potential prognostic markers.

Fractional allelic loss of tumor suppressor genes identifies malignancy and predicts clinical outcome in follicular thyroid tumors

Thyroid follicular tumors can be challenging diagnostically and clinically, because the cytologic and histologic features can be subtle and prognosis is also difficult to predict. In this study, we analyzed thyroid follicular tumors with known long-term follow-up for a molecular panel of tumor suppressor genes to determine whether this molecular approach has prognostic significance. Microdissection and DNA extraction were performed from tumor and normal tissue. Polymerase chain reaction (PCR) was performed for 13 short tandem repeats at or near tumor suppressor genes. PCR product was detected using semiquantitative capillary gel electrophoresis and fractional allelic loss (FAL) was calculated. We included eight adenomas, three minimally invasive carcinomas, four angioinvasive carcinomas, and three widely invasive carcinomas with a mean follow-up of 77 months. Three patients died of disease and an additional two are alive with disease recurrence/metastasis. The mean FAL for benign tumors (14%) was significantly different from that of malignant tumors (56%, p < 0.001). Patients with a follicular tumor who had no evidence of disease recurrence had a mean FAL of 22% and those with disease recurrence or death from disease had a mean of 78% (p < 0.002). Based on these results, a tumor suppressor gene panel for allelic imbalance in follicular-derived tumors (FTT) may correlate with both malignancy and outcome in patients with follicular-derived carcinomas of the thyroid.

Molecular classification of papillary thyroid carcinoma: distinct BRAF, RAS, and RET/PTC mutation-specific gene expression profiles discovered by DNA microarray analysis

Thyroid cancer poses a significant clinical challenge, and our understanding of its pathogenesis is incomplete. To gain insight into the pathogenesis of papillary thyroid carcinoma, transcriptional profiles of four normal thyroids and 51 papillary carcinomas (PCs) were generated using DNA microarrays. The tumors were genotyped for their common activating mutations: BRAF V600E point mutation, RET/PTC1 and 3 rearrangement and point mutations of KRAS, HRAS and NRAS. Principal component analysis based on the entire expression data set separated the PCs into three groups that were found to reflect tumor morphology and mutational status. By combining expression profiles with mutational status, we defined distinct expression profiles for the BRAF, RET/PTC and RAS mutation groups. Using small numbers of genes, a simple classifier was able to classify correctly the mutational status of all 40 tumors with known mutations. One tumor without a detectable mutation was predicted by the classifier to have a RET/PTC rearrangement and was shown to contain one by fluorescence in situ hybridization analysis. Among the mutation-specific expression signatures were genes whose differential expression was a direct consequence of the mutation, as well as genes involved in a variety of biological processes including immune response and signal transduction. Expression of one mutation-specific differentially expressed gene, TPO, was validated at the protein level using immunohistochemistry and tissue arrays containing an independent set of tumors. The results demonstrate that mutational status is the primary determinant of gene expression variation within these tumors, a finding that may have clinical and diagnostic significance and predicts success for therapies designed to prevent the consequences of these mutations.

Role of the BLT2, a leukotriene B4 receptor, in Ras transformation

Oncogenic Ras is known to drive both the Rac and Raf-MAP-kinase pathways, which act in concert to cause cell transformation. Unlike the Raf-MAP-kinase cascade, however, the downstream elements of Rac pathway are not fully understood. Previously, we showed that cytosolic phospholipase A2 (cPLA2) and subsequent metabolism of arachidonic acid act downstream of Rac to mediate the transformation signaling induced by Ha-Ras(V12). In the present study, we observed that leukotriene B4 (LTB4) and its synthetic enzymes as well as BLT2, the low-affinity LTB4 receptor, are all elevated in Ha-Ras(V12)-transformed cells. In addition, the malignant phenotypes of Ras-transformed cells were markedly inhibited by BLT2 blockade, as was their tumorigenicity in vivo. Finally, in situ hybridization analysis revealed that expression of BLT2 is significantly upregulated in a variety of human cancers. Taken together, our results suggest that an LTB4-BLT2-linked cascade plays a crucial mediatory role in the cell transformation induced by oncogenic Ha-Ras(V12), possibly acting downstream of Rac-cPLA2.

Fine-Needle Aspiration of Thyroid Nodules: Past, Present, and Future

OBJECTIVE

To present a review of the traditional and more recent techniques and applications of thyroid fine-needle aspiration biopsy.

METHODS

We describe the cytologic features and differential diagnoses of various thyroid lesions, outline recommendations for diagnostic categories, and discuss new techniques that have shown some promise in the diagnosis of thyroid nodule fine-needle aspiration specimens.

RESULTS

Fine-needle aspiration biopsy of the thyroid has proved to be an excellent diagnostic tool in the initial management of thyroid nodules. Numerous studies have shown its high sensitivity and specificity in diagnosing malignant tumors of the thyroid, especially papillary thyroid carcinoma. As with other diagnostic tests, however, its effectiveness is highly dependent on the expertise of the operator performing the procedure and the adequacy of the specimen for interpretation of the cytomorphologic features. On-site evaluation of thyroid specimens promotes adequate specimen sampling and reduces the incidence of nondiagnostic specimens. Diagnostic reports on thyroid fine-needle aspiration should include patient demographics and pertinent clinical history, site and size of the thyroid nodule, mode of aspiration, number of needle passes, assessment of specimen adequacy, diagnosis, and recommendations. Although immunohistochemical and molecular markers have received considerable attention recently, additional studies are needed before they can be used to separate benign from malignant follicular thyroid lesions.

CONCLUSION

Overall, fine-needle aspiration biopsy of thyroid nodules has proved to be sensitive, specific, and well accepted by patients because of minimal discomfort and complications.

Ki-ras mutational analysis in rat follicular-cell proliferative lesions of the thyroid gland induced by radioactive iodine and potassium perchlorate

Although in both human and experimental pathology ras mutations have been related to the origin and progression of follicular-cell tumours, reports differ considerably with respect to the frequency of such mutations. The present paper reports, using direct sequencing, the incidence of Ki-ras mutations (codons 12 and 13) in follicular-cell carcinomas of the thyroid gland in Wistar rats induced by administration of radioactive iodine and potassium perchlorate. Direct sequencing revealed no mutations in the amplified gene segment of any of the 72 carcinoma samples studied. This absence of mutations agrees with some and is in sharp contrast with other previous reports in the literature, both for experimental animals and in studies of human thyroid follicular-cell carcinoma. Our results suggest that Ki-ras activation via mutations at codons 12 and 13 is neither a constant event nor an early event in the development of rat thyroid follicular-cell carcinoma.

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.

RB and cyclin dependent kinase pathways: defining a distinction between RB and p16 loss in lung cancer

The genetic components of the RB:CDK:cyclin:p16 tumor suppressor pathway undergo mutational and epigenetic alterations in a wide range of human cancers and serve as critical targets for inactivation by the transforming oncoproteins of several DNA tumor viruses. Lung cancer has been a useful model system for these studies as it was the first tumor to demonstrate an important role for RB in the genesis of a common adult malignancy and was also the first human cancer to demonstrate genetic evidence for a multi-component RB:p16 tumor suppressor pathway. Lung tumorigenesis, however, is a complex disease process that requires longstanding carcinogen exposure in order to acquire somatic alterations at many distinct genetic loci. Understanding the multifunctional properties of RB to regulate cell proliferation, differentiation, and apoptosis and how they relate to the sequential accumulation of other clonal gene defects will be essential in order to understand the specific patterns of gene inactivation observed in different subtypes of lung cancer and to fulfill the promise of 'molecular target' therapeutics.

Secondary malignant giant-cell tumour of bone: molecular abnormalities of p53 and H-ras gene correlated with malignant transformation

AIMS

We report two cases of secondary malignant giant-cell tumour occurring without irradiation therapy. To elucidate the mechanism of malignant transformation in this tumour, we searched for the molecular abnormalities of p53, MDM2 and the H-ras genes.

METHODS AND RESULTS

These cases were retrieved after a review of 103 cases of primary giant-cell tumour of bone, registered in our institute. One case occurred in the distal femur of a 42-year-old female after surgical curettage, while the other arose in the acetabulum of a 25-year-old male after en bloc resection. Microscopically, the malignant tumour in the distal femur was composed of a proliferation of ovoid or fusiform cells arranged in fascicles with high mitotic activities. The malignant transformed tumour in the acetabulum was made up of pleomorphic tumour cells with atypical mitoses. In the tumour of the distal femur, both p53 and H-ras mutations were detected. Abnormal nuclear accumulation of p53 protein and c-myc expression were also revealed by immunohistochemistry. In both cases, the recurrent malignant tumour over-expressed MMP-9 and revealed a higher MIB-1-labelling index compared with the primary conventional giant-cell tumour.

CONCLUSIONS

Our results suggest that multiple oncogene or tumour suppressor gene mutations may play an important role during malignant transformation in conventional giant-cell tumours.

H-, K-, and N-ras gene mutation in atypical fibroxanthoma and malignant fibrous histiocytoma

Atypical fibroxanthoma (AFX) which is histologically similar to malignant fibrous histiocytoma (MFH), occurs in the sun-exposed skin. The presence of mutations at codons 12 and 13 of the H- and K-ras genes and in exons 1 and 2, which include codons 12, 13, and 61, of the N-ras gene was studied in 8 cases of AFX and 8 cases of storiform-pleomorphic-type MFH using polymerase chain reaction (PCR)-restriction fragment length polymorphism and PCR-single-conformation polymorphism. Two of the 8 cases of MFH showed ras mutations in the H-ras gene at codon 12 (GGC-AGC) and in the K-ras gene at codon 13 (GGC-GAC). H- and K-ras gene mutations were not seen in any of the cases of AFX (0 of 8). N-ras gene mutation was not detected in either the AFX (0 of 8) or MFH (0 of 8) cases. In conclusion, although the number of cases in this study was small, H- and K-ras genes were present in some of the MFH cases and accordingly may play an important role in the pathogenesis of MFH. In addition, the finding that H-, K-, and N-ras gene mutations are not present in AFX may indicate why AFX has a more favorable behavior than MFH.

Genetic markers in thyroid neoplasia

Cancer is a disease of genes. Detection of genetic abnormalities associated with cancers of various cell types can now be used for genetic counseling, diagnosis or treatment selection. In the case of thyroid cancer, genetic testing for mutations of the RET oncogene has had a profound effect on the management of medullary thyroid carcinomas. There is also considerable information on the genetic changes associated with development and progression of cancers of thyroid follicular cells, although these have not yet proven to be of practical value for clinical diagnosis or to guide prognosis and therapy.

H-ras oncogene mutation in dedifferentiated chondrosarcoma: polymerase chain reaction-restriction fragment length polymorphism analysis

Dedifferentiated chondrosarcomas, which are known for their poor prognosis, are characterized by conventional chondrosarcoma with high-grade anaplastic components. Activating mutations in ras genes are a common genetic abnormality in human malignancies. The presence of point mutations at codons 12 and 13 of the H-ras gene was studied in 20 formalin-fixed paraffin-embedded chondrosarcomas, comprising 11 cases of conventional chondrosarcoma (six Grade 1 cases and five Grade 2 cases) and nine cases of dedifferentiated chondrosarcoma, using polymerase chain reaction-restriction fragment length polymorphism and direct sequencing analysis. H-ras mutations were only seen in two out of the nine cases of dedifferentiated chondrosarcoma (2/9, 22%) and they were not seen in any of the cases of conventional chondrosarcoma (0/11, 0%). Dedifferentiated chondrosarcomas had a worse prognosis than conventional chondrosarcomas (P < .01); among the patients with dedifferentiated chondrosarcomas, those with H-ras mutation (n = 2) tended to have a worse prognosis than those without (n = 7), although the difference was not statistically significant (P = 0.068). Our results would seem to suggest that H-ras mutation may occur during the course of dedifferentiation and may also have some effect on malignant potential.

H-ras oncogene mutation in dedifferentiated liposarcoma. Polymerase chain reaction-restriction fragment length polymorphism analysis

Point mutations of the ras gene family (K-ras, H-ras, and N-ras) are thought to be involved in the development of a variety of human tumors. Dedifferentiated liposarcoma is characterized by the coexistence of well-differentiated (WD) and high-grade anaplastic (HG) components. The presence of point mutations at codons 12 and 13 of the H-ras gene was studied in 34 liposarcomas, comprising 15 well-differentiated liposarcomas and 19 dedifferentiated liposarcomas, and in 8 storiform-pleomorphic type malignant fibrous histiocytomas (MFHs) using polymerase chain reaction-restriction fragment length polymorphism and direct sequencing analysis. The 2 components of dedifferentiated liposarcoma were analyzed independently. H-ras mutations were seen only in dedifferentiated liposarcomas (4/19 [21%]), 1 in WD components and 3 in HG components. The mutation was not seen in any of 15 cases of well-differentiated liposarcoma. MFHs showed an H-ras mutation in 1 (12%) of 8 cases. Our results seem to suggest that the H-ras mutation is a relatively uncommon event in dedifferentiated liposarcoma, which may demonstrate an epiphenomenon of dedifferentiation in dedifferentiated liposarcoma.

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.

Molecular abnormalities of p53, MDM2, and H-ras in synovial sarcoma

Forty-nine cases of synovial sarcoma were evaluated for mutation of the p53 gene, amplification of the MDM2 gene and mutation of the H-ras gene, and for the relation of these factors to overall survival and clinicopathologic parameters. All investigations were carried out on formalin-fixed paraffin-embedded materials. Furthermore, we evaluated the expression of p53 protein, MDM2, and p21(WAF1/CIP1) immunohistochemically in these cases, together with an assessment of proliferative activities using monoclonal antibody MIB-1. Nine of the 49 cases (18.4%) had p53 gene alteration detected by polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and direct sequencing. Eleven cases (24%) showed nuclear accumulation of p53 protein in more than 10% of the tumor cells. Among them, only three cases contained gene mutations. There was no correlation between p53 nuclear accumulation and p53 gene alteration. MDM2 gene amplification, as shown by differential PCR, was observed in 19 out of 47 cases (40%). Nineteen out of 49 cases (38.8%) showed immunoreactivity for MDM2. MDM2 gene amplification and the expression of MDM2 protein showed a significant positive relationship (P = 0.0004). Moreover, MDM2 immunoreaction was significantly correlated with nuclear accumulation of p53 protein (P = 0.023). Positive immunoreaction for p21(WAF1/CIP1) was observed in 21 out of 48 cases (43.8%). p21(WAF1/CIP1) expression was correlated with p53 protein expression. H-ras gene mutations were seen in only three cases (6.1%). All mutations were in codon 12 (one GGC-to-AGC [Gly-to-Ser] mutation and two GGC-to-GAC [Gly-to-Ap] mutations). The gene alteration of p53, MDM2, and H-ras did not affect the patients' prognosis. Although the cases with positive immunoreaction for p53 tended to have a worse prognosis, the difference was not statistically significant (P = 0.13). No correlation was observed between MIB-1 LI and the immunohistochemical expression of p53, MDM2, and p21(WAF1/CIP1) or the mutation status of p53 and H-ras. On the other hand, high MIB-1 LI (more than 10) significantly correlated with poor prognosis (P < 0.0001). Our results suggest that p53 gene mutation does not appear to be a major prognostic factor and H-ras mutations are infrequent in synovial sarcoma.

N-ras mutation in poorly differentiated thyroid carcinomas: correlation with bone metastases and inverse correlation to thyroglobulin expression

Codon 61 of the N-ras oncogene was screened for mutations in 99 surgically resected thyroid carcinomas by a polymerase chain resection (PCR)-based method (PCR-primer introduced restriction with enrichment of mutant alleles [PCR-PIREMA]). A point mutation of the N-ras oncogene at the codon 61 was detected in 16 of 99 (16.2%) thyroid carcinomas examined by this method. No RAS alteration was detected in the group of 11 medullary thyroid carcinomas, while 3 of 31 (10.0%) papillary carcinomas, 2 of 5 (40%) follicular carcinomas, 8 of 44 (18.2%) poorly differentiated carcinomas, and 3 of 5 (60%) undifferentiated carcinomas showed an activation of N-RAS proto-oncogene. Interestingly, two primary follicular tumors and their corresponding bone metastases, showed N-ras mutations. In the same cases we evaluated the expression of thyroglobulin by immunohistochemical analysis. Although the majority of well-differentiated carcinomas expressed a high level of thyroglobulin, the expression of the same antigen was absent or only occasional weakly positive in 33 of 44 poorly differentiated carcinomas. Interestingly, N-ras mutation was restricted to the group of tumours with low or absent thyroglobulin expression, suggesting that this genetic change is prevalent in less differentiated tumors.

Ras mutations are uncommon in sporadic thyroid cancer in children and young adults

Mutations in the ras genes (H-ras, K-ras, and N-ras) occur in 10-15% of all human cancers, and commonly arise from single base substitutions at codons 12, 13, or 61. Although ras mutations have been found in adult thyroid cancers, they were absent from the two studies which examined childhood thyroid cancers. Both studies included only children with radiation induced thyroid cancer, and it remains unclear if ras mutations occur in children without radiation exposure. To answer this question, we examined archival tissue blocks from 31 children with papillary thyroid cancer (PTC) 4 with follicular thyroid cancer (FTC), 2 with medullary thyroid cancer (MTC), and 1 with lymphoma (LYM). Only 1 patient with PTC had previous radiation exposure. Genomic DNA was extracted and used for PCR amplification of the ras genes. The PCR products were analyzed by oligospecific hybridization for mutations at codons 12, 13, and 61. Two of the PTCs (6.5%) contained ras mutations. Both patients had class II disease and no history of previous radiation exposure. One patient subsequently developed bone and lung metastases. The patient with lymphoma also had a ras mutation (N-61), but ras mutations were absent from all FTC and MTC. These results suggest that ras mutations are uncommon in spontaneous childhood thyroid cancer, but occur with a frequency similar to that found in previous reports of adult differentiated thyroid cancers. The number of subjects was too small to determine if ras mutations are more common in patients with aggressive papillary thyroid cancer.

Fine-needle aspiration biopsy cytology of hyalinizing trabecular adenomas of the thyroid

Cytologic smears from fine-needle aspirates of three histologically and ultrastructurally confirmed hyalinizing trabecular adenomas of the thyroid (HTAT) were reviewed. In two cases a cytodiagnosis of HTAT was suggested, and in one patient a diagnosis of trabecular epithelial neoplasm was made. In all three cases, small clusters and sheets of epithelial cells with abundant, filamentous, vacuolated, and ill-defined cytoplasm were present. The nuclei were slightly pleomorphic and showed nuclear overlapping, nuclear grooves, and intranuclear cytoplasmic inclusions. Small and irregular fragments of acellular hyalinized material (AHM) were noted within the tumor cell clusters in the first two cases. In the third patient, large syncytial sheets and anastomotic cords of epithelial cells showing ill-defined, filamentous cytoplasm, slightly pleomorphic nuclei, nuclear overlapping, intranuclear cytoplasmic inclusions, and nuclear grooves were present. Fragments of AHM were not observed within clusters and syncytial sheets of tumor cells.

The molecular genetics of endocrine tumours

The molecular genetics of endocrine tumours is an area of great interest, due to the heterogeneity of endocrine tumour types, the association of hormone over-production in some cases, and the wide variation in tumour behaviour. Genes implicated fall into functional categories such as oncogenes, in which mutations tend to cause activation, and tumour suppressor genes, in which mutations lead to loss of function. Oncogenes include the receptor tyrosine kinases such as RET, signal transduction proteins and other molecules such as cell cycle regulators and nuclear proteins. Tumour suppressor genes include cell cycle regulators such as p53 and other molecules such as the MEN 1 gene. Loss of heterozygosity studies help in the initial localisation of the latter. Endocrine tumours, as with other tumours, develop as a result of a combination of genetic events, and in the paediatric age group they often occur in the setting of familial cancer syndromes. In this review we analyse the main genetic lesions which have been described in endocrine tumours. There has been an explosion of knowledge in the last 5 years including the identification of the causative genes for MEN 2 and most recently for MEN 1. Characterisation of such genes also aids in the study of somatic mutations in sporadic versions of the same tumour types as occur in the familial syndromes. Identification of a genetic predisposition to a certain tumour has management implications that are still to be clarified in most cases, although in the case of MEN 2 the guidelines for prophylactic thyroidectomy are generally well accepted.