Mean telomere length and risk of incident colorectal carcinoma: a prospective, nested case-control approach

DNA methylation-based telomere length is associated with HIV infection, physical frailty, cancer, and all-cause mortality

Telomere length (TL) is an important indicator of cellular aging. Shorter TL is associated with several age-related diseases including coronary heart disease, heart failure, diabetes, osteoporosis, and cancer. Recently, a DNA methylation-based TL (DNAmTL) estimator has been developed as an alternative method for directly measuring TL. In this study, we examined the association of DNAmTL with cancer prevalence and mortality risk among people with and without HIV in the Veterans Aging Cohort Study Biomarker Cohort (VACS, N = 1917) and Women's Interagency HIV Study Cohort (WIHS, N = 481). We profiled DNAm in whole blood (VACS) or in peripheral blood mononuclear cells (WIHS) using an array-based method. Cancer prevalence was estimated from electronic medical records and cancer registry data. The VACS Index was used as a measure of physiologic frailty. Models were adjusted for self-reported race and ethnicity, batch, smoking status, alcohol consumption, and five cell types (CD4, CD8, NK, B cell, and monocyte). We found that people with HIV had shorter average DNAmTL than those without HIV infection [beta = -0.25, 95% confidence interval (-0.32, -0.18), p = 1.48E-12]. Greater value of VACS Index [beta = -0.002 (-0.003, -0.001), p = 2.82E-05] and higher cancer prevalence [beta = -0.07 (-0.10, -0.03), p = 1.37E-04 without adjusting age] were associated with shortened DNAmTL. In addition, one kilobase decrease in DNAmTL was associated with a 40% increase in mortality risk [hazard ratio: 0.60 (0.44, 0.82), p = 1.42E-03]. In summary, HIV infection, physiologic frailty, and cancer are associated with shortening DNAmTL, contributing to an increased risk of all-cause mortality.

Association of Telomere Length with Colorectal Cancer Risk and Prognosis: A Systematic Review and Meta-Analysis

(1) Background: Colorectal cancer risk and survival have previously been associated with telomere length in peripheral blood leukocytes and tumor tissue. A systematic review and meta-analysis of the literature was conducted. The PubMed, Embase, and Web of Science databases were searched through March 2022. (2) Methods: Relevant studies were identified through database searching following PRISMA guidelines. Risk estimates were extracted from identified studies; meta-analyses were conducted using random effects models. (3) Results: Fourteen studies were identified (eight on risk; six on survival) through systematic review. While no association was observed between circulating leukocyte telomere length and the risk of colorectal cancer [overall OR (95% CI) = 1.01 (0.82-1.24)], a worse survival for those with shorter telomeres in leukocytes and longer telomeres in tumor tissues was observed [Quartile1/Quartile2-4 overall HR (95% CI) = 1.41 (0.26-7.59) and 0.82 (0.69-0.98), respectively]. (4) Conclusions: Although there was no association with colorectal cancer risk, a poorer survival was observed among those with shorter leukocyte telomere length. Future larger studies evaluating a potentially non-linear relationship between telomeres and colorectal cancer are needed.

Pre-diagnostic telomere length and colorectal cancer risk

BACKGROUND

Progressive telomere shortening may be related to genomic instability and carcinogenesis. Prospective evidence relating telomere length (TL) with colorectal cancer (CRC) risk has been limited and inconsistent.

METHODS

We examined the association between pre-diagnostic peripheral blood leukocyte TL and CRC risk in two matched case-control studies nested within the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS). Relative leukocyte TL was measured using qPCR among 356 incident CRC cases and 801 controls (NHS: 186/465, HPFS: 170/336).

RESULTS

We did not find a significant association between pre-diagnostic TL and CRC risk [in all participants, multivariable-adjusted odds ratio (OR) (95% CI) for TL Quartile 1 (shortest) vs. Quartile 4 (longest) = 1.36 (0.85, 2.17), P-trend = 0.27; OR (95% CI) per 1 SD decrease in TL = 1.12 (0.92, 1.36)].

CONCLUSIONS

Our prospective analysis did not support a significant association between pre-diagnostic leukocyte TL and CRC risk.

Association Between Leukocyte Telomere Length and Colorectal Cancer Risk in the Singapore Chinese Health Study

Telomeres and telomerase play important roles in maintaining chromosome integrity and genomic stability. To address a lack of consensus about the association between leukocyte telomere length and colorectal cancer, we investigated this association in the Singapore Chinese Health Study.

Cutaneous nevi and internal cancer risk: Results from two large prospective cohorts of US women

Elevated cutaneous nevus number has been linked to longer telomeres. Recently, a large systematic Mendelian randomization study identified a significant positive association between telomere length and risk of cancer. Here, we hypothesized that higher nevus count, as a phenotypic marker of longer telomere, may be associated with increased risk of internal cancer, and prospectively examined the association between nevus count and total as well as site-specific cancer risk among participants in the Nurses' Health Study (NHS, 1986-2012) and the Nurses' Health Study 2 (NHS2, 1989-2013) using Cox proportional hazards models. During 3,900,264 person-years of follow-up, we documented a total of 23,004 internal cancer cases (15,484 in the NHS and 7,520 in the NHS2). Compared to participants who had no nevi, the multivariate hazard ratios of total cancer (excluding skin cancer) were 1.06 (95% confidence interval [CI], 1.03-1.09) for women with 1-5 nevi, 1.08 (95% CI, 1.03-1.15) for those who had 6-14 nevi and 1.19 (95% CI, 1.05-1.35) for those with 15 or more nevi (p trend <0.0001). Moreover, because nevus count has been associated with risk of breast cancer previously, we conducted a secondary analysis by excluding breast cancer from the outcomes of interest. The results were very similar to those of our primary analysis. For individual cancer, most of the associations with nevus count were positive but not statistically significant. In conclusion, we identified the number of cutaneous nevi as a phenotypic marker associated with internal cancer risk, which may be explained by telomere biology.

Mendelian randomisation: A powerful and inexpensive method for identifying and excluding non-genetic risk factors for colorectal cancer

Colorectal cancer (CRC) is the third most common cancer in economically developed countries and a major cause of cancer-related mortality. The importance of lifestyle and diet as major determinants of CRC risk is suggested by differences in CRC incidence between countries and in migration studies. Previous observational epidemiological studies have identified associations between modifiable environmental risk factors and CRC, but these studies can be susceptible to reverse causation and confounding, and their results can therefore conflict. Mendelian randomisation (MR) analysis represents an approach complementary to conventional observational studies examining associations between exposures and disease. The MR strategy employs allelic variants as instrumental variables (IVs), which act as proxies for non-genetic exposures. These allelic variants are randomly assigned during meiosis and can therefore inform on life-long exposure, whilst not being subject to reverse causation. In previous studies MR frameworks have associated several modifiable factors with CRC risk, including adiposity, hyperlipidaemia, fatty acid profile and alcohol consumption. In this review we detail the use of MR to investigate and discover CRC risk factors, and its future applications.

Telomere length in the colon is related to colorectal adenoma prevalence

Telomere length has been associated with risk of several cancers. However, studies of the relationship between telomere length and colorectal cancer risk have been inconsistent. This study examined the relationship between telomere length in normal colon tissue and the prevalence of colorectal adenoma, a precursor to colorectal cancer. This nested case-control study consisted of 85 patients aged 40 to 65 undergoing a screening colonoscopy: 40 cases with adenoma(s) detected at colonoscopy and 45 controls with normal colonoscopy. During the colonoscopy, two pinch biopsies of healthy, normal appearing mucosa were obtained from the descending colon. Relative telomere length (rTL) was quantified in DNA extracted from colon mucosa using quantitative real-time PCR. Logistic regression was used to assess the relationship between telomere length and adenoma prevalence and estimate odds ratios and 95% confidence intervals. rTL was significantly longer in colon tissue of individuals with adenomas compared to healthy individuals (p = 0.008). When rTL was categorized into quartiles according to the distribution of rTL among controls, individuals with the longest telomeres had increased odds of adenoma when compared to individuals with shortest telomeres (OR = 4.58, 95% CI: 1.19, 17.7). This study suggests that long telomeres in normal colon tissue are associated with increased colorectal cancer risk.

Leucocytes telomere length and breast cancer risk/ susceptibility: A case-control study

BACKGROUND

Telomere length in peripheral blood leukocytes (PBL-TL) was proposed as a biomarker of cancer risk. Recent scientific evidence suggested PBL-TL plays a diverse role in different cancers. Inconsistent results were obtained on PBL-TL in relation to breast cancer risk and specifically to the presence of BRCA1 and BRCA2 mutations. The aim of the present case-control study was to analyse the correlation between family history of breast cancer or presence of a BRCA mutation and PBL-TL in the hypothesis that TL is a modifier of cancer risk.

METHODS

PBL-TL was measured using the real-time quantitative PCR method in DNA for 142 cases and 239 controls. All the women enrolled were characterized for cancer family history. A subgroup of 48 women were classified for the presence of a BRCA mutation. PBL-TL were summarized as means and standard deviations, and compared by standard analysis of variance. A multivariable Generalised Linear Model was fitted to the data with PBL-TL as the dependent variable, case/control status and presence of a BRCA/VUS mutation as factors, and age in 4 strata as a covariate.

RESULTS

Age was significantly associated with decreasing PBL-TL in controls (p = 0.01), but not in BC cases. The telomere length is shorter in cases than in controls after adjusting for age. No effect on PBL-TL of BMI, smoke nor of the most common risk factors for breast cancer was observed. No association between PBL-TL and family history was detected both in BC cases and controls. In the multivariate model, no association was observed between BRCA mutation and decreased PBL-TL. A statistically significant interaction (p = 0.031) between case-control status and a BRCA-mutation/VUS was observed, but no effect was detected for the interaction of cancer status and BRCA or VUS.

CONCLUSION

Our study fails to provide support to the hypothesis that PBL-TL is associated with the risk of hereditary BC, or that is a marker of inherited mutations in BRCA genes.

Telomere length differences between colorectal polyp subtypes: a colonoscopy-based case-control study

Background

Short telomeres have been associated with increased risk of many cancers, particularly cancers of the gastrointestinal tract including esophagus and stomach. However, the association between telomere length (TL) and colorectal cancer and its precursors, colorectal polyps, is not clear.

Methods

We investigated the relationship between TL and risk of colorectal polyp subtypes in a colonoscopy-based study in western Washington. Participants were 35–79 year-old enrollees at an integrated health care system, who underwent a colonoscopy between 1998 and 2007 (n = 190), completed a self-administered questionnaire, provided blood samples, and were distinguished as having adenomas, serrated polyps, or as polyp-free controls through a standardized pathology review. Telomere length (T) relative to a single copy gene (S) was measured in circulating leukocytes from stored buffy coat samples using quantitative polymerase chain reaction. Multivariable polytomous logistic regression was used to compare case groups with polyp-free controls and other case groups; adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated.

Results

TL in the shortest tertile (T/S ratio < 0.58) was associated with increased risk of adenomas and serrated polyps [OR (95%CI) were 1.77(0.81–3.88) and 2.98(1.15–7.77), respectively). When evaluated by lesion severity within each pathway, short TL was more strongly associated with advanced adenomas and sessile serrated polyps [OR (95% CI) = 1.90(0.76–4.73) and 3.82(0.86–16.86), respectively], although the associations were not statistically significant.

Conclusions

Our results suggest that short TL may be associated with an increased risk of colorectal polyps in both the adenoma-carcinoma and serrated pathways. The risk was particularly notable for sessile serrated polyps, although the association was not statistically significant and sample size was limited.

Leukocyte telomere length throughout the continuum of colorectal carcinogenesis

Considering the high prevalence of colorectal cancer (CRC) and relatively high mortality there is strong interest in identification of clinically relevant biomarkers. Telomere shortening is supposed to contribute to genomic instability and crucially involved in process of carcinogenesis. Peripheral blood leukocyte (PBL) telomere length was previously investigated in several studies as potential biomarker for CRC but with controversial results. This prompted us to investigate relative PBL telomere length in association with different histological findings throughout the continuum of colorectal carcinogenesis in order to reflect the whole spectrum of putative CRC development in a large study involving 2011 individuals. The study based on the Colorectal Cancer Study of Austria (CORSA), including 384 CRC cases as well as age- and gender-matched 544 high-risk adenomas, 537 low-risk adenoma patients and 546 colonoscopy-negative controls. Relative expression of telomeric repeats and the single copy reference gene, albumin (T/S ratio) was determined using monochrome multiplex quantitative PCR (MMQPCR). Telomeres were found to be significantly longer in CRC patients compared to control subjects (P = 3.61x10^-6). Yet, no significant differences in telomere length could be detected for high-risk (P = 0.05956) and low-risk colorectal adenoma patients (P = 0.05224). In addition, results presented in this manuscript highlight the impact of various epidemiological factors on PBL telomere length and its involvement in CRC. However, further large studies also including colorectal adenomas are necessary to confirm these results.

Association Between Telomere Length and Risk of Cancer and Non-Neoplastic Diseases: A Mendelian Randomization Study

IMPORTANCE

The causal direction and magnitude of the association between telomere length and incidence of cancer and non-neoplastic diseases is uncertain owing to the susceptibility of observational studies to confounding and reverse causation.

OBJECTIVE

To conduct a Mendelian randomization study, using germline genetic variants as instrumental variables, to appraise the causal relevance of telomere length for risk of cancer and non-neoplastic diseases.

DATA SOURCES

Genomewide association studies (GWAS) published up to January 15, 2015.

STUDY SELECTION

GWAS of noncommunicable diseases that assayed germline genetic variation and did not select cohort or control participants on the basis of preexisting diseases. Of 163 GWAS of noncommunicable diseases identified, summary data from 103 were available.

DATA EXTRACTION AND SYNTHESIS

Summary association statistics for single nucleotide polymorphisms (SNPs) that are strongly associated with telomere length in the general population.

MAIN OUTCOMES AND MEASURES

Odds ratios (ORs) and 95% confidence intervals (CIs) for disease per standard deviation (SD) higher telomere length due to germline genetic variation.

RESULTS

Summary data were available for 35 cancers and 48 non-neoplastic diseases, corresponding to 420 081 cases (median cases, 2526 per disease) and 1 093 105 controls (median, 6789 per disease). Increased telomere length due to germline genetic variation was generally associated with increased risk for site-specific cancers. The strongest associations (ORs [95% CIs] per 1-SD change in genetically increased telomere length) were observed for glioma, 5.27 (3.15-8.81); serous low-malignant-potential ovarian cancer, 4.35 (2.39-7.94); lung adenocarcinoma, 3.19 (2.40-4.22); neuroblastoma, 2.98 (1.92-4.62); bladder cancer, 2.19 (1.32-3.66); melanoma, 1.87 (1.55-2.26); testicular cancer, 1.76 (1.02-3.04); kidney cancer, 1.55 (1.08-2.23); and endometrial cancer, 1.31 (1.07-1.61). Associations were stronger for rarer cancers and at tissue sites with lower rates of stem cell division. There was generally little evidence of association between genetically increased telomere length and risk of psychiatric, autoimmune, inflammatory, diabetic, and other non-neoplastic diseases, except for coronary heart disease (OR, 0.78 [95% CI, 0.67-0.90]), abdominal aortic aneurysm (OR, 0.63 [95% CI, 0.49-0.81]), celiac disease (OR, 0.42 [95% CI, 0.28-0.61]) and interstitial lung disease (OR, 0.09 [95% CI, 0.05-0.15]).

CONCLUSIONS AND RELEVANCE

It is likely that longer telomeres increase risk for several cancers but reduce risk for some non-neoplastic diseases, including cardiovascular diseases.

Prospective and longitudinal evaluations of telomere length of circulating DNA as a risk predictor of hepatocellular carcinoma in HBV patients

Prospective and longitudinal epidemiological evidence is needed to assess the association between telomere length and risk of hepatocellular carcinoma (HCC). In 323 cancer-free Korean-American HBV patients with 1-year exclusion window (followed for >1 year and did not develop HCC within 1 year), we measured the relative telomere length (RTL) in baseline serum DNAs and conducted extensive prospective and longitudinal analyses to assess RTL-HCC relationship. We found that long baseline RTL conferred an increased HCC risk compared to short RTL [hazard ratio (HR) = 4.93, P = 0.0005). The association remained prominent when the analysis was restricted to patients with a more stringent 5-year exclusion window (HR = 7.51, P = 0.012), indicating that the association was unlikely due to including undetected HCC patients in the cohort, thus minimizing the reverse-causation limitation in most retrospective studies. Adding baseline RTL to demographic variables increased the discrimination accuracy of the time-dependent receiver operating characteristic analysis from 0.769 to 0.868 (P = 1.0 × 10-5). In a nested longitudinal subcohort of 16 matched cases-control pairs, using a mixed effects model, we observed a trend of increased RTL in cases and decreased RTL in controls along 5 years of follow-up, with a significant interaction of case/control status with time (P for interaction=0.002) and confirmed the association between long RTL and HCC risk [odds ratio [OR] = 3.63, P = 0.016]. In summary, serum DNA RTL may be a novel non-invasive prospective marker of HBV-related HCC. Independent studies are necessary to validate and generalize this finding in diverse populations and assess the clinical applicability of RTL in HCC prediction.

Association between telomere length and the risk of colorectal cancer: a meta-analysis of observational studies

BACKGROUND

Human chromosomes are capped and stabilized by telomeres. Telomere length regulates a 'cellular mitotic clock' that defines the number of cell divisions and hence, cellular life span. This study aimed to synthesize the evidence on the association between peripheral blood leucocytes (PBL) telomere length and the risk of colorectal cancer (CRC).

METHODS

We searched relevant studies in electronic databases. When two or more observational studies reported the same outcome measures, we performed pooled analysis. All the analyses were performed on PBL using PCR. The odds ratio (OR) and its 95% confidence interval (CI) were used to assess the strength of association.

RESULTS

Seven studies (with 8 datasets) were included in this meta-analysis; 3 prospective studies, 3 retrospective studies and 1 study with a separate prospective and retrospective designs. The pooled analysis of 4 prospective studies (summary OR 1.01, 95% CI: 0.77-1.34, I ²:30%) and 4 retrospective studies (summary OR 1.65, 95% CI: 0.96-2.83, I ²:96%) showed no relationship between PBL telomere length and the CRC risk. A subgroup analysis of 2 prospective studies exclusively on females also showed no association between PBL telomere length and the CRC risk (summary OR, 1.17, 95% CI:0.72-1.91, I ²:57%).

CONCLUSION

The current analysis is insufficient to provide evidence on the relationship between PBL telomere length and the risk of CRC. Findings suggest that there may be a complex relationship between PBL telomere length and the CRC risk or discrepancy between genetics, age of patients and clinical studies. Future well powered, large prospective studies on the relationship between telomere length and the risk of CRC, and the investigations of the biologic mechanisms are recommended.

Skin phenotypes can offer some insight about the association between telomere length and cancer susceptibility

The role of telomere biology in cancer has been studied for a wide variety of different cancers but the association with telomere length has been controversial. This is because some cancers have been found to be associated with longer telomeres in circulating white cells whilst other cancer types are more common in individuals with shorter telomeres. Hence, there has been some skepticism as to whether telomere length may be helpful in estimating cancer risk. For melanoma, however, results have been fairly consistent showing that longer telomeres are associated with an increased risk. This link was first discovered because of a link between longer telomeres and a high number of naevi. In contrast, for cutaneous squamous cell carcinomas, the relationship is reversed with higher risk in individuals with shorter telomeres. Differences in skin phenotypes with the presence of high number of naevi versus photoageing with solar elastosis and solar keratoses have already been valuable for dermatologists as the former phenotype is associated with melanoma whilst the latter is more common in patients with squamous cell carcinoma of the skin. The hypothesis is that the differences in cutaneous phenotypes already observed by dermatologists for skin cancers may, in fact, be useful as well for cancer prediction in general as it may reflect underlying telomere biology. This manuscript will address the evidence for links between telomere biology, skin phenotypes and cancer risk.

Integration of Telomere Length Dynamics into Systems Biology Framework: A Review

Telomere length dynamics plays a crucial role in regulation of cellular processes and cell fate. In contrast to epidemiological studies revealing the association of telomere length with age, age-related diseases, and cancers, the role of telomeres in regulation of transcriptome and epigenome and the role of genomic variations in telomere lengthening are not extensively analyzed. This is explained by the fact that experimental assays for telomere length measurement are resource consuming, and there are very few studies where high-throughput genomics, transcriptomics, and/or epigenomics experiments have been coupled with telomere length measurements. Recent development of computational approaches for assessment of telomere length from whole genome sequencing data pave a new perspective on integration of telomeres into high-throughput systems biology analysis framework. Herein, we review existing methodologies for telomere length measurement and compare them to computational approaches, as well as discuss their applications in large-scale studies on telomere length dynamics.

Genetic determinants of telomere length and risk of common cancers: a Mendelian randomization study

Epidemiological studies have reported inconsistent associations between telomere length (TL) and risk for various cancers. These inconsistencies are likely attributable, in part, to biases that arise due to post-diagnostic and post-treatment TL measurement. To avoid such biases, we used a Mendelian randomization approach and estimated associations between nine TL-associated SNPs and risk for five common cancer types (breast, lung, colorectal, ovarian and prostate cancer, including subtypes) using data on 51 725 cases and 62 035 controls. We then used an inverse-variance weighted average of the SNP-specific associations to estimate the association between a genetic score representing long TL and cancer risk. The long TL genetic score was significantly associated with increased risk of lung adenocarcinoma (P = 6.3 × 10(-15)), even after exclusion of a SNP residing in a known lung cancer susceptibility region (TERT-CLPTM1L) P = 6.6 × 10(-6)). Under Mendelian randomization assumptions, the association estimate [odds ratio (OR) = 2.78] is interpreted as the OR for lung adenocarcinoma corresponding to a 1000 bp increase in TL. The weighted TL SNP score was not associated with other cancer types or subtypes. Our finding that genetic determinants of long TL increase lung adenocarcinoma risk avoids issues with reverse causality and residual confounding that arise in observational studies of TL and disease risk. Under Mendelian randomization assumptions, our finding suggests that longer TL increases lung adenocarcinoma risk. However, caution regarding this causal interpretation is warranted in light of the potential issue of pleiotropy, and a more general interpretation is that SNPs influencing telomere biology are also implicated in lung adenocarcinoma risk.

Prediagnostic telomere length and risk of B-cell lymphoma-Results from the EPIC cohort study

Recent epidemiological investigations have reported on the association between telomere length (TL) and a number of malignancies, including B-cell lymphoma (BCL). The reported results for BCLs are however inconsistent. We carried out a nested case-control study to determine whether TL is associated with future risk of BCL. Using quantitative polymerase chain reaction, the relative TL (i.e. the ratio of telomere repeat copy number to single gene copy number) was measured in mononuclear cell DNA of prediagnostic peripheral blood samples of 464 lymphoma cases and 464 matched controls (median time between blood collection and diagnosis, 4.6 years). Conditional logistic regression was used to analyze the association between TL and the risk of developing lymphoma and histologic subtypes. TL was significantly longer in cases compared to controls (p = 0.01). Multivariable models showed a significantly increased risk of BCL [odds ratio (OR) = 1.66, 1.80 and 3.20 for quartiles 2-4, respectively, p-trend = 0.001], diffuse large B-cell lymphoma (DLBCL) (OR = 1.20, 2.48 and 2.36 for quartiles 2-4, respectively, p-trend = 0.03) and follicular lymphoma (FL) (OR = 1.39, 1.90 and 2.69 for quartiles 2-4, respectively, p-trend = 0.02) with increasing TL. This study suggests an association between longer leucocyte TL and increased risk of BCL which was most pronounced for DLBCL and FL.

Toward a molecular classification of colorectal cancer: the role of telomere length

Telomere biology is central to the maintenance of genomic stability and telomeric dysfunction is thought to be an early stage in carcinogenesis. Reports of telomere lengths and their ascribed colorectal cancer (CRC) risks have been discordant, with both very short and very long telomeres implicated. Nevertheless, telomeres appear to play a very central role in cancer initiation. Telomere length changes also appear to impact disease burden, progression, and overall survival. This review covers contemporary views on telomere biology and CRC risk, with a brief overview of analytical methods employed in telomere measurement. We conclude with arguments in favor of including telomere assessment in the molecular profiling of CRCs.

Lymphocyte telomere length is long in BRCA1 and BRCA2 mutation carriers regardless of cancer-affected status

BACKGROUND

Telomere length has been linked to risk of common diseases, including cancer, and has previously been proposed as a biomarker for cancer risk. Germline BRCA1 and BRCA2 mutations predispose to breast, ovarian, and other cancer types.

METHODS

We investigated telomere length in BRCA mutation carriers and their non-carrier relatives and further examined whether telomere length is a modifier of cancer risk in mutation carriers. We measured mean telomere length in DNA extracted from whole blood using high-throughput quantitative PCR. Participants were from the EMBRACE study in United Kingdom and Eire (n = 4,822) and comprised BRCA1 (n = 1,628) and BRCA2 (n = 1,506) mutation carriers and their non-carrier relatives (n = 1,688).

RESULTS

We find no significant evidence that mean telomere length is associated with breast or ovarian cancer risk in BRCA mutation carriers. However, we find mutation carriers to have longer mean telomere length than their non-carrier relatives (all carriers vs. non-carriers, Ptrend = 0.0018), particularly in families with BRCA2 mutations (BRCA2 mutation carriers vs. all non-carriers, Ptrend = 0.0016).

CONCLUSIONS

Our findings lend little support to the hypothesis that short mean telomere length predisposes to cancer. Conversely, our main and unexpected finding is that BRCA mutation carriers (regardless of cancer status) have longer telomeres than their non-mutation carrier, non-cancer-affected relatives. The longer telomere length in BRCA2 mutation carriers is consistent with its role in DNA damage response. Overall, it seems that increased telomere length may be a consequence of these mutations, but is not itself directly related to the increased cancer risk in carriers.

IMPACT

The finding that mutation carriers have longer mean telomere lengths than their non-carrier relatives is unexpected but biologically plausible and could open up new lines of research into the functions of the BRCA proteins. To our knowledge, this is the largest study of telomere length in BRCA mutation carriers and their relatives. The null cancer-risk association supports recent large prospective studies of breast and ovarian cancer and indicates that mean telomere length would not be a useful biomarker in these cancers. Cancer Epidemiol Biomarkers Prev; 23(6); 1018-24. ©2014 AACR.

The association of telomere length with colorectal cancer differs by the age of cancer onset

OBJECTIVES:

Telomeres are nucleoprotein structures that cap the end of chromosomes and shorten with sequential cell divisions in normal aging. Short telomeres are also implicated in the incidence of many cancers, but the evidence is not conclusive for colorectal cancer (CRC). Therefore, the aim of this study was to assess the association of CRC and telomere length.

METHODS:

In this case–control study, we measured relative telomere length from peripheral blood leukocytes (PBLs) DNA with quantitative PCR in 598 CRC patients and 2,212 healthy controls.

RESULTS:

Multivariate analysis indicated that telomere length was associated with risk for CRC, and this association varied in an age-related manner; younger individuals (≤50 years of age) with longer telomeres (80–99 percentiles) had a 2–6 times higher risk of CRC, while older individuals (>50 years of age) with shortened telomeres (1–10 percentiles) had 2–12 times the risk for CRC. The risk for CRC varies with extremes in telomere length in an age-associated manner.

CONCLUSIONS:

Younger individuals with longer telomeres or older individuals with shorter telomeres are at higher risk for CRC. These findings indicate that the association of PBL telomere length varies according to the age of cancer onset and that CRC is likely associated with at minimum two different mechanisms of telomere dynamics.

Longer telomeres are associated with cancer risk in MMR-proficient hereditary non-polyposis colorectal cancer

Aberrant telomere length measured in blood has been associated with increased risk of several cancer types. In the field of hereditary non-polyposis colorectal cancer (CRC), and more particularly in Lynch syndrome, caused by germline mutations in the mismatch repair (MMR) genes, we recently found that cancer-affected MMR gene mutation carriers had shorter telomeres and more pronounced shortening of telomere length with age than controls and unaffected MMR gene mutation carriers. Here we evaluate blood telomere length in MMR-proficient hereditary non-polyposis CRC, i.e. familial CRC type X (fCRC-X). A total of 57 cancer-affected and 57 cancer-free individuals from 34 Amsterdam-positive fCRC-X families were analyzed and compared to the data previously published on 144 cancer-affected and 100 cancer-free MMR gene mutation carriers, and 234 controls. Relative telomere length was measured using a monochrome multiplex quantitative PCR method, following strict measures to avoid sources of bias and adjusting by age. Despite the retrospective nature of our study, the results show that longer telomeres associate with cancer risk in fCRC-X, thus identifying different patterns of telomere length according to the status of the MMR system.

Telomere length in peripheral blood leukocytes is associated with risk of colorectal cancer in Chinese population

Background

Human telomeres, tandem repeats of TTAGGG nucleotides at the ends of chromosomes, are essential for maintaining genomic integrity and stability. Results of previous epidemiologic studies about the association of telomere length with risk of colorectal cancer (CRC) have been conflicting.

Methods

A case-control study was conducted in a Han population in Wuhan, central China. The relative telomere length (RTL) was measured in peripheral blood leukocytes (PBLs) using quantitative real-time polymerase chain reaction (PCR) in 628 CRC cases and 1,256 age and sex frequency matched cancer-free controls. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using unconditional logistic regression models to evaluate the association between RTL and CRC risk.

Results

Using median RTL in the controls as the cutoff, individuals with shorter RTL were associated with a significantly increased risk of CRC (adjusted OR = 1.27, 95%CI: 1.05–1.55). When participants were further categorized into 3 and 4 groups according to the tertile and quartile RTL values of controls, significant relationships were still observed between shorter RTL and increased CRC risk (OR per tertile = 1.13, 95%CI: 1.00–1.28, P_trend = 0.045; OR per quartile = 1.12, 95%CI: 1.03–1.23, P_trend = 0.012). In stratified analyses, significant association between shorter RTL and increased CRC risk was found in females, individuals younger than 60 years old, never smokers and never drinkers.

Conclusions

This study suggested that short telomere length in PBLs was significantly associated with an increased risk of CRC in Chinese Han population. Further validation in large prospective studies and investigation of the biologic mechanisms are warranted.

A genome-wide association scan (GWAS) for mean telomere length within the COGS project: identified loci show little association with hormone-related cancer risk

Mean telomere length (TL) in blood cells is heritable and has been reported to be associated with risks of several diseases, including cancer. We conducted a meta-analysis of three GWAS for TL (total n=2240) and selected 1629 variants for replication via the "iCOGS" custom genotyping array. All ∼200 000 iCOGS variants were analysed with TL, and those displaying associations in healthy controls (n = 15 065) were further tested in breast cancer cases (n = 11 024). We found a novel TL association (Ptrend < 4 × 10(-10)) at 3p14.4 close to PXK and evidence (Ptrend < 7 × 10(-7)) for TL loci at 6p22.1 (ZNF311) and 20q11.2 (BCL2L1). We additionally confirmed (Ptrend < 5 × 10(-14)) the previously reported loci at 3q26.2 (TERC), 5p15.3 (TERT) and 10q24.3 (OBFC1) and found supportive evidence (Ptrend < 5 × 10(-4)) for the published loci at 2p16.2 (ACYP2), 4q32.2 (NAF1) and 20q13.3 (RTEL1). SNPs tagging these loci explain TL differences of up to 731 bp (corresponding to 18% of total TL in healthy individuals), however, they display little direct evidence for association with breast, ovarian or prostate cancer risks.

Telomeres and telomere dynamics: relevance to cancers of the GI tract

Aberrations in telomere length and telomere maintenance contribute to cancer development. In this article, we review the basic principles of telomere length in normal and tumor tissue and the presence of the two main telomere maintenance pathways as they pertain to gastrointestinal tract cancer. Peripheral blood telomeres are shorter in patients with many types of gastrointestinal tract cancers. Telomere length in tumor DNA also appears to shorten early in cancer development. Tumor telomere shortening is often accompanied by telomerase activation to protect genetically damaged DNA from normal cell senescence or apoptosis, allowing immortalized but damaged DNA to persist. Alternative lengthening of telomeres is another mechanism used by cancer to maintain telomere length in cancer cells. Telomerase and alternative lengthening of telomeres activators and inhibitors may become important chemopreventive or chemotherapeutic agents as our understanding of telomere biology, specific telomere-related phenotypes and its relationship to carcinogenesis increases.

Telomere length varies by DNA extraction method: implications for epidemiologic research

BACKGROUND

Both shorter and longer telomeres in peripheral blood leukocyte (PBL) DNA have been associated with cancer risk. However, associations remain inconsistent across studies of the same cancer type. This study compares DNA preparation methods to determine telomere length from patients with colorectal cancer.

METHODS

We examined PBL relative telomere length (RTL) measured by quantitative PCR (qPCR) in 1,033 patients with colorectal cancer and 2,952 healthy controls. DNA was extracted with phenol/chloroform, PureGene, or QIAamp.

RESULTS

We observed differences in RTL depending on DNA extraction method (P < 0.001). Phenol/chloroform-extracted DNA had a mean RTL (T/S ratio) of 0.78 (range 0.01-6.54) compared with PureGene-extracted DNA (mean RTL of 0.75; range 0.00-12.33). DNA extracted by QIAamp yielded a mean RTL of 0.38 (range 0.02-3.69). We subsequently compared RTL measured by qPCR from an independent set of 20 colorectal cancer cases and 24 normal controls in PBL DNA extracted by each of the three extraction methods. The range of RTL measured by qPCR from QIAamp-extracted DNA (0.17-0.58) was less than from either PureGene or phenol/chloroform (ranges, 0.04-2.67 and 0.32-2.81, respectively).

CONCLUSIONS

RTL measured by qPCR from QIAamp-extracted DNA was less than from either PureGene or phenol/chloroform (P < 0.001).

IMPACT

Differences in DNA extraction method may contribute to the discrepancies between studies seeking to find an association between the risk of cancer or other diseases and RTL.

Telomere length and Parkinson's disease in men: a nested case-control study

BACKGROUND AND PURPOSE

Telomere shortening has been implicated in neurodegenerative disorders. However, available data on the association between telomere length and Parkinson's disease (PD) are inconclusive.

METHODS

A nested case-control design was used amongst men participating in the prospective Physicians' Health Study. A large proportion of participants provided blood samples in 1997 and they were followed through 2010. Men with self-reported PD were age-matched to controls in a 1:2 ratio. Quantitative PCR was used to determine the telomere repeat copy number to single gene copy number ratio (TSR) in genomic DNA extracted from peripheral blood leukocytes. TSR was used as a measure for relative telomere length (RTL) in our analyses. Conditional logistic regression was used to determine the risk of PD associated with RTL.

RESULTS

Data on RTL were available from 408 cases and 809 controls. Median TSR was shorter in controls than in cases (47.7 vs. 50.2; P = 0.02). The age-adjusted odds ratio (OR) for PD was 0.66 [95% confidence interval (CI) 0.46-0.95; Ptrend over quartiles 0.02] comparing the lowest to the highest quartile. The pattern of association was unchanged when comparing RTL below versus above the median (age-adjusted OR 0.75; 95% CI 0.59-0.96). Associations were similar after additional adjustment for many covariates.

CONCLUSION

Contrary to what was expected, in this large nested case-control study amongst men shorter telomeres were associated with reduced PD risk. Future research on the nature of this counterintuitive association is warranted.

Telomere length and telomerase activity; a Yin and Yang of cell senescence

Telomeres are repeating DNA sequences at the tip ends of the chromosomes that are diverse in length and in humans can reach a length of 15,000 base pairs. The telomere serves as a bioprotective mechanism of chromosome attrition at each cell division. At a certain length, telomeres become too short to allow replication, a process that may lead to chromosome instability or cell death. Telomere length is regulated by two opposing mechanisms: attrition and elongation. Attrition occurs as each cell divides. In contrast, elongation is partially modulated by the enzyme telomerase, which adds repeating sequences to the ends of the chromosomes. In this way, telomerase could possibly reverse an aging mechanism and rejuvenates cell viability. These are crucial elements in maintaining cell life and are used to assess cellular aging. In this manuscript we will describe an accurate, short, sophisticated and cheap method to assess telomere length in multiple tissues and species. This method takes advantage of two key elements, the tandem repeat of the telomere sequence and the sensitivity of the qRT-PCR to detect differential copy numbers of tested samples. In addition, we will describe a simple assay to assess telomerase activity as a complementary backbone test for telomere length.

Multiple independent variants at the TERT locus are associated with telomere length and risks of breast and ovarian cancer

TERT-locus SNPs and leukocyte telomere measures are reportedly associated with risks of multiple cancers. Using the Illumina custom genotyping array iCOGs, we analyzed ∼480 SNPs at the TERT locus in breast (n = 103,991), ovarian (n = 39,774) and BRCA1 mutation carrier (n = 11,705) cancer cases and controls. Leukocyte telomere measurements were also available for 53,724 participants. Most associations cluster into three independent peaks. The minor allele at the peak 1 SNP rs2736108 associates with longer telomeres (P = 5.8 × 10(-7)), lower risks for estrogen receptor (ER)-negative (P = 1.0 × 10(-8)) and BRCA1 mutation carrier (P = 1.1 × 10(-5)) breast cancers and altered promoter assay signal. The minor allele at the peak 2 SNP rs7705526 associates with longer telomeres (P = 2.3 × 10(-14)), higher risk of low-malignant-potential ovarian cancer (P = 1.3 × 10(-15)) and greater promoter activity. The minor alleles at the peak 3 SNPs rs10069690 and rs2242652 increase ER-negative (P = 1.2 × 10(-12)) and BRCA1 mutation carrier (P = 1.6 × 10(-14)) breast and invasive ovarian (P = 1.3 × 10(-11)) cancer risks but not via altered telomere length. The cancer risk alleles of rs2242652 and rs10069690, respectively, increase silencing and generate a truncated TERT splice variant.

A systematic review of leukocyte telomere length and age in adults

OBJECTIVE

To provide a systematic review of the relationship between age and leukocyte telomere length (LTL) in adults.

METHODS

Relevant studies were identified by a systematic search of Medline, EMBASE and ISI Web of Knowledge databases. Key data, such as age and LTL, were extracted from the studies along with correlation coefficients and yearly attrition rates where available. Obtained data were used to calculate weighted means and correlation coefficients.

RESULTS

Overall, 124 cross-sectional studies and 5 longitudinal studies were identified. A statistically significant inverse correlation between mean age and mean LTL across cross-sectional studies was observed for both absolute (r=-0.338, p<0.0001) and relative LTL (r=-0.295, p=0.0088). From mean LTL and ages, a yearly telomere loss of 24.7 base pairs (BP)/year was estimated by weighted linear regression. Weighted means of within study correlation of age and TL and yearly telomere loss rate estimates from cross-sectional studies were also in a similar order of magnitude (-0.380 and 21.91 BP/year). The few longitudinal studies reported somewhat higher mean telomere loss rates (between 32.2 and 45.5 BP/year).

CONCLUSION

While a decrease of LTL with age is out of question, data on variation of the decrease according to sex, age and other potential determinants especially from longitudinal data are still sparse.

Long telomeres in peripheral blood leukocytes are associated with an increased risk of soft tissue sarcoma

BACKGROUND

Human telomeres consisting of long, tandem repeats of the nucleotide sequence TTAGGG at the chromosome ends are essential for maintaining chromosomal stability. Previous epidemiologic studies have indicated that shorter telomere length in peripheral blood leukocytes (PBLs) is associated with the development of many cancers. However, the relation between PBL telomere length and the risk of soft tissue sarcoma (STS) has not been investigated.

METHODS

The relative telomere length (RTL) was determined in PBLs using real-time polymerase chain reaction in this case-control study. The study participants included 137 patients with histologically confirmed STS (cases) who had received no prior chemotherapy or radiotherapy and 137 healthy controls who were frequency-matched to cases on age, sex, and ethnicity.

RESULTS

Patients in the case group had significantly longer RTL than controls (1.46 ± 0.42 for cases vs 1.15 ± 0.39 for controls; P < .001). By using median RTL in the controls as a cutoff level, individuals who had long telomere length were associated with a significantly increased risk of STS compared with those who had short telomere length (adjusted odds ratio, 4.71; 95% confidence interval, 2.63-8.44). When participants were categorized further into 3 or 4 groups according to the tertile or quartile RTL values of healthy controls, a significant dose-response relation was observed between longer RTL and increased risks of STS.

CONCLUSIONS

The current results provided the first epidemiologic evidence that longer telomere length in PBLs is associated significantly with an increased risk of STS, potentially suggesting an important role for telomere maintenance in STS development.

Shorter peripheral blood telomeres are a potential biomarker for patients with advanced colorectal adenomas

BACKGROUND

Colorectal cancer (CRC) can be prevented by the early detection and removal of advanced adenomas (AAs) by colonoscopy. Our aim was to evaluate peripheral blood leukocyte (PBL) telomere length as a potential biomarker for the presence of AAs.

METHODS

PBL telomere length was measured in patients with AAs (n=35), in a control group of similarly aged patients who had a normal colonoscopy (n=145) and in a separate population group with no history of cancer, again similarly aged (n=495). Telomere measurements were performed using a quantitative PCR assay and reported as ratios of telomere and single copy gene measurements.

RESULTS

Telomere lengths tended to be lower in patients with AAs than in patients in the normal colonoscopy group (p<0.001) as well as those in the population group (p=0.011). A telomere/single copy gene ratio of 0.5 was found to have an estimated 94% sensitivity and a 56% specificity for AAs; a combination of sensitivity and specificity for which a value of >0.5 would reduce the odds of a patient having AAs by a factor of 0.11 (the negative likelihood ratio). Thirty three percent of individuals in the population group tested above this cutoff and could be considered at low risk for AAs.

CONCLUSIONS

PBL telomeres are shortened in patients with colorectal neoplasia, suggesting that PBL telomere length could be a promising non-invasive blood biomarker to pre-screen for risk of AAs prior to colonoscopy.

TERT-CLPTM1L polymorphism rs401681 contributes to cancers risk: evidence from a meta-analysis based on 29 publications

Background

Some common genetic variants of TERT-CLPTM1L gene, which encode key protein subunits of telomerase, have been suggested to play a crucial role in tumorigenesis. The TERT-CLPTM1L polymorphism rs401681 was of special interest for cancers risk but with inconclusive results.

Methodology/Principal Findings

We performed a comprehensive meta-analysis of 29 publications with a total of 91263 cases and 735952 controls. We assessed the strength of the association between rs401681 and overall cancers risk and performed subgroup analyses by cancer type, ethnicity, source of control, sample size and expected power. Rs401681 C allele was found to be associated with marginally increased cancers risk, with per allele OR of 1.04 (95%CI = 1.00–1.08, P_{heterogeneity}<0.001) and an expected power of 1.000. Following further stratified analyses, the increased cancers risk were discovered in subgroups of lung, bladder, prostate, basal cell carcinomas and Asians, while a declined risk of pancreatic cancer and melanoma were detected.

Conclusions/Significance

These findings suggested that rs401681 C allele was a low-penetrance risk allele for the development of cancers of lung, bladder, prostate and basal cell carcinoma, but a potential protective allele for melanoma and pancreatic cancer.

Genetic and lifestyle influence on telomere length and subsequent risk of colon cancer in a case control study

BACKGROUND

Telomeres cap the ends of chromosomes and help maintain genomic stability and integrity. Telomere length (TL) has been linked to a number of diseases, including a variety of cancers; however, the association between TL and risk for colorectal cancer is unclear.

METHODS

We investigate the association between genetic, diet, and lifestyle factors and TL and the association between TL and colorectal cancer using data from a population-based case-control study of colon (249 cases and 371 controls) and rectal cancer (276 cases and 372 controls) conducted in Utah. DNA samples came from immortalized cell lines for colon cancer and directly from whole blood for rectal cancer. We genotyped 11 single nucleotide polymorphisms in five genes associated with telomeres, TERT, MEN1, MRE11A, RECQL5, and TNKS.

RESULTS

TL was measured using quantitative PCR. TERT rs2853676 (p=0.044) and RECQL5 rs820152 (p=0.001) were associated with TL at <0.05 level of significance. After adjusting for age and sex, BMI and cigarette smoking were significantly inversely associated with TL among controls. Use of aspirin/NSAIDs interacted significantly with TERT rs10069690 and rs2242652 to alter TL. Longer TL was significantly associated with reduced colon cancer risk after adjusting for age and sex (OR = 0.94 95% confidence intervals 0.89-0.99 per decile of TL). Further adjustment for BMI and cigarette smoking attenuated the association so that it was no longer significant.

CONCLUSIONS

In summary several genetic and lifestyle factors were observed to influence TL. These factors also appear to confound associations between TL and colon cancer.

Association of leukocyte telomere length with colorectal cancer risk: nested case-control findings from the Shanghai Women's Health Study

BACKGROUND

Telomeres are specialized chromatin structures essential for maintenance of chromosomal integrity and stability. Abnormal alteration of telomere length has been linked to several cancers; however, epidemiologic evidence about the association of telomere length with colorectal cancer risk has been conflicting.

METHODS

We conducted a nested case-control study to evaluate the association between telomere length and colorectal cancer risk using peripheral blood samples collected before cancer diagnosis. The study included 441 women with incident colorectal cancer and 549 matched controls. Monochrome multiplex quantitative PCR was applied to measure relative telomere length. Multiple logistic regressions were used to derive adjusted OR with 95% confidence intervals (CI) as the measure of association between telomere length and subsequent colorectal cancer risk.

RESULTS

A U-shaped association was observed between telomere length and colorectal cancer risk (test for nonlinearity P = 0.0112). Women with telomere length in the third quintile (40th-60th percentiles) had the lowest risk of colorectal cancer, and the risks were elevated with a shorter or longer telomere length. This U-shaped association did not statistically differ for colon cancer and rectum cancer.

CONCLUSIONS AND IMPACT

Our prospective study revealed a U-shaped association between telomere length in peripheral blood cells and colorectal cancer risk. Our findings provide strong evidence that both very short and very long telomeres are associated with increased risk of colorectal cancer.

TERC polymorphisms are associated both with susceptibility to colorectal cancer and with longer telomeres

BACKGROUND AND AIMS

Shorter telomeres have been associated with increased risk of malignancy, including colorectal cancer (CRC). Telomere length is heritable and may be an intermediate phenotype linked to genetic susceptibility to CRC.

METHODS

In a large sample, the study investigated whether candidate single nucleotide polymorphisms (SNP) in 'telomere biology' genes were associated with telomere length in leucocytes. SNP associated with an increased risk of CRC were searched for separately.

RESULTS

Carriers of the common allele at SNP rs10936599, near the telomerase RNA component (TERC) locus, had significantly longer telomeres. It was independently found that the same rs10936599 allele was associated with increased risk of both CRC and colorectal adenomas. Neither telomere length nor CRC risk was associated with variation near telomerase reverse transcriptase or other telomere biology genes. In silico analysis showed that SNP rs2293607 was strongly correlated with rs10936599, mapped within TERC transcripts, had a predicted effect on messenger RNA folding and lay at a reported transcription factor binding site. TERC mRNA were expressed, differing only at the alleles of rs2293607, in CRC cell line HCT116. The long-telomere/CRC-risk allele was associated with higher levels of TERC mRNA and the formation of longer telomeres.

CONCLUSIONS

Common genetic variation at TERC is associated with both longer telomeres and an increased risk of CRC, a potential mechanism being reduced levels of cell senescence or death. This finding is somewhat paradoxical, given retrospective studies reporting that CRC cases have shorter telomeres than controls. One possibility is that that association actually results from poorer survival in patients with longer telomeres.

Surrogate tissue telomere length and cancer risk: shorter or longer?

Telomeres play a critical role in chromosome stability. Telomere length (TL) shortening is a risk factor for cancers. Measuring TL in surrogate tissues that can be easily collected may provide a potential tool for early detection of cancers. A number of studies on surrogate tissue TL and cancer risks have been conducted and results are inconsistent, including positive, negative, or null associations. In this article, we reviewed the published data on surrogate tissue TL in relation to cancer risks, discussed the possible reasons for the differences in the results and future directions and challenges for this line of research.

Biological monitoring of carcinogens: current status and perspectives

Biomonitoring exposures to carcinogens is common practice and a variety of biomarkers have been developed to assess both exposures and biochemical/biological effects. However, their clinical and preventive relevance is still uncertain. The understanding of cancer as a genetic disease has dramatically evolved during last decades, showing that cancer cell types acquire their characteristics with different strategies, time frames and microenvironments. Therefore, the place of current biomarkers within this complex scenario of gene-environment interactions leading to cancer cannot be defined. Reasons are manifold. Most studies assessed cancer risk on a group basis through snapshots taken at unknown time-points of the postulated chain of events. Little attention has been paid to the variety and variability of exposures, and no prospective study validated the indicators of biochemical/biological effects. New opportunities and suggestions for biomonitoring exposures to carcinogens could derive from exploring the exposome that combines exposures from all sources both external and internal. The discovery of new biomarkers and the identification of relevant gene-specific pathways could be achieved through metabolomic and genome-wide studies. In conclusion, it is possible to envisage personalized biomonitoring procedures, such as those already implemented in the context of nutrition and clinical oncology.

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.

Telomere attrition and decreased fetuin-A levels indicate accelerated biological aging and are implicated in the pathogenesis of colorectal cancer

PURPOSE

Increasing chronological age is a risk factor for many types of cancer including colorectal. An understanding of the biology of aging and factors which regulate it may provide insight into cancer pathogenesis. The role of telomere biology in both the cancer and aging process could prove useful in this regard.

EXPERIMENTAL DESIGN

Using quantitative PCR, we determined telomere length in the peripheral blood leukocytes of 64 colorectal cancer (CRC) patients and 1,348 controls. We also measured telomere length in 32 colorectal tumor samples and matched normal tissue. We aimed to assess whether telomere lengths were reflected in circulating mediators of inflammation and redox control factors, including fetuin-A, a circulating modulator of calcium homeostasis.

RESULTS

CRC patients had shorter telomeres [adjusted mean ratio of relative telomere repeat copy number to single-copy gene number (RelT/S) = 0.61] compared with chronologically older controls (mean age = 75, adjusted mean RelT/S = 0.70; ANCOVA, P = 0.004). Telomere length in tumor tissue [median = 0.43, interquartile range (IQR) = 0.40] was significantly shorter than adjacent normal tissue (median = 0.65, IQR = 0.28; P = 0.004). Patients with low fetuin-A levels were shown to have significantly shorter telomeres (P = 0.041). Patients with rectal tumors had significantly higher levels of fetuin-A than those with colonic tumors (P = 0.045).

CONCLUSIONS

We have observed that patients with CRC display clear evidence of telomere attrition compared with controls. This is congruent with accelerated biological aging in the pathogenesis of CRC. An imbalance in redox control mechanisms and calcium homeostasis may be a contributing factor to telomere dynamics in our patients. Furthermore, fetuin-A levels can be used to distinguish between colon and rectal cancers.

Epidemiologic evidence for a role of telomere dysfunction in cancer etiology

Telomeres, the dynamic nucleoprotein structures at the ends of linear chromosomes, maintain the genomic integrity of a cell. Telomere length shortens with age due to the incomplete replication of DNA ends with each cell division as well as damage incurred by oxidative stress. Patterns of telomere shortening, genomic instability, and telomerase expression in many cancer tissues compared to adjacent normal tissue implicate telomere crisis as a common crucial event in malignant transformation. In order to understand the role of telomere length in cancer etiology, most epidemiologic studies have measured average telomere length of peripheral blood or buccal cell DNA as a surrogate tissue biomarker of telomere dysfunction and cancer risk. In this review, we present the results from epidemiologic investigations conducted of telomere length and cancer risk. We note differences in reported associations based on study design, which may be due to biases intrinsic to retrospective studies. Finally, we conclude with study design considerations as future investigations are needed to elucidate the relationship between telomere length and a number of cancer sites.

Shortened telomere length is associated with increased risk of cancer: a meta-analysis

BACKGROUND

Telomeres play a key role in the maintenance of chromosome integrity and stability, and telomere shortening is involved in initiation and progression of malignancies. A series of epidemiological studies have examined the association between shortened telomeres and risk of cancers, but the findings remain conflicting.

METHODS

A dataset composed of 11,255 cases and 13,101 controls from 21 publications was included in a meta-analysis to evaluate the association between overall cancer risk or cancer-specific risk and the relative telomere length. Heterogeneity among studies and their publication bias were further assessed by the χ(2)-based Q statistic test and Egger's test, respectively.

RESULTS

The results showed that shorter telomeres were significantly associated with cancer risk (OR = 1.35, 95% CI = 1.14-1.60), compared with longer telomeres. In the stratified analysis by tumor type, the association remained significant in subgroups of bladder cancer (OR = 1.84, 95% CI = 1.38-2.44), lung cancer (OR = 2.39, 95% CI = 1.18-4.88), smoking-related cancers (OR = 2.25, 95% CI = 1.83-2.78), cancers in the digestive system (OR = 1.69, 95% CI = 1.53-1.87) and the urogenital system (OR = 1.73, 95% CI = 1.12-2.67). Furthermore, the results also indicated that the association between the relative telomere length and overall cancer risk was statistically significant in studies of Caucasian subjects, Asian subjects, retrospective designs, hospital-based controls and smaller sample sizes. Funnel plot and Egger's test suggested that there was no publication bias in the current meta-analysis (P = 0.532).

CONCLUSIONS

The results of this meta-analysis suggest that the presence of shortened telomeres may be a marker for susceptibility to human cancer, but single larger, well-design prospective studies are warranted to confirm these findings.

The association of telomere length and cancer: a meta-analysis

BACKGROUND

Telomeres shorten with each cell division and are essential for chromosomal stability. Short telomeres in surrogate tissues (e.g., blood cells) are associated with increased cancer risk in several case-control studies, but findings are inconsistent in prospective studies.

METHODS

We systematically reviewed studies published prior to August 30, 2010, on the association between telomere length (TL) in surrogate tissues and cancer. There were 27 reports on 13 cancers and/or incident cancer investigating this association. The majority, 16, were retrospective case--control studies, 11 were prospective studies. Meta-analyses were conducted to determine ORs and 95% CIs for these studies.

RESULTS

Studies on bladder, esophageal, gastric, head and neck, ovarian, renal, and overall incident cancer found associations between short telomeres and these cancers. Non-Hodgkin lymphoma, breast, lung, and colorectal cancer reports were inconsistent. Single studies on endometrial, prostate, and skin cancers were null. In a random-effects meta-analysis, short TL was significantly associated with cancer in retrospective studies (pooled OR for the shortest TL quartile compared with the longest: 2.9, 95% CI: 1.75-4.8, P < 0.0001). The pooled OR for prospective studies was 1.16 (95% CI: 0.87-1.54, P = 0.32). All studies combined yielded a pooled OR of 1.96 (95% CI: 1.37-2.81, P = 0.0001) for the association of short TL and cancer.

CONCLUSION AND IMPACT

There is suggestive evidence that short surrogate tissue TL is associated with cancer; the strongest evidence exists for bladder, esophageal, gastric, and renal cancers. Additional prospective studies with consistent methodology are needed to confirm this hypothesis.

The association of telomere length and cancer: a meta-analysis

BACKGROUND

Telomeres shorten with each cell division and are essential for chromosomal stability. Short telomeres in surrogate tissues (e.g., blood cells) are associated with increased cancer risk in several case-control studies, but findings are inconsistent in prospective studies.

METHODS

We systematically reviewed studies published prior to August 30, 2010, on the association between telomere length (TL) in surrogate tissues and cancer. There were 27 reports on 13 cancers and/or incident cancer investigating this association. The majority, 16, were retrospective case--control studies, 11 were prospective studies. Meta-analyses were conducted to determine ORs and 95% CIs for these studies.

RESULTS

Studies on bladder, esophageal, gastric, head and neck, ovarian, renal, and overall incident cancer found associations between short telomeres and these cancers. Non-Hodgkin lymphoma, breast, lung, and colorectal cancer reports were inconsistent. Single studies on endometrial, prostate, and skin cancers were null. In a random-effects meta-analysis, short TL was significantly associated with cancer in retrospective studies (pooled OR for the shortest TL quartile compared with the longest: 2.9, 95% CI: 1.75-4.8, P < 0.0001). The pooled OR for prospective studies was 1.16 (95% CI: 0.87-1.54, P = 0.32). All studies combined yielded a pooled OR of 1.96 (95% CI: 1.37-2.81, P = 0.0001) for the association of short TL and cancer.

CONCLUSION AND IMPACT

There is suggestive evidence that short surrogate tissue TL is associated with cancer; the strongest evidence exists for bladder, esophageal, gastric, and renal cancers. Additional prospective studies with consistent methodology are needed to confirm this hypothesis.

No association between telomere length in peripheral blood leukocytes and the risk of nonmelanoma skin cancer

BACKGROUND

Recent reports have shown that telomere length was associated with the risk of various cancers, but the results have been inconsistent.

METHODS

We prospectively evaluated the association of telomere length in peripheral blood leukocytes with the risk of skin squamous cell carcinoma (SCC) in 241 cases and 241 controls within the Health Professionals Follow-up Study (HPFS), and the risk of skin basal cell carcinoma (BCC) in 623 cases and 1,943 controls within the Nurses' Health Study (NHS).

RESULTS

No significant association was observed between telomere length and risk of SCC (longest quartile vs. shortest quartile, OR = 1.09, 95%CI: 0.62-1.93, P = 0.81). Null findings were also observed between telomere length and risk of BCC in 2 independent sets (OR = 0.96, 95%CI: 0.49-1.87, P = 0.83; and OR = 0.91, 95%CI: 0.66-1.25, P = 0.39).

CONCLUSION

We found no evidence that telomere length in peripheral blood leukocytes was associated with risk of nonmelanoma skin cancer.

IMPACT

Our prospective study suggests that telomere length in peripheral blood leukocytes is less likely to play a substantial role in nonmelanoma skin cancer development.

Telomere length and variation in telomere biology genes in individuals with osteosarcoma

Osteosarcoma, the most common primary bone tumor, occurs most frequently in adolescents. Chromosomal aneuploidy is common in osteosarcoma cells, suggesting underlying chromosomal instability. Telomeres, located at chromosome ends, are essential for genomic stability; several studies have suggested that germline telomere length (TL) is associated with cancer risk. We hypothesized that TL and/or common genetic variation in telomere biology genes may be associated with risk of osteosarcoma. We investigated TL in peripheral blood DNA and 713 single nucleotide polymorphisms (SNPs) from 39 telomere biology genes in 98 osteosarcoma cases and 69 orthopedic controls. For the genotyping component, we added 1363 controls from the Prostate, Lung, Colorectal, and Ovarian Cancer ScreeningTrial. Short TL was not associated with osteosarcoma risk overall (OR 1.39, P=0.67), although there was a statistically significant association in females (OR 4.35, 95% Cl 1.20-15.74, P=0.03). Genotype analyses identified seven SNPs in TERF1 significantly associated with osteosarcoma risk after Bonferroni correction by gene. These SNPs were highly linked and associated with a reduced risk of osteosarcoma (OR 0.48-0.53, P=0.0001-0.0006). We also investigated associations between TL and telomere gene SNPs in osteosarcoma cases and orthopedic controls. Several SNPs were associated with TL prior to Bonferroni correction; one SNP in NOLA2 and one in MEN1 were marginally non-significant after correction (P(adj)=0.057 and 0.066, respectively). This pilot-study suggests that females with short telomeres may be at increased risk of osteosarcoma, and that SNPs in TERF1 are inversely associated with osteosarcoma risk.

No association between TERT-CLPTM1L single nucleotide polymorphism rs401681 and mean telomere length or cancer risk

BACKGROUND

A recent study reported genetic variants in the TERT-CLPTM1L locus that were associated with mean telomere length, and with risk of multiple cancers.

METHODS

We evaluated the association between single nucleotide polymorphism (SNP) rs401681 (C > T) and mean telomere length, using quantitative real-time PCR, in blood-extracted DNA collected from 11,314 cancer-free participants from the Sisters in Breast Screening study, the Melanoma and Pigmented Lesions Evaluative Study melanoma family study, and the SEARCH Breast, Colorectal, Melanoma studies. We also examined the relationship between rs401618 genotype and susceptibility to breast cancer (6,800 cases and 6,608 controls), colorectal cancer (2,259 cases and 2,181 controls), and melanoma (787 cases and 999 controls).

RESULTS

The "per T allele" change in mean telomere length (DeltaCt), adjusted for age, study plate, gender, and family was 0.001 [95% confidence intervals (CI), 0.01-0.02; P trend = 0.61]. The "per T allele" odds ratio for each cancer was 1.01 for breast cancer (95% CI, 0.96-1.06; P trend = 0.64), 1.02 for colorectal cancer (95% CI, 0.94-1.11; P trend = 0.66), and 0.99 for melanoma (95% CI, 0.84-1.15; P trend = 0.87).

CONCLUSIONS

We found no evidence that this SNP was associated with mean telomere length, or with risk of breast cancer, colorectal cancer, or melanoma.

IMPACT

Our results indicate that the observed associations between rs401681 and several cancer types might be weaker than previously described. The lack of an association in our study between this SNP and mean telomere length suggests that any association with cancer risk at this locus is not mediated through TERT.

Mean leukocyte telomere length and risk of incident colorectal carcinoma in women: a prospective, nested case-control study

BACKGROUND

To date, no prospective epidemiological data are available, particularly in women, on mean leukocyte telomere length as a risk predictor.

METHODS

Using leukocyte DNA samples collected at baseline in a prospective cohort of over 28,000 initially healthy women, we examined the relationship between mean leukocyte telomere repeat copy number to single gene copy number (TSR) in 134 incident cases of colorectal carcinoma (CRC), and 357 matched controls; all were Caucasian.

RESULTS

The observed log(e)-transformed TSRs were similar between cases and controls (p=0.79). Using an adjusted analysis, we found no evidence for an association of the log(e)-TSRs with CRC risk [adjusted odds ratio (OR)=0.943, 95% confidence interval (CI)=0.647-1.376, p=0.762]. Stratified analysis by median follow-up time, or postmenopausal status also showed similar null findings.

CONCLUSIONS

In concordance with our previous findings in Caucasian men, the present study in Caucasian women found no evidence for an association of mean leukocyte telomere length with risk of incident CRC, further suggesting that leukocyte telomere length may not be a useful indicator for risk assessment.

Telomere length in prospective and retrospective cancer case-control studies

Previous studies have reported that shorter mean telomere length in lymphocytes was associated with increased susceptibility to common diseases of aging, and may be predictive of cancer risk. However, most analyses have examined retrospectively collected case-control studies. Mean telomere length was measured using high-throughput quantitative real-time PCR. Blood for DNA extraction was collected after cancer diagnosis in the East Anglian SEARCH Breast (2,243 cases and 2,181 controls) and SEARCH Colorectal (2,249 cases and 2,161 controls) studies. Prospective case-control studies were conducted for breast cancer (199 cases) and colorectal cancer (185 cases), nested within the EPIC-Norfolk cohort. Blood was collected at least 6 months prior to diagnosis, and was matched to DNA from two cancer-free controls per case. In the retrospective SEARCH studies, the age-adjusted odds ratios for shortest (Q4) versus longest (Q1) quartile of mean telomere length was 15.5 [95% confidence intervals (CI), 11.6-20.8; p-het = 5.7 x 10(-75)], with a "per quartile" P-trend = 2.1 x 10(-80) for breast cancer; and 2.14 (95% CI, 1.77-2.59; p-het = 7.3 x 10(-15)), with a per quartile P-trend = 1.8 x 10(-13) for colorectal cancer. In the prospective EPIC study, the comparable odds ratios (Q4 versus Q1) were 1.58 (95% CI, 0.75-3.31; p-het = 0.23) for breast cancer and 1.13 (95% CI, 0.54-2.36; p-het = 0.75) for colorectal cancer risk. Mean telomere length was shorter in retrospectively collected cases than in controls but the equivalent association was markedly weaker in the prospective studies. This suggests that telomere shortening largely occurs after diagnosis, and therefore, might not be of value in cancer prediction.