Do Molecular Profiles of Primary Versus Metastatic Radioiodine Refractory Differentiated Thyroid Cancer Differ?

Management of metastatic radioiodine refractory differentiated thyroid cancer (DTC) can be a therapeutic challenge. Generally, little is known about the paired molecular profile of the primary tumor and the metastases and whether they harbor the same genetic abnormalities. The present study compared the molecular profile of paired tumor specimens (primary tumor/metastatic sites) from patients with radioiodine refractory DTC in order to gain insight into a possible basis for resistance to radioiodine. Twelve patients with radioiodine refractory metastases were studied; median age at diagnosis of 61 years (range, 25-82). Nine patients had papillary TC (PTC), one had follicular TC (FTC), and two had Hürthle cell TC (HTC). Distant metastases were present in the lungs (n = 10), bones (n = 4), and liver (n = 1). The molecular profiling of paired tumors was performed with a panel of 592 genes for Next Generation Sequencing, RNA-sequencing, and immunohistochemistry. Digital microfluidic PCR was used to investigate TERT promoter mutations. The genetic landscape of all paired sites comprised BRAF, NRAS, HRAS, TP53, ATM, MUTYH, POLE, and NTRK genes, including BRAF and NTRK fusions. BRAF V600E was the most common point mutation in the paired specimens (5/12). TERT promoter mutation C228T was detected in one case. PD-L1 expression at metastatic sites was highly positive (95%) for one patient with HTC. All specimens were stable for microsatellite instability testing, and the tumor mutation burden was low to intermediate. Therefore, the molecular profile of DTC primary and metastatic lesions can show heterogeneity, which may help explain some altered responses to therapeutic intervention.

White-tailed eagle (Haliaeetus albicilla) and great cormorant (Phalacrocorax carbo) nestlings as spatial sentinels of Baltic acidic sulphate soil associated metal contamination

Sulphate soils, characterised by low pH conditions, are found worldwide, and are potentially large sources of metal contamination, often exceeding industrial emissions. Metal leaching from sulphate soils has been shown to be harmful to aquatic organisms, but the cascading effect on exposure in apex avian predators has not been studied earlier. With the present study we aimed at evaluating the potential of white-tailed eagle (Haliaeetus albicilla) and great cormorant (Phalacrocorax carbo) nestlings, collected from nests located either in sulphate soil or control areas, for monitoring spatial contaminant trends of metals typically associated with sulphate soils. In blood of white-tailed eagles, the concentrations of aluminium and cobalt were significantly higher in sulphate soil areas. In blood of great cormorants, the concentrations of copper and manganese were so, while the concentration of zinc was found to be lower. Also, we observed an interaction between the latitude and soil type in cobalt and lithium concentrations of great cormorants, showing that concentrations in the sulphate soil associated nestlings rose more steeply towards the north than in the control group. Latitudinal trends of higher concentrations in the south were found in cadmium, manganese, and copper of white-tailed eagle nestlings, while thallium of white-tailed eagle nestlings, and thallium and zinc of great cormorant nestlings showed a latitudinal trend of higher concentrations in the north. Concentrations of several metals correlated positively within a species indicating covariation in metal exposure. Generally, the metal concentrations in both species were similar to levels reported to be below toxicity thresholds in other species. These results indicate, that white-tailed eagle and great cormorant nestling metal burdens may indicate environmental contamination from acidic sulphate soil runoff, and that they may act as indicators of latitudinal gradient identifying different contamination sources.

Differential Clinicopathological Risk and Prognosis of Major Papillary Thyroid Cancer Variants

CONTEXT

Individualized management, incorporating papillary thyroid cancer (PTC) variant-specific risk, is conceivably a useful treatment strategy for PTC, which awaits comprehensive data demonstrating differential risks of PTC variants to support.

OBJECTIVE

This study sought to establish the differential clinicopathological risk of major PTC variants: conventional PTC (CPTC), follicular-variant PTC (FVPTC), and tall-cell PTC (TCPTC).

METHODS

This was a retrospective study of clinicopathological outcomes of 6282 PTC patients (4799 females and 1483 males) from 26 centers and The Cancer Genome Atlas in 14 countries with a median age of 44 years (interquartile range, 33-56 y) and median follow-up time of 37 months (interquartile range, 15-82 mo).

RESULTS

The cohort consisted of 4702 (74.8%) patients with CPTC, 1126 (17.9%) with FVPTC, and 239 (3.8%) with TCPTC. The prevalence of high-risk parameters was significantly different among the three variants, including extrathyroidal invasion, lymph node metastasis, stages III/IV, disease recurrence, mortality, and the use (need) of radioiodine treatment (all P < .001), being highest in TCPTC, lowest in FVPTC, and intermediate in CPTC, following an order of TCPTC > CPTC ≫ FVPTC. Recurrence and mortality in TCPTC, CPTC, and FVPTC were 27.3 and 6.7%, 16.1 and 2.5%, and 9.1 and 0.6%, corresponding to events per 1000 person-years (95% confidence interval [CI]) of 92.47 (64.66-132.26) and 24.61 (12.31-49.21), 34.46 (30.71-38.66), and 5.87 (4.37-7.88), and 24.73 (18.34-33.35) and 1.68 (0.54-5.21), respectively. Mortality hazard ratios of CPTC and TCPTC over FVPTC were 3.44 (95% CI, 1.07-11.11) and 14.96 (95% CI, 3.93-56.89), respectively. Kaplan-Meier survival analyses showed the best prognosis in FVPTC, worst in TCPTC, and intermediate in CPTC in disease recurrence-free probability and disease-specific patient survival. This was particularly the case in patients at least 45 years old.

CONCLUSION

This large multicenter study demonstrates differential prognostic risks of the three major PTC variants and establishes a unique risk order of TCPTC > CPTC ≫ FVPTC, providing important clinical implications for specific variant-based management of PTC.

IQGAP1 plays an important role in the invasiveness of thyroid cancer

PURPOSE

This study was designed to explore the role of IQGAP1 in the invasiveness of thyroid cancer and its potential as a novel prognostic marker and therapeutic target in this cancer.

EXPERIMENTAL DESIGN

We examined IQGAP1 copy gain and its relationship with clinicopathologic outcomes of thyroid cancer and investigated its role in cell invasion and molecules involved in the process.

RESULTS

We found IQGAP1 copy number (CN) gain ≥ 3 in 1 of 30 (3%), 24 of 74 (32%), 44 of 107 (41%), 8 of 16 (50%), and 27 of 41 (66%) of benign thyroid tumor, follicular variant papillary thyroid cancer (FVPTC), follicular thyroid cancer (FTC), tall cell papillary thyroid cancer (PTC), and anaplastic thyroid cancer, respectively, in the increasing order of invasiveness of these tumors. A similar tumor distribution trend of CN ≥ 4 was also seen. IQGAP1 copy gain was positively correlated with IQGAP1 protein expression. It was significantly associated with extrathyroidal and vascular invasion of FVPTC and FTC and, remarkably, a 50%-60% rate of multifocality and recurrence of BRAF mutation-positive PTC (P = 0.01 and 0.02, respectively). The siRNA knockdown of IQGAP1 dramatically inhibited thyroid cancer cell invasion and colony formation. Coimmunoprecipitation assay showed direct interaction of IQGAP1 with E-cadherin, a known invasion-suppressing molecule, which was upregulated when IQGAP1 was knocked down. This provided a mechanism for the invasive role of IQGAP1 in thyroid cancer. In contrast, IQGAP3 lacked all these functions.

CONCLUSIONS

IQGAP1, through genetic copy gain, plays an important role in the invasiveness of thyroid cancer and may represent a novel prognostic marker and therapeutic target for this cancer.

Highly prevalent genetic alterations in receptor tyrosine kinases and phosphatidylinositol 3-kinase/akt and mitogen-activated protein kinase pathways in anaplastic and follicular thyroid cancers

CONTEXT

Genetic alterations in receptor tyrosine kinases (RTKs) and phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK pathways have not been fully defined in anaplastic and follicular thyroid cancers [anaplastic thyroid cancer (ATC), follicular thyroid cancer (FTC)].

OBJECTIVE

The objective of the study was to explore a wide-range genetic basis for the involvement of these pathways in ATC.

DESIGN

We examined mutations and copy number gains of a large panel of genes in these pathways and corresponding phosphorylation of ERK (p-ERK) and Akt.

RESULTS

We found frequent copy gains of RTK genes, including EGFR, PDGFRalpha and -beta, VEGFR1 and 2, KIT, and MET and in PIK3Ca, PIK3Cb, and PDK1 genes in the PI3K/Akt pathway. Mutations of Ras, PIK3Ca, PTEN, and BRAF genes and RET/PTC rearrangements were common, whereas mutations in PDK1, Akt1, Akt2, and RTK genes were uncommon in ATC. Overall, 46 of 48 ATC (95.8%) harbored at least one genetic alteration, and coexistence of two or more was seen in 37 of 48 ATC (77.1%). These genetic alterations were somewhat less common in FTC. Genetic alterations that could activate both the PI3K/Akt and MAPK pathways were found in 39 of 48 ATC (81.3%). RTK gene copy gains were preferentially associated with p-Akt, suggesting their dominant role in activating the PI3K/Akt pathway. The phosphorylation of Akt was far more common than p-ERK in FTC, and both were relatively common and often coexisted in ATC.

CONCLUSIONS

Genetic alterations in the RTKs and PI3K/Akt and MAPK pathways are extremely prevalent in ATC and FTC, providing a strong genetic basis for an extensive role of these signaling pathways and the development of therapies targeting these pathways for ATC and FTC, particularly the former.

Genetic alterations and their relationship in the phosphatidylinositol 3-kinase/Akt pathway in thyroid cancer

PURPOSE

To investigate the overall occurrence and relationship of genetic alterations in the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in thyroid tumors and explore the scope of this pathway as a therapeutic target for thyroid cancer.

EXPERIMENTAL DESIGN

We examined collectively the major genetic alterations and their relationship in this pathway, including PIK3CA copy number gain and mutation, Ras mutation, and PTEN mutation, in a large series of primary thyroid tumors.

RESULTS

Occurrence of any of these genetic alterations was found in 25 of 81 (31%) benign thyroid adenoma (BTA), 47 of 86 (55%) follicular thyroid cancer (FTC), 21 of 86 (24%) papillary thyroid cancer (PTC), and 29 of 50 (58%) anaplastic thyroid cancer (ATC), with FTC and ATC most frequently harboring these genetic alterations. PIK3CA copy gain was associated with increased PIK3CA protein expression. A mutual exclusivity among these genetic alterations was seen in BTA, FTC, and PTC, suggesting an independent role of each of them through the PI3K/Akt pathway in the tumorigenesis of the differentiated thyroid tumors. However, coexistence of these genetic alterations was increasingly seen with progression from differentiated tumor to undifferentiated ATC. Their coexistence with BRAF mutation was also frequent in PTC and ATC.

CONCLUSIONS

The data provide strong genetic implication that aberrant activation of PI3K/Akt pathway plays an extensive role in thyroid tumorigenesis, particularly in FTC and ATC, and promotes progression of BTA to FTC and to ATC as the genetic alterations of this pathway accumulate. Progression of PTC to ATC may be facilitated by coexistence of PI3K/Akt pathway-related genetic alterations and BRAF mutation. The PI3K/Akt pathway may thus be a major therapeutic target in thyroid cancers.

Gene expression and functional evidence of epithelial-to-mesenchymal transition in papillary thyroid carcinoma invasion

Papillary thyroid carcinomas (PTCs) that invade into local structures are associated with a poor prognosis, but the mechanisms for PTC invasion are incompletely defined, limiting the development of new therapies. To characterize biological processes involved in PTC invasion, we analyzed the gene expression profiles of microscopically dissected intratumoral samples from central and invasive regions of seven widely invasive PTCs and normal thyroid tissue by oligonucleotide microarray and performed confirmatory expression and functional studies. In comparison with the central regions of primary PTCs, the invasive fronts overexpressed TGF beta, NFkappaB and integrin pathway members, and regulators of small G proteins and CDC42. Moreover, reduced levels of mRNAs encoding proteins involved in cell-cell adhesion and communication were identified, consistent with epithelial-to-mesenchymal transition (EMT). To confirm that aggressive PTCs were characterized by EMT, 34 additional PTCs were examined for expression of vimentin, a hallmark of EMT. Overexpression of vimentin was associated with PTC invasion and nodal metastasis. Functional, in vitro studies demonstrated that vimentin was required both for the development and maintenance of a mesenchymal morphology and invasiveness in thyroid cancer cells. We conclude that EMT is common in PTC invasion and that vimentin regulates thyroid cancer EMT in vitro.

Association of aberrant methylation of tumor suppressor genes with tumor aggressiveness and BRAF mutation in papillary thyroid cancer

The role of aberrant tumor suppressor gene methylation in the aggressiveness of papillary thyroid cancer (PTC) has not been documented. By showing promoter methylation-induced gene silencing in PTC-derived cell lines, we first demonstrated the functional consequence of methylation of several recently identified tumor suppressor genes, including those for tissue inhibitor of metalloproteinase-3 (TIMP3), SLC5A8, death-associated protein kinase (DAPK) and retinoic acid receptor beta2 (RARbeta2). We then investigated the role of methylation of these genes in the aggressiveness of PTC by examining the relationship of their aberrant methylation to clinicopathological characteristics and BRAF mutation in 231 primary PTC tumors. Methylation of TIMP3, SLC5A8 and DAPK was significantly associated with several aggressive features of PTC, including extrathyroidal invasion, lymph node metastasis, multifocality and advanced tumor stages. Methylation of these genes was also significantly associated with BRAF mutation in PTC, either individually or collectively in various combinations. Methylation of these genes, either individually or collectively, occurred more frequently in more aggressive classical and tall-cell PTC subtypes than in less aggressive follicular-variant PTC, with the latter known to infrequently harbor BRAF mutation. Several other tumor suppressor genes investigated were not methylated. These results suggest that aberrant methylation and hence silencing of TIMP3, SLC5A8, DAPK and RARbeta2, in association with BRAF mutation, may be an important step in PTC tumorigenesis and progression.

Molecular genetic study comparing follicular variant versus classic papillary thyroid carcinomas: association of N-ras mutation in codon 61 with follicular variant

Although the follicular variant of papillary thyroid carcinoma (FVPTC) has been classified as a papillary cancer based on nuclear features, its follicular growth pattern and potential for hematogenous spread are more characteristic of follicular carcinoma. To gain insight into the biologic nature of FVPTC, we compared genetic alterations characteristic of papillary and follicular thyroid carcinomas in 24 FVPTCs and 26 classic PTC (CPTCs). In FVPTCs, we observed ras mutation in 6 of 24 cases (25%), BRAF mutation in 1 of 13 cases (7.6%), and ret rearrangement in 5 of 12 cases (41.7%). In CPTCs, we found ras mutation in no case, BRAF mutation in 3 of 10 cases (30%), and ret rearrangement in 5 of 11 cases (45%). One FVPTC exhibited simultaneous ras mutation and ret/PTC1 rearrangement, and one CPTC harbored simultaneous BRAF mutation and ret/PTC3 rearrangement. Based on these findings, we concluded that ras mutation correlates with follicular differentiation of thyroid tumors whereas ret activation is associated with papillary nuclei but not with papillary architecture. ret activation is not exclusive of ras or BRAF mutation, whereas ras and BRAF mutations are mutually exclusive. The implications of these results for follicular and papillary carcinogenesis are discussed.

BRAF mutation predicts a poorer clinical prognosis for papillary thyroid cancer

CONTEXT

Use of BRAF mutation in papillary thyroid cancer (PTC) has the potential to improve risk stratification of this cancer.

OBJECTIVE

The objective of the study was to investigate the prognostic value of BRAF mutation in patients with PTC.

DESIGN, SETTING, AND SUBJECTS

In a multicenter study of 219 PTC patients, data on their clinicopathological characteristics and clinical courses between 1990 and 2004 were retrospectively collected, and their tumor BRAF mutation status was determined. Associations of BRAF mutation with initial tumor characteristics and subsequent recurrence were analyzed.

MAIN OUTCOME MEASURE

Relationships between the BRAF mutation status and clinicopathological outcomes, including recurrence, were measured.

RESULTS

We found a significant association between BRAF mutation and extrathyroidal invasion (P < 0.001), lymph node metastasis (P < 0.001), and advanced tumor stage III/IV (P = 0.007) at initial surgery. This association remained significant on multivariate analysis, adjusting for conventional clinicopathological predictors of recurrence excluding the histological PTC subtype, but was lost when the tumor subtype was included in the model. BRAF mutation was also significantly associated with tumor recurrence, 25 vs. 9% with and without mutation, respectively (P = 0.004), during a median of 15 (interquartile range, 3-29) months of follow-up. This association remained significant on multivariate analysis adjusting for conventional clinicopathological predictors of recurrence, even including the PTC subtype (odds ratio, 4.0; 95% confidence interval, 1.1-14.1; P = 0.03). BRAF mutation was even an independent predictor of recurrence in patients with stage I/II disease, 22 vs. 5% with and without BRAF mutation, respectively (P = 0.002). BRAF mutation was also more frequently associated with absence of tumor I-131 avidity and treatment failure of recurrent disease.

CONCLUSIONS

In patients with PTC, BRAF mutation is associated with poorer clinicopathological outcomes and independently predicts recurrence. Therefore, BRAF mutation may be a useful molecular marker to assist in risk stratification for patients with PTC.

High prevalence and possible de novo formation of BRAF mutation in metastasized papillary thyroid cancer in lymph nodes

CONTEXT

The role of the T1799A BRAF mutation in lymph node metastasis of papillary thyroid cancer (PTC) is not clear.

OBJECTIVE

Our objective was to explore the relationship between BRAF mutation and lymph node metastasis of PTC by examining the mutation in both the primary tumors and their paired lymph node metastases.

DESIGN

We isolated genomic DNA from primary thyroid tumors and paired lymph node metastases and performed direct sequencing of exon 15 of the BRAF gene mutation that carries the T1799A mutation.

RESULTS

In a series of 33 cases, 21 harbored the T1799A mutation in the primary tumors, and 17 (81%) of them harbored the same mutation also in the paired lymph node metastases. Twelve cases did not harbor the T1799A mutation in the primary tumors, among which nine cases also did not harbor BRAF mutation in the lymph node-metastasized tumors, whereas the other three did harbor the T1799A mutation in lymph node-metastasized tumor tissues. A novel tandem TG1799-1800AA mutation within one allele was found in a lymph node-metastasized tumor but not in the primary tumor. This mutation results in the change of codon 600 (GTG) of the gene to GAA with the consequent amino acid change (V600E) in the B-type Raf (BRAF) protein, same as that caused by the T1799A mutation alone.

CONCLUSION

The high prevalence of BRAF mutation in lymph node-metastasized PTC tissues from BRAF mutation-positive primary tumors and the possible de novo formation of BRAF mutation in lymph node-metastasized PTC were consistent with a role of BRAF mutation in facilitating the metastasis and progression of PTC in lymph nodes.

Akt1 contains a functional leucine-rich nuclear export sequence

Nuclear Akt1 expression and Akt activation are common in cancer invasion. However, the mechanisms for this association and its causal role in invasion are uncertain. In an effort to identify potential mechanisms for regulating Akt subcellular localization, we analyzed the Akt gene sequences and identified a highly conserved leucine-rich potential nuclear export sequence (NES). Initial experiments demonstrated that leptomycin B induced nuclear Akt1 localization. Transient expression experiments demonstrated that, in comparison to wild-type Akt1, NES-mutated (AKT/NES) Akt1 has reduced interactions with CRM-1 and persistent nuclear localization. Subsequent stable transfection experiments in Akt1-/- fibroblasts confirmed that expression of AKT/NES resulted in persistent nuclear localization and activation1. Finally, stable expression of AKT/NES in Akt1-/- fibroblasts was sufficient to enhance cell migration in vitro. Thus, Akt1 contains a functional NES and mutation of the NES results in nuclear-predominant Akt1 activation that is sufficient to induce migration.

ret/PTC1 and ret/PTC3 in thyroid tumors from Chernobyl liquidators: comparison with sporadic tumors from Ukrainian and French patients

Like children exposed to Chernobyl fallout, the workers who cleaned up after the accident, also known as liquidators, have exhibited an increased incidence of thyroid cancer. A high prevalence of ret/PTC3 rearrangement has been found in pediatric post-Chernobyl thyroid tumors, but this feature has not been investigated in liquidator thyroid tumors. In this study we analyzed the prevalence of ret/PTC1 and ret/PTC3 in thyroid tumors from 21 liquidators, 31 nonirradiated adult Ukrainian patients, and 34 nonirradiated adult French patients. ret rearrangements in carcinomas were found in 83.3% of liquidators, 64.7% of Ukrainian patients, and 42.9% of French patients. The prevalence of ret/PTC1 was statistically similar in the three groups. The prevalence of ret/PTC3 was significantly higher in liquidators than in French patients (P = 0.03) but it was also high in nonirradiated Ukrainian patients who exhibited values intermediate between liquidators and French patients. In adenomas the prevalence of rearrangement was significantly higher in all Ukrainians than in French patients (P = 0.004). Like children exposed to Chernobyl fallout, liquidators showed a high prevalence of ret/PTC3. This finding suggests that irradiation had the same effect regardless of age. However, given the high rate of ret/PTC3 in nonirradiated adult Ukrainians, the possibility of genetic susceptibility or low-level exposure to radiation in that group cannot be excluded.

Chronic expression of RET/PTC 3 enhances basal and insulin-stimulated PI3 kinase/AKT signaling and increases IRS-2 expression in FRTL-5 thyroid cells

The RET/PTC3 oncogene is a genetically rearranged and constitutively activated tyrosine kinase receptor that is common in papillary thyroid cancer. Because RET/PTC3 is chronically overexpressed in these thyroid cancer cells, and RET/PTC3-expressing tumors are associated with overactivity of tyrosine kinase signaling pathways and a more aggressive clinical course, we questioned whether chronic RET/PTC3 expression enhances cellular responses to thyroid mitogens in vitro. We stably transfected FRTL-5 cells with the RET/PTC3 gene; transfected and control cell lines were cultured without insulin, TSH, or serum. Thymidine incorporation into DNA was enhanced in the RET/PTC3 cells, but transformation was not observed. RET/PTC3 cells demonstrated higher basal and insulin-stimulated levels of activated Akt, both of which were reduced by LY294002, a PI3 kinase inhibitor, but not PD98059, a MEK inhibitor. By contrast, mitogen activated protein kinase (MAP kinase) was only minimally activated in RET/PTC3 cells before and after stimulation. Consistent with preferential activation of PI3 kinase, increased levels of total and phosphorylated IRS2 protein, relative activation of PDK-1, and enhanced IRS2-p85 interactions were identified in RET/PTC3-expressing cells. RET/PTC3 cells were also sensitized to insulin-induced thymidine incorporation; this effect was blocked by PI3 kinase (LY294002) rather than MEK 1/2 (PD98059) inhibitors. In summary, we have demonstrated that RET/PTC3 expression enhances basal and insulin-stimulated DNA synthesis through PI3 kinase, cooperatively activates Akt with insulin via PI3 kinase, and preferentially activates the Akt rather than MAP kinase pathway in FRTL-5 cells.

Akt activation and localisation correlate with tumour invasion and oncogene expression in thyroid cancer

INTRODUCTION

Akt activation is involved in the pathogenesis of inherited thyroid cancer in Cowden's syndrome and in sporadic thyroid cancers. In cell culture, Akt regulates thyroid cell growth and survival; but recent data suggest that Akt also regulates cell motility in non-thyroid cell lines. We therefore sought to evaluate the role of Akt in thyroid cancer progression.

METHODS

We evaluated 46 thyroid cancer, 20 thyroid follicular adenoma, and adjacent normal tissues samples by immunohistochemistry for activated Akt (pAkt), Akt 1, 2, and 3, and p27 expression. Immunoblots were performed in 14 samples.

RESULTS

Akt activation was identified in 10/10 follicular cancers, 26/26 papillary cancers, and 2/10 follicular variant of papillary cancers, but in only 4/66 normal tissue samples and 2/10 typical benign follicular adenomas. Immunoactive pAkt was greatest in regions of capsular invasion; and was localised to the nucleus in follicular cancers and the cytoplasm in papillary cancers, except for invasive regions of papillary cancers where it localised to both compartments. Immunoactive Akt 1, but not Akt 2 or Akt 3, correlated with pAkt localisation, and nuclear pAkt was associated with cytoplasmic expression of p27. In vitro studies using human thyroid cancer cells demonstrated that nuclear translocation of Akt 1 and pAkt were associated with cytoplasmic p27 and cell invasion and migration. Cell migration and the localisation of Akt 1, pAkt, and p27 were inhibited by PI3 kinase, but not MEK inhibition.

DISCUSSION

These data suggest an important role for nuclear activation of Akt 1 in thyroid cancer progression.

BRAF T1796A transversion mutation in various thyroid neoplasms

A high prevalence of activating mutation of the B type Raf kinase (BRAF) gene was recently reported in papillary thyroid cancer (PTC). However, the frequency of this mutation in several other types of thyroid neoplasms was not thoroughly investigated. In the present study, in addition to PTC, we evaluated various thyroid tumor types for the most common BRAF T1796A mutation by direct genomic DNA sequencing. We found a high and similar frequency (45%) of the BRAF T1796A mutation in two geographically distinct PTC patient populations: one composed of sporadic cases from North America, and the other from Kiev, Ukraine, that included individuals who were exposed to the Chernobyl nuclear accident. In contrast, we found BRAF mutation in only 20% of anaplastic thyroid cancers and no mutation in medullary thyroid cancers and benign thyroid hyperplasia. We also confirmed previous reports that the BRAF T1796A mutation did not occur in benign thyroid adenomas and follicular thyroid cancers. Specific analysis of the Ukraine patients with confirmed history of radiation exposure failed to show a higher incidence of BRAF mutation. Our results suggest that frequent occurrence of BRAF mutation is inherently associated with PTC, irrespective of geographic origin, and is apparently not a radiation-susceptible mutation. The lack or low prevalence of BRAF mutation in other thyroid neoplasms is consistent with the notion that other previously defined genetic alterations on the same signaling pathway are sufficient to cause tumorigenesis in most thyroid neoplasms.

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.

Fine-needle aspiration of thyroid follicular neoplasm: diagnostic use of thyroid peroxidase immunocytochemistry with monoclonal antibody 47

BACKGROUND

We previously demonstrated that thyroid peroxidase (TPO) immunocytochemistry with monoclonal antibody 47 can help to differentiate benign (staining score, 80% or more) from malignant (staining score, less than 80%) thyroid nodules on fine-needle aspiration (FNA) samples. In the present study we assessed the use of TPO immunocytochemistry in the cytologic diagnosis of thyroid follicular neoplasms.

METHODS

A total of 109 histologically proven follicular tumors were studied. There were 60 microfollicular adenomas, 23 atypical adenomas, 17 oncocytic adenomas, and 9 follicular carcinomas. Adequate preoperative FNA samples were available in all cases. TPO immunocytochemistry was performed on one half of the slides.

RESULTS

The staining score was less than 80% in all follicular carcinomas, whereas it was 80% or more in 68 of 100 benign tumors. There was no false negative and 32 false positives for diagnosis of malignancy. The false positives were 10 microfollicular adenomas, 13 atypical adenomas, and 9 oncocytic adenomas. TPO immunocytochemistry has a sensitivity of 100% and a specificity of 68% for screening of follicular cancer.

CONCLUSIONS

TPO immunocytochemistry with monoclonal antibody 47 on FNA samples is a highly sensitive and fairly specific method to distinguish benign from malignant follicular neoplasms. This technique can help to reduce the number of surgical procedures for benign thyroid nodules without increased risk of overlooking malignancy.