Telomerase as a tool for the differential diagnosis of human hepatocellular carcinoma

Prediction of the prognosis of advanced hepatocellular carcinoma by TERT promoter mutations in circulating tumor DNA

BACKGROUND ANDAIM

Human telomerase reverse transcriptase (TERT) promoter mutations were the most prevalent mutations in patients with hepatocellular carcinoma (HCC). We tried to detect the mutations with plasma circulating tumor DNA (ctDNA) in patients with advanced HCC and elucidated their clinical utility.

METHODS

Circulating tumor DNA in plasma was extracted from 130 patients with advanced HCC who were treated with systemic chemotherapy (n = 86) or transcatheter arterial chemoembolization (n = 44), and TERT promoter mutations were examined with digital droplet polymerase chain reaction. The correlations between these mutations and the clinical outcome of patients were analyzed.

RESULTS

Of the 130 patients examined, 71 patients (54.6%) were positive for TERT promoter mutations in ctDNA, of which 64 patients were -124bp G > A and 10 were -146bp G > A. The presence of TERT promoter mutations was correlated with large intrahepatic tumor size (P = 0.05) and high des-gamma carboxyprothrombin (P = 0.005). Overall survival of the patients with the mutations was significantly shorter than those without them (P < 0.001), and the patients with high (≥ 1%) fractional abundance of the mutant alleles showed shorter survival than those with low (< 1%) fractional abundance. Multivariate analysis revealed that TERT promoter mutation (hazard ratio [HR]: 1.94; 95% confidence interval [CI], 1.18-3.24; P < 0.01), systemic chemotherapy (HR: 2.38; 95% CI, 1.29-4.57; P < 0.01), and vascular invasion (HR: 2.16; 95% CI, 1.22-3.76; P < 0.01) were significant factors for poor overall survival.

CONCLUSIONS

TERT promoter mutations in ctDNA were associated with short survival and could be a valuable biomarker for predicting the prognosis of patients with advanced HCC.

Human Telomerase Reverse Transcriptase Gene Promoter Mutation in Serum of Patients with Hepatocellular Carcinoma

BACKGROUND

Mutations in the human telomerase reverse transcriptase (hTERT) gene promoter have been reported in hepatocellular carcinoma (HCC); however, analyses of these mutations in liquid biopsies have been technically difficult because of the high GC content of the regions of interest within this promoter. We evaluated the feasibility and prognostic value of hTERT promoter mutations identified in circulating cell-free DNA (cfDNA) from the serum of patients with HCC.

OBJECTIVE

A cohort of HCC patients (n = 36) who were curatively treated by surgical resection between June 2003 and September 2014 were enrolled in this study.

METHODS

The presence of hTERT promoter mutations in cfDNA from the patients' serum was analyzed via modified droplet digital polymerase chain reaction, and associations were sought between specific promoter mutations and patients' disease-free survival (DFS).

RESULTS

The G>A hTERT mutation at -124 bp was detected in the serum of 25 patients (69%). Although no marked differences were observed between the characteristics of the serum mutation-positive and serum mutation-negative patient groups, the DFS of patients with the mutation was significantly shorter than that of the serum mutation-negative patients (p = 0.02). Among 18 clinicopathologic and background liver factors examined, the presence of the -124 bp G>A mutation was an independent and significant predictor of patients' DFS (hazard ratio = 3.01, 95% confidence interval 1.11-10.5, p = 0.03) in multivariate analyses.

CONCLUSIONS

The -124 bp G>A hTERT promoter mutation was observed in the serum of 69% of HCC patients who underwent surgical resection and was an independent predictor of disease progression in HCC.

Frequency and geographic distribution of TERT promoter mutations in primary hepatocellular carcinoma

Primary hepatocellular carcinoma (HCC) mainly develops in subjects chronically infected with hepatitis B (HBV) and C (HCV) viruses through a multistep process characterized by the accumulation of genetic alterations in the human genome. Nucleotide changes in coding regions (i.e. TP53, CTNNB1, ARID1A and ARID2) as well as in non-coding regions (i.e. TERT promoter) are considered cancer drivers for HCC development with variable frequencies in different geographic regions depending on the etiology and environmental factors. Recurrent hot spot mutations in TERT promoter (G > A at-124 bp; G > A at -146 bp), have shown to be common events in many tumor types including HCC and to up regulate the expression of telomerases. We performed a comprehensive review of the literature evaluating the differential distribution of TERT promoter mutations in 1939 primary HCC from four continents. Mutation rates were found higher in Europe (56.6%) and Africa (53.3%) than America (40%) and Asia (42.5%). In addition, HCV-related HCC were more frequently mutated (44.8% in US and 69.7% in Asia) than HBV-related HCC (21.4% in US and 45.5% in Africa). HCC cases associated to factors other than hepatitis viruses are also frequently mutated in TERT promoter (43.6%, 52.6% and 57.7% in USA, Asia and Europe, respectively). These results support a major role for telomere elongation in HCV-related and non-viral related hepatic carcinogenesis and suggest that TERT promoter mutations could represent a candidate biomarker for the early detection of liver cancer in subjects with HCV infection or with metabolic liver diseases.

Modification of human embryonic stem cell-derived dendritic cells with mRNA for efficient antigen presentation and enhanced potency

AIM

Dendritic cell (DC)-based vaccines are designed to exploit the intrinsic capacity of these highly effective antigen presenting cells to prime and boost antigen-specific T-cell immune responses. Successful development of DC-based vaccines will be dependent on the ability to utilize and harness the full potential of these potent immune stimulatory cells. Recent advances to generate DCs derived from human embryonic stem cells (hESCs) that are suitable for clinical use represent an alternative strategy from conventional approaches of using patient-specific DCs. Although the differentiation of hESC-derived DCs in serum-free defined conditions has been established, the stimulatory potential of these hESC-derived DCs have not been fully evaluated.

METHODS

hESC-derived DCs were differentiated in serum-free defined culture conditions. The delivery of antigen into hESC-derived DCs was investigated using mRNA transfection and replication-deficient adenoviral vector transduction. hESC-derived DCs modified with antigen were evaluated for their capacity to stimulate antigen-specific T-cell responses with known HLA matching. Since IL-12 is a key cytokine that drives T-cell function, further enhancement of DC potency was evaluated by transfecting mRNA encoding the IL-12p70 protein into hESC-derived DCs.

RESULTS

The transfection of mRNA into hESC-derived DCs was effective for heterologous protein expression. The efficiency of adenoviral vector transduction into hESC-derived DCs was poor. These mRNA-transfected DCs were capable of stimulating human telomerase reverse transcriptase antigen-specific T cells composed of varying degrees of HLA matching. In addition, we observed the transfection of mRNA encoding IL-12p70 enhanced the T-cell stimulation potency of hESC-derived DCs.

CONCLUSION

These data provide support for the development and modification of hESC-derived DCs with mRNA as a potential strategy for the induction of T-cell-mediated immunity.

The differentiation-inducing effect of Nordy on HPV-16 subgenes-immortalized human endocervical cells H8

The lipoxygenase inhibitor nordihydroguaiaretic acid, a natural product purified from Larrea divaricata and Guaiacum officinale, showed a marked capacity to induce differentiation of various human malignant tumor cell lines. Nordy, a derivative of nordihydroguaiaretic acid, has been shown to effectively inhibit the growth of malignant human tumors transplanted in mice. However, it is unknown whether Nordy plays an important role in inducing the differentiation effects of human papillomavirus (HPV)-16 subgenes-immortalized human endocervical cells H8. In this study, we showed that Nordy arrested H8 cells in the G0/G1 phase, promoted cell differentiation in morphology, downregulated the expression of HPV-16 E6 mRNA and nuclear antigen Ki67, and inhibited telomerase activity on HPV-16 subgenes-immortalized human endocervical cells H8. Taken together, Nordy could suppress proliferation by inhibiting proliferation-related events and promote cell differentiation in H8 cell. The results suggested that Nordy might be a potential tumor therapeutic agent.

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.

High expression of telomerase is an independent prognostic indicator of poor outcome in hepatoblastoma

Telomerase, an enzyme related with cellular immortality, has been extensively studied in many kinds of malignant tumours for clinical diagnostic or prognostic utilities. Telomerase activity is mainly regulated by the expression of hTERT (human telomerase reverse transcriptase), which is a catalytic component of human telomerase. To evaluate whether the levels of hTERT mRNA provides a molecular marker of hepatoblastoma malignancy, we examined hTERT mRNA expression levels in the primary hepatoblastoma tissues by fluorescent RT–PCR using LightCycler technology and followed up the clinical outcomes in 63 patients listed in the Japanese Study Group of Pediatric Liver Tumor between 1991 and 2002. The hTERT mRNA expression was detected in 61 (96.8%) specimens and their expression levels ranged between 0.1/1000 and 745.1/1000 copies of PBGD gene that was used as an internal control. Among these cases, frozen 39 tumour samples and 14 adjacent noncancerous liver tissues were analysed for semiquantitative telomerase assay. In the 39 tumour samples, the levels of telomerase activity ranged between 0.11 and 2709 TPG and 12 (30.7%) had high telomerase activity (>100 TPG), whereas only nine of 14 noncancerous liver tissue samples showed telomerase activity which was less than 1.0 TPG. The levels of telomerase activity were significantly correlated with the levels of hTERT mRNA expression (P<0.001). The frequency of high hTERT mRNA expression and/or high telomerase activity did not significantly associate with the clinicopathological factors except for stage of disease. The prognosis of the patients with high hTERT mRNA expression was significantly worse than that of others (P<0.01), as was the patients with high telomerase activity (P<0.01). Multivariate analysis indicated that high levels of hTERT mRNA expression as well as telomerase activity are independent prognosis-predicting factors in patients with hepatoblastoma.

Telomerase and c-myc expression in hepatocellular carcinomas

BACKGROUND

Telomerase is activated in the majority of cancer tissues and immortalized cell lines. The hTERT (human telomerase reverse transcriptase-major component of telomerase) gene promoter has been cloned and contains many c-myc binding sites that mediate hTERT transcriptional activation. Thus far, the role of hTERT in tumorigenesis in hepatocellular carcinoma (HCC) has been little studied using RNA in situ hybridization. The relationship between c-myc and telomerase in human HCC tissue is undetermined.

MATERIALS AND METHODS

The telomerase activity was assayed using TRAP in specimens from 23 HCC patients, hTERTmRNA was detected using in situ hybridization from 57 HCC patients. The immunohistochemistry for c-myc and DNA sequence for hTERT promoter, and tumour differentiation in relation to hTERT and c-myc expression were determined in 57 specimens.

RESULT

hTERTmRNA was found in 47/57 (82.5%) HCC specimens using in situ hybridization. The hTERT expression paralleled telomerase activity, but hTERTmRNA regulation was not significantly associated with c-myc level ( P<0.954) The DNA sequence analysis of the hTERT promoter in specimens from 17 HCC revealed 15 cases of nucleotide transition (T-->C) over 5'-end of distal E-box and one case of nucleotide transversion (G-->C) over 5'-end of proximal E-box. Neither the hTERT expression (P< 0.890) nor c-myc level (P < 0.348) were related to HCC differentiation.

CONCLUSIONS

The hTERT expression paralleled telomerase activity. The telomerase activity in HCC was not only regulated by c-myc. Another pathways might contribute to hTERT and telomerase activity regulation. The lack of telomerase activity in specimens from 17.4% of HCC cases might indicate an alternative pathway for maintaining telomere length. Furthermore, both the telomerase activity and c-myc had no significant role in HCC differentiation.

Distinguishing well-differentiated hepatocellular carcinoma from benign liver by the physical features of fine-needle aspirates

Distinguishing well-differentiated hepatocellular carcinoma (HCC) from benign hepatic lesions is challenging for pathologists in limited diagnostic material such as needle-core tissue biopsy and fine-needle aspiration (FNA) biopsy. The objective of this study is to test a hypothesis that the fortification of liver by reticulin along single cell plates should protect benign hepatic lesions from breakdown by the force of aspiration and smearing, whereas the decreased reticulin in well-differentiated HCC would result in finely granular FNA smear. The study involved FNA biopsies of 67 cases of well-differentiated HCC and 109 cases of benign hepatic lesions, including cirrhosis (22), liver cell adenoma (8), steatosis (7), focal nodular hyperplasia (6), liver with cholestasis (6), and unremarkable liver sampled from nodular hepatic lesions consistent with the regenerative nodules (60). A slide with the most sample from each case by gross inspection was mixed together. Two observers blinded to the diagnoses were asked to separate the slides into two groups based on smear characteristics by gross inspection. Fragments of rigid fine-needle cores was present in 109 out of 109 cases of benign hepatic lesions but absent in 61 out of 67 cases of well-differentiated HCC, which presented as finely granular smears. The difference is statistically significant. (P<0.001, df=1, chi2=149.3). Using the physical characteristic of liver aspirates as the screening test for malignancy, the sensitivity is 91%, specificity is 100%, positive predictive value is 100%, negative predictive value is 94.8%, and efficiency is 96.6%. In conclusion, the smear characteristics of liver samples in FNA biopsy correlate to their reticulin status on histology. This physical characteristic can be used as the first clue to distinguish malignant and benign liver aspirates prior to microscopic examination.

Cellular distribution of telomerase reverse transcriptase in human hepatocellular carcinoma

BACKGROUND AND AIM

Telomerase is the enzyme that synthesizes telomeric DNA, and the activation of telomerase is closely related to cellular immortality. Telomerase activity has been reported in many human cancer tissues and is regulated by the expression of human telomerase reverse transcriptase (hTERT). The aim of the present study was to identify hTERT-expressing cells in human liver tissues and evaluate the feasibility of the hTERT promoter for gene therapy of hepatocellular carcinoma (HCC).

METHODS

The authors examined the cellular distribution of hTERT transcripts in surgically resected HCC by in situ hybridization.

RESULTS

Among 20 samples, hTERT expression was observed in 15 HCC. Transcripts of hTERT were homogenously distributed in the cytoplasm of HCC cells in nine of 15 cases; six of 15 cases displayed a heterogeneous staining pattern. All poorly differentiated HCC that expressed hTERT showed a homogenous pattern of staining. None of the non-cancerous hepatocytes were positive for the transcripts, but infiltrating lymphocytes were faintly stained. The homogenous expression of hTERT was also observed in the vascular invasion of HCC.

CONCLUSIONS

The results indicate that most HCC cells express hTERT RNA and that the promoter is a good candidate as a target for gene therapy. However, careful consideration must be taken concerning the potential effects on lymphocytes.

Screening for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is common throughout the world and most often develops as a late complication of chronic viral hepatitis or cirrhosis of any cause. As a result of the high prevalence rate of chronic hepatitis C, the incidence of HCC is rising in the United States, as well as in European and Asian countries. The overall survival rate of HCC is poor, and surgical resection and liver transplantation are the only curative treatment options. Screening for HCC offers the best hope for early detection, eligibility for treatment, and improved survival. Most physicians routinely screen at-risk patients with chronic viral hepatitis and cirrhosis for HCC, despite the lack of official guidelines. The current consensus recommendations are to screen healthy hepatitis B virus carriers with annual or semiannual serum alpha-fetoprotein; carriers with chronic hepatitis or cirrhosis and patients with cirrhosis of any etiology are surveyed with twice yearly serum alpha-fetoprotein and liver ultrasound. This article will review the current recommendations for HCC screening, the rationale that led to these recommendations, and the challenges of cost-effectiveness research in this area.

Identification of serum anti-human telomerase reverse transcriptase (hTERT) auto-antibodies during progression to hepatocellular carcinoma

Human telomerase reverse transcriptase, hTERT, is the catalytic component of human telomerase. Expression of hTERT confers telomerase activity, indicating that hTERT is the rate-limiting component of human telomerase. Here we report the detection of anti-hTERT auto-antibodies in the sera derived patients with hepatocellular carcinoma using recombinant, purified hTERT as an antigen in an enzyme linked immunosorbent assay (ELISA). The levels of anti-hTERT antibodies in serum correlated with progression to hepatocellular carcinoma. In contrast, we detected only low levels of anti-hTERT auto-antibodies in the sera derived from 18 normal volunteers. The observation of hTERT auto-antibodies in the sera derived from cancer patients suggests that such auto-antibodies constitute novel and specific tumor marker.

The relationship between telomere length and telomerase activity in gynecologic cancers

OBJECTIVE

In recent years, many studies have been published regarding telomere length and telomerase activity in malignant tissues. However, it is not enough that telomere length and telomerase activity in gynecologic cancers have been measured at same time. We investigated the relationship between telomere length and telomerase activity in gynecologic cancers.

METHODS

A total of 52 gynecologic cancers (15 ovarian cancers, 23 endometrial cancers, 14 cervical cancers) were obtained at the time of surgery. The specimens were analyzed for telomerase activity and telomere length with the TRAP(EZE) ELISA kit and Southern blot, respectively.

RESULTS

Telomerase activity was detected in 42 of 50 (84.0%) of all evaluable specimens, in 11/15 (73.3%) ovarian, 18/22 (81.8%) endometrial, and in 13/13 (100%) cervical cancers. The difference of positive strength (DeltaA value) between stage I and III was statistically significant (P = 0.01, ANOVA test). Changes in telomere length by shortening or elongation were detected in 35 of 52 (67.3%) tumors, in 9/15 (60.0%) ovarian, 17/23 (73.9%) endometrial, and 9/14 (64.3%) cervical cancers. There was no detectable relationship between telomere length and stage of disease, pathologic diagnosis (ovarian, endometrial, and cervical cancers), or telomerase activity.

CONCLUSIONS

There was no relationship between telomerase activity and telomere length. The clinical significance of telomere length appears to be limited in gynecologic cancers.

Telomerase activity in clinically normal dogs and dogs with malignant lymphoma

OBJECTIVES

To determine whether telomerase activity was present in lymph nodes, buffy coat, and serum samples from dogs with malignant lymphoma (ML) and in liver, lymph node, buffy coat, and serum samples from clinically normal dogs

SAMPLE POPULATION

Tissue specimens and blood samples were obtained from 11 clinically normal adult dogs (age range, 1 to 4 years) and 14 client-owned dogs with ML.

PROCEDURE

The telomere repeat amplification protocol assay was used to quantify telomerase activity in the tissues from clinically normal dogs and dogs with ML.

RESULTS

Of 11 clinically normal dogs, 8 had lymph node samples, 5 had liver samples, and 1 had buffy coat samples with detectable telomerase activity. None of the serum samples from the clinically normal dogs had detectable telomerase activity. Of 14 dogs with ML, 9 had lymph node samples, 3 had buffy coat samples, and 1 had serum samples with measurable telomerase activity.

CONCLUSIONS AND CLINICAL RELEVANCE

Telomerase activity was not specific to tumor cells and overlapped with that found in cells from clinically normal dogs. Telomerase activity in neoplastic lymph nodes was not substantially different from that found in lymph nodes from clinically normal dogs. The determination of telomerase activity cannot be used as a sole diagnostic test for cancer. Therapeutic modalities directed toward the telomerase enzyme may not be feasible in dogs, because somatic tissues from clinically normal dogs possess variable amounts of telomerase activity.

Telomerase activity as a predictive marker for recurrence of hepatocellular carcinoma after hepatectomy

BACKGROUND

Expression of telomerase activity and stabilization of telomeres are concomitant with attainment of immortality in tumor cells. Telomerase activity levels in hepatocellular carcinoma (HCC) may serve as a predictive marker for recurrence after surgery.

METHODS

Telomerase activity levels in HCC were measured in 37 patients undergoing hepatectomy by the telomeric repeat amplification protocol. The clinicopathologic factors and telomerase activity were analyzed to identify factors that were important in affecting recurrence of HCC and recurrence-free survival.

RESULTS

Telomerase activity was detected in 23 patients (62.2%), and was not significantly associated with seven other HCC-related factors. After a median follow-up of 34 months, 24 patients (64.9%) had recurrence of HCC. In univariate analyses, telomerase activity of more than 20 total product generated (TPG) and portal vein invasion were found to be significantly related to a shorter time to recurrence. Multivariate analysis demonstrated that telomerase activity (>20 TPG) was significantly related to an increased risk of recurrence (relative risk 2.36, 95% confidence interval 1.03 to 5.43, P = 0.04).

CONCLUSIONS

Telomerase activity can be identified as an independent predictor for recurrence after resection of HCC.

Reduction of telomerase activity in human liver cancer cells by a histone deacetylase inhibitor

The presence of telomerase has been demonstrated recently in many different malignancies. Several reports documented that in human hepatocellular carcinoma, the level of telomerase activity parallels its differentiation stage. In the present study, the effect of the differentiation-inducing agent sodium butyrate on telomerase activity in four human liver cancer cell lines was investigated using the telomeric repeat amplification protocol. We assayed telomerase activity before and after butyrate treatment and in cell cycle synchronized non-dividing quiescent cells. In addition, telomerase reverse transcriptase levels were measured at the mRNA level. All four cell lines possessed high but not identical levels of telomerase activity. Telomerase activity was significantly reduced by treatment with sodium butyrate as well as trichostatin A in a dose- and time-dependent fashion, paralleling the reduction of cell proliferation. Although methotrexate, hydroxyurea, and colchicine synchronized the cell cycle at G1, S, and G2/M, respectively, and thereby also caused proliferating cells to cease dividing and become quiescent, in this case telomerase activity remained essentially unaltered compared to the control cultures. Moreover, levels of mRNA encoding telomerase reverse transcriptase were not always significantly altered by either sodium butyrate treatment or cell cycle synchronization. These results suggest that sodium butyrate, as a histone deacetylase inhibitor, effectively reduces telomerase activity without affecting transcription levels of the reverse transcriptase component.

Telomerase activity is repressed during differentiation along the hepatocytic and biliary epithelial lineages: verification on immortal cell lines from the same origin

Recent investigations indicate that telomerase activity regulates the life span of cells by compensating for telomere shortening during DNA replication. In addition, as differentiation progresses, telomerase activity is reduced in several different cell lineages. These findings lend support to the theory that more immature cells have greater remaining proliferative capacity and longer life span. However, it has not been directly demonstrated that the differentiation along a hepatocytic or a bile ductal lineage is accompanied by reduction of telomerase activity. In this study, we present direct evidence that telomerase activity is reduced during hepatocytic and biliary epithelial differentiation by using our unique cell lines including a stem-like cell line, ETK-1. When hepatocytic differentiation was induced in ETK-1 by 5-azacytidine, telomerase activity decreased significantly. Similarly, when we compared the telomerase activity on SSP-25 and RBE cell lines from the same origin but representing different maturation stages of cholangiocarcinoma, more mature cells were found to possess significantly lower activity. These results indicate that the generally accepted relationship between telomerase activity and differentiation stage also applies in the hepatocytic and biliary epithelial lineages.

Telomerase activity in peripheral blood for diagnosis of hepatoma

BACKGROUND

Telomerase activity may be used as a molecular marker for the detection of circulating hepatoma cells in blood of patients with hepatoma.

METHODS

Telomerase activity in peripheral blood from hepatocellular carcinoma (HCC) patients was assessed by using a highly sensitive and non-radioisotope telomerase polymerase chain reaction (PCR) ELISA. Initially, tissue telomerase activity was measured in the hepatoma and non-tumour portions by using PCR ELISA within the same specimen, to compare its sensitivity with the conventional telomeric repeat amplification protocol (TRAP) method. Second, telomerase activity was measured in the peripheral blood obtained from patients with HCC, patients with chronic liver disease and in healthy controls.

RESULTS

Of the 17 HCC patients, telomerase activity was found to be positive in 14 (82%) by using TRAP and 15 (88%) by using PCR ELISA, indicating that PCR ELISA is a reliable tool for the measurement of telomerase activity. By using the Telomerase PCR ELISA assay, telomerase activities in the peripheral blood of 20 HCC patients was 1.65 +/- 0.78 units. This was significantly greater than the results obtained for 20 chronic liver disease patients (0.43 +/- 0.36 units) and 20 healthy controls (0.39 +/- 0.14 units; P < 0.0001).When the arbitrary cut-off level was set at 0.7 units (maximum value of healthy controls + 0.1), the positive frequency of telomerase activity was 25% for chronic liver disease and 80% for HCC patients (sensitivity 80%, specificity 75%). Among the HCC patients, high telomerase activity in the peripheral blood was shown at stage III HCC with vascular invasion (2.10 +/- 0.62 units, n = 9). This was significantly higher than patients at stage II of HCC (1.28 +/- 0.72 units, n = 11, without vascular invasion; P = 0.012).

CONCLUSION

These results suggest that peripheral blood telomerase activity, which may reflect haematogenous micrometastasis, is potentially a practical diagnostic/predictive marker of HCC.

Detection of telomerase activity in biopsy specimens for diagnosis of biliary tract cancers

BACKGROUND

Telomerase activity is detectable in more than 85% of primary cancers. We determined telomerase activity in biopsy specimens obtained from biliary tract cancers to evaluate the clinical application of telomerase activity detection in combination with p53 immunostaining and routine histologic examination.

METHODS

Biopsy specimens obtained during percutaneous transhepatic cholangioscopy from 13 patients with cholangiocarcinoma, 3 patients with gallbladder carcinoma, and 4 patients with intrahepatic bile duct stones were evaluated by routine histologic examination, p53 immunostaining, and telomerase activity. Semiquantitative determination of telomerase activity was performed using a fluorescence-based telomeric repeat amplification protocol.

RESULTS

Thirteen of 16 specimens of malignant tissue had detectable telomerase activity, whereas no specimen of nonmalignant tissue had detectable telomerase activity. A p53 overexpression was recognized by immunostaining in 9 of 16 samples with cancers. Combining both telomerase activity and p53 overexpression resulted in the detection of all cancer with a sensitivity of 100%. There were no false-positive results by either modality (specificity 100%).

CONCLUSIONS

The detection of telomerase activity in biopsy specimens and p53 overexpression in combination with routine histologic examination may improve the diagnosis of biliary tract cancers. (Gastrointest Endosc 2000;52:380-6).

Expression of telomerase-associated protein 1 and telomerase reverse transcriptase in hepatocellular carcinoma

To know whether two protein components of human telomerase (human telomerase-associated protein 1 (hTEP1) and human telomerase reverse transcriptase (hTERT) are useful markers for telomerase activation in human liver diseases, we examined mRNA levels of these and telomerase activity in human liver samples. Twenty-three human hepatocellular carcinomas (HCCs) and corresponding adjacent livers were analysed for hTEP1 and hTERT expression by semiquantitative reverse transcription-polymerase chain reaction, and for telomerase activity by a telomeric repeat amplification protocol assay. Thirteen liver samples (ten HCCs and three dysplastic nodules) that were biopsied with 21-gauge needles were analysed for hTERT expression. hTEP1 was expressed in all samples examined. No correlation between hTEP1 expression and telomerase activity was observed. hTERT expression significantly correlated with telomerase activity (P< 0.001). The positivity of hTERT for HCC and corresponding non-cancerous liver was 100% and 30.4% respectively (P < 0.001). Seventy-four per cent (17/23) of HCCs showed strong hTERT expression, but none of the non-cancerous liver tissues did. hTERT expression of the 21-gauge needle biopsied specimens showed no significant difference from that of the surgical samples. The present study revealed that hTERT is strongly expressed in most HCCs, and that hTERT but not hTEP1 is a key component regulating telomerase activity in human liver.

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.

Quantitative evaluation of telomerase activity in small liver tumors: analysis of ultrasonography-guided liver biopsy specimens

BACKGROUND/AIMS

Telomerase activity which restores the length of telomere repeat arrays is frequently detectable in various malignancies, including hepatocellular carcinoma. The aim of this study was to determine the diagnostic usefulness of the quantitative measurement of telomerase activity in small liver tumors, which has not yet been established.

METHODS

Fifty-eight liver specimens from tumorous and non-tumorous portions of 29 small liver tumors equal to or less than 3.0 cm were obtained by ultrasonography-guided liver biopsy, and of these, 25 were diagnosed as hepatocellular carcinoma and four as adenomatous hyperplasia. The telomerase activities in these specimens and control specimens were examined quantitatively by telomeric repeat amplification protocol with standard control.

RESULTS

The mean telomerase activity in cirrhosis without liver tumor was 0.4+/-0.6 (+/-S.D.) arbitrary units (AU) and that in 29 non-tumorous parts of the tumors was 4.5+/-7.4 AU. The mean telomerase activity in 13 tumors equal to or less than 2 cm in diameter was 77.1+/-133.7 AU and that in 16 tumors more than 2 cm was 152.7+/-215.2 AU. The mean telomerase activity in the 4 adenomatous hyperplasias was 5.5+/-4.5 AU; those of hepatocellular carcinoma with Edmondson-Steiner classification I, II, III and IV were 49.6+/-47.4 (n = 10), 240.1+/-273.6 (n = 9), 119.2+/-174.6 (n = 4) and 144.6+/-80.2 (n = 2) AU, respectively.

CONCLUSIONS

The telomerase activity was significantly higher in hepatocellular carcinoma compared to adenomatous hyperplasia and non-neoplastic tissue, indicating that the quantitation of telomerase activity would be useful for the diagnosis of small hepatocellular carcinoma.

Tuberculin purified protein derivative up-regulates the telomerase activity of peripheral blood mononuclear cells from patients with pulmonary tuberculosis

Telomerase activity was detectable in cells of tuberculous pleural effusions at high percentage. To investigate the possible role of telomerase in the immune function, we examined the proliferating state and the expression of telomerase activity in peripheral blood mononuclear cells (PBMC) from 13 patients with pulmonary tuberculosis (TB) and 13 healthy volunteers in response to tuberculin purified protein derivative (PPD) challenge. Exposure of cells to phytohemagglutinin (PHA) significantly promoted PBMC proliferation during a 6 day-period in both TB patient and healthy volunteer groups. PPD treatment also significantly promoted PBMC proliferation during a 6 day-period in TB patient group, but had no significant effect in healthy volunteer group. During the same period, telomerase activity was detected in every PHA- and PPD-treated samples of the TB patient group. However, the telomerase activity was not detected in PPD-treated samples from healthy donors and all the untreated samples. Our results indicate that the telomerase activity in PBMC could be induced by PPD stimulation in TB patients. Telomerase activity may thus play a permissive role in cell division and clonal expansion of the immune cells in response to TB.

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.

Telomerase activity in the differentiation of benign and malignant adrenal tumors

BACKGROUND

Telomerase is an RNA-dependent DNA polymerase that extends the ends of chromosomes by synthesizing the 6 oligonucleotide repeat TTAGGG and thus serves as a marker for cellular immortality. Although absent in most adult somatic tissues, telomerase activity is present in stem cells and is reactivated in nearly all primary human malignancies. In this study we sought to determine whether tumors of the adrenal glands contain telomerase activity and whether telomerase activity can be used to differentiate benign and malignant tumors of the adrenal glands.

METHODS

Tissue was obtained from 23 specimens at adrenalectomy. Adjacent normal adrenal tissue was obtained for control. All specimens were rapidly frozen and stored at -80 degrees C until assay. Telomerase activity was determined by the telomeric repeat amplification protocol (TRAP).

RESULTS

Telomerase activity was present in 5 of 23 (22%) of the adrenal tumors. All 3 malignant tumors were strongly TRAP positive. There was a single cortical adenoma that had very weak telomerase activity. The single TRAP-positive tumor of the adrenal medulla was a ganglioneuroma.

CONCLUSIONS

Benign adrenal tumors infrequently contain telomerase activity, whereas telomerase reactivation appears to be common in malignant tumors of the adrenal glands. These data suggest that determination of telomerase activity may offer a novel way to facilitate the differentiation of benign and malignant adrenal tumors.

Telomerase activity in gastrointestinal stromal tumors

BACKGROUND

Telomerase activity has been observed in 80-90% of carcinomas derived from various organs. However, to the authors' knowledge this report is the first assessment of telomerase activity in gastrointestinal stromal tumors (GISTs).

METHODS

Telomerase activity was analyzed by the telomerase repeat amplification protocol assay in 29 tumors from 26 patients (23 primary tumors from 22 patients, 1 pair of primary and metastatic tumors from 1 patient, and 4 metastatic tumors from 3 patients). Phenotypes, tumor cell proliferation, and overexpression of p53 protein were evaluated immunohistochemically.

RESULTS

Seven of 24 primary tumors (29%) and 5 of 5 metastatic tumors (100%) showed telomerase activity. Telomerase activity positive (+) GISTs were significantly larger (P < 0.05) and showed a significantly higher rate of proliferation than telomerase activity negative (-) tumors (P < 0.0001). All telomerase activity (+) GISTs were classified histologically as high risk tumors. Conversely, 15 of the 17 telomerase (-) GISTs were classified histologically as low risk tumors (P < 0.0001). With regard to p53 immunoreactivity, two and seven telomerase activity (+) tumors showed diffuse and sporadic positivity, respectively, whereas only five telomerase activity (-) tumors showed only focal or sporadic positivity. Telomerase activity was correlated significantly with poor prognosis (P < 0.05) in the patients in whom the primary GISTs were evaluated (n = 23).

CONCLUSIONS

Telomerase activity may be a useful marker for evaluating the malignant potential of GIST. A distinct subgroup of GISTs is a target for therapy with a telomerase inhibitor.

Telomerase activity and telomere length in human hepatocellular carcinoma

Telomerase activity is activated and telomere length altered in various types of cancers, including hepatocellular carcinoma (HCC). A total of 39 HCC tissues and the corresponding non-tumour livers were analysed and correlated with clinical parameters. Telomere length was determined by terminal restriction fragment assay, and telomerase activity was assayed by telomeric repeat amplification protocol. Telomerase activity was positive in 24 of the 39 tumour tissues (1.15-285.13 total product generated (TPG) units) and in six of the 39 non-tumour liver tissues (1.05-1.73 TPG units). In the 28 cases analysed for telomere length, telomere length was shortened in 11 cases, lengthened in six cases, and unaltered in 11 cases compared with non-tumour tissues. Neither telomere length nor telomerase activity was correlated to any clinical parameters.

Telomerase activity in hepatocellular carcinoma and adjacent liver tissues

BACKGROUND AND OBJECTIVES

Activation of telomerase and stabilization of telomeres are considered necessary for immortalization of tumor cells. Telomerase activity was analyzed in 69 hepatocellular carcinomas and adjacent chronic liver disease tissues. The telomerase activity level was examined in relation to clinicopathologic features.

METHODS

Telomerase activity was determined by a telomeric repeat amplification protocol. Immature and mature leukocytes were removed from homogenized tissue of adjacent livers using anti-CD45 and anti-CD15 monoclonal antibody-coated magnetic beads.

RESULTS

Telomerase activity was detected in hepatocellular carcinomas and leukocytes, but not in liver cells from adjacent chronic liver disease tissues after the separation of leukocytes. All hepatocellular carcinomas displayed telomerase activity, and the activity level correlated with the degree of differentiation (P=0.021) and patient survival (P=0.039).

CONCLUSIONS

These results indicate that activation of telomerase may be required as a critical step in hepatocarcinogenesis and tumor development, and detection of telomerase activity with removal of contaminating leukocytes may be useful in the characterization or prognostication of hepatocellular carcinoma.

Effect of acetic acid on telomerase activity in cervical intraepithelial neoplasia

OBJECTIVE

To evaluate whether the telomerase activity in CIN lesions can be affected by a chemical solution of acetic acid, which is required to apply to the cervix prior to colposcopy-directed biopsy.

MATERIALS AND METHODS

Thirty-five patients with histologically confirmed high-grade squamous intraepithelial lesions of the cervix entered the study. Two specimens were collected from each patient, one before and one after the cervix was swabbed with 5% acetic acid. The standard telomeric repeat assay protocol (TRAP) was used to examine telomerase activity in these fresh frozen tissue samples. Normal cervical tissues from 10 control individuals were also examined for the presence of telomerase activity. A total of 80 specimens was analyzed.

RESULTS

Telomerase activity was detectable in 27 of 35 (77.1%) fresh tissue samples, 15 of 35 (42.9%) tissue samples swabbed with 5% acetic acid, and 0 of 10 (0%) normal cervical tissue samples, respectively. Twelve samples became telomerase negative after 5% acetic acid applied. Among the 15 telomerase-positive tissue samples swabbed with 5% acetic acid, 12 had relative weak telomerase activity compared to corresponding fresh tissue samples, the other 3 remained the same. Therefore, it is concluded that telomerase activity was affected by 5% acetic acid in 24 of 27 (88.9%) samples. Telomerase activity in HeLa cell line was also inhibited by 5% acetic acid.

CONCLUSION

We reported a relative high percentage of telomerase expression in high-grade CIN lesions when compared with previous reports. If detection of telomerase activity is to become a tool for diagnosis and prognosis of cervical neoplasias, applying acetic acid prior to colposcopy-directed biopsy that is submitted for telomerase assay should be avoided in order to increase the detection rate.

Surgical significance of telomerase activity in noncancerous liver tissue from patients with hepatocellular carcinoma

Telomerase activity has been detected in tissue from noncancerous liver of patients with chronic liver disease, but its functional significance remains to be elucidated. We therefore evaluated the telomerase activity in surgically obtained noncancerous liver tissue from 20 hepatocellular carcinoma (HCC) patients. Two samples of noncancerous liver tissue were obtained from each patient: one from the parenchyma adjacent to the HCC nodules of the resected specimen; the other from the parenchyma distant from the HCC nodules of the remnant liver. Telomerase activity was assayed by a non-radioisotope quantitative system based on "TRAP-eze." Five samples from the noncancerous liver tissue adjacent to the HCC nodules (25.0%) were telomerase-positive; all such cases showed high-grade malignant potential, such as intrahepatic metastasis and/or portal vascular invasion and infiltration of the fibrous capsule in the corresponding HCC nodules, and telomerase positivity showed neither a relationship with the histological activity index scores nor a correlation with liver function. Interestingly, no telomerase activity was detected in any of the 20 samples obtained from the parenchyma of the remnant liver. These results indicate that telomerase in noncancerous liver tissue is associated not with the hepatic condition accompanying HCC, but with the biological characteristics of the tumor itself, and may derive from infiltrating cancer cells. Determination of telomerase status may aid in designing more effective surgical procedures.

Demonstration of constant upregulation of the telomerase RNA component in human gastric carcinomas using in situ hybridization

Upregulation of the ribonucleoprotein telomerase seems to be a prerequisite for immortality, a feature of malignant cells. Using a polymerase chain reaction (PCR)-based assay, it is possible to demonstrate telomerase activity (TA) in specimens of most human malignancies, whereas it is absent from most normal tissues. It remains unclear, however, why between 5 and 50 per cent of various malignant tumour samples give negative results when TA is measured by the telomeric repeat amplification protocol (TRAP). The expectation that reverse transcription (RT)-PCR for detection of the telomerase RNA component (hTR) would be able to complement or to replace the TRAP assay failed, since malignant as well as non-malignant tissue samples gave positive results in most instances. In the present study, in situ hybridization (ISH) was developed to demonstrate the RNA component of human telomerase at the single cell level. With this method, 13 specimens of fresh frozen gastric carcinoma and four of normal, dysplastic, or inflamed gastric mucosa were investigated and the results were compared with those obtained by RT-PCR and the TRAP assay. In addition, ISH was performed on formalin-fixed sections of the same cases. The TRAP assay revealed positive results in 8 out of 13 gastric carcinomas and was negative in all non-malignant tissues. RT-PCR led to amplification of the telomerase RNA component in all specimens tested, irrespective of the presence or absence of malignant cells. By ISH, all gastric carcinomas showed strong telomerase RNA component-specific signals over malignant cells, whereas only a few grains were detectable over some types of normal somatic cells, including activated lymphocytes. In conclusion, high expression of the telomerase RNA component was restricted to the malignant cells of all the gastric carcinomas investigated, as shown by ISH. This indicates that the absence of TA in a proportion of carcinomas is due to methodological problems of the TRAP assay and is not caused by biological factors. The detection of high levels of the telomerase RNA component by ISH is thus a useful technique for demonstrating malignant cells in frozen and formalin-fixed pathological specimens.

Roles of epidemiology, pathology, molecular biology, and biomarkers in the investigation of occupational lung cancer

The pathology and molecular biology of lung cancer demonstrate that these tumors evolve through a series of mutations, molecular changes, and corresponding morphologic changes. To elucidate how occupational and environmental factors influence lung cancer histogenesis it is important not only to understand epidemiology and the interactions between etiologic agents but also to integrate information from pathology, biochemistry and molecular biology. This review focuses on the range of techniques currently available for characterizing lung cancer and how their prudent use can be beneficial in the identification of occupational carcinogens. Because many occupational and environmental lung cancers are caused by multiple etiologic agents, the integration of histology with cellular, biochemical and molecular biomarker techniques may provide new approaches for understanding the disease process.

Telomerase activity in the female reproductive tract and neoplasms

OBJECTIVE

To study a possible utility of telomerase determination for cancer diagnosis.

METHODS

In a total of 227 tissue samples comprising 114 normal tissues of the reproductive age, 10 fallopian tubes of the postmenopausal age, and 103 neoplastic tissues from female reproductive tracts, telomerase activity was determined. Using densitometrical analysis, telomerase activity was compared between carcinoma tissues and normal counterparts.

RESULTS

A total of 97.3% (71/73) of cancer samples comprising ovarian carcinoma, endometrial carcinoma, and epidermoid carcinoma of the cervix and 89.5% (77/86) of the epithelia of the reproductive-aged uterus and fallopian tube showed telomerase activity. The epithelia of the fallopian tube of reproductive age showed significantly higher frequency of positivity (16/18) than the postmenopausal epithelia of the tube (3/10). No difference in telomerase activity was found between endometrial carcinomas and normal proliferative endometria. A significantly higher activity was found in ovarian epithelial carcinoma and epidermoid carcinoma of the cervix than in normal counterparts, although 92% (11/12) of the normal exocervix and 30% (3/10) of the normal ovary showed telomerase activity.

CONCLUSIONS

Most epithelia of the female reproductive tract maintain telomerase activity during the reproductive age. Therefore, the detection of malignancies by telomerase determination may be feasible in ovarian carcinoma and epidermoid carcinoma of the cervix, but requires accurate quantification of telomerase activity.

Telomerase activity in hepatocellular carcinoma as a predictor of postoperative recurrence

Telomerase is a ribonucleoprotein that stabilizes telomeres and allows unlimited cell division. It has been reported that most cancer cells evince reactivated telomerase. We examined telomerase activity in 29 patients with hepatocellular carcinoma (HCC) by a polymerase chain reaction-based semiquantitative assay. Of 24 HCCs, telomerase activity was positive in 23 (95.8%), of which 16 showed strong activity. In 11 well differentiated HCCs, telomerase activity was strong in 5, weak in 5, and undetected in 1 and in 13 moderately differentiated HCCs, it was strong in 11 and weak in 2. Five of 6 HCCs less than 2 cm in diameter expressed strong telomerase activity, while weak telomerase activity was detected in 7 of 19 (36.8%) resected noncancerous liver tissues from the HCC patients. Five of these 7 patients (71%) manifested recurrence within 6 months after surgery. The recurrence rate in these patients whose noncancerous liver tissue was positive for telomerase activity was significantly higher than that in patients in whom it was negative (P = 0.017). These results suggest that the presence of telomerase activity may be a useful diagnostic marker of HCC, regardless of tumor size, and that its detection in resected noncancerous liver tissues may serve as a useful predictor of postoperative recurrence.

Preclinical and clinical strategies for development of telomerase and telomere inhibitors

BACKGROUND

Telomerase is an important enzyme whose activity has been convincingly demonstrated in humans recently. It is required for maintenance of ends of chromosomes (telomeres) during cell division. Since its presence has been selectively demonstrated in dividing cells including tumor cells, it has generated considerable excitement as a potential anti-cancer strategy.

DESIGN

In this article, we review the current relevant biology of the enzyme, the challenges encountered in the preclinical phase of target development and the current efforts that focus on telomeres and telomerase as therapeutic targets. We also speculate on the potential toxicities and mechanisms of resistance that may be encountered during use of such therapies.

A survey of telomerase activity in human cancer

Research on the association of the ribonucleoprotein enzyme, telomerase, with human cancer has expanded rapidly in recent years. Essentially all major types of cancer have been screened and the presence of telomerase activity has been detected in the vast majority of cases. In this article we provide a summary, in table form, of the current data.

Telomeres, Telomerase and Leukaemia

There is increasing evidence supporting the hypothesis that telomere shortening both in vitro and in vivo is the clock that counts cell divisions and determines the onset of cellular senescence. Cells overcome the senescence mechanisms by stabilising telomere length, probably due to the activity of telomerase that specifically elongates telomeres. The striking observation that almost all malignant cancers have telomerase activity indicate that there is intensive selective pressure of telomerase activation with the progression of malignancy. Indirect support for this view is that benign or pre-cancerous lesions are telomerase silent. The fact that telomerase activity is observed in over 85% of human primary malignancies raises the possibilities that it may be a new marker of cancer with diagnostic and therapeutic potentials. Can such ideas be applied to leukaemias and preleukaemias? Since normal haematopoietic stem cells and their progeny express telomerase activity, it is important to consider whether or not telomere shortening and telomerase activity play any role in leukaemic progression. Telomere reduction has been observed in various leukaemias including in ALL, AML, transformed leukaemias from MDS and late stage of CML and CLL and might be indicative of the length of the disease. Elevated telomerase activity has also been found in ALL, AML, CML and CLL. In AML, patients with chromosomal abnormalities 11q, -5, -7 had higher telomerase activity and unfavourable prognosis; while those with favourable cytogenetics such as t(8:21), inversion 16 showed low levels of telomerase. This suggests that telomerase activity may be a marker for poor prognosis of AML. Unanswered at present is the potential role of telomeres and telomerase in the progression of benign to malignant tumours. Further studies on the expression and regulation of the individual components of telomerase may enable us to clarify the diagnostic and therapeutic potential of telomerase in leukaemias.