Telomerase activity in the differential diagnosis of papillary carcinoma of the thyroid

Thyroid-stimulating hormone receptor (TSHR) as a target for imaging differentiated thyroid cancer

BACKGROUND

Of the half a million cases of thyroid cancer diagnosed annually, 95% are differentiated thyroid cancers. Although clinical guidelines recommend surgical resection followed by radioactive iodine ablation, loss of sodium-iodine symporter expression causes up to 20% of differentiated thyroid cancers to become radioactive iodine refractory. For patients with radioactive iodine refractory disease, there is an urgent need for new diagnostic and therapeutic approaches. We evaluated the thyroid-stimulating hormone receptor as a potential target for imaging of differentiated thyroid cancer.

METHODS

We immunostained tissue microarrays containing 52 Hurthle cell carcinomas to confirm thyroid-stimulating hormone receptor expression. We radiolabeled chelator deferoxamine conjugated to recombinant human thyroid-stimulating hormone analog superagonist TR1402 with 89Zr (t1/2 = 78.4 h, β+ =22.7%) to produce [89Zr]Zr-TR1402. We performed in vitro uptake assays in high-thyroid-stimulating hormone receptor and low-thyroid-stimulating hormone receptor-expressing THJ529T and FTC133 thyroid cancer cell lines. We performed in vivo positron emission tomography/computed tomography and biodistribution studies in male athymic nude mice bearing thyroid-stimulating hormone receptor-positive THJ529T tumors.

RESULTS

Immunohistochemical analysis revealed 62% of patients (27 primary and 5 recurrent) were thyroid-stimulating hormone receptor membranous immunostain positive. In vitro uptake of 1nM [89Zr]Zr-TR1402 was 38 ± 17% bound/mg in thyroid-stimulating hormone receptor-positive THJ529T thyroid cancer cell lines compared to 3.2 ± 0.5 in the low-expressing cell line (P < .01), with a similar difference seen in FTC133 cell lines (P < .0001). In vivo and biodistribution studies showed uptake of [89Zr]Zr-TR1402 in thyroid-stimulating hormone receptor-expressing tumors, with a mean percentage of injected dose/g of 1.9 ± 0.4 at 3 days post-injection.

CONCLUSION

Our observation of thyroid-stimulating hormone receptor expression in tissue microarrays and [89Zr]Zr-TR1402 accumulation in thyroid-stimulating hormone receptor-positive thyroid cancer cells and tumors suggests thyroid-stimulating hormone receptor is a promising target for imaging of differentiated thyroid cancer.

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.

Telomere length is related to alternative splice patterns of telomerase in thyroid tumors

Telomere dysfunction and aberrant telomerase expression play important roles in tumorigenesis. In thyroid tumors, three possibly inhibitory splice variants of the active full-length isoform of human telomerase reverse transcriptase (hTERT) may be expressed. These variants might regulate telomerase activity and telomere length because it is the fraction of the full-length isoform, rather than the total transcript level, that correlates with enzymatic activity. Telomerase reactivation may be critical in the early stages of tumorigenesis, when progressive telomere shortening may be limiting cell viability. The aim of this study was to investigate the relationship between telomere length and hTERT splice variant expression patterns in benign and well-differentiated malignant thyroid tumors. Telomere lengths of 61 thyroid tumors were examined by fluorescence in situ hybridization, comparing tumors with adjacent normal thyroid tissue on the same slide. Expression patterns of hTERT splice variants were evaluated by quantitative and nested RT-PCR. Telomere length was inversely correlated with percentage of full-length hTERT expression rather than with total hTERT expression levels. Short telomeres and high fractions of full-length hTERT transcripts were associated with follicular and papillary thyroid carcinomas, whereas long telomeres and low levels of full-length hTERT were associated with benign thyroid nodules. Intermediate levels of full-length hTERT and telomere length were found in follicular variant of papillary thyroid carcinomas and follicular adenomas.

Telomerase detection in the diagnosis and prognosis of cancer

Telomerase, a critical enzyme responsible 'for cellular immortality, is usually repressed in somatic cells except for lymphocytes and self-renewal cells, but is activated in approximately 85% of human cancer tissues. The human telomerase reverse transcriptase (hTERT) is the catalytic component of human telomerase. In cancers in which telomerase activation occurs at the early stages of the disease, telomerase activity and hTERT expression are useful markers for the detection of cancer cells. In other cancers in which telomerase becomes upregulated upon tumor progression, they are useful as prognostic indicators. However, careful attention should be paid to false-negative results caused by the instability of telomerase and of the hTERT mRNA and the presence of PCR inhibitors, as well as to false-positive results caused by the presence of alternatively spliced hTERT mRNA and normal cells with telomerase activity. Recently, methods for the in situ detection of the hTERT mRNA and protein have been developed. These methods should facilitate the unequivocal detection of cancer cells, even in tissues containing a background of normal telomerase-positive cells.

Molecular markers in thyroid cancer diagnostics

Although fine-needle aspiration biopsy (FNA) remains the mainstay of the preoperative workup of thyroid nodules, it does not provide a diagnosis in up to 20% of nodules. This group of indeterminate lesions, including lesions with cellular atypia, suspicious cytology, and demonstrating a follicular pattern, provides one of the greatest challenges to researchers in thyroid cancer today. Over the last 2 decades, considerable work has been done to find molecular markers to resolve this diagnostic dilemma. This article explores some of the markers including galectin-3, HBME-1, BRAF, RET/PTC, PAX8-PPARgamma, hTERT, telomerase, miRNA, and microarray and multigene assays. Although no one marker has proven to be a panacea, several combinations of markers have shown great promise as an adjunct to FNA.

Thyroglobulin may affect telomerase activity in thyroid follicular cells

Telomerase (TA) activity is known to be present in malignant tumor cells, but not in most somatic differentiated cells. TA shows relatively high activity in thyroid cancer cells, but reports vary. This fact prompted us to elucidate whether cell component inhibitors of TA in the thyroid follicles can modulate its activity. The activity of TA extracted from Hela cells was inhibited by mixing with the supernatant fraction of human thyroid tissue extract. To examine the effect of iodine, thyroid hormones (l-T3 and l-T4) and human thyroglobulin (hTg) contained in the thyroid follicles, l-T3, l-T4 and hTg were added to the TRAP assay system in vitro, using TA from Hela cells. Iodine, l-T3 and l-T4 did not affect TA activity, but hTg inhibited the TA activity in a dose-dependent manner (IC(50) of hTg: ca 0.45 microM: inhibiting concentration of hTg was from 0.15 microM to 3.0 microM). The hTg inhibition was not evident in the RT-PCR system, suggesting no effect of hTg on Taq DNA polymerase activity. The hTg inhibition of TA activity was attenuated by dNTP but not significantly by TS primer. These data suggest that hTg contained in thyroid follicular cells of various thyroid diseases may affect the TA activity measured in biopsied thyroid specimens, and that the reduction of the TA activity by hTg may induce slow progression and growth, and low grade malignancy of thyroid cancer, particularly differentiated carcinoma.

Differentiating alternative splice variant patterns of human telomerase reverse transcriptase in thyroid neoplasms

BACKGROUND

Although fine-needle aspiration (FNA) biopsy of thyroid nodules is very sensitive in detecting thyroid malignancy, it remains ambiguous in 20-30% of cases. Current biomarkers for thyroid cancer lack either the sensitivity or specificity to substantially address this clinical problem. The aim of this study was to investigate the gene expression patterns of human telomerase reverse transcriptase (hTERT) alternative splice variants in benign and malignant thyroid tumors in an attempt to find a more reliable biomarker in the differential diagnosis of thyroid nodules.

METHODS

One hundred and thirty-three thyroid tumors from eight histopathological tumor types were collected from patients undergoing thyroid surgery at Johns Hopkins Hospital. Gene expression patterns of hTERT alternative splice variants were investigated in the tumors by nested reverse transcriptase-PCR. Telomerase enzyme activity was evaluated in a subset of 16 samples associated with the different hTERT patterns. Association of c-myc expression and hTERT patterns was also examined.

RESULTS

Malignant thyroid tumors exhibited a greater proportion of the active full-length hTERT transcript (0.57 +/- 0.15) than inactive splice variants, alpha(-) (0.13 +/- 0.02), or beta(-)/alpha(-)beta(-) deletion transcripts (0.30 +/- 0.11; p < 0.001). The opposite was observed in benign tumors, which exhibited greater proportions of beta(-)/alpha(-)beta(-) deletion transcripts (0.64 +/- 0.08) than either the full-length (0.19 +/- 0.06) or alpha(-) deletion transcripts (0.17 +/- 0.02; p < 0.001). Similar results were observed among a diagnostically challenging subset of 50 thyroid tumors that were suspicious for malignancy on FNA. Further, increased telomerase enzymatic activity was only associated with expression of the full-length hTERT isoform. In contrast, c-myc expression, which has been implicated in hTERT regulation, correlated with overall hTERT transcription without specificity for expression of the full-length isoform.

CONCLUSIONS

These differences in gene expression patterns of hTERT alternative splice variants may provide a useful adjunct to FNA diagnosis of suspicious thyroid tumors.

Molecular diagnostic methods in the diagnosis and follow-up of well-differentiated thyroid carcinoma

Thyroid cancers are the most common endocrine malignancies and are being diagnosed with increased frequency in modern clinical practice. Among other diagnostic modalities, fine-needle aspiration (FNA) biopsy of clinically suspicious thyroid nodules is becoming increasingly popular. Preliminary investigations have suggested that molecular diagnostic assays using tumor-specific markers may improve the sensitivity and accuracy of FNA and so may be expected to reduce the frequency of open surgical procedures by identifying those patients with demonstrably benign lesions who do not require definitive surgical excision of their lesions for diagnosis. At the same time, thyroid-specific mRNA assays (especially thyroglobulin mRNA testing) have been used by investigators in the postoperative follow-up of patients with thyroid cancer as a potential means of detecting tumor recurrence in the peripheral blood. Although these studies have not all reported unqualified successes--indeed, some problems based on both technical and biologic limitations have been identified-these assays still hold out the possibility that potentially important new advances in the management of patients with well-differentiated thyroid cancer may be offered by these and other molecular diagnostic methods.

Electrochemical Telomerase Assay with Ferrocenylnaphthalene Diimide as a Tetraplex DNA-Specific Binder

Spectroscopic studies revealed that ferrocenylnaphthalene diimide (1) can bind to tetraplex DNA at high potassium ion concentration. The tetraplex DNA was stabilized by the binding of 1, and this effect was larger than that of any other tetraplex stabilizers, which are known as a telomerase inhibitor. Quantitative analysis with circular dichroism and a quartz crystal microbalance strongly suggested a 3:1 binding stoichiometry of 1 to the tetraplex DNA. The telomere sequence could be extended by telomerase with the telomerase substrate primer on the surface of an electrode as proven by an increased current signal of 1 bound to the tetraplex DNA formed on the electrode. This is the first example of electrochemical detection of telomerase activity without relying on PCR.

Diagnostic molecular markers in thyroid cancer

The use of molecular assays to analyze clinical tissues in the diagnosis and management of thyroid cancer, similar to other tumors, will likely allow for more accurate characterization of the aggressiveness of individual tumors and may allow for the early diagnosis of recurrence. The application of these methods to thyroid nodules and nodal metastases is less encumbered by difficulties arising from amplification of transcripts in non-thyroid cells. For these tissues, these assays are likely to be used clinically in the near-future. New data arising from cDNA arrays identifying novel markers of malignancy or tumor aggressiveness make this a growing area of interest. The use of molecular assays in diagnosing distant metastases is more problematic due to issues with ectopic expression of either full length or splice variants of genes thought to be thyroid-specific. Assay quantitation is a complex problem owing to variability in the level of expression of "housekeeping" genes and the variety of phlebotomy and RT-PCR methods reported. Additional research in this area is clearly required before a recommendation can be given regarding clinically applicability of these tests.

Topoisomerase II alpha and telomerase expression in papillary thyroid carcinomas

BACKGROUND

Altered topoisomerase II alpha (Topo II alpha) expression and telomerase activity (TA) reflect tumour cell growth and malignant transformation.

METHODS

We examined TA by using a TRAP assay and expression of Topo II alpha by immunohistochemical analysis in a series of 27 cases of papillary thyroid carcinoma (PTC).

RESULTS

Topo II alpha labelling index (LI) ranged from 0.1 to 4.2% and was significantly associated with patient age (r=-0.42, p=0.003), with higher levels of Topo II alpha in patients under 40 years. There was no relationship between Topo II alpha LI, AGES score or other clinical outcome. TA was detected in 14 PTC, with relative levels ranging from 1.2 to 102 units. A significant positive correlation between the multiplicity of tumoral foci and the TA levels (p<10(-2)) was noted.

CONCLUSION

We concluded that Topo II alpha cannot be used as a marker of tumour aggressiveness. Furthermore, enhanced Topo II alpha expression in PTCs from patients less than 40 years old suggests that this age group might benefit from Topo II inhibitor chemotherapy.

[Thyroid carcinomas of the follicular epithelium: tumor markers and oncogenes]

Several genes control cell growth, differentiation and apoptosis. Any alteration in the sequence or expression of these genes can cause an uncontrolled growth of the tissue and produce a tumor. Quantitative and qualitative gene expression studies using genes as tumor markers are essential for the diagnosis and prognosis of the tumor and its behavior. Oncogenes are genes that stimulate cell growth and have an increased expression. On the contrary, tumor suppressor genes are genes that inhibit cell growth and have a decreased expression in tumor cells. To study these tumor markers we apply simple and random molecular biology techniques such as polymerase chain reaction (PCR), reverse transcription and genomic sequencing. In the case of thyroid epithelial neoplasia, tumor markers such as PTEN/MMAC1/TEP1, telomerase, RET/PTC, b-catenine, PAX8/PPAR(1, ciclooxygenase, thyroid stimulating hormonal receptor (TSHR), and thyro-globulin are being investigated. These markers are analyzed for somatic mutations in the genetic sequence, chromosomical rearrangements, alterations in the promoter zone that affect gene expression, regulation and studies of genes at mRNA level. A deeper study of these markers is deemed to help improve the accuracy of tumor diagnosis, behavior and prognosis. Hence, more effective therapeutic options will be adapted to each individual, eventually reducing hospital costs.

Molecular pathogenesis of thyroid cancer

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

Telomerase activity in surgical specimens and fine-needle aspiration biopsies from hyperplastic and neoplastic human thyroid tissues

BACKGROUND

Telomerase activity (TA) indicates malignancy, but activated lymphocytes also express TA. Correlation between TA in thyroid tissues and fine-needle aspiration (FNA) samples and knowledge about TA in adjacent tissue are of importance.

METHODS

The telomeric repeat amplification protocol assay followed by enzyme-linked immunosorbent assay detection was performed on 78 thyroid cases including 53 suspected malignancies, preoperative and perioperative FNA specimens, and adjacent tissue.

RESULTS

Benign lesions in cancer-suspected cases were TA negative. Eight of 13 papillary (62%) and 4 of 5 follicular (80%) tumors were TA positive (TA+). Lower TA was observed in conventional papillary cancer than in follicular, tall cell variant of papillary and anaplastic cancers. Adjacent tissues with lymphocyte infiltration were TA+ in 9 of 17 cases (53%). Nine of 65 adjacent tissues (14%) were TA+. Three of 6 preoperative and 9 of 11 perioperative FNA samples from malignant tumors corresponded to the tissue TA. CONCLUSIONS; High TA may reflect more severe thyroid cancer. Telomerase activity in FNA biopsies does not add reliable diagnostic information, and presence of lymphocytes can give false-positive results.

Telomerase as tumor marker

Telomerase, a critical enzyme responsible for continuous cell growth, is repressed in most somatic cells except proliferating progenitor cells and activated lymphocytes, and activated in approximately 85% of human cancer tissues. Telomerase activity is a useful cancer-cell detecting marker in some types of cancers in which almost all cases show telomerase activation. In other types in which telomerase becomes upregulated according to tumor progression, it is a useful prognostic indicator. Detection of human telomerase reverse transcriptase (hTERT) mRNA or protein in various clinical samples is also applicable. However, careful attention should be paid to the false negative results due to the instability of this enzyme or hTERT mRNA and the existence of polymerase chain reaction inhibitors as well as the false-positive results due to the contamination by normal cells with telomerase activity. If these pitfalls are avoided, in situ detection of hTERT mRNA or protein will facilitate the reliability of telomerase as a tumor marker.

Human telomerase reverse transcriptase (hTERT) gene expression in FNA samples from thyroid neoplasms

Identifying a tumor marker that can help distinguish benign from malignant thyroid tumors is crucial, because up to 30% of thyroid fine-needle aspirations (FNA) are diagnosed as 'suspicious' or follicular neoplasm for malignancy. Recently, the detection of human telomerase reverse transcriptase (hTERT) gene expression in thyroid FNA samples has been identified as a promising diagnostic marker in distinguishing benign and malignant thyroid tumors. Twenty-seven FNA samples from thyroid tumors that were suspected to be malignant were collected preoperatively, hTERT gene expression was examined by reverse transcriptase-polymerase chain reaction (RT-PCR), and the cytological and histological results were compared. The results demonstrated that 13 (92.8%) of 14 thyroid carcinomas, including eight of eight papillary, three of four follicular, and two of two Hürthle cell thyroid carcinomas have corresponding FNA samples that were positive for hTERT. Meanwhile, eight (61.5%) of 13 benign thyroid nodules, including three of six nodular goiter, two of two Graves' disease, two of two Hürthle cell adenomas, and one of three follicular adenomas were positive for hTERT. In conclusion, hTERT was more prevalent in malignant thyroid FNA samples than in the benign thyroid FNA samples. Notably, the extent of the differences in hTERT expression between benign and malignant follicular thyroid tumors require further investigation. Moreover, further information including semi-quantitative real-time RT-PCR, is required to verify whether hTERT mRNA expression could serve as an adjunctive molecular marker for the preoperative diagnosis of thyroid malignancies.

Antisense hTERT inhibits thyroid cancer cell growth

Activation of telomerase represents an early step in carcinogenesis. Increased telomerase expression in malignant thyroid tumors suggests that inactivation of telomerase may represent a potential chemotherapeutic target. The purpose of this study was to inhibit the protein component of telomerase, hTERT, in a human thyroid cancer cell line in vitro and in vivo using an antisense strategy. A 235-bp fragment of hTERT cDNA was subcloned, and sense and antisense hTERT expression vectors were constructed. These vectors were transfected into a human thyroid carcinoma cell line (FRO). Tumorigenic potential was determined by cellular growth assay, rate of apoptosis, anchorage-independent growth, and tumor growth in a nude mouse model. Significant down-regulation of hTERT expression was seen in the antisense transfected cells, compared with control and those transfected with the sense vector. A decrease in telomerase activity by TRAP assay was observed in the antisense hTERT cells but not in cells transfected with the sense hTERT construct. Inhibition of cell growth was observed after approximately 20 population doublings in the antisense-hTERT clones and was associated with an increase in the rate of apoptosis and a change in cellular morphology. Moreover, anchorage-independent growth was reduced in vitro, and tumor growth rate was diminished in vivo in the antisense hTERT clones. Inhibition of telomerase activity with antisense hTERT in human thyroid cancer cells is achievable and may represent a novel target to inhibit tumor growth.

Thyroid carcinomas that express telomerase follow a more aggressive clinical course in children and adolescents

With each cell division, DNA is lost from the telomeres, limiting the number of divisions, and leading to senescence. Malignant tumors maintain immortality by expressing a specific DNA repair enzyme, telomerase, that replaces this DNA. We hypothesized that tumors which express telomerase would have the highest recurrence risk and we tested this by determining telomerase expression in 27 papillary thyroid carcinomas (PTC), 5 follicular thyroid carcinomas (FTC) and 13 benign thyroid lesions from children and adolescents. Patients were 6-21 yr of age (mean+/-SE=16.6+/-4.1 yr) and followed from 0-14.1 yr (mean+/-SE=4.71+/-3.5 yr). Original tumors were sectioned, and immunostained for telomerase. Telomerase-specific staining was determined by two independent, blind examiners and graded from absent (Grade 0) to intense (Grade 3). Telomerase was detected in a similar majority of benign (11/13, 85%) and malignant tumors (24/32, 75%). However, the intensity of telomerase expression was greater among FTC (mean+/-SE=2.4+/-0.5 relative intensity) followed by PTC (mean+/-SE=1.9+/-1.0 relative intensity) and benign tumors (mean+/-SE=1.8+/-1.0 relative intensity). Autoimmune lesions had lower telomerase expression (mean+/-SE=1.25+/-0.5 relative intensity) compared to FTC (p=0.01), PTC (p=0.06) and benign lesions (p=0.15). Among PTC, 19 (70%) expressed telomerase, and 8 (30%) did not. Direct invasion (no.=4, 21%), distant metastasis (no.=2, 10%) and recurrence (no.=7, 37%) developed exclusively in PTC that expressed telomerase (p=0.02). Disease-free survival was also shorter for PTC that expressed telomerase (p=0.06). Recurrence developed in 1/2 (50%) FTC that expressed telomerase. We conclude that childhood thyroid cancers which express telomerase have an increased risk of tissue invasion, metastasis, and recurrence.

Alternative lengthening of telomeres in mammalian cells

Some immortalized mammalian cell lines and tumors maintain or increase the overall length of their telomeres in the absence of telomerase activity by one or more mechanisms referred to as alternative lengthening of telomeres (ALT). Characteristics of human ALT cells include great heterogeneity of telomere size (ranging from undetectable to abnormally long) within individual cells, and ALT-associated PML bodies (APBs) that contain extrachromosomal telomeric DNA, telomere-specific binding proteins, and proteins involved in DNA recombination and replication. Activation of ALT during immortalization involves recessive mutations in genes that are as yet unidentified. Repressors of ALT activity are present in normal cells and some telomerase-positive cells. Telomere length dynamics in ALT cells suggest a recombinational mechanism. Inter-telomeric copying occurs, consistent with a mechanism in which single-stranded DNA at one telomere terminus invades another telomere and uses it as a copy template resulting in net increase in telomeric sequence. It is possible that t-loops, linear and/or circular extrachromosomal telomeric DNA, and the proteins found in APBs, may be involved in the mechanism. ALT and telomerase activity can co-exist within cultured cells, and within tumors. The existence of ALT adds some complexity to proposed uses of telomere-related parameters in cancer diagnosis and prognosis, and poses challenges for the design of anticancer therapeutics designed to inhibit telomere maintenance.

Telomerase in endocrine and endocrine-dependent tumors

Telomerase, the ribonucleoprotein enzyme that elongates chromosomal ends, or telomeres, is repressed in most normal somatic cells but reactivated in transformed cells to compensate for the progressive erosion of the telomeres during cell divisions. In accordance with this hypothesis, the presence of telomerase activity has been reported in more than 90% of human cancers, whereas most normal tissues or benign tumors contain low or undetectable telomerase activity. Reactivation of telomerase has also been widely reported in endocrine neoplasms and in hormone-related cancers. In the present study, we review the most recent publications on telomerase in these types of tumors. The hormonal regulation of telomerase activity and the possible strategies for cancer therapy based on the inhibition of telomerase has also been discussed.

In situ detection of hTERT mRNA relates to Ki-67 labeling index in papillary thyroid carcinoma

BACKGROUND

Telomerase is activated in most human cancers but is inactivate in adult somatic tissues except for some proliferating cell lineages. The maintenance of telomerase activity may be a critical step of cellular immortalization and transformation.

MATERIALS AND METHODS

We analyzed the expression of human telomerase reverse transcriptase (hTERT) using in situ hybridization and compared it to Ki-67 immunoreactivity in 29 cases of papillary thyroid carcinoma (PTC) and 17 cases of benign thyroid disease.

RESULTS

The hTERT messenger RNA (mRNA) was expressed in the cytoplasm of carcinoma cells with moderate (n = 10) to strong intensity (n = 10) in 69% (20 of 29) PTC cases. Human TERT was found in only 29% (5 of 17) cases of benign thyroid disease. Human TERT gene expression was preferentially detected in PTC (P = 0.021). The Ki-67 labeling index was observed in 16 cases of PTC (16 of 29; 55.2%). This result was significantly different from that of benign thyroid disease (P = 0.014). The Ki-67 labeling index related to the intensity of hTERT mRNA expression (r = 0.51; P = 0.005) and was inversely associated with the follicular variant of PTC (r = -0.413; P = 0.026). No statistically significant difference was found between hTERT expression and histological subtype of PTC.

CONCLUSIONS

Our results demonstrated that expression of hTERT could be detected using in situ hybridization in PTCs and was significantly distinguishable from that of benign thyroid disease. Human TERT expression was related to the Ki-67 labeling index, indicating that coupling of telomerase activation with cell proliferation was the associated mechanism for tumorigenesis.

Telomerase activity and telomere length in thyroid neoplasia: biological and clinical implications

Despite several recent studies, the biological status and clinical relevance of telomerase expression in tumours derived from the thyroid follicular cell remain controversial. This study has analysed a series of normal, benign, and malignant thyroid samples using two novel approaches: the use of purified epithelial cell fractions to eliminate false-positives due to telomerase-positive infiltrating lymphocytes; and the simultaneous measurement of telomere length to provide a clearer interpretation of telomere dynamics in thyroid neoplasia. The data obtained support the prediction that the epithelial component of non-neoplastic thyroid and of follicular adenomas is telomerase-negative, any positive results being explicable by lymphocyte infiltration. In contrast, many malignant tumours, both follicular and papillary, were telomerase-positive. However, serial dilution of extracts indicated a wide spectrum of activity in these cancers, possibly related to variation in the proportion of telomerase-positive cells. Furthermore, an unexpectedly high proportion were telomerase-negative, a finding which was not explicable by technical problems such as TRAP (telomeric repeat amplification protocol) assay sensitivity. Many of these apparently telomerase-negative tumours had abnormally long telomeres. Correlation of telomerase and telomere length data suggests that thyroid cancers fall into three biological groups: telomerase-positive lesions, consistent with the conventional model of telomere erosion followed by telomerase reactivation; telomerase-negative tumours, which maintain telomere length by a mechanism independent of telomerase; and telomerase-negative tumours which are still undergoing telomere erosion and may therefore be composed of mortal cancer cells. From a clinical standpoint, it is concluded that telomerase detection on unfractionated tissue, such as fine needle aspirates, is of no value as a marker of malignancy in follicular lesions, due to both low sensitivity and specificity.

Minimal residual disease in thyroid carcinoma

The detection of disseminated tumor cells in differentiated (DTC) and medullary thyroid carcinomas (MTC) is one of the main topics in current thyroid cancer research. Immunocytochemistry and polymerase chain reaction (PCR) provide the tools for the identification of a small number of thyroid cancer cells in peripheral blood and cervical lymph nodes. Thyroid-specific markers, such as thyroglobulin (Tg) mRNA and thyroid peroxidase (TPO) mRNA, have been detected with RT-PCR in blood samples of tumor patients and healthy control subjects. To prevent false-positive results, quantitative PCR systems were established. Tumor-specific markers, such as telomerase activity and cytokeratin 20 (CK20), have been detected in various epithelial tumors. Amplification products of these markers were found in blood samples and in fine-needle aspiration (FNA) biopsies of patients with thyroid carcinomas. Using molecular detection of disseminated tumor cells in cervical lymph nodes with CK20 RT-PCR, a higher percentage of involved lymph nodes was detected compared to immunohistochemistry. The results of the presented studies may help researchers to develop more sensitive methods for early tumor cell dissemination, and refine risk groups that might benefit from more extensive surgical procedures or adjuvant therapy. However, the prognostic value of minimal residual disease (MRD) in thyroid carcinoma has to be confirmed in large or multicenter prospective studies.

Human telomerase reverse transcriptase expression in Diff-Quik-stained FNA samples from thyroid nodules

Fine-needle aspiration (FNA) is a highly sensitive method in the differential diagnosis of thyroid nodules. However, 10% of thyroid FNAs are indeterminate for cancer, and thus additional markers may be useful diagnostically. The authors have demonstrated previously that human telomerase reverse transcriptase (hTERT) gene expression is useful in the distinction of benign lesions from malignant lesions. They therefore wondered whether the detection of hTERT gene expression was feasible using archival slides. To establish an experimental system, ribonucleic acid was extracted from human anaplastic thyroid carcinoma cell line (ARO) in cytologic specimens, and reverse transcription-polymerase chain reaction (RT-PCR) for hTERT expression was performed. RT-PCR analysis for hTERT gene detection was then performed using 58 Diff-Quik-stained archival FNA samples collected retrospectively. RT-PCR for human thyroglobulin (hTg) or beta-actin gene expression served as a positive control. Successful PCR results were obtained from 48 of the 58 cases. All 10 slides in which no RT-PCR products were noted were older than 3 years. hTERT gene expression was demonstrated in FNAs from two of seven cases (29%) of hyperplastic nodule, one of one case (100%) of Hashimoto's thyroiditis, three of eight cases (38%) of follicular adenoma, three of eight cases (38%) of Hürthle cell adenoma, three of four cases (75%) of follicular carcinoma, two of two cases (100%) of Hürthle cell carcinoma, and 11 of 18 cases (61%) of papillary carcinoma. All but one of the available 33 corresponding frozen samples exhibited the same RT-PCR results. This study demonstrates that Diff-Quik-stained thyroid FNA specimens less than 3 years old can be used for the detection of hTERT gene expression by RT-PCR. This test, along with careful cytopathologic examination, may improve our ability to differentiate benign lesions from malignant lesions in indeterminate FNA samples from thyroid nodules.

Does telomerase activity add to the value of fine needle aspirations in evaluating thyroid nodules?

BACKGROUND

Telomerase replaces DNA sequences that are lost with cell division. Increased activity has been documented in malignant cells. Fine needle aspiration (FNA) has a 90% sensitivity for diagnosis of papillary carcinomas, but a specificity of 52%. This often leads to unnecessary surgery.

METHODS

Telomeric repeat amplification protocol assays were performed on FNA specimens of thyroid nodules in 19 patients. These results were compared with the surgical pathology using chi-square analysis.

RESULTS

There were 5 malignant and 14 benign nodules. Telomerase activity was found in 3 of 5 malignant (60%) and 9 of 14 benign (64%): sensitivity was 60%, specificity was 36%.

CONCLUSION

Telomerase assays did not add any additional information to FNA alone. Inflammatory changes associated with benign and malignant lesions can possess telomerase activity independent of the malignant state.

Thyroid cytology and histology

Fine needle aspiration (FNA) is an economical procedure that allows prompt evaluation of a thyroidal mass. Careful attention to each step of the aspiration will allow good specimens to be obtained. The cytopathologist should obtain the aspirates or else should accompany the clinician performing the aspirations. Unsatisfactory specimens should constitute less than 5% of the total. Reliable diagnoses can be made of papillary carcinoma, medullary carcinoma, anaplastic carcinoma, chronic lymphocytic thyroiditis, benign cystic lesions and the usual colloid-rich adenomatoid nodules. The diagnosis of follicular neoplasms and some cellular adenomatoid nodules remains problematical. Therefore, some thyroid operations inevitably yield benign follicular lesions.

Detection of telomerase activity in peritoneal lavage fluid from patients with gastric cancer using immunomagnetic beads

Cytologic examination of peritoneal lavage fluid is a useful predictor of peritoneal recurrence in gastric cancer. However, this technique is not overly sensitive and requires special abilities in the cytologist. In this study, telomerase activity was used to detect free cancer cells in peritoneal lavage fluid from patients with gastric cancer. In the first part, 12 lavage-fluid samples obtained from 12 patients with gastric cancer were analysed using the conventional telomeric repeat amplification protocol (TRAP) assay. Three of five patients with early gastric cancer had positive telomerase activity. These false-positive results may have been due to lymphocyte contamination. Furthermore, polymerase chain reaction inhibitors were also detected in the lavage-fluid samples. Therefore, we developed a novel method for elimination of haematopoietic cell and Taq polymerase inhibitors to increase the accuracy of the TRAP assay using immunomagnetic beads, which bind to most normal and neoplastic human epithelial cells. Telomerase activity was found in 10 of 20 (50%) lavage-fluid samples from patients with serosal or subserosal invasion. Cytologic examination was positive in nine of 20 (45%) samples. Both the telomerase activity and cytology were negative in all 14 patients without serosal or subserosal invasion. These results suggest that the TRAP assay combined with immunomagnetic beads might be useful for detection of free cancer cells in the peritoneal space in gastric cancer without the aid of an experienced cytologist.

Thyroid cancer

The management of patients with thyroid cancer can be optimized by developing multidisciplinary groups of highly specialized individuals. The completeness of surgery and its morbidity are mostly surgeon-dependent. Similarly, the decisions regarding selection of adjuvant treatments, doses, follow-up schemes, and so forth require depth of knowledge and understanding of the disease; its variables; factors that govern its course; and the values, limitations, and side effects of alternative therapies.

Molecular diagnostic tests in the diagnosis and management of thyroid carcinoma

The application of molecular analysis of gene expression to clinical tissue samples represents one of the most exciting new areas in "translational" thyroid cancer research. Current data suggest that molecular diagnostic assays may improve the sensitivity and accuracy of fine needle aspiration of thyroid nodules, fine needle aspiration of metastases, and detection of recurrent disease in peripheral blood samples. It is likely that at least some of these tests will become useful adjuncts in the diagnostic armamentarium of clinical endocrinologists in the future.

Clinical significance of telomerase activity in biopsy specimens of gastric cancer

Telomerase has been reported to be activated in most immortal cells and human cancers. The purpose of this study was to assess the clinical significance of telomerase activity in biopsy specimens of gastric cancer. Telomerase activity in endoscopic biopsy specimens obtained preoperatively from 31 patients with gastric cancer was determined semiquantitatively using the telomeric repeat amplification protocol assay, a polymerase chain reaction-based assay. Cancer tissues had significantly higher telomerase activity than adjacent normal tissues (13.9 +/-2.0% vs. 7.0 +/- 0.8%; p < 0.05). The ratio of the telomerase activity in cancer tissues to that in normal tissues (telomerase index) was significantly higher in tumors invading the proper muscle layer or deeper or in tumors with moderate or marked lymphatic invasion than in tumors without these invasive factors (4.7 +/- 1.4 vs. 1.1 +/- 0.1 for depth of invasion and 4.4 +/- 1.3 vs. 1.2 +/- 0.2 for lymphatic invasion; p < 0.05 for both). These results suggest that the analysis of telomerase activity in biopsy specimens might contribute to preoperative assessment of the invasive activity or stage of gastric cancer.

Human telomerase reverse transcriptase (hTERT) gene expression in FNA samples from thyroid neoplasms

BACKGROUND

Although fine-needle aspiration (FNA) is the most sensitive method for the detection of thyroid carcinoma, it cannot provide a definitive diagnosis of malignancy in 60% of the patients operated on for suspicious lesions. Recently, human telomerase reverse transcriptase (hTERT) has been found to be a diagnostic marker of malignancy. We therefore sought to determine whether hTERT gene expression could serve as an adjunct to FNA in the differential diagnosis of thyroid nodules.

METHODS

Twenty-four FNA samples from thyroid nodules that were suspected of malignancy were collected. RNA was extracted, and hTERT gene expression was examined by RT-PCR. Cytologic and histologic examinations were also performed.

RESULTS

Two of three follicular, three of three Hürthle cell, and eight of eight papillary thyroid carcinomas had corresponding FNA samples that were positive for hTERT. One of two Hürthle cell adenomas was hTERT positive. FNA samples from three follicular adenomas and five hyperplastic nodules were negative for hTERT. Positive and negative predictive values were 93% and 90%, respectively.

CONCLUSIONS

The detection of hTERT gene expression in thyroid FNA samples holds promise as a diagnostic marker in the distinction of benign from malignant thyroid lesions. Its application could alter the surgical management of these patients.

Telomerase activity in thyroid malignancy

Telomerase activity seems to play a role in the development and pathogenesis of thyroid carcinoma. Its incidence of expression and its application as a tumor marker remain to be elucidated. Thyroid tissues obtained during thyroidectomy from 1996-1998 were rapidly frozen and stored at -80 degrees C until processed. Telomerase activity was determined using telomeric repeat amplification protocol (TRAP). Histology of the tissue examined (67 benign and 59 malignant) was reviewed. Telomerase activity was detected in 15 of 52 papillary carcinomas (29%); 1 of 1 thyroid lymphoma (100%); 1 of 2 anaplastic carcinomas (50%); and 2 of 16 lymphocytic thyroiditis specimens (13%). Telomerase activity was not detectable in 35 normal thyroid, 9 follicular adenoma, 7 nodular hyperplasia, 2 follicular carcinoma, and 2 medullary carcinoma. Lymphocytic thyroiditis was detected in 8 of 37 (22%) apparently normal thyroid tissues adjacent to papillary thyroid carcinoma and telomerase activity was present in 2 of these 8 specimens (25%). In conclusion, telomerase does not appear to be frequently activated in papillary thyroid carcinoma. The association of lymphocytic thyroiditis with papillary thyroid carcinoma may limit its clinical usefulness as a tumor marker.

Three molecular determinants of malignant conversion and their potential as therapeutic targets

The past decade has been marked by an explosion of knowledge regarding the dysregulation of cancer at the molecular level. It has become apparent that oncogenes, tumor suppressor genes, and other ancillary molecules interact in complex pathways that govern cellular homeostasis. We review three molecular events that have been implicated in tumorigenesis and define pathways ripe for the development of new therapeutic approaches: 1) activation of telomerase, 2) dysregulation of the patched/sonic hedgehog pathway, and 3) mutation of the INK4 alpha-ARF locus.

Decrease of telomere length in thyroid adenomas without telomerase activity

In somatic cells, telomeres shorten with population doubling, thus limiting their capacity to divide. Telomerase, which synthesizes telomeric repeats, can compensate for such shortening. Telomerase activity is known to be absent from most somatic differentiated cells but is present in germline cells, immortal cell lines, or a large majority of malignant tumors. Autonomous thyroid adenomas are benign tumors composed of highly differentiated cells characterized by TSH-independent function and growth. Telomere length and telomerase activity were measured in autonomous and hypofunctioning adenomas and their surrounding tissues. A significant decrease of 3.8+/-1.0 kilobases (kb) was observed in the length of the terminal restriction fragments (TRF) in 12 autonomous adenomas (8.6+/-1.1 kb), compared with the TRF length of their surrounding tissues (12.4+/-1.6 kb). The same kind of decrease, 3.5+/-1.2 kb, was also observed in 16 hypofunctioning adenomas (12.3+/-1.7 kb in surrounding tissue and 8.8+/-1.6 kb in the adenomas). No telomerase activity was detected either in the 12 autonomous adenomas studied or in most of the quiescent tissues (10 of 12). Most of the hypofunctioning adenomas tested (15 of 16) did not display telomerase activity. These results suggest that the cells have undergone a higher number of cell divisions in the adenomas than in the surrounding tissue. Moreover, there is a larger spread of the TRF length distribution in autonomous adenomas than in the collateral tissue. This could reflect the heterogeneity in proliferation status of the cells in the nodule, some of which have reached the end of their life span, whereas others are still proliferating (but with no malignant potential for the autonomous adenomas). In conclusion, benign adenomas exhibit a shorter and more variable telomere length than the normal collateral quiescent tissue, with no telomerase activity to compensate this loss in telomere length.

Diagnosis of malignant epithelial thyroid lesions: fine needle aspiration and histopathologic correlation

Fine needle aspiration is a diagnostic tool useful as a guide to patient management. We believe that its role in solving the diagnostic dilemmas presented by thyroid nodules is still underappreciated. Current fiscal constraints in health care might bring about a wider use of this simple technique to select patients for surgery. Care in sampling a mass is essential to obtain aspirates that are representative of the lesion and adequate in quantity for interpretation. Several aspirates are needed from all but the smallest masses. Most thyroid carcinomas are well-differentiated with a low grade of malignancy. The majority of these are papillary carcinomas, which are easily diagnosed in good cytologic smears. With fine needle aspirates the goal is to diagnose a follicular neoplasm and to separate it from the adenomatoid nodule. The follicular neoplasm then can be classified as adenoma or carcinoma with the histologic sections. The minimally invasive carcinoma still can be challenging to recognize. We hope that the cytologic criteria and histopathologic correlations presented here will help general pathologists who interpret aspirates. We believe that in the near future additional immunohistochemical methods and genetic markers will be used increasingly to discriminate among the neoplasms and to provide prognostic information.