H. Dean Hosgood

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 χ2-based Q statistic test and Eggers 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 Eggers 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.

Millions Dead: How Do We Know and What Does It Mean? Methods Used in the Comparative Risk Assessment of Household Air Pollution

In the Comparative Risk Assessment (CRA) done as part of the Global Burden of Disease project (GBD-2010), the global and regional burdens of household air pollution (HAP) due to the use of solid cookfuels, were estimated along with 60+ other risk factors. This article describes how the HAP CRA was framed; how global HAP exposures were modeled; how diseases were judged to have sufficient evidence for inclusion; and how meta-analyses and exposure-response modeling were done to estimate relative risks. We explore relationships with the other air pollution risk factors: ambient air pollution, smoking, and secondhand smoke. We conclude with sensitivity analyses to illustrate some of the major uncertainties and recommendations for future work. We estimate that in 2010 HAP was responsible for 3.9 million premature deaths and ∼4.8% of lost healthy life years (DALYs), ranking it highest among environmental risk factors examined and one of the major risk factors of any type globally.

The 5p15.33 locus is associated with risk of lung adenocarcinoma in never-smoking females in Asia.

Genome-wide association studies of lung cancer reported in populations of European background have identified three regions on chromosomes 5p15.33, 6p21.33, and 15q25 that have achieved genome-wide significance with p-values of 10−7 or lower. These studies have been performed primarily in cigarette smokers, raising the possibility that the observed associations could be related to tobacco use, lung carcinogenesis, or both. Since most women in Asia do not smoke, we conducted a genome-wide association study of lung adenocarcinoma in never-smoking females (584 cases, 585 controls) among Han Chinese in Taiwan and found that the most significant association was for rs2736100 on chromosome 5p15.33 (p = 1.30×10−11). This finding was independently replicated in seven studies from East Asia totaling 1,164 lung adenocarcinomas and 1,736 controls (p = 5.38×10−11). A pooled analysis achieved genome-wide significance for rs2736100. This SNP marker localizes to the CLPTM1L-TERT locus on chromosome 5p15.33 (p = 2.60×10−20, allelic risk = 1.54, 95% Confidence Interval (CI) 1.41–1.68). Risks for heterozygote and homozygote carriers of the minor allele were 1.62 (95% CI; 1.40–1.87), and 2.35 (95% CI: 1.95–2.83), respectively. In summary, our results show that genetic variation in the CLPTM1L-TERT locus of chromosome 5p15.33 is directly associated with the risk of lung cancer, most notably adenocarcinoma.

Four distinct pathways of hemoglobin uptake in the malaria parasite Plasmodium falciparum

During the bloodstage of malaria infection, the parasite internalizes and degrades massive amounts of hemoglobin from the host red blood cell. Using serial thin-section electron microscopy and three-dimensional reconstruction, we demonstrate four independent, but partially overlapping, hemoglobin-uptake processes distinguishable temporally, morphologically, and pharmacologically. Early ring-stage parasites undergo a profound morphological transformation in which they fold, like a cup, onto themselves and in so doing take a large first gulp of host cell cytoplasm. This event, which we term the “Big Gulp,” appears to be independent of actin polymerization and marks the first step in biogenesis of the parasites lysosomal compartment—the food vacuole. A second, previously identified uptake process, uses the cytostome, a well characterized and morphologically distinct structure at the surface of the parasite. This process is more akin to classical endocytosis, giving rise to small (<0.004 fl) vesicles that are marked by the early endosomal regulatory protein Rab5a. A third process, also arising from cytostomes, creates long thin tubes previously termed cytostomal tubes in an actin-dependent manner. The fourth pathway, which we term phagotrophy, is similar to the Big Gulp in that it more closely resembles phagocytosis, except that phagotrophy does not require actin polymerization. Each of these four processes has aspects that are unique to Plasmodium, thus opening avenues to antimalarial therapy.

A Prospective Study of Telomere Length Measured by Monochrome Multiplex Quantitative PCR and Risk of Non-Hodgkin Lymphoma

Purpose: Telomere length plays an important role in the maintenance of chromosomal stability and in tumorigenesis. We hypothesized that telomere length in peripheral WBC DNA obtained from healthy individuals would be a predictor of future risk of developing non-Hodgkin lymphoma. Experimental Design: Using a new assay to measure relative telomere length, monochrome multiplex quantitative PCR, which strongly correlates with telomere length measured by Southern blot (Spearman r = 0.91, P < 0.0001) and has high precision (coefficient of variation = 7%), we compared telomere length in peripheral WBC DNA in 107 incident male non-Hodgkin lymphoma cases and 107 matched controls within the prospective Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study cohort. Results: Median (10th, 90th percentile) telomere length was 1.10 (0.79, 1.43) in cases and 1.02 (0.78, 1.26) in controls (P = 0.0017, Wilcoxon sign test). There was a strong dose-response relationship between quartiles of telomere length and risk of non-Hodgkin lymphoma overall [odds ratios (95% confidence intervals) by quartile: 1.0; 1.1 (0.4-2.7); 1.8 (0.7-4.9); and 3.6 (1.4-8.9); P trend = 0.003], and this association was similar across the most common non-Hodgkin lymphoma subtypes present in this study. Conclusion: These results suggest that longer telomere length may be a potential predictor for future risk of non-Hodgkin lymphoma. (Clin Cancer Res 2009;15(23):7429–33)

Longer telomere length in peripheral white blood cells is associated with risk of lung cancer and the rs2736100 (CLPTM1L-TERT) polymorphism in a prospective cohort study among women in China.

A recent genome-wide association study of lung cancer among never-smoking females in Asia demonstrated that the rs2736100 polymorphism in the TERT-CLPTM1L locus on chromosome 5p15.33 was strongly and significantly associated with risk of adenocarcinoma of the lung. The telomerase gene TERT is a reverse transcriptase that is critical for telomere replication and stabilization by controlling telomere length. We previously found that longer telomere length measured in peripheral white blood cell DNA was associated with increased risk of lung cancer in a prospective cohort study of smoking males in Finland. To follow up on this finding, we carried out a nested case-control study of 215 female lung cancer cases and 215 female controls, 94% of whom were never-smokers, in the prospective Shanghai Women’s Health Study cohort. There was a dose-response relationship between tertiles of telomere length and risk of lung cancer (odds ratio (OR), 95% confidence interval [CI]: 1.0, 1.4 [0.8–2.5], and 2.2 [1.2–4.0], respectively; P trend = 0.003). Further, the association was unchanged by the length of time from blood collection to case diagnosis. In addition, the rs2736100 G allele, which we previously have shown to be associated with risk of lung cancer in this cohort, was significantly associated with longer telomere length in these same study subjects (P trend = 0.030). Our findings suggest that individuals with longer telomere length in peripheral white blood cells may have an increased risk of lung cancer, but require replication in additional prospective cohorts and populations.

A Prospective Study of Telomere Length Measured by Monochrome Multiplex Quantitative PCR and Risk of Lung Cancer

PURPOSE Telomere length plays an important role in chromosomal stability and tumorigenesis, and its measurement in peripheral white blood cell DNA may be a predictor of the development of lung cancer. EXPERIMENTAL DESIGN Using a new method - monochrome multiplex quantitative PCR - which reduces measurement variability, we compared telomere length relative to standard DNA in white blood cell DNA in 229 incident male lung cancer cases and 229 matched controls within the prospective Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study of male smokers. RESULTS Median (10th, 90th percentile) telomere length was 1.13 (0.86, 1.45) in cases and 1.08 (0.85, 1.38) in controls (P=0.038). Telomere length was inversely associated with pack-years of smoking (Spearmans correlation r=-0.16, P=0.02) among controls. Compared to subjects with shorter telomere length (≤median), subjects with greater telomere length (>median) had a 1.6-fold (95% CI, 1.06-2.36) increased risk of lung cancer. There was a significant linear relationship between quartiles of telomere length and risk of lung cancer (odds ratios (95% confidence intervals) by quartile: 1.00, 0.98 (0.55-1.73), 1.62 (0.95-2.77), and 1.50 (0.84-2.68); P(trend)=0.05). In addition, subgroup analysis showed that greater telomere length was associated with an increased risk of lung cancer among longer-term smokers (>38 years) (OR, 1.90; 95% CI, 1.00-3.59) but not among shorter-term smokers (≤38 years) (OR, 1.08; 95% CI, 0.56-2.11) (P(interaction)=0.01). CONCLUSIONS Our results suggest that greater telomere length may be associated with higher risk of lung cancer among male smokers.

In-home coal and wood use and lung cancer risk: a pooled analysis of the International Lung Cancer Consortium.

Background Domestic fuel combustion from cooking and heating is an important public health issue because roughly 3 billion people are exposed worldwide. Recently, the International Agency for Research on Cancer classified indoor emissions from household coal combustion as a human carcinogen (group 1) and from biomass fuel (primarily wood) as a probable human carcinogen (group 2A). Objectives We pooled seven studies from the International Lung Cancer Consortium (5,105 cases and 6,535 controls) to provide further epidemiological evaluation of the association between in-home solid-fuel use, particularly wood, and lung cancer risk. Methods Using questionnaire data, we classified subjects as predominant solid-fuel users (e.g., coal, wood) or nonsolid-fuel users (e.g., oil, gas, electricity). Unconditional logistic regression was used to estimate the odds ratios (ORs) and to compute 95% confidence intervals (CIs), adjusting for age, sex, education, smoking status, race/ethnicity, and study center. Results Compared with nonsolid-fuel users, predominant coal users (OR = 1.64; 95% CI, 1.49–1.81), particularly coal users in Asia (OR = 4.93; 95% CI, 3.73–6.52), and predominant wood users in North American and European countries (OR = 1.21; 95% CI, 1.06–1.38) experienced higher risk of lung cancer. The results were similar in never-smoking women and other subgroups. Conclusions Our results are consistent with previous observations pertaining to in-home coal use and lung cancer risk, support the hypothesis of a carcinogenic potential of in-home wood use, and point to the need for more detailed study of factors affecting these associations.

Household coal use and lung cancer: systematic review and meta-analysis of case–control studies, with an emphasis on geographic variation

BACKGROUND Emissions from household coal combustion associated with cooking and heating are an important public health issue, particularly in China where hundreds of millions of people are exposed. Although coal emissions are a known human carcinogen, there is still uncertainty about the level of risk for lung and other cancers. METHODS We performed a meta-analysis on 25 case-control studies (10,142 cases and 13,416 controls) to summarize the association between household coal use and lung cancer risk, and to explore the effect modification of this association by geographical location. RESULTS Using random-effects models, household coal use was found to be associated with lung cancer risk among all studies throughout the world [odds ratio (OR) = 2.15; 95% confidence interval (CI) = 1.61-2.89, N(studies) = 25], and particularly among those studies carried out in mainland China and Taiwan (OR = 2.27; 95% CI = 1.65-3.12, N(studies) = 20). Stratification by regions of mainland China and Taiwan found a variation in effects across the regions, with south/southeastern (OR = 3.27; 95% CI = 1.27-8.42, N(studies) = 3) and southwestern China (OR = 2.98; 95% CI = 1.18-7.53, N(studies) = 3) experiencing the highest risk. The elevated risk associated with coal use throughout Asia was also observed when stratifying studies by gender, smoking status, sample size, design (population vs hospital case-control) and publication language. No significant publication bias was found (p(Beggs) = 0.15). CONCLUSIONS Our results provide evidence that although the carcinogenic effect of coal use varies by location, coals from many locations exhibit elevated lung cancer risks.

Telomere Length in White Blood Cell DNA and Lung Cancer: A Pooled Analysis of Three Prospective Cohorts

We investigated the relationship between telomere length and lung cancer in a pooled analysis from three prospective cohort studies: the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, conducted among men and women in the United States, and previously published data from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Trial conducted among male smokers in Finland, and the Shanghai Womens Health Study (SWHS), which is comprised primarily of never-smokers. The pooled population included 847 cases and 847 controls matched by study, age, and sex. Leukocyte telomere length was measured by a monochrome multiplex qPCR assay. We used conditional logistic regression models to calculate ORs and their 95% confidence intervals (CI) for the association between telomere length and lung cancer risk, adjusted for age and pack-years of smoking. Longer telomere length was associated with increased lung cancer risk in the pooled analysis [OR (95% CI) by quartile: 1.00; 1.24 (0.90-1.71); 1.27 (0.91-1.78); and 1.86 (1.33-2.62); P trend = 0.000022]. Findings were consistent across the three cohorts and strongest for subjects with very long telomere length, i.e., lung cancer risks for telomere length [OR (95% CI)] in the upper half of the fourth quartile were 2.41 (1.28-4.52), 2.16 (1.11-4.23), and 3.02(1.39-6.58) for the PLCO trial, the ATBC trial, and the SWHS, respectively. In addition, the association persisted among cases diagnosed more than 6 years after blood collection and was particularly evident for female adenocarcinoma cases. Telomere length in white blood cell DNA may be a biomarker of future increased risk of lung cancer in diverse populations.