Telomerase activity in human breast cancer and benign breast lesions: diagnostic applications in clinical specimens, including fine needle aspirates

Telomerase activity and telomere length in women with breast cancer or without malignancy: A systematic review and meta-analysis

AIM

We performed a systematic review and meta-analysis to assess whether telomerase activity and telomere length are associated with breast cancer.

METHODS

PubMed, Web of Science, Embase, LILACS, Scielo, Embase, and CNKI databases were searched to obtain relevant articles published through May 10, 2023, following PRISMA guidelines and a registered PROSPERO protocol (CRD42022335402). We included observational studies reporting telomerase activity or telomere length in patients with breast cancer compared with women with benign lesions or normal tissue (control women). The Newcastle-Ottawa Scale was used to evaluate the quality of studies. Data were expressed as odds ratios (OR) and 95 % confidence intervals (CI). Random effects and inverse variance methods were used to meta-analyze associations. The I2 test was used to assess heterogeneity.

RESULTS

The meta-analysis of telomerase shows significantly greater activity in patients with breast cancer than in those without malignancies (OR = 23.46, 95 % CI 14.07-39.11, p < 0.00001, I2 = 72 %). There were non-significant differences in relative telomere length (OR = 1.16, 95 % CI = 0.90-1.49, p = 0.26, I2 = 86 %) and leukocyte telomere length (OR = 2.32, 95 % CI = 0.89-6.08, p = 0.09, I2 = 98 %) between women with and without breast cancer. In subgroup analyses by world regions of studies, both telomerase activity and telomere length displayed the same trends as in their respective meta-analyses. In sensitivity analyses, variables showed their respective same trends.

CONCLUSION

Telomerase activity is higher in patients with breast cancer than in women without malignancies. There were no significant differences in either relative telomere length or leukocyte telomere length in women with and without breast cancer. PROSPERO protocol CRD42022335402.

Sensitive bioanalytical methods for telomerase activity detection: a cancer biomarker

Telomerase is an enzyme that protects the length of telomeres by adding guanine-rich repetitive sequences. In tumors, gametes, and stem cells, telomerase activity is exerted. Telomerase activity can be a cancer biomarker for therapeutic and diagnosis approaches. So, a number of studies concentrating on the discovery of telomerase activity were reported. Bioanalytical devices, in comparison with other tests, have numerous advantages including low expense, simplicity, and excellent sensitivity and specificity. In this article we reviewed recent studies on the subject of various bioanalytical methods based on different nanomaterials. Optical, electrochemical, and quartz crystal microbalance (QCM) are prominent analytical techniques that are mentioned in this paper.

Generation of Immortalised But Unstable Cells after hTERT Introduction in Telomere-Compromised and p53-Deficient vHMECs

Telomeres, the natural ends of chromosomes, hide the linear telomeric DNA from constitutive exposure to the DNA damage response with a lariat structure or t-loop. Progressive telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in t-loop collapse and unmasked telomeres. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptosis, but they can also promote tumour initiation when cell cycle checkpoints are disabled. In this setting, telomere dysfunction promotes increasing chromosome instability (CIN) through breakage-fusion-bridge cycles. Excessive instability may hamper cell proliferation but might allow for the appearance of some rare advantageous mutations that could be selected and ultimately favour neoplastic progression. With the aim of generating pre-malignant immortalised cells, we ectopically expressed telomerase in telomere-compromised variant human mammary epithelial cells (vHMECs), proficient and deficient for p53, and analysed structural and numerical chromosomal aberrations as well as abnormal nuclear morphologies. Importantly, this study provides evidence that while immortalisation of vHMECs at early stages results in an almost stable karyotype, a transient telomere-dependent CIN period—aggravated by p53 deficiency—and followed by hTERT overexpression serves as a mechanism for the generation of immortal unstable cells which, due to their evolving karyotype, could attain additional promoting properties permissive to malignancy.

Telomerase Activity in Breast Cancer in Western India (Gujarat)

The purpose of this study was to examine the association of telomerase activity with clinical and histopathological prognostic variables in primary breast cancer (n=64). Telomerase activity in breast cancer was also compared with that in benign (n=10) and non-malignant tissues (n=8; post-lumpectomy tissues histopathologically defined as containing no residual tumor). The parameter was assessed using the Telomerase PCR ELISA kit. Values above OD 0.120 were considered positive. Estrogen and progesterone receptors (ER and PgR) were assayed by the dextran-coated charcoal method and levels >10 fmol/mg cytosol protein were taken as positive. Telomerase activity was detected in 20% and 50% of the patients with benign lesions and primary breast cancer, respectively, and in 50% of post-lumpectomy breast tissues histopathologically defined as containing no residual tumor. Telomerase activity was present in all stages of breast carcinoma and showed a significant inverse correlation with lymph node status (p=0.006), lymphatic invasion (p=0.035) and necrosis (p=0.033). Moreover, when stage II patients were grouped according to nodal involvement, a trend towards significance was observed (p=0.055). No correlation was observed with ER and PgR. The results of our study suggest that telomerase activity might be associated with the presence of cancer cells. Furthermore, telomerase activation may occur early in breast cancer and may be periodically downregulated during subsequent tumor progression.

Evaluation of Telomerase in Canine Mammary Tissues by Immunohistochemical Analysis and a Polymerase Chain Reaction-Based Enzyme-Linked Immunosorbent Assay

The enzyme telomerase is considered a potential marker for neoplastic tissue and is used as a diagnostic and prognostic tool in clinical medicine and therapeutics. For this reason, the possible role of telomerase activation in the process of malignant transformation is currently the subject of intense research efforts. The focus of the study reported here was to detect telomerase in 37 canine mammary samples, by comparing two methods: immunohistochemical (IHC) analysis for detecting the catalytic subunit of the enzyme, telomerase reverse transcriptase (TERT), and the telomeric repeat amplification protocol–enzyme-linked immunosorbent assay (TRAP-ELISA), a polymerase chain reaction (PCR)-based technique that uses a colorimetric detection method. Using the TRAP-ELISA, samples were considered positive when they yielded a difference of at least 0.2 absorbance units between the readings at 450 nm versus 690 nm wavelength. On the basis of this criterion, 18 negative and 19 positive cases were obtained. Specific immunohistochemical staining was observed mainly in the nucleoli, to a lesser extent in the nuclei, and rarely in the cytoplasm of epithelial cells. A sample was considered positive when at least 10% of the epithelial cells had specific staining. The Pearson correlation between the TRAP-ELISA and IHC results was significant only when IHC nucleolar ( r = 0.53, P < 0.01) or nuclear ( r = 0.36, P < 0.05) staining or their combination ( r = 0.58, P < 0.01) was considered. Thus, IHC staining of nucleoli and nuclei can be considered as an alternative method to the TRAP-ELISA. The detection of telomerase in normal mammary gland and fibrocystic mastopathy using both methods does not support the idea that telomerase may be used as a specific marker of mammary neoplasia in dogs.

Telomerase activity in breast cancer patients: association with poor prognosis and more aggressive phenotype

Telomerase expression is an important mechanism of tumor unlimited replicative potential. The aim of this study was to evaluate prognostic impact of telomerase activity in breast cancer patients and to correlate telomerase activity with established prognostic factors. We analyzed tissue of 102 malignant breast lesions and 20 healthy breast tissues. Telomerase activity was determined by telomeric repeat amplification protocol assay. Telomerase activity was present in 77 (75.49 %) of 102 breast cancers. Telomerase activity in breast cancers was statistically significantly higher in comparison with the activity in normal breast tissue. The levels of telomerase activity were significantly positively correlated with tumor size, axillary nodal status, histological grade, HER-2/neu protein expression in tumor tissue and expression of the nuclear antigen Ki-67. A statistically significant negative correlation was found between the presence of ER and telomerase activity. There was no correlation between telomerase activity and concentration of PR or the age of patients. Kaplan-Meier analysis showed that patients with higher telomerase activity had significantly shorter 10-year disease-free survival (p < 0.0001) and 10-year overall survival (p < 0.0001) than those with lower telomerase activity. These results were confirmed by logistic regression analysis. Our results support the prognostic role of telomerase activity and its relationship with the more aggressive phenotype of breast cancer.

Telomerase activity Simplification of assay and detection in bladder tumor and urinary exfoliated cells

Detection of telomerase activity can differentiate malignant from benign cells. However, the original telomeric repeat amplification protocol (TRAP) methods had a number of limitations including a radioisotope labeling [α(32)P] dCTP [α(32)P] dGTP system. We developed digoxigenin labeled CX primer to detect telomerase activity without using radioisotope and attempted to detect telomerase activity of bladder tumor and exfoliated cells in bladder cancer patients. Telomerase activity was detected in 5 (71%) of 7 patients diagnosed with grade 1, 31 (97%) of 32 grade 2, and 11 (100%) of 11 grade 3 bladder tumors. In urinary exfoliated cells, 32 (82%) of 39 grades 1 or 2 bladder tumors were positive for telomerase activity but 20 (51%) of 39 were positive for urinary cytology (P < 0.01). Ten (91%) of 11 of grade 3 tumors were positive for telomerase activity and 11 (100%) of 11 were positive urinary cytology. Three of 100 noncancerous patients were positive for telomerase activity. Sensitivity, specificity, and positive predictive value of telomerase activity assay in urinary exfoliated cells were 84%, 97%, and 93%, respectively. Telomerase activity may be a useful diagnostic marker to detect the existence of immortal cancer cells in the urine.

Prevalence of telomerase activity in human cancer

Telomerase activity has been measured in a wide variety of cancerous and non-cancerous tissue types, and the vast majority of clinical studies have shown a direct correlation between it and the presence of cancerous cells. Telomerase plays a key role in cellular immortality and tumorigenesis. Telomerase is activated in 80-90% of human carcinomas, but not in normal somatic cells, therefore, its detection holds promise as a diagnostic marker for cancer. Measurable levels of telomerase have been detected in malignant cells from various samples: tissue from gestational trophoblastic neoplasms; squamous carcinoma cells from oral rinses; lung carcinoma cells from bronchial washings; colorectal carcinoma cells from colonic luminal washings; bladder carcinoma cells from urine or bladder washings; and breast carcinoma or thyroid cancer cells from fine needle aspirations. Such clinical tests for telomerase can be useful as non-invasive and cost-effective methods for early detection and monitoring of cancer. In addition, telomerase activity has been shown to correlate with poor clinical outcome in late-stage diseases such as non-small cell lung cancer, colorectal cancer, and soft tissue sarcomas. In such cases, testing for telomerase activity can be used to identify patients with a poor prognosis and to select those who might benefit from adjuvant treatment. Our review of the latest medical advances in this field reveals that telomerase holds great promise as a biomarker for early cancer detection and monitoring, and has considerable potential as the basis for developing new anticancer therapies.

The potential utility of telomere-related markers for cancer diagnosis

The role telomeres and telomerase play in the initiation and progression of human cancers has been extensively evaluated. Telomeres are nucleoprotein complexes comprising the hexanucleotide DNA repeat sequence, TTAGGG and numerous telomere-associated proteins, including the six member Shelterin complex. The main function of the telomere is to stabilize the ends of the chromosomes. However, through multiple mechanisms, telomeres can become dysfunctional, which may drive genomic instability leading to the development of cancer. The majority of human cancers maintain, or actively lengthen, telomeres through up-regulation of the reverse transcriptase telomerase. Because there are significant differences in telomere length and telomerase activity between malignant and non-malignant tissues, many investigations have assessed the potential to utilize these molecular markers for cancer diagnosis. Here, we critically evaluate whether measurements of telomere lengths and telomerase levels may be clinically utilized as diagnostic markers in solid tumours, with emphasis on breast and prostate cancer as representative examples. Future directions focusing on the direct detection of dysfunctional telomeres are explored. New markers for telomere dysfunction may eventually prove clinically useful.

DETECTION OF DISSEMINATED TUMOR CELLS IN PERIPHERAL BLOOD

Metastases are the major cause of cancer-related deaths in patients with solid epithelial malignancies, such as breast, colorectal and prostate carcinomas. Hematogenous spreading of tumor cells from a primary tumor can be considered as a crucial step in the metastasis cascade leading eventually to the formation of clinically manifest metastases. Consequently, as shown in recent studies, the detection of disseminated tumor cells in peripheral blood might be of clinical relevance with respect to individual patient prognosis and staging or monitoring of therapy. However, the rarity of disseminated tumor cells in peripheral blood renders the application of sensitive techniques mandatory for their detection. The emergence of highly sophisticated reverse transciptase-polymerase chain reaction (RT-PCR) assays, combining a preanalytical enrichment step with the assessment of multiple molecular tumor markers expressed in disseminated tumor cells, provides a powerful tool in detecting disseminated tumor cells with high sensitivity and specificity. This review will discuss currently used tumor markers as well as experimental means to enhance the sensitivity and specificity of RT-PCR assays to detect disseminated tumor cells in the peripheral blood of patients with breast, colorectal, and prostate cancers, and their clinical relevance assessed in recent studies.

Defining the steps that lead to cancer: replicative telomere erosion, aneuploidy and an epigenetic maturation arrest of tissue stem cells

Recently, an influential sequencing study found that more than 1700 genes had non-silent mutations in either a breast or colorectal cancer, out of just 11 breast and 11 colorectal tumor samples. This is not surprising given the fact that genomic instability is the hallmark of cancer cells. The plethora of genomic alterations found in every carcinoma does not obey the 'law of genotype-phenotype correlation', since the same histological subtype of cancer harbors different gene mutations and chromosomal aberrations in every patient. In an attempt to make sense out of the observed genetic and chromosomal chaos in cancer, I propose a cascade model. According to this model, tissue regeneration depends on the proliferation and serial activation of stem cells. Replicative telomere erosion limits the proliferative life span of adult stem cells and results in the Hayflick limit (M1). However, local tissue exhaustion or old age might promote the activation of M1-deficient tissue stem cells. Extended proliferation of these cells leads to telomere-driven chromosomal instability and aneuploidy (abnormal balance of chromosomes and/or chromosome material). Several of the aforementioned steps have been already described in the literature. However, in contrast to common theories, it is proposed here that the genomic damage blocks the epigenetic differentiation switch. As a result of aneuploidy, differentiation-specific genes cannot be activated by modification of methylation patterns. Consequently, the phenotype of cancer tissue is largely determined by the epigenetic maturation arrest of tissue stem cells, which in addition enables a fraction of cancer cells to proliferate, invade and metastasize, as normal adult stem cells do. The new model combines genetic and epigenetic alterations of cancer cells in one causative cascade and offers an explanation for why identical histologic cancer types harbor a confusing variety of chromosomal and gene aberrations. The Viennese Cascade, as presented here, may end the debate on if and how 'tumor-unspecific' aneuploidy leads to cancer.

[Mechanism of cell proliferation--cell cycle, oncogenes, and senescence]

Cell proliferation is regulated through a transition between the G0 phase and cell cycle. We isolated a mammalian temperature-sensitive mutant cell line defective in the function from the G0 phase to cell cycle. Senescent human somatic cells fail to enter into the cell cycle from the G0 phase with stimulation by any growth factor. Telomere shortening was found to be a cause of cellular senescence, and reexpression of telomerase immortalized human somatic cells. Immortalized human somatic cells showed normal phenotypes and were useful not only for basic research but also for clinical and applied fields. The importance of p53 and p21 activation/induction i now well accepted in the signal transduction process from telomere shortening to growth arrest, but the precise mechanism is largely unknown as yet. We found that the MAP kinase cascade and histone acetylase have an important role in the signaling process to express p21. Tumor tissues and cells were found to have strong telomerase activity, while most normal somatic human tissues showed very weak or no activity. Telomerase activity was shown to be a good marker for early tumor diagnosis because significant telomerase activity was detected in very early tumors or even in some precancerous tissues compared with adjacent normal tissues. Telomere/telomerase is a candidate target for cancer chemotherapeutics, and an agent that abrogated telomere functions was found to kill tumor cells effectively by inducing apoptosis whereas it showed no effect on the viability of normal cells.

Diagnostic value of telomerase expression in breast fine-needle aspiration biopsies

Fine-needle aspiration biopsy (FNAB) of breast is a minimally invasive sampling procedure with a proven value in the initial evaluation of patients with palpable breast lesions. FNAB is a simple, cost-effective, and relatively nontraumatic procedure that has replaced open surgical biopsy in majority of academic institutions across the world. There are, however, inherent limitations in the ability of FNAB to reliably diagnose small percentage of cases that are difficult to diagnose by cytomorphology alone and require excisional biopsy. This shortcoming may be minimized if the morphology can be complemented by a reliable diagnostic adjunct. This retrospective study was designed to assess the added value of telomerase immunostain in interpretation of breast FNABs. Telomerase is a ribonucleoprotein enzyme that has been shown to be activated in different malignant tumors, including breast cancer. Immunocytochemical detection of this molecular marker on cytologic smears and cellblocks may be helpful for interpretation of FNAB specimens. In our retrospective study, we found that 56% of the malignant breast cases (28/50) showed positive telomerase immunostaining while only 4% of the negative cases (2/50) stained with telomerase (positive predictive value: 93%, negative predictive value: 69%). Expression of telomerase on highly suspicious breast fine-needle aspirations may upgrade the diagnosis to malignancy. However, a negative telomerase cannot exclude the possibility of carcinoma.

The role of telomeres and telomerase in the pathology of human cancer and aging

Cellular senescence, the state of permanent growth arrest, is the inevitable fate of replicating normal somatic cells. Postulated to underlie this finite replicative span is the physiology of telomeres, which constitute the ends of chromosomes. The repetitive sequences of these DNA-protein complexes progressively shorten with each mitosis. When the critical length is bridged, telomeres trigger DNA repair and cell cycle checkpoint mechanisms that result in chromosomal fusions, cell cycle arrest, senescence and/or apoptosis. Should senescence be bypassed at such time, continued cell divisions in the face of dysfunctional telomeres and activated DNA repair machinery can result in the genomic instability favourable for oncogenesis. The longevity and malignant progression of the thus transformed cell requires coincident telomerase expression or other means to negate the constitutional telomeric loss. Practically then, telomeres and telomerase may represent plausible prognostic and screening cancer markers. Furthermore, if the argument is extended, with assumptions that telomeric attrition is indeed the basis of cellular senescence and that accumulation of the latter equates to aging at the organismal level, then telomeres may well explain the increased incidence of cancer with human aging.

Telomerase activity in “suspicious” thyroid cytology

BACKGROUND

Telomerase activity (TA) has been detected in most malignant neoplasms, including thyroid carcinomas. The authors studied the utility of TA detection as an ancillary tool to thyroid fine-needle aspiration (FNA) for patients with nonconclusive cytologic diagnoses.

METHODS

Material obtained by FNA from palpable thyroid nodules in 167 consecutive patients was processed for conventional cytologic studies and simultaneously for TA study. Another 8 patients were excluded from TA because of the presence of lymphocytes. All patients with negative results cases were followed for > 1 year, and those who had tumors that were suspicious or positive by FNA or TA underwent resection for pathologic study of nodules. TA was analyzed by telomere repeat amplification protocol-polymerase chain reaction analysis.

RESULTS

After excluding 20 patients because of insufficient material for cytologic study, 120 patients had negative results for malignant cells in cytology material, and the remaining 27 patients had results that were either suspicious (n = 21 patients) or positive (n = 6 patients). Histopathologic confirmation was obtained in 23 patients, including 18 with suspicious cytology (1 with scanty material) and 5 with positive FNA. The histopathologic diagnoses were nodular hyperplasia in 5 patients, follicular adenoma in 3 patients, papillary carcinoma in 11 patients, follicular carcinoma in 1 patient, medullary carcinoma in 2 patients, and lymphoma in 1 patient. TA was detected in 6 of 18 histologically confirmed thyroid neoplasms (1 of 3 follicular adenomas, 3 of 11 papillary carcinomas, 0 of 1 follicular carcinoma, 1 of 2 medullary carcinomas, and 1 of 1 lymphoma), including 1 neoplasm with scanty atypical cells.

CONCLUSIONS

The detection of TA helped to confirm neoplasia in 6 of 23 suspicious thyroid nodules. Although it was less sensitive than FNA, TA specificity was 100% for neoplasia and 87.5% for malignancy. The sensitivity of thyroid FNA increased with the use of TA detection when cytology was nonconclusive for malignancy.

Telomerase activity predicts malignancy in percutaneous image-guided needle biopsy specimens of the abdomen and pelvis

PURPOSE

To determine prospectively if assessment of telomerase activity in percutaneous needle biopsy specimens improves sensitivity and specificity in the diagnosis of abdominal and pelvic malignancy.

MATERIALS AND METHODS

The study was approved by the institutional review board, and written informed consent was obtained from all patients. A prospective double-blinded design was used to assess telomerase activity in abdominal and pelvic biopsy specimens from 99 patients (64 men, 35 women; age range, 22-87 years). After the clinical sample was retrieved, a study specimen from an extra needle pass was divided and independently analyzed for cytologic characteristics and telomerase activity. The final diagnosis was based on chart review at a minimum 1-year follow-up. Statistical analyses included sensitivity, specificity, and accuracy of cytologic examination and/or telomerase activity in predicting malignancy.

RESULTS

Data from study specimens indicated that the sensitivity, specificity, and accuracy of telomerase activity (n=99) in predicting malignancy were 55%, 79%, and 60%, respectively. For cytologic examination (n=86), the sensitivity, specificity, and accuracy in predicting malignancy were 74%, 94%, and 78%, respectively. Combining the two tests (n=86) and classifying a positive reading with either test as malignant improved sensitivity (83%) (P <.05) without altering specificity (76%). In 20 patients who had clinical sample reports that were classified as indeterminate, telomerase activity (n=20) yielded a higher sensitivity (62%) (P <.05) and similar specificity (86%) compared with cytologic examination (n=15), which yielded a sensitivity of 11% and a specificity of 83%.

CONCLUSION

In percutaneous biopsy specimens of the abdomen and pelvis, the combination of cytologic examination and telomerase activity yielded an increased sensitivity in predicting malignancy. In addition, assessing telomerase activity can help identify cancer even when cytologic results are indeterminate.

Antitumor effects of specific telomerase inhibitor GRN163 in human glioblastoma xenografts

Telomerase is a ribonucleoprotein complex that elongates telomeric DNA and appears to play an important role in cellular immortalization of cancers. Because telomerase is expressed in the vast majority of malignant gliomas but not in normal brain tissues, it is a logical target for gliomaspecific therapy. The telomerase inhibitor GRN163, a 13-mer oligonucleotide N3'-->P5' thio-phosphoramidate (Geron Corporation, Menlo Park, Calif.), is complementary to the template region of the human telomerase RNA subunit hTR. When athymic mice bearing U-251 MG human brain tumor xenografts in their flanks were treated intratumorally with GRN163, a significant growth delay in tumor size was observed (P < 0.01 in all groups) as compared to the tumor size in mice receiving a mismatched oligonucleotide or the carrier alone. We also investigated biodistribution of the drug in vivo in an intracerebral rat brain-tumor model. Fluorescein-labeled GRN163 was loaded into an osmotic minipump and infused directly into U-251 MG brain tumors over 7 days. Examination of the brains revealed that GRN163 was present in tumor cells at all time points studied. When GRN163 was infused into intracerebral U-251 MG tumors shortly after their implantation, it prevented their establishment and growth. Lastly, when rats with larger intracerebral tumors were treated with the inhibitor, GRN163 increased animal survival times. Our results demonstrate that the antitelomerase agent GRN163 inhibits growth of glioblastoma in vivo, exhibits favorable intracerebral tumor uptake properties, and prevents the growth of intracerebral tumors. These findings support further development of this compound as a potential anticancer agent.

Telomerase in breast cancer: a critical evaluation

Human chromosomes have highly specialized structures at their ends termed telomeres, repetitive, non-coding DNA sequences (5'-TTAGGG-3'), ranging in size from 5 to 20 kb in human cells. These highly specialized structures prevent chromosome ends from being recognized as double-strand DNA breaks, and they also provide protection from destabilizing agents. The mechanism for maintaining telomere integrity is controlled by telomerase, a ribonucleoprotein enzyme that specifically restores telomere sequences lost during replication by using an intrinsic RNA component as a template for polymerization. Telomerase has two core functional components required for its activity: the catalytic subunit of human telomerase reverse transcriptase (hTERT) and a telomerase RNA template (hTR). Telomerase is activated in the majority of immortal cell lines in culture and in most malignant tumors. This review outlines our current understanding of telomerase in breast cancer development and critically evaluates potential utilities in diagnosis, prognosis, and therapy.

Loss of p53 function accelerates acquisition of telomerase activity in indefinite lifespan human mammary epithelial cell lines

We describe novel effects of p53 loss on immortal transformation, based upon comparison of immortally transformed human mammary epithelial cell (HMEC) lines lacking functional p53 with closely related p53(+) lines. Our previous studies of p53(+) immortal HMEC lines indicated that overcoming the stringent replicative senescence step associated with critically short telomeres (agonescence), produced indefinite lifespan lines that maintained growth without immediately expressing telomerase activity. These telomerase(-) 'conditionally immortal' HMEC underwent an additional step, termed conversion, to become fully immortal telomerase(+) lines with uniform good growth. The very gradual conversion process was associated with slow heterogeneous growth and high expression of the cyclin-dependent kinase inhibitor p57(Kip2). We now show that p53 suppresses telomerase activity and is necessary for the p57 expression in early passage p53(+) conditionally immortal HMEC lines, and that p53(-/-) lines exhibit telomerase reactivation and attain full immortality much more rapidly. A p53-inhibiting genetic suppressor element introduced into early passages of a conditionally immortal telomerase(-) p53(+) HMEC line led to rapid induction of hTERT mRNA, expression of telomerase activity, loss of p57 expression, and quick attainment of uniform good growth. These studies indicate that derangements in p53 function may impact malignant progression through direct effects on the conversion process, a potentially rate-limiting step in HMEC acquisition of uniform unlimited growth potential. These studies also provide evidence that the function of p53 in suppression of telomerase activity is separable from its cell cycle checkpoint function.

Chromosome aberrations in solid tumors

Chromosome aberrations in human solid tumors are hallmarks of gene deregulation and genome instability. This review summarizes current knowledge regarding aberrations, discusses their functional importance, suggests mechanisms by which aberrations may form during cancer progression and provides examples of clinical advances that have come from studies of chromosome aberrations.

Novel alternatively spliced variant with a deletion of 52 BP in exon 6 of the progesterone receptor gene is observed frequently in breast cancer tissues

The human progesterone receptor (PR) is a ligand-activated nuclear transcription factor that mediates progesterone action in target tissues. We found a novel alternatively spliced variant (ASV) of the PR mRNA in breast cancer tissues. The deleted transcript was characterized by an out-of-frame deletion of 52 bp in exon 6 (PR delta6/2 ASV). The PR delta6/2 ASV mRNA results in a partial defect in the region of the ligand-binding domain of the hormone receptor, where conserved residues are missing from the core of the protein. To clarify the clinical significance of the PR delta6/2 ASV, we investigated the expression of this ASV in noncancerous and cancerous tissues from patients with breast cancer using RT-PCR. The novel PR delta6/2 mRNA was detected in 24 of 39 (61.5%) cancerous tissues and in 3 of 39 (7.7%) noncancerous tissues from patients with breast cancer. PR delta6/2 ASV mRNA was expressed more frequently in breast cancer tissues than in noncancerous tissues (p < 0.0001), which suggests a possible relationship between the expression of PR delta6/2 and breast cancer. Our observations may provide a novel strategy for the genetic diagnosis of breast cancer.

Telomerase as a prognostic marker in breast cancer: high-throughput tissue microarray analysis of hTERT and hTR

Telomerase activity (TA) has been shown to correlate with poor clinical outcome in various tumour entities, indicating that tumours expressing this enzyme may be more aggressive and that TA may be a useful prognostic marker. For breast cancer, however, TA is a controversial prognostic marker; whereas some studies suggest an association between TA and disease outcome, others do not find this association. This study used tissue microarrays (breast carcinoma prognosis arrays) containing 611 samples (each 0.6 mm in diameter) from the tumour centre of paraffin-embedded breast carcinomas to analyse the catalytic subunit of telomerase, human telomerase reverse-transcriptase (hTERT), and the internal RNA component (hTR), which are the core components of the telomerase holoenzyme complex. hTERT protein expression was obtained by immunohistochemistry (human anti-telomerase antibody Ab-2, Calbiochem), and hTR RNA was measured by radioactive in situ hybridization. hTERT and hTR expression were determined semi-quantitatively and graded (scores 1-4). Clinical data, such as histological subtype, pT stage, tumour diameter, pN stage, BRE grade, tumour-specific survival (in months), patient's age and others, were available for statistical analysis. A statistically significant correlation was found between tumour-specific survival (overall survival) and hTERT expression (p < 0.0001) or hTR expression (p = 0.00110). Tumours with higher scores (scores 3, 4) for hTR and/or hTERT were associated with a worse prognosis. In multivariate analysis, hTERT expression was an independent prognostic factor. Previous studies, focusing on analysis of TA in smaller numbers of fresh-frozen breast carcinomas by the TRAP assay, gave controversial results with respect to TA as a prognostic marker. Using tissue microarrays from 611 breast carcinomas, this study has demonstrated that increased expression levels of the telomerase core components, hTERT and hTR, are associated with lower overall survival. These findings suggest that TA should be included in future validation studies as a prognostic marker in breast cancer.

Transcription and alternative splicing of telomerase reverse transcriptase in benign and malignant breast tumours and in adjacent mammary glandular tissues: implications for telomerase activity

Telomerase activity was determined in 15 breast cancers, 24 benign breast lesions, and 36 breast tissues adjacent to benign or malignant tumours. A positive TRAP (telomeric repeat amplification protocol) signal was detected in 67% of carcinomas and 29% of benign tumours. In five of ten cases, non-invaded breast tissues adjacent to telomerase-positive carcinomas also displayed telomerase activity. Conversely, in peritumoural specimens adjacent to benign lesions, telomerase activity was never detected. To investigate the regulatory mechanisms of telomerase activity in breast tissues, the expression of telomerase subunits was assessed, as well as the presence of alternatively spliced variants of human telomerase reverse transcriptase (hTERT). The presence of the hTERT full-length transcript appeared necessary for telomerase activity in breast carcinomas. Specifically, all telomerase-positive carcinomas expressed the hTERT full-length message, together with different combinations of alternatively spliced variants, whereas in telomerase-negative cancers, the hTERT full-length transcript was not detectable, or its abundance was markedly lower than that of alternatively spliced variants. Results obtained in benign tumours and normal tissues surrounding carcinomas instead showed that the presence of hTERT full-length transcript was not sufficient to determine telomerase activity. These findings suggest that in non-neoplastic tissues there are other mechanisms that suppress telomerase activity downstream from hTERT transcription and mRNA splicing and that such mechanisms have been lost during neoplastic transformation.

Expression of telomerase reverse transcriptase (TERT) in malignant mesotheliomas

To evaluate the usefulness of determinations of telomerase activity for distinguishing malignant from benign mesothelial lesions, immunohistochemical (using a rabbit polyclonal antibody and the peroxidase method; n = 68) and in situ hybridization (using sense and antisense oligonucleotide probes; n = 46) studies were made on malignant mesotheliomas (epithelioid, 39; sarcomatoid, 18, including 2 of the desmoplastic type; and biphasic, 11) and 19 benign mesothelial lesions (benign mesothelial hyperplasia, 3; and reactive pleuritis, 16). In addition, biochemical studies of telomerase activity were made in 9 of the malignant mesotheliomas. Telomerase activity was detected histochemically in all but one of the malignant mesotheliomas, but only in one (pleuritis) of the benign lesions, in which it was present only in activated lymphocytes. Antisense hybridization signals indicated the presence of telomerase mRNA mainly in the cytoplasm of the malignant cells. Sense probes gave negative results. Biochemical determinations revealed a strong telomerase activity in the 9 malignant mesotheliomas examined. This study demonstrates the usefulness of immunohistochemical staining for the evaluation of mesotheliomas. The required immunostaining can be performed using paraffin sections of formalin-fixed tissues.

Telomere and telomerase in oncology

Shortening of the telomeric DNA at the chromosome ends is presumed to limit the lifespan of human cells and elicit a signal for the onset of cellular senescence. To continually proliferate across the senescent checkpoint, cells must restore and preserve telomere length. This can be achieved by telomerase, which has the reverse transcriptase activity. Telomerase activity is negative in human normal somatic cells but can be detected in most tumor cells. The enzyme is proposed to be an essential factor in cell immortalization and cancer progression. In this review we discuss the structure and function of telomere and telomerase and their roles in cell immortalization and oncogenesis. Simultaneously the experimental studies of telomerase assays for cancer detection and diagnosis are reviewed. Finally, we discuss the potential use of inhibitors of telomerase in anti-cancer therapy.

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.

High telomerase activity is associated with cell cycle deregulation and rapid progression in endometrioid adenocarcinoma of the uterus

Telomerase activity, a mechanism granting cellular immortality, has been detected in most cancer entities, but its association with clinical, histopathologic, and prognostic parameters is not fully understood. We investigated whether quantitative telomerase levels are correlated to established prognostic factors, telomere lengths, cell cycle kinetics, and the clinical course in endometrioid adenocarcinoma of the uterus (EC). A modified telomeric repeat amplification protocol (TRAP) was used to quantify the relative telomerase activity in a series of 53 primary tumors. Mean telomere length was determined by Southern blot analysis. Cell cycle kinetics were studied immunohistochemically on paraffin sections using monoclonal antibodies to 2 distinct proliferation-specific proteins: Ki-67, which is expressed throughout the cell cycle, and a novel cell cycle-associated protein, repp86, the expression of which is restricted to the cell cycle phases S, G2, and M. The ratio of the 2 immunolabeling indices defines the rate of transition through the restriction point. Telomerase activity was detected in 50 of 53 ECs (94%). Its levels correlated significantly with FIGO stage (P =.01) and FIGO grade (P =.003) but not with myometrial invasion. They were weakly associated with the overall proliferative activity (Ki-67, r =.48) but significantly with the repp86 index (r =.64) and even more strongly with the repp86:Ki-67 ratio (r =.77). There was no correlation with mean telomere length. In the group of tumors with high telomerase activity, 5 patients had relapses and 2 died of the disease within a median follow-up period of 29 months. Recurrence showed no relation to FIGO grade and stage. No events were observed in the group with low telomerase activity. In a multivariate model including tumor stage, histopathologic grade, depth of myometrial invasion, and Ki-67 indices, telomerase activity emerged as the only independent predictor of disease progression (P =.0002). It is concluded that beyond a link to proliferation, high telomerase activity reflects a deregulation of the cell cycle associated with an increased rate of cells entering S phase and a higher degree of malignancy. Therefore, quantitative analysis of telomerase activity may be useful for identifying EC patients at high risk for recurrence.

Effects of chemopreventive and antitelomerase agents on the spontaneous immortalization of breast epithelial cells

BACKGROUND

Activation of telomerase is an early event in the development of breast and other cancers that may lead to cell immortalization, a critical and rate-limiting step in cancer progression. Breast epithelial cells from women with Li-Fraumeni syndrome (LFS) immortalize spontaneously and reproducibly in culture. We, therefore, tested whether immortalization of these cells could be prevented by treating them with chemopreventive agents and by inhibiting telomerase activity.

METHODS

Noncancerous, preimmortal breast epithelial cells derived from a patient with LFS were treated for 3 months with nontoxic concentrations of the chemopreventive agents oltipraz, difluoromethylornithine, tamoxifen, and retinoic acid or with two different telomerase inhibitors. The frequency of spontaneous immortalization of LFS-derived cells was estimated by an approach based on fluctuation analyses. Statistical analyses were two-sided.

RESULTS

The frequency of spontaneous immortalization events of LFS-derived breast epithelial cells was reduced by long-term treatment with retinoic acid (P<0.001) or tamoxifen (P<0.05) compared with solvent-treated cells. The frequency of immortalization was also reduced by treating LFS-derived cells with an antitelomerase antisense oligonucleotide (P<0.001) or by inducing the cells to express a dominant negative mutant of telomerase (P<0.025) compared with cells treated with a control oligonucleotide or with empty vector, respectively.

CONCLUSIONS

Treatment of preimmortal LFS breast epithelial cells with chemopreventive and antitelomerase agents decreased the frequency of spontaneous immortalization in vitro. These studies validate the application of a new cell culture model system to screen the effects of novel chemopreventive agents by use of cell immortalization as an end point. The results also suggest that the telomerase ribonucleoprotein complex may be an important molecular target for breast cancer prevention.

Culture models of human mammary epithelial cell transformation

Human pre-malignant breast diseases, particularly ductal carcinoma in situ (DCIS) already display several of the aberrant phenotypes found in primary breast cancers, including chromosomal abnormalities, telomerase activity, inactivation of the p53 gene, and overexpression of some oncogenes. Efforts to model early breast carcinogenesis in human cell cultures have largely involved studies of in vitro transformation of normal finite lifespan human mammary epithelial cells (HMEC) to immortality and malignancy. We present a model of HMEC immortal transformation consistent with the known in vivo data. This model includes a recently described, presumably epigenetic process, termed conversion, which occurs in cells that have overcome stringent replicative senescence and are thus able to maintain proliferation with critically short telomeres. The conversion process involves reactivation of telomerase activity, and acquisition of good uniform growth in the absence and presence of TGFbeta. We propose that overcoming the proliferative constraints set by senescence, and undergoing conversion, represent key rate-limiting steps in human breast carcinogenesis, and occur during early stage breast cancer progression.

Role of telomerase in cell senescence and oncogenesis

The ends of linear chromosomes are capped by specialized nucleoprotein structures termed telomeres. Telomeres comprise tracts of noncoding hexanucleotide repeat sequences that, in combination with specific proteins, protect against degradation, rearrangement, and chromosomal fusion events. Due to the polarity of conventional DNA synthesis, a net loss of telomeric sequences occurs at each cell division. It has been proposed that this cumulative telomeric erosion is a limiting factor in replicative capacity and elicits a signal for the onset of cellular senescence. To proliferate beyond the senescent checkpoint, cells must restore telomere length. This can be achieved by telomerase, an enzyme with reverse-transcriptase activity. This enzyme is absent in differentiated somatic tissues, but telomerase reactivation has been detected in most tumors. Much investigative effort is focusing on telomere dynamics with a view to possible manipulation of cellular proliferative potential. In this article, we review the role of telomeres and telomerase in senescence and tumor progression, and we discuss the potential use of telomerase in diagnosis and treatment.

Telomerase activity is frequently found in metaplastic and malignant human nasopharyngeal tissues

Telomerase is a specialized ribonucleoprotein polymerase that directs the synthesis of telomere repeats at chromosome ends. Accumulating evidence has indicated that telomerase is stringently repressed in normal human somatic tissues but reactivated in cancers and immortal cells, suggesting that reactivation of telomerase plays an important role in carcinogenesis. In this study, the status of telomerase activity in diseased human nasopharyngeal lesions was determined by the telomeric repeat amplification protocol (TRAP). Fifty-four patients participated including 17 inflammation or hyperplasia, eight with squamous metaplasia, and 29 with different stages of carcinomas. Telomerase activity was detected in 1 of 17 (5.9%) inflammatory or lymphoid hyperplastic tissues, 3 of 8 (37.5%) squamous metaplastic, and 25 of 29 (86.2%) carcinoma tissues. The differences in telomerase expression in these groups is statistically significant (P < 0.001). Levels of telomerase activity correlated with tumour stage (P = 0.024). These results suggest that telomerase reactivation plays a role in the carcinogenesis of nasopharyngeal cancer. Since telomerase activity is found in the majority of nasopharyngeal cancers and a subset of metaplasia, this enzyme may be served as a reference to monitoring the status of abnormal nasopharyngeal tissues.

Cellular proliferative and telomerase activity in canine mammary gland tumors

In canine mammary tumors, we examined the telomerase activity, proliferative activity by proliferative cell nuclear antigen (PCNA) immunohistochemistry, and percentage of apoptotic cells by the deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) method. The relationship between these measures and histopathologic malignancy was also investigated. PCNA index was highest in malignant tumors (adenocarcinoma: 27.0%; malignant mixed tumor: 15.7%), followed by benign tumors (adenoma: 4.4%; benign mixed tumor: 5.3%), hyperplasia (2.1%), and normal mammary gland (0.9%). In adenoma and adenocarcinoma, papillary and solid types showing higher cellularity tended to have higher PCNA indices than did cystic and tubular types. Although the TUNEL index was <1% in all cases, the relationship between this measure and histopathologic diagnosis showed the same tendency as observed in PCNA immunostaining. Telomerase activity was detectable in all adenomas, benign mixed tumors, and adenocarcinomas examined. In contrast, all normal mammary glands, hyperplasias, and malignant mixed tumors were negative for telomerase. Relative telomerase activity (RTA) of adenocarcinoma (56.5) was significantly higher than that of adenoma (27.8) and benign mixed tumor (33.9), and a significant positive correlation (P < 0.001) was noted between RTA and PCNA index. No significant correlations were noted between either PCNA or TUNEL index and clinical features such as metastasis and tumor diameter. PCNA index and telomerase activity may be useful markers for judging malignancy of canine mammary tumors.

Inhibition of telomerase activity by a hammerhead ribozyme targeting the RNA component of telomerase in human melanoma cells

Reactivation of telomerase, an RNA-dependent DNA polymerase that synthesizes new telomeric repeats at the end of chromosomes, is a very common feature in human cancers. Telomerase is thought to be essential in maintaining the proliferative capacity of tumor cells and, as a consequence, it could represent an attractive target for new anti-cancer therapies. In this study, we generated a hammerhead ribozyme composed of a catalytic domain with flanking sequences complementary to the RNA component of human telomerase and designed to cleave specifically a site located at the end of the telomerase template sequence. In vitro the ribozyme induced cleavage of a synthetic RNA substrate obtained by cloning a portion of the RNA component of human telomerase. The extent of cleavage was dependent on the ribozyme/substrate ratio as well as the Mg2+ concentration. Moreover, when added to cell extracts from two human melanoma cell lines (JR8 and M14), or three melanoma surgical specimens, the ribozyme inhibited telomerase activity in a concentration- and time-dependent manner. When the ribozyme was delivered to growing JR8 melanoma cells by (N-(1-(2,3 dioleoxyloxy)propil)-N,N,N trimethylammonium methylsulfate-mediated transfer, a marked inhibition of telomerase activity was observed. Next, the ribozyme sequence was cloned in an expression vector and JR8 cells were transfected with it. The cell clones obtained showed a reduced telomerase activity and telomerase RNA levels and expressed the ribozyme. Moreover, ribozyme transfectants had significantly longer doubling times than control cells and showed a dendritic appearance in monolayer culture. No telomere shortening, however, was observed in these clones. Overall, our results indicate that the hammerhead ribozyme is a potentially useful tool for the inactivation of telomerase in human tumors.

Telomeres, telomerase, and myc. An update

Normal human somatic cells have a finite life span in vivo as well as in vitro and retire into senescence after a predictable time. Cellular senescence is triggered by the activation of two interdependent mechanisms. One induces irreversible cell cycle exit involving activation of two tumorsuppressor genes, p53 and pRb, and the proper time point is indicated by a critical shortening of chromosomal ends due to the end-replication problem of DNA synthesis. The development of a malignant cancer cell is only possible when both mechanisms are circumvented. The majority of human cancers and tumor cell lines produce telomerase, a ribonucleoprotein with two components required for core enzyme activity: telomerase RNA (TR) and a telomerase reverse transcriptase protein (TERT). Telomerase adds hexameric DNA repeats (TTAGGG) to telomeric ends and thus compensates the progressive loss of telomeric sequences inherent to DNA replication. While TR of telomerase is present in almost all human cells, human TERT (hTERT) was found rate limiting for telomerase activity. Ectopic expression of hTERT in otherwise mortal human cells induced efficient elongation of telomeres and permanent cell growth. While hTERT-mediated immortalization seems to have no effect on growth potential and cell cycle check points, it bestows an increased susceptibility to experimental transformation. One oncogene that might activate TERT in the natural context is c-myc. Myc genes are frequently deregulated in human tumors and myc overexpression may cause telomerase reactivation and telomere stabilization which, in turn, would allow permanent proliferation. Is this a general strategy of incipient cancer cells to escape senescence? Several recent observations indicate that other scenarios may be conceived as well.

Telomerase RNA expression during progression of gastric cancer

Telomerase, an enzyme associated with cellular immortality and malignancy, is stringently repressed in most normal somatic cells but is reactivated in malignant tumor cells and immortal cell lines, indicating that activation of telomerase may play an important role in tumorigenesis and immortalization. The pattern of human telomerase RNA (hTR) expression during progression of gastric cancer was investigated by a radioactive in situ hybridization (ISH) assay. Paraffin-embedded sections of 85 archival samples from Korean patients with benign and various malignant stages of gastric carcinomas as well as normal and regenerative tissues were studied. In normal gastric mucosae and regenerative lesions such as chronic peptic ulcer and hyperplastic polyps, only a weak degree of hTR expression was noted, and the expression was limited to basal cells of the gastric glands. Also, a moderate degree of hTR expression was present in the germinal centers of lymphoid follicles present in the submucosa. In tubular adenomas, the degree of hTR expression was also generally weak, but, unlike normal gastric mucosa, the expression was rather diffuse and occasionally focal in distribution. However, moderate to intense and usually diffuse hTR expression was present in all cancerous tissues at different stages. Although some heterogeneity of hTR expression was noted, there was a tendency for intensity of hTR expression to increase gradually as the cancer progressed to a more advanced stage. Our results indicate that upregulation of telomerase expression is associated with gastric cancer development or plays some role in gastric carcinogenesis. Upregulation of hTR expression detected by ISH assay may be a useful marker or tool for the early detection of gastric cancer.

Telomerase activity and prognosis in primary breast cancers

PURPOSE

Recent studies associate telomerase activity with prognostic factors and survival. We compared quantitative telomerase activity in primary tumors with traditional prognostic factors and outcome in a group of invasive but nonmetastatic breast cancers.

PATIENTS AND METHODS

Telomerase activity was measured in 203 invasive breast cancers by the quantitative telomeric repeat amplification protocol method. Telomerase expression was compared with 28S rRNA level, tumor content, and clinical variables, including outcome. For clinical correlations, telomerase activity was standardized by two methods: (1) a correction for cellularity using 28S rRNA levels, and (2) a correction for the histologically determined invasive proportion of the specimen.

RESULTS

Telomerase activity was found in 82% of breast cancers with measurable 28S rRNA levels. Telomerase activity was associated with the proliferative index (P <.01) of the tumor but not with any other prognostic variable. Neither uncorrected nor corrected telomerase activity was associated with relapse-free or overall survival in this study.

CONCLUSION

Telomerase activity level was associated with the proliferative index of invasive breast cancers, but its measurement in samples from this group of nonmetastatic breast cancer patients did not predict survival.

Telomerase activity in the human breast

Telomerase is a ribonucleoprotein enzyme which appears to play an important role in carcinogenesis. Telomerase reactivation seems to be associated with immortalization and malignancy. Using a PCR-based assay, we examined telomerase activity in 50 breast tissue specimens, prospectively obtained from 37 women undergoing elective breast surgery. The specimens examined included normal breast (n=13), benign breast lesions (n=5), ductal carcinoma in situ (n=8) and infiltrating ductal carcinoma (n=24). All normal breast, benign breast and DCIS specimens lacked telomerase activity. Sixteen (67%) of 24 infiltrating carcinomas. In infiltrating ductal cancer, there was a statistically significant association between telomerase activity and nodal metastasis. The present results indicate that telomerase activity is associated with acquisition of invasive malignancy in the human breast and may have a role in complementing cytopathological diagnosis. Telomerase activity as a prognostic marker should be included in future validation studies. In DCIS, telomerase activity may be a late event associated with invasion of the basement membrane.

Telomerase is a highly sensitive and specific molecular marker in fine-needle aspirates of breast lesions

PURPOSE

Telomerase has been detected in a majority of human malignant tumors, making telomerase activity (TA) one key difference between mortal and immortal cells. In this study, we evaluated in blind-trial fashion the association of TA with cytologic and final clinical/pathologic diagnosis in fine-needle aspirates (FNAs) of breast lesions.

MATERIALS AND METHODS

In 172 FNAs, including 80 samples that were cytologically malignant, 18 that were atypical but not diagnostic for malignancy, and 74 that were cytologically benign, TA was determined by a modified nonradioactive telomeric repeat amplification protocol (TRAP) assay. Final diagnosis was made by pathologic examination of follow-up surgical material available for all the cytologically malignant samples, a majority of the cytologically atypical samples, and a portion of the cytologically benign samples.

RESULTS

TA was detected in 85 of 172 samples. Comparison of the cytologic and histologic diagnoses with TA showed that 80 of 87 samples from patients with breast cancer were telomerase-positive, resulting in a sensitivity of 92%. TA was found in four of five FNAs from carcinomas that were considered cytologically atypical but not diagnostic for malignancy. Eighty of 85 samples from patients with benign breast lesions were telomerase-negative, revealing a specificity of 94%. The five positive cases in this group were all fibroadenomas with low TA. Among the 18 cases with a cytologic diagnosis of atypia, there was a strong positive relationship between TRAP findings and histologic diagnosis.

CONCLUSION

The detection of TA in FNAs of breast lesions is a highly sensitive and specific marker of malignancy and may be used as an adjunct in cases with an equivocal cytologic diagnosis.

Telomerase activity in ductal carcinoma in situ and invasive breast cancer

The increasing number of breast carcinoma in situ detected by screening procedures makes it imperative to develop improved markers to stratify the risk of invasive cancer. Telomerase is detectable in invasive cancer, but not in normal tissues. We have microdissected frozen tissue blocks containing both DCIS and invasive cancer to assay the telomerase activity of these two lesions. The 46 available cases of concurrent DCIS and invasive breast cancer resulted in 43 DCIS samples and 38 invasive cancer samples adequate for analysis. Seventy per cent of the DCIS and all invasive cancer samples tested had detectable telomerase activity. In addition, we analysed telomerase activity in ten cases of DCIS that were not associated with invasive cancer, and detected telomerase activity in seven (70%). Mixing experiments showed no evidence of telomerase inhibitors in telomerase negative samples. Furthermore, periductal inflammatory infiltrates were shown to be a potential confounding source of telomerase activity. Since DCIS lesions appear to be heterogeneous with respect to telomerase activity, and telomerase activation appears to precede the development of invasive cancer, telomerase activity may be a useful adjunct in stratifying the risk of developing invasive breast cancer in patients with DCIS.

Applications of telomerase research in the fight against cancer

Telomerase, an enzyme that confers immortality upon cells and that is active in the majority of human tumors, has emerged as a powerful new marker and potential prognostic indicator and therapeutic target for cancer. Furthermore, investigations into the biology of telomerase have revealed important clues into the causes of cell death and have made progress toward answering one of the most important questions of cancer research - what gives a tumor cell an advantage over normal cells? In this article, we present the current state of telomerase research and critically assess both its potential and the pitfalls of its application in cancer diagnosis and treatment.

Analysis of telomerase expression and proliferative activity in the different layers of cyclic endometrium

To gain better insights into cell kinetics under physiological conditions, telomerase activity in the functional and basal layers of cyclic endometrium (n = 33) was compared with the immunostaining of glandular and stromal cells within these layers (n = 25). Two immunohistochemical proliferation markers were used to demarcate cells in the G1 phase of the cell cycle. In contrast to previous expectations, telomerase activity and both glandular and stromal proliferative activities were all significantly higher in the functional than in the basal endometrium (P < 0.002). The course of telomerase activity in the endometrial layers during the ovarian cycle was significantly associated with the proliferative scores for the functional and basal endometrial glands and the functional stroma but not the stromal compartment of the basal layer. Our findings indicate that the telomerase activity in cyclic endometrium is associated with the total number of proliferating glandular and stromal cells in the functional layer. Proliferating daughter cells of telomerase-competent stem cells may account for the lower levels of telomerase detected in normal basal endometrium.

Part II. Telomerase expression in cerebrospinal fluid specimens as an adjunct to cytologic diagnosis

The diagnosis of meningeal carcinomatosis hinges on the cytologic examination of cerebrospinal fluid (CSF), which has a known low sensitivity for the identification of malignant cells. Often only 'suspicious' or 'atypical' diagnoses can be rendered, and specimens are commonly unsatisfactory for evaluation due to poor morphologic preservation. Telomerase is widely expressed in most brain metastases, medulloblastomas, lymphomas, oligodendrogliomas, and is expressed focally in glioblastomas. Little is known about the level of telomerase expression in these tumors, except for brain metastases, where a four-fold variation in telomerase levels exists. In our laboratory, as few as ten carcinoma cells can be detected by a sensitive polymerase chain reaction-based assay, the telomeric repeat amplification protocol (TRAP), for telomerase, but it was unclear whether varying levels of telomerase expressed by different types of metastases would influence detection. Using the TRAP protocol, we studied 281 CSF samples from a wide variety of patients with neurologic and non-neurologic conditions for telomerase expression. An adjusted specificity of 90% and a sensitivity of 64% were achieved for detection of malignant cells in CSF by telomerase expression. The TRAP assay for telomerase detection may serve as an adjunct to the traditional examination of CSF. Neither previously documented four-fold variation in the levels of telomerase expression in brain metastases, high CSF protein levels nor high white blood cell counts precluded detection of malignant cells in CSF.