Mortality among Rocketdyne workers who tested rocket engines, 1948-1999

In vitro and in vivo mammalian mutation assays support a nonmutagenic mechanism of carcinogenicity for hydrazine

Hydrazine has been described as a mutagenic, probable human carcinogen. It is mutagenic in in vitro systems such as bacterial reverse mutation (Ames) tests and some yeast systems, as well as in in vivo systems with drosophila. It was shown to cause chromosome damage both in vitro and in vivo but was negative in some well-validated mammalian mutation systems such as CHO HPRT assays. Importantly, there is only one in vivo gene mutation test reported, which was negative. Our objective was to determine if hydrazine is mutagenic in mammalian test systems. Thus, we conducted an in vitro gene mutation test in Muta™Mouse lung epithelial cells (FE1 cell assay) and a regulatory-compliant in vivo Big Blue® mouse test. Consistent with previous reports, an additional six-well Ames assay showed that hydrazine was mutagenic to bacteria. The FE1 cell assay was negative in conditions with and without metabolic activation when tested to cytotoxicity limits. In the Big Blue® mouse study, female mice received dosages of hydrazine up to 10.9 mg/kg via drinking water for 28 days. This dose is comparable to a dose used in a carcinogenicity study where female mice had significant increases in hepatocellular adenoma at 11.5 mg/kg. There were no increases in mutant frequency in liver and lung, two tissues sensitive to the carcinogenic effects of hydrazine in mice. Our research shows that hydrazine is not mutagenic in mammalian cells either in vitro or in vivo, indicating mutagenicity may not play a role in the carcinogenicity of hydrazine.

Respiratory effects of trichloroethylene

Trichloroethylene (TCE) is a chlorinated solvent that has been used widely around the world in the twentieth century for metal degreasing and dry cleaning. Although TCE displays general toxicity and is classified as a human carcinogen, the association between TCE exposure and respiratory disorders are conflicting. In this review we aimed to systematically evaluate the current evidence for the respiratory effects of TCE exposure and the implications for the practicing clinician. There is limited evidence of an increased risk of lung cancer associated with TCE exposure based on animal and human data. However, the effect of other chlorinated solvents and mixed solvent exposure should be further investigated. Limited data are available to support an association between TCE exposure and respiratory tract disorders such as asthma, chronic bronchitis, or rhinitis. The most consistent data is the association of TCE with autoimmune and vascular diseases such as systemic sclerosis and pulmonary veno-occlusive disease. Although recent data are reassuring regarding the absence of an increased lung cancer risk with TCE exposure, clinicians should be aware of other potential respiratory effects of TCE. In particular, occupational exposure to TCE has been linked to less common conditions such as systemic sclerosis and pulmonary veno-occlusive disease.

Occupational exposure to chlorinated solvents and risk of head and neck cancer in men: a population-based case-control study in France

BACKGROUND

Few epidemiological studies have investigated the link between occupational exposure to solvents and head and neck cancer risk, and available findings are sparse and inconsistent. The objective of this study was to examine the association between occupational exposure to chlorinated solvents and head and neck cancer risk.

METHODS

We analyzed data from 4637 men (1857 cases and 2780 controls) included in a population-based case-control study, ICARE (France). Occupational exposure to five chlorinated solvents (perchloroethylene [PCE], trichloroethylene [TCE], methylene chloride [MC], chloroform [CF], and carbon tetrachloride [CT]) was assessed through job-exposure matrices. Odds ratios (ORs) and confidence intervals (95% CI) were estimated by unconditional logistic regression, adjusted for age, tobacco smoking, alcohol consumption, asbestos exposure, and other potential confounders.

RESULTS

We observed no association between chlorinated solvent exposure and head and neck cancer risk, despite a non-significant increase in risk among subjects who had the highest cumulative level of exposure to PCE, (OR = 1.81; 95% CI = 0.68 to 4.82). In subsite analysis, the risk of laryngeal cancer increased with cumulative exposure to PCE (p for trend = 0.04). The OR was 3.86 (95% CI = 1.30 to 11.48) for those exposed to the highest levels of PCE. A non-significant elevated risk of hypopharyngeal cancer was also observed in subjects exposed to the highest levels of MC (OR = 2.36; 95% CI = 0.98 to 5.85).

CONCLUSION

Our findings provide evidence that high exposure to PCE increases the risk of laryngeal cancer, and suggest an association between exposure to MC and hypopharyngeal cancer. Exposure to other chlorinated solvents was not associated with the risk of head and neck cancer.

Occupational exposure to solvents and risk of head and neck cancer in women: a population-based case-control study in France

OBJECTIVE

Our objective was to investigate the association between head and neck cancer and occupational exposure to chlorinated, oxygenated and petroleum solvents in women.

METHODS

Investigation of occupational and environmental CAuses of REspiratory cancers (ICARE), a French population-based case-control study, included 296 squamous cell carcinomas of the head and neck (HNSCC) in women and 775 female controls. Lifelong occupational history was collected. Job-exposure matrices allowed to assess exposure to 5 chlorinated solvents (carbon tetrachloride; chloroform; methylene chloride; perchloroethylene; trichloroethylene), 5 petroleum solvents (benzene; special petroleum product; gasoline; white spirits and other light aromatic mixtures; diesel, fuels and kerosene) and 5 oxygenated solvents (alcohols; ketones and esters; ethylene glycol; diethyl ether; tetrahydrofuran). OR and 95% CIs, adjusted for smoking, alcohol drinking, age and geographical area, were estimated with logistic models.

RESULTS

Elevated ORs were observed among women ever exposed to perchloroethylene (OR=2.97, 95% CI 1.05 to 8.45) and trichloroethylene (OR=2.15, 95% CI 1.21 to 3.81). These ORs increased with exposure duration (OR=3.75, 95% CI 0.64 to 21.9 and OR=4.44, 95% CI 1.56 to 12.6 for 10 years or more, respectively). No significantly increased risk of HNSCC was found for occupational exposure to the other chlorinated, petroleum or oxygenated solvents.

CONCLUSIONS

These findings suggest that exposure to perchloroethylene or trichloroethylene may increase the risk of HNSCC in women. In our study, there is no clear evidence that the other studied solvents are risk factors for HNSCC.

Target Organ Metabolism, Toxicity, and Mechanisms of Trichloroethylene and Perchloroethylene: Key Similarities, Differences, and Data Gaps

Trichloroethylene (TCE) and perchloroethylene or tetrachloroethylene (PCE) are high-production volume chemicals with numerous industrial applications. As a consequence of their widespread use, these chemicals are ubiquitous environmental contaminants to which the general population is commonly exposed. It is widely assumed that TCE and PCE are toxicologically similar; both are simple olefins with three (TCE) or four (PCE) chlorines. Nonetheless, despite decades of research on the adverse health effects of TCE or PCE, few studies have directly compared these two toxicants. Although the metabolic pathways are qualitatively similar, quantitative differences in the flux and yield of metabolites exist. Recent human health assessments have uncovered some overlap in target organs that are affected by exposure to TCE or PCE, and divergent species- and sex-specificity with regard to cancer and noncancer hazards. The objective of this minireview is to highlight key similarities, differences, and data gaps in target organ metabolism and mechanism of toxicity. The main anticipated outcome of this review is to encourage research to 1) directly compare the responses to TCE and PCE using more sensitive biochemical techniques and robust statistical comparisons; 2) more closely examine interindividual variability in the relationship between toxicokinetics and toxicodynamics for TCE and PCE; 3) elucidate the effect of coexposure to these two toxicants; and 4) explore new mechanisms for target organ toxicity associated with TCE and/or PCE exposure.

Residential cancer cluster investigation nearby a Superfund Study Area with trichloroethylene contamination

PURPOSE

Trichloroethylene (TCE) is an industrial solvent associated with liver cancer, kidney cancer, and non-Hodgkin's lymphoma (NHL). It is unclear whether an excess of TCE-associated cancers have occurred surrounding the Middlefield-Ellis-Whisman Superfund site in Mountain View, California. We conducted a population-based cancer cluster investigation comparing the incidence of NHL, liver, and kidney cancers in the neighborhood of interest to the incidence among residents in the surrounding four-county region.

METHODS

Case counts and address information were obtained using routinely collected data from the Greater Bay Area Cancer Registry, part of the Surveillance, Epidemiology, and End Results program. Population denominators were obtained from the 1990, 2000, and 2010 US censuses. Standardized incidence ratios (SIRs) with two-sided 99 % confidence intervals (CIs) were calculated for time intervals surrounding the US Censuses.

RESULTS

There were no statistically significant differences between the neighborhood of interest and the larger region for cancers of the liver or kidney. A statistically significant elevation was observed for NHL during one of the three time periods evaluated (1996-2005: SIR = 1.8, 99 % CI 1.1-2.8). No statistically significant NHL elevation existed in the earlier 1988-1995 (SIR = 1.3, 99 % CI 0.5-2.6) or later 2006-2011 (SIR = 1.3, 99 % CI 0.6-2.4) periods.

CONCLUSION

There is no evidence of an increased incidence of liver or kidney cancer, and there is a lack of evidence of a consistent, sustained, or more recent elevation in NHL occurrence in this neighborhood. This evaluation included existing cancer registry data, which cannot speak to specific exposures incurred by past or current residents of this neighborhood.

Occupational Exposure to Hydrazine and Subsequent Risk of Lung Cancer: 50-Year Follow-Up

Purpose

Hydrazine is carcinogenic in animals, but there is inadequate evidence to determine if it is carcinogenic in humans. This study aimed to evaluate the association between hydrazine exposure and the risk of lung cancer.

Methods

The cause specific mortality rates of a cohort of 427 men who were employed at an English factory that produced hydrazine between 1945 and 1971 were compared with national mortality rates.

Results

By the end of December 2012 205 deaths had occurred. For men in the highest exposure category with greater than two years exposure and after more than ten years since first exposure the relative risks compared with national rates were: 0.85 (95% CI: 0.18–2.48) for lung cancer, 0.61 (95% CI: 0.07–2.21) for cancers of the digestive system, and 0.44 (95% CI: 0.05–1.57) for other cancers.

Conclusions

After 50 years of follow up, the results provide no evidence of an increased risk of death from lung cancer or death from any other cause.

Health effects of occupational exposure to uranium: do physicochemical properties matter?

PURPOSE

Physicochemical properties of uranium, including isotopic composition and solubility, are determinants of its toxicity. We reviewed epidemiological studies in civilian and military workers known to be exposed to uranium with different physicochemical properties to investigate its long-term effects, such as cancerous and circulatory diseases.

MATERIALS AND METHODS

We systematically searched the Pubmed and the Scopus databases to identify studies of uranium- processing workers (published between 1980 and 2013) and veterans of the wars in the Persian Gulf and the Balkans (published between 1991 and 2013) in which defined outcomes, such as lung, lymphohematopoietic, kidney cancers, and circulatory diseases were examined. RESULTS from these studies in terms of risk of each health outcome (mortality or incidence) and analyses of dose-response relationship were examined to present the impact of uranium physicochemical properties on the observed results.

RESULTS

Twenty-seven articles were reviewed. There is some evidence for increased lung cancer risk among uranium-processing workers. The evidence is less strong for lymphohematopoietic cancer. We found that most of the studies insufficiently assessed the physicochemical properties of uranium and some of them used proxies for the exposure assessment and risk estimation analyses. Studies of veterans of the wars in the Persian Gulf and the Balkans are uninformative in respect to internal uranium exposure.

CONCLUSIONS

Existing epidemiological data on the physicochemical properties of uranium and associated health outcomes are inconclusive. Further studies among certain groups of uranium-processing workers (uranium-enrichment and fuel-fabrication workers) could contribute to our knowledge of the health effects of uranium with respect to its physicochemical properties.

The Relationship between the Occupational Exposure of Trichloroethylene and Kidney Cancer

Trichloroethylene (TCE) has been widely used as a degreasing agent in many manufacturing industries. Recently, the International Agency for Research on Cancer presented “sufficient evidence” for the causal relationship between TCE and kidney cancer. The aim of this study was to review the epidemiologic evidences regarding the relationship between TCE exposure and kidney cancer in Korean work environments. The results from the cohort studies were inconsistent, but according to the meta-analysis and case–control studies, an increased risk for kidney cancer was present in the exposure group and the dose–response relationship could be identified using various measures of exposure. In Korea, TCE is a commonly used chemical for cleaning or degreasing processes by various manufacturers; average exposure levels of TCE vary widely. When occupational physicians evaluate work-relatedness kidney cancers, they must consider past exposure levels, which could be very high (>100 ppm in some cases) and associated with jobs, such as plating, cleaning, or degreasing. The exposure levels at a manual job could be higher than an automated job. The peak level of TCE could also be considered an important exposure-related variable due to the possibility of carcinogenesis associated with high TCE doses. This review could be a comprehensive reference for assessing work-related TCE exposure and kidney cancer in Korea.

Impact of chemical exposure on cancer mortality in a French cohort of uranium processing workers

BACKGROUND

Nuclear workers may be exposed to a variety of chemical hazards, in addition to radiation. We examined the effect of chemical exposures on cancer mortality among French uranium processing workers at the AREVA NC Pierrelatte facility.

METHODS

A cohort of 2,897 uranium processing workers employed for at least 6 months was followed from 1968 through 2006. Exposure to uranium and potentially carcinogenic chemicals was assessed with a plant-specific job-exposure matrix. Mortality hazard ratios (HRs) for cancers of the lung, lymphohematopoietic system, kidney and bladder, brain and central nervous system (BCNS), and prostate were estimated for each specific chemical exposure, with Cox regression models stratified for sex and calendar period and adjusted for socioeconomic status. Additional adjustments enabled us to examine the effect of co-exposure to uranium and other chemicals.

RESULTS

Exposure to aromatic solvents was associated with increased risk of BCNS malignancies after adjustment for other chemicals (HR=6.53, 95% CI=1.14-37.41; n=6) and for other chemicals and uranium (HR=7.26, 95% CI=0.90-58.19) in the annual exposure status model. Selected groups of lymphohematopoietic cancers were found associated with solvent exposure. Inconclusive results were found regarding chromium (VI) exposure, since only 2 workers died from lung cancer among 109 exposed.

CONCLUSION

Based on our pilot study, it seemed important to take into account chemical exposures in the analyses of cancer mortality among French uranium processing workers.

Trichloroethylene: Mechanistic, epidemiologic and other supporting evidence of carcinogenic hazard

The chlorinated solvent trichloroethylene (TCE) is a ubiquitous environmental pollutant. The carcinogenic hazard of TCE was the subject of a 2012 evaluation by a Working Group of the International Agency for Research on Cancer (IARC). Information on exposures, relevant data from epidemiologic studies, bioassays in experimental animals, and toxicity and mechanism of action studies was used to conclude that TCE is carcinogenic to humans (Group 1). This article summarizes the key evidence forming the scientific bases for the IARC classification. Exposure to TCE from environmental sources (including hazardous waste sites and contaminated water) is common throughout the world. While workplace use of TCE has been declining, occupational exposures remain of concern, especially in developing countries. The strongest human evidence is from studies of occupational TCE exposure and kidney cancer. Positive, although less consistent, associations were reported for liver cancer and non-Hodgkin lymphoma. TCE is carcinogenic at multiple sites in multiple species and strains of experimental animals. The mechanistic evidence includes extensive data on the toxicokinetics and genotoxicity of TCE and its metabolites. Together, available evidence provided a cohesive database supporting the human cancer hazard of TCE, particularly in the kidney. For other target sites of carcinogenicity, mechanistic and other data were found to be more limited. Important sources of susceptibility to TCE toxicity and carcinogenicity were also reviewed by the Working Group. In all, consideration of the multiple evidence streams presented herein informed the IARC conclusions regarding the carcinogenicity of TCE.

Mortality among 24,865 workers exposed to polychlorinated biphenyls (PCBs) in three electrical capacitor manufacturing plants: a ten-year update

The objective of this analysis was to evaluate mortality among a cohort of 24,865 capacitor-manufacturing workers exposed to polychlorinated biphenyls (PCBs) at plants in Indiana, Massachusetts, and New York and followed for mortality through 2008. Cumulative PCB exposure was estimated using plant-specific job-exposure matrices. External comparisons to US and state-specific populations used standardized mortality ratios, adjusted for gender, race, age and calendar year. Among long-term workers employed 3 months or longer, within-cohort comparisons used standardized rate ratios and multivariable Poisson regression modeling. Through 2008, more than one million person-years at risk and 8749 deaths were accrued. Among long-term employees, all-cause and all-cancer mortality were not elevated; of the a priori outcomes assessed only melanoma mortality was elevated. Mortality was elevated for some outcomes of a priori interest among subgroups of long-term workers: all cancer, intestinal cancer and amyotrophic lateral sclerosis (women); melanoma (men); melanoma and brain and nervous system cancer (Indiana plant); and melanoma and multiple myeloma (New York plant). Standardized rates of stomach and uterine cancer and multiple myeloma mortality increased with estimated cumulative PCB exposure. Poisson regression modeling showed significant associations with estimated cumulative PCB exposure for prostate and stomach cancer mortality. For other outcomes of a priori interest--rectal, liver, ovarian, breast, and thyroid cancer, non-Hodgkin lymphoma, Alzheimer disease, and Parkinson disease--neither elevated mortality nor positive associations with PCB exposure were observed. Associations between estimated cumulative PCB exposure and stomach, uterine, and prostate cancer and myeloma mortality confirmed our previous positive findings.

Human health effects of trichloroethylene: key findings and scientific issues

BACKGROUND

In support of the Integrated Risk Information System (IRIS), the U.S. Environmental Protection Agency (EPA) completed a toxicological review of trichloroethylene (TCE) in September 2011, which was the result of an effort spanning > 20 years.

OBJECTIVES

We summarized the key findings and scientific issues regarding the human health effects of TCE in the U.S. EPA's toxicological review.

METHODS

In this assessment we synthesized and characterized thousands of epidemiologic, experimental animal, and mechanistic studies, and addressed several key scientific issues through modeling of TCE toxicokinetics, meta-analyses of epidemiologic studies, and analyses of mechanistic data.

DISCUSSION

Toxicokinetic modeling aided in characterizing the toxicological role of the complex metabolism and multiple metabolites of TCE. Meta-analyses of the epidemiologic data strongly supported the conclusions that TCE causes kidney cancer in humans and that TCE may also cause liver cancer and non-Hodgkin lymphoma. Mechanistic analyses support a key role for mutagenicity in TCE-induced kidney carcinogenicity. Recent evidence from studies in both humans and experimental animals point to the involvement of TCE exposure in autoimmune disease and hypersensitivity. Recent avian and in vitro mechanistic studies provided biological plausibility that TCE plays a role in developmental cardiac toxicity, the subject of substantial debate due to mixed results from epidemiologic and rodent studies.

CONCLUSIONS

TCE is carcinogenic to humans by all routes of exposure and poses a potential human health hazard for noncancer toxicity to the central nervous system, kidney, liver, immune system, male reproductive system, and the developing embryo/fetus.

Trichloroethylene and cancer: systematic and quantitative review of epidemiologic evidence for identifying hazards

We conducted a meta-analysis focusing on studies with high potential for trichloroethylene (TCE) exposure to provide quantitative evaluations of the evidence for associations between TCE exposure and kidney, liver, and non-Hodgkin lymphoma (NHL) cancers. A systematic review documenting essential design features, exposure assessment approaches, statistical analyses, and potential sources of confounding and bias identified twenty-four cohort and case-control studies on TCE and the three cancers of interest with high potential for exposure, including five recently published case-control studies of kidney cancer or NHL. Fixed- and random-effects models were fitted to the data on overall exposure and on the highest exposure group. Sensitivity analyses examined the influence of individual studies and of alternative risk estimate selections. For overall TCE exposure and kidney cancer, the summary relative risk (RRm) estimate from the random effects model was 1.27 (95% CI: 1.13, 1.43), with a higher RRm for the highest exposure groups (1.58, 95% CI: 1.28, 1.96). The RRm estimates were not overly sensitive to alternative risk estimate selections or to removal of an individual study. There was no apparent heterogeneity or publication bias. For NHL, RRm estimates for overall exposure and for the highest exposure group, respectively, were 1.23 (95% CI: 1.07, 1.42) and 1.43 (95% CI: 1.13, 1.82) and, for liver cancer, 1.29 (95% CI: 1.07, 1.56) and 1.28 (95% CI: 0.93, 1.77). Our findings provide strong support for a causal association between TCE exposure and kidney cancer. The support is strong but less robust for NHL, where issues of study heterogeneity, potential publication bias, and weaker exposure-response results contribute uncertainty, and more limited for liver cancer, where only cohort studies with small numbers of cases were available.

Occupational exposures to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx: a quantitative literature review

PURPOSE

The role of occupational risk factors in oral and pharyngeal cancer is not well known and is possibly underestimated. This quantitative review summarizes epidemiological findings on exposure to asbestos, polycyclic aromatic hydrocarbons and solvents, and cancers of the oral cavity and pharynx.

METHODS

A systematic literature search was performed. We analyzed 63 publications: 8 from case-control studies and 55 from cohort studies. For agents with at least five available studies with homogenous exposure, a series of meta-analyses was conducted to provide quantitative pooled estimates of risks, using random effect models.

RESULTS

Exposure to asbestos (meta-RR 1.25; 95% CI 1.10-1.42) and to polycyclic aromatic hydrocarbons (meta-RR 1.14; 95% CI 1.02-1.28) was found to be associated with oral and pharyngeal cancer risk. On the other hand, no association was found with exposure to solvents in general (meta-RR 0.98; 95% CI 0.77-1.23) but the strong heterogeneity between studies suggested differences in exposures. The small number of studies with homogeneous exposure did not allow meta-analyses for specific solvents.

CONCLUSIONS

Future investigations should overcome common weaknesses of past studies, in terms of sample size, characterization of exposure, and classification of cancer sites.

Contemporary epidemiology of renal cell cancer

We analyzed renal cell cancer incidence patterns in the United States and reviewed recent epidemiologic evidence with regard to environmental and host genetic determinants of renal cell cancer risk. Renal cell cancer incidence rates continued to rise among all racial/ethnic groups in the United States, across all age groups, and for all tumor sizes, with the most rapid increases for localized stage disease and small tumors. Recent cohort studies confirmed the association of smoking, excess body weight, and hypertension with an elevated risk of renal cell cancer, and suggested that these factors can be modified to reduce the risk. There is increasing evidence for an inverse association between renal cell cancer risk and physical activity and moderate intake of alcohol. Occupational exposure to trichloroethylene has been positively associated with renal cell cancer risk in several recent studies, but its link with somatic mutations of the von Hippel-Lindau gene has not been confirmed. Studies of genetic polymorphisms in relation to renal cell cancer risk have produced mixed results, but genome-wide association studies with larger sample size and a more comprehensive approach are underway. Few epidemiologic studies have evaluated risk factors by subtypes of renal cell cancer defined by somatic mutations and other tumor markers.

Comparative assessing for radiological, chemical, and physical exposures at the French uranium conversion plant: Is uranium the only stressor?

This study presents the pattern of exposure to uranium and other occupational pollutants known to be potentially carcinogenic, mutagenic or toxic and used at the main uranium conversion plant in France. For different uranium compounds specified according to their solubility and purity, and 16 other categories of pollutants: chemicals, fibres, vapours, dust, and heat a time- and plant-specific job exposure matrix (JEM) was created covering the period 1960-2006. For 73 jobs and for each pollutant the amount and frequency of exposure were assessed on a four-level scale by different time periods. The JEM shows 73% sensitivity and 83% specificity. Although exposure assessment was semi-quantitative, the JEM allows computing of individual cumulative exposure score for each pollutant across time. Despite the predominant natural uranium compounds exposure, the amount of exposure to other pollutants such as TCE and other chlorinated products, asbestos, and fibres, is important at the plant. Numerous correlations detected between uranium compounds exposure and exposure to chemicals warrants improving biological monitoring of exposed workers and accounting for associated exposures in epidemiological studies. Results of this study will be used for further investigation of association between exposure and mortality among uranium conversion workers cohort.

A meta-analysis of occupational trichloroethylene exposure and liver cancer

OBJECTIVE

Findings from epidemiologic studies of trichloroethylene (TCE) exposure and liver cancer have been inconsistent. To quantitatively evaluate this association and to examine sources of heterogeneity, we conducted a meta-analysis of occupational studies of TCE exposure and liver/biliary tract cancer.

METHODS

We identified 14 occupational cohort studies of TCE exposed workers and one case-control study that met our inclusion criteria. Nine studies specifically identified TCE as a workplace exposure, and were classified as Group I cohort studies. Subcohorts of workers, identified within eight of these studies as more likely exposed to TCE than the total cohort, were analyzed separately.

RESULTS

The combined liver/biliary cancer summary relative risk estimate (SRRE) for all studies was 1.08 (95% CI 0.91-1.29; heterogeneity (H)-P-value=0.12). For the total study populations in the Group I cohorts, the SRRE was 1.14 (95% CI 0.93-1.39; H-P-value=0.05) and for the subcohorts, the SRRE was 1.30 (95% CI 1.09-1.55). Within this subcohort analysis, the association for the European studies of workers from various industries (SRRE=1.38; based on four studies) was higher than the association for the US studies of aerospace and aircraft workers (SRRE=0.97, based on four studies).

CONCLUSION

Although positive associations were observed for some analyses, results were inconsistent across occupational groups (aerospace/aircraft vs. other industries combined), study location, and incidence versus mortality endpoints. In addition, exposure-response trends were not observed consistently across studies. Interpretation is also limited by the potential impact of uncontrolled confounding by other occupational or lifestyle exposures such as smoking or alcohol consumption. Given these limitations, the currently available epidemiologic data are not sufficient to support a causal relation between occupational TCE exposure and liver/biliary cancer.