The Upper Midwest Health Study: gliomas and occupational exposure to chlorinated solvents

Research Recommendations for Selected IARC-Classified Agents: Impact and Lessons Learned

BACKGROUND

The International Agency for Research on Cancer (IARC) Monographs program assembles expert working groups who publish a critical review and evaluation of data on agents of interest. These comprehensive reviews provide a unique opportunity to identify research needs to address classification uncertainties. A multidisciplinary expert review and workshop held in 2009 identified research gaps and needs for 20 priority occupational chemicals, metals, dusts, and physical agents, with the goal of stimulating advances in epidemiological studies of cancer and carcinogen mechanisms. Overarching issues were also described.

OBJECTIVES

In this commentary we review the current status of the evidence for the 20 priority agents identified in 2009. We examine whether identified Research Recommendations for each agent were addressed and their potential impact on resolving classification uncertainties.

METHODS

We reviewed the IARC classifications of each of the 20 priority agents and identified major new epidemiological and human mechanistic studies published since the last evaluation. Information sources were either the published Monograph for agents that have been reevaluated or, for agents not yet reevaluated, Advisory Group reports and literature searches. Findings are described in view of recent methodological developments in Monographs evidence evaluation processes.

DISCUSSION

The majority of the 20 priority agents were reevaluated by IARC since 2009. The overall carcinogen classifications of 9 agents advanced, and new cancer sites with either "sufficient" or "limited" evidence of carcinogenicity were also identified for 9 agents. Examination of published findings revealed whether evidence gaps and Research Recommendations have been addressed and highlighted remaining uncertainties. During the past decade, new research addressed a range of the 2009 recommendations and supported updated classifications for priority agents. This supports future efforts to systematically apply findings of Monograph reviews to identify research gaps and priorities relevant to evaluation criteria established in the updated IARC Monograph Preamble. https://doi.org/10.1289/EHP12547.

Case-control study of brain and other central nervous system cancer among workers at semiconductor and storage device manufacturing facilities

OBJECTIVE

This study evaluated the relationship between brain and other central nervous system cancer ('CNS cancer') and exposures at two semiconductor and electronic module manufacturing facilities and at a storage device manufacturing facility.

METHODS

The case-control study, nested in a cohort of 126 836 employees, compared 120 CNS cancer cases and 1028 matched controls with respect to employment in 10 process groups and estimated cumulative exposure to 31 known or possible carcinogens.

RESULTS

CNS cancer was associated with module manufacturing operations at two facilities. Module manufacturing is a process that begins with production of ceramic substrates followed by attachment of completed semiconductor chips and metal-containing circuitry resulting in a high performing electronic device. Positive associations with the highest tertile of estimated cumulative exposure were found for several chemicals, including 2-butoxyethanol, cyclohexanone, ortho-dichlorobenzene, cadmium, molybdenum, trichloroethylene and vinyl chloride.

CONCLUSIONS

Results suggested positive associations between CNS cancer and specific operations and chemicals experienced in the semiconductor and electronic module manufacturing industry. However, lack of external support for these findings precludes a causal interpretation, and the observed associations may have been due to chance.

Brain cancer cluster investigation around a factory emitting dichloromethane

Background

The health risks associated with dichloromethane (DCM) for the general population living near industrial activities have not yet been quantified, primarily due to lack of epidemiological datasets. In the absence of such human data, we undertook a cancer cluster investigation in Cyprus around a historically using DCM plant producing shoe soles that were globally exported. We designed the methodology to investigate the possible existence of a cancer cluster in the area around the factory (point zero) and within a radius of 500 meters.

Methods

A retrospective comparative population study was designed using a group of cancer patients living or working in the chosen geographical area around the factory.

Results

Mean stack emissions of DCM of 88 mg/Nm3 and flow rates of 850 g/h exceeded the permissible DCM limits established for industrial zones. Brain and central nervous system (CNS) cancer incidence rates showed significant (P < 0.001) increase in the study area around the plant when compared with those observed in other areas of Cyprus. Calculated standardized incidence ratios for brain/CNS after adjusting for the age at diagnosis ranged from 11.3-25.7 [mean 6.5 (3.02 : 12.3)] for the study area.

Conclusions

We showed the association between chronic, unintentional DCM exposures and brain/CNS cancer cases for the general population located in a residential area being in close proximity with a plant historically emitting DCM.

Occupational solvent exposure and risk of glioma in the INTEROCC study

Background:

The aetiology of glioma remains largely unknown. Occupational solvent exposure has been suggested as a putative cause of glioma, but past studies have been inconsistent. We examined the association between a range of solvents and glioma risk within the INTEROCC project, a study of brain tumours and occupational exposures based on data from seven national case–control studies conducted in the framework of the INTERPHONE study. We also investigated associations according to tumour grade.

Methods:

Data from the seven countries were standardised and then combined into one aggregate data set. Pooled odds ratios (ORs) were estimated for adjusted models that included sex, age, country–region of residence and level of educational attainment. Exposures to any solvent or 11 specific solvents or subgroups were assessed using a modified version of the FINJEM job exposure matrix (JEM) specifically developed for the study, called INTEROCC-JEM.

Results:

Analysis included 2000 glioma cases and 5565 controls. For glioma and ever/never exposure to any solvent, the OR was 0.91 (95% confidence interval: 0.74–1.11). All ORs were <1.0 for specific solvents/subgroups. There were no increases in risk according to high or low grade of tumour.

Conclusions:

The results of this study show no consistent associations for any solvent exposures overall or by grade of tumour.

Occupational exposure to organic solvents: a risk factor for pulmonary veno-occlusive disease

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary hypertension characterised by predominant remodelling of pulmonary venules. Bi-allelic mutations in the eukaryotic translation initiation factor 2α kinase 4 (EIF2AK4) gene were recently described as the major cause of heritable PVOD, but risk factors associated with PVOD remain poorly understood. Occupational exposures have been proposed as a potential risk factor for PVOD, but epidemiological studies are lacking.

A case–control study was conducted in consecutive PVOD (cases, n=33) and pulmonary arterial hypertension patients (controls, n=65). Occupational exposure was evaluated via questionnaire interview with blinded assessments using an expert consensus approach and a job exposure matrix (JEM).

Using the expert consensus approach, PVOD was significantly associated with occupational exposure to organic solvents (adjusted OR 12.8, 95% CI 2.7–60.8), with trichloroethylene being the main agent implicated (adjusted OR 8.2, 95% CI 1.4–49.4). JEM analysis independently confirmed the association between PVOD and trichloroethylene exposure. Absence of significant trichloroethylene exposure was associated with a younger age of disease (54.8±21.4 years, p=0.037) and a high prevalence of harbouring bi-allelic EIF2AK4 mutations (41.7% versus 0%, p=0.015).

Occupational exposure to organic solvents may represent a novel risk factor for PVOD. Genetic background and environmental exposure appear to influence the phenotypic expression of the disease.

The epidemiology of glioma in adults: a "state of the science" review

Gliomas are the most common primary intracranial tumor, representing 81% of malignant brain tumors. Although relatively rare, they cause significant mortality and morbidity. Glioblastoma, the most common glioma histology (∼45% of all gliomas), has a 5-year relative survival of ∼5%. A small portion of these tumors are caused by Mendelian disorders, including neurofibromatosis, tuberous sclerosis, and Li-Fraumeni syndrome. Genomic analyses of glioma have also produced new evidence about risk and prognosis. Recently discovered biomarkers that indicate improved survival include O⁶-methylguanine-DNA methyltransferase methylation, isocitrate dehydrogenase mutation, and a glioma cytosine-phosphate-guanine island methylator phenotype. Genome-wide association studies have identified heritable risk alleles within 7 genes that are associated with increased risk of glioma. Many risk factors have been examined as potential contributors to glioma risk. Most significantly, these include an increase in risk by exposure to ionizing radiation and a decrease in risk by history of allergies or atopic disease(s). The potential influence of occupational exposures and cellular phones has also been examined, with inconclusive results. We provide a “state of the science” review of current research into causes and risk factors for gliomas in adults.

Does occupational exposure to solvents and pesticides in association with glutathione S-transferase A1, M1, P1, and T1 polymorphisms increase the risk of bladder cancer? The Belgrade case-control study

OBJECTIVE

We investigated the role of the glutathione S-transferase A1, M1, P1 and T1 gene polymorphisms and potential effect modification by occupational exposure to different chemicals in Serbian bladder cancer male patients.

PATIENTS AND METHODS

A hospital-based case-control study of bladder cancer in men comprised 143 histologically confirmed cases and 114 age-matched male controls. Deletion polymorphism of glutathione S-transferase M1 and T1 was identified by polymerase chain reaction method. Single nucleotide polymorphism of glutathione S-transferase A1 and P1 was identified by restriction fragment length polymorphism method. As a measure of effect size, odds ratio (OR) with corresponding 95% confidence interval (95%CI) was calculated.

RESULTS

The glutathione S-transferase A1, T1 and P1 genotypes did not contribute independently toward the risk of bladder cancer, while the glutathione S-transferase M1-null genotype was overrepresented among cases (OR = 2.1, 95% CI = 1.1-4.2, p = 0.032). The most pronounced effect regarding occupational exposure to solvents and glutathione S-transferase genotype on bladder cancer risk was observed for the low activity glutathione S-transferase A1 genotype (OR = 9.2, 95% CI = 2.4-34.7, p = 0.001). The glutathione S-transferase M1-null genotype also enhanced the risk of bladder cancer among subjects exposed to solvents (OR = 6,5, 95% CI = 2.1-19.7, p = 0.001). The risk of bladder cancer development was 5.3-fold elevated among glutathione S-transferase T1-active patients exposed to solvents in comparison with glutathione S-transferase T1-active unexposed patients (95% CI = 1.9-15.1, p = 0.002). Moreover, men with glutathione S-transferase T1-active genotype exposed to pesticides exhibited 4.5 times higher risk in comparison with unexposed glutathione S-transferase T1-active subjects (95% CI = 0.9-22.5, p = 0.067).

CONCLUSION

Null or low-activity genotypes of the glutathione S-transferase A1, T1, and P1 did not contribute independently towards the risk of bladder cancer in males. However, in association with occupational exposure, low activity glutathione S-transferase A1 and glutathione S-transferase M1-null as well as glutathione S-transferase T1-active genotypes increase individual susceptibility to bladder cancer.

Human health effects of tetrachloroethylene: key findings and scientific issues

BACKGROUND

The U.S. Environmental Protection Agency (EPA) completed a toxicological review of tetrachloroethylene (perchloroethylene, PCE) in February 2012 in support of the Integrated Risk Information System (IRIS).

OBJECTIVES

We reviewed key findings and scientific issues regarding the human health effects of PCE described in the U.S. EPA's Toxicological Review of Tetrachloroethylene (Perchloroethylene).

METHODS

The updated assessment of PCE synthesized and characterized a substantial database of epidemiological, experimental animal, and mechanistic studies. Key scientific issues were addressed through modeling of PCE toxicokinetics, synthesis of evidence from neurological studies, and analyses of toxicokinetic, mechanistic, and other factors (tumor latency, severity, and background rate) in interpreting experimental animal cancer findings. Considerations in evaluating epidemiological studies included the quality (e.g., specificity) of the exposure assessment methods and other essential design features, and the potential for alternative explanations for observed associations (e.g., bias or confounding).

DISCUSSION

Toxicokinetic modeling aided in characterizing the complex metabolism and multiple metabolites that contribute to PCE toxicity. The exposure assessment approach-a key evaluation factor for epidemiological studies of bladder cancer, non-Hodgkin lymphoma, and multiple myeloma-provided suggestive evidence of carcinogenicity. Bioassay data provided conclusive evidence of carcinogenicity in experimental animals. Neurotoxicity was identified as a sensitive noncancer health effect, occurring at low exposures: a conclusion supported by multiple studies. Evidence was integrated from human, experimental animal, and mechanistic data sets in assessing adverse health effects of PCE.

CONCLUSIONS

PCE is likely to be carcinogenic to humans. Neurotoxicity is a sensitive adverse health effect of PCE.

Malignant tumours of the central nervous system in Kazakhstan--incidence trends from 2004-2011

In the article were observed the epidemiological aspects of malignant tumors of the central nervous system (MT CNS) in Kazakhstan in a retrospective study for the years 2004-2011. The material of the study was consolidated accounting data of oncology centers on patients with MT CNS (C70-72) with first time established diagnosis. Calculated were crude, age, standardized (world standard), aligned and predicted incidence of MT CNS among both male and female populations. It was found that over the studied period, there were 4,604 cases of MT CNS. The average annual crude incidence rate of MT CNS in total population was 3.7±0.10/0000. Trends in aligned incidence rates in the whole country had a tendency to increase (T=+0.9%). Defined levels of morbidity MT CNS in the whole population in different regions of Kazakhstan: low up to 2.870/0000, the average from 2.87 to 4.450/0000 and high from 4.450/0000 and above on the basis of which was given the space-time estimate. Age and sex differences in MT CNS incidence were also clearly established.