Malignant lymphomas and leukemias, and exposures in the wood industry: an industry-based case-referent study

Wood dust and risk of leukemia: Systematic review and meta-analysis

OBJECTIVES

This study aimed to perform a systematic review and meta-analysis to investigate the relationship between wood dust exposure and leukemia. The objectives included synthesizing available evidence, assessing its quality, identifying potential sources of heterogeneity, and drawing conclusions regarding the association between wood dust and leukemia.

METHODS

A systematic literature search was conducted to identify studies meeting that report on the association between wood dust and leukemia. The Joanna Briggs Institute Critical Appraisal tools were employed to ensure robust quality assessment. Meta-analysis, using random-effects models, synthesized evidence from studies with low risk of bias. Overall odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Subgroup analyses explored potential sources of heterogeneity.

RESULTS

The meta-analysis included a comprehensive review of various study types, encompassing 7 studies that examined the association between wood dust exposure and leukemia risk. The analysis revealed a statistically significant positive association, with an overall odds ratio (OR) of 1.56 (95% CI: 1.15-2.12). This indicates that individuals exposed to wood dust are 1.56 times more likely to develop leukemia compared to those not exposed, with the 95% confidence interval ranging from 1.15 to 2.12, highlighting a substantial risk elevation across different study designs. Quality assessment using The Joanna Briggs Institute Critical Appraisal tools demonstrated a low risk of bias across all included studies, enhancing the credibility of the observed association. Subgroup analyses were conducted to explore potential sources of heterogeneity within the studies. Notably, subgroup analysis based on the year of the study revealed significant differences, as indicated by an I^2 value of 87%. The robustness of these results underscores the importance of addressing wood dust exposure as an occupational hazard, particularly in industries related to woodworking and forestry.

CONCLUSION

This meta-analysis provides robust evidence supporting an increased risk of leukemia associated with wood dust exposure implying proactive measures in people exposed to dust.

Childhood cancer risk in offspring of parents occupationally exposed to dusts: A register-based nested case-control study from Sweden of 5 decades

BACKGROUND

Some largely inconsistent associations between parental occupational dust exposure and childhood cancer have been reported, with maternal exposures inadequately studied. The authors examined whether maternal or paternal occupational exposure to animal, wood, textile, or paper dust around a child's birth was associated with an increased risk of childhood cancer, both overall and by type (leukemias, lymphomas, central nervous system tumors, and other cancers).

METHODS

In this nationwide, register-based, case-control study, children who were diagnosed with cancer from 1960 to 2015 were compared with up to 25 matched controls regarding maternal and paternal occupational dust exposure (9653 cases in maternal analyses and 12,521 cases in paternal analyses). Exposures were assessed using a job-exposure matrix and occupational information from census and register data. By using conditional logistic regression models, adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated.

RESULTS

Neither maternal nor paternal occupational exposure to animal, wood, textile, or paper dust was associated with childhood cancer overall, leukemias, or central nervous system tumors. Maternal, but not paternal, wood dust exposure was associated with an increased risk of lymphoma (OR, 1.42; 95% CI, 1.10-1.84), particularly non-Hodgkin lymphoma (OR, 2.03; 95% CI, 1.21-3.40).

CONCLUSIONS

The current study did not confirm the associations reported previously but is the first to suggest a link between maternal occupational exposure to wood dust around pregnancy and lymphoma in the offspring.

Formaldehyde exposure and leukemia risk: a comprehensive review and network-based toxicogenomic approach

Formaldehyde is a widely used but highly reactive and toxic chemical. The International Agency for Research on Cancer classifies formaldehyde as a Group 1 carcinogen, based on nasopharyngeal cancer and leukemia studies. However, the correlation between formaldehyde exposure and leukemia incidence is a controversial issue. To understand the association between formaldehyde exposure and leukemia, we explored biological networks based on formaldehyde-related genes retrieved from public and commercial databases. Through the literature-based network approach, we summarized qualitative associations between formaldehyde exposure and leukemia. Our results indicate that oxidative stress-mediated genetic changes induced by formaldehyde could disturb the hematopoietic system, possibly leading to leukemia. Furthermore, we suggested major genes that are thought to be affected by formaldehyde exposure and associated with leukemia development. Our suggestions can be used to complement experimental data for understanding and identifying the leukemogenic mechanism of formaldehyde.

Occupational exposure to organic dust and risk of lymphoma subtypes in the EPILYMPH case-control study

Objectives This study aimed to estimate the risk of lymphoma and its major subtypes in relation to occupational exposure to specific organic dusts. Methods We explored the association in 1853 cases and 1997 controls who participated in the EpiLymph case-control study, conducted in six European countries in 1998-2004. Based on expert assessment of lifetime occupational exposures, we calculated the risk of the major lymphoma subtypes associated with exposure to six specific organic dusts, namely, flour, hardwood, softwood, natural textile, synthetic textile, and leather, and two generic (any types) groups: wood and textile dusts. Risk was predicted with unconditional regression modeling, adjusted by age, gender, study center, and education. Results We observed a 2.1-fold increase in risk of follicular lymphoma associated with ever exposure to leather dust [95% confidence interval (CI) 1.01-4.20]. After excluding subjects who ever worked in a farm or had ever been exposed to solvents, risk of B-cell lymphoma was elevated in relation to ever exposure to leather dust [odd ratio (OR) 2.2, 95% CI 1.00-4.78], but it was not supported by increasing trends with the exposure metrics. Risk of Hodgkin lymphoma was elevated (OR 2.0, 95% CI 0.95-4.30) for exposure to textile dust, with consistent upward trends by cumulative exposure and three independent exposure metrics combined (P=0.023, and P=0.0068, respectively). Conclusions Future, larger studies might provide further insights into the nature of the association we observed between exposure to textile dust and risk of Hodgkin lymphoma.

Occupational exposure to formaldehyde and risk of non hodgkin lymphoma: a meta-analysis

BACKGROUND

Formaldehyde, a widely used chemical, is considered a human carcinogen. We report the results of a meta-analyses of studies on the relationship between occupational exposure to formaldehyde and risk of non-Hodgkin lymphoma (NHL).

METHODS

We performed a systematic review and meta-analysis according to international guidelines and we identified 12 reports of occupational populations exposed to formaldehyde. We evaluated inter-study heterogeneity and we applied a random effects model. We conducted a cumulative meta-analysis and a meta-analysis according to estimated average exposure of each study population.

RESULTS

The meta-analysis resulted in a summary relative risk (RR) for NHL of 0.93 (95% confidence interval 0.83-1.04). The cumulative meta-analysis suggests that higher RRs were detected in studies published before 1986, while studies available after 1986 did not show an association. No differences were found between different levels of occupational exposure. Conclusions Notwithstanding some limitations, the results of this meta-analysis do not support the hypothesis of an association between occupational exposure to formaldehyde and risk of NHL.

Does formaldehyde have a causal association with nasopharyngeal cancer and leukaemia?

BACKGROUND

The South Korean criteria for occupational diseases were amended in July 2013. These criteria included formaldehyde as a newly defined occupational carcinogen, based on cases of "leukemia or nasopharyngeal cancer caused by formaldehyde exposure". This inclusion was based on the Internal Agency for Research on Cancer classification, which classified formaldehyde as definite human carcinogen for nasopharyngeal cancer in 2004 and leukemia in 2012.

METHODS

We reviewed reports regarding the causal relationship between occupational exposure to formaldehyde in Korea and the development of these cancers, in order to determine whether these cases were work-related.

RESULTS

Previous reports regarding excess mortality from nasopharyngeal cancer caused by formaldehyde exposure seemed to be influenced by excess mortality from a single plant. The recent meta-risk for nasopharyngeal cancer was significantly increased in case-control studies, but was null for cohort studies (excluding unexplained clusters of nasopharyngeal cancers). A recent analysis of the largest industrial cohort revealed elevated risks of both leukemia and Hodgkin lymphoma at the peak formaldehyde exposure, and both cancers exhibited significant dose-response relationships. A nested case-control study of embalmers revealed that mortality from myeloid leukemia increased significantly with increasing numbers of embalms and with increasing formaldehyde exposure. The recent meta-risks for all leukemia and myeloid leukemia increased significantly. In South Korea, a few cases were considered occupational cancers as a result of mixed exposures to various chemicals (e.g., benzene), although no cases were compensated for formaldehyde exposure. The peak formaldehyde exposure levels in Korea were 2.70-14.8 ppm in a small number of specialized studies, which considered anatomy students, endoscopy employees who handled biopsy specimens, and manufacturing workers who were exposed to high temperatures.

CONCLUSION

Additional evidence is needed to confirm the relationship between formaldehyde exposure and nasopharyngeal cancer. All lymphohematopoietic malignancies, including leukemia, should be considered in cases with occupational formaldehyde exposure.

Assessment of lipid peroxidation and p53 as a biomarker of carcinogenesis among workers exposed to formaldehyde in the cosmetic industry

Despite the wide use of cosmetic products, they exert a number of health effects on tissues ranging from irritation to cancer. Our study aimed at assessing the effect of formaldehyde on lipid peroxidation and verifying the susceptibility to carcinogenesis using p53 as a biomarker among workers exposed to formaldehyde in cosmetic industry. Our entire exposed group (n = 40) and the controls (n = 20) were subjected to estimation of formate in urine, serum malondialdehyde (MDA), and p53. Also, complete blood picture, liver, and kidney function tests were carried out. The study revealed significant increase in the levels of formate, MDA, and p53 in the exposed group compared with their control group. Our results showed that workers in cosmetic industry had significant exposure to formaldehyde. Furthermore, the study pointed to the negative impact of formaldehyde as a cause of oxidative stress and suspicious carcinogen.

Occupational exposure to pentachlorophenol causing lymphoma and hematopoietic malignancy for two generations

Objective:

Pentachlorophenol (PCP) is characterized as likely carcinogen of lymphoma and hematopoietic neoplasm. But the carcinogenicity to human was uncertain based on population studies. A systematic review was conducted to explore two kinds of associations, one was between the workers exposed to PCP with lymphoma and hematopoietic neoplasm, the other was between childhood lymphoma and leukemia with their parents exposed to PCP.

Methods:

Systematic search for epidemiologic studies was carried out and the data were collected from MEDLINE database and from the reference lists of relevant studies. Data were extracted from 20 included studies published between 1986 and 2012.

Results:

The meta-analysis suggested a significant association between lymphoma and workers’ occupational exposing to PCP, for the pooled odds ratio = 2.57 (95% confidence interval (CI) = 1.52–4.35). The subgroup analysis indicated significant association for non-Hodgkin’s lymphoma, but not for Hodgkin’s disease. The cohort studies also showed comparatively higher relative risk (RR) and standardized mortality ratio (SMR). Two of the cohort studies found increased RR as the cumulative exposure time added. Another cohort study discovered that the white males had significantly elevated non-Hodgkin’s lymphoma mortality (SMR = 1.98, 95% CI = 1.15–3.17), and males of other races had increased leukemia mortality (SMR = 4.57, 95% CI = 1.25–11.7). For the relationship of childhood leukemia and parental exposure to PCP, three published studies suggested an increased risk of childhood leukemia because of their parental exposure to PCP at the preconception period.

Conclusion:

Our review provided the evidence that occupational exposure of workers to PCP might increase the risk of lymphoma and hematopoietic neoplasm in themselves and in their children.

Critical review and synthesis of the epidemiologic evidence on formaldehyde exposure and risk of leukemia and other lymphohematopoietic malignancies

Purpose

Recent epidemiologic studies indicate elevated risks for some lymphohematopoietic malignancies (LHM) related to formaldehyde exposure. We performed a systematic review of literature to assess the strength and consistency of associations.

Methods

We summarized published literature in the PubMed database of the National Library of Medicine during 1966–2012. Literature was categorized according to study design and population: industrial cohort studies, professional cohort studies, and population-based case–control studies.

Results

Findings from occupational cohort and population-based case–control studies were very inconsistent for LHM, including myeloid leukemia. Apart from some isolated exceptions, relative risks were close to the null, and there was little evidence for dose–response relations for any of the LHM.

Conclusions

At present, there is no consistent or strong epidemiologic evidence that formaldehyde is causally related to any of the LHM. The absence of established toxicological mechanisms further weakens any arguments for causation. To be informative, future epidemiologic research should improve on formaldehyde exposure assessment and apply modern diagnostic schemes for specific LHM.

Is exposure to formaldehyde in air causally associated with leukemia?--A hypothesis-based weight-of-evidence analysis

Recent scientific debate has focused on the potential for inhaled formaldehyde to cause lymphohematopoietic cancers, particularly leukemias, in humans. The concern stems from certain epidemiology studies reporting an association, although particulars of endpoints and dosimetry are inconsistent across studies and several other studies show no such effects. Animal studies generally report neither hematotoxicity nor leukemia associated with formaldehyde inhalation, and hematotoxicity studies in humans are inconsistent. Formaldehyde's reactivity has been thought to preclude systemic exposure following inhalation, and its apparent inability to reach and affect the target tissues attacked by known leukemogens has, heretofore, led to skepticism regarding its potential to cause human lymphohematopoietic cancers. Recently, however, potential modes of action for formaldehyde leukemogenesis have been hypothesized, and it has been suggested that formaldehyde be identified as a known human leukemogen. In this article, we apply our hypothesis-based weight-of-evidence (HBWoE) approach to evaluate the large body of evidence regarding formaldehyde and leukemogenesis, attending to how human, animal, and mode-of-action results inform one another. We trace the logic of inference within and across all studies, and articulate how one could account for the suite of available observations under the various proposed hypotheses. Upon comparison of alternative proposals regarding what causal processes may have led to the array of observations as we see them, we conclude that the case for a causal association is weak and strains biological plausibility. Instead, apparent association between formaldehyde inhalation and leukemia in some human studies is better interpreted as due to chance or confounding.

Formaldehyde and leukemia: an updated meta-analysis and evaluation of bias

OBJECTIVE

Formaldehyde exposures are common, and data linking these exposures to leukemia have been mixed and controversial. The objective of this analysis is to review the current epidemiologic literature on formaldehyde and leukemia.

METHODS

We performed an updated meta-analysis focusing on high-exposure groups and myeloid leukemia and included two large recent studies: one involving >25,000 workers in US formaldehyde industries and the other involving a cohort of >13,000 funeral directors and embalmers.

RESULTS

Formaldehyde was associated with increased risks of leukemia (relative risk = 1.53; 95% confidence interval = 1.11 to 2.21; P = 0.005; 14 studies), specifically myeloid leukemia (relative risk = 2.47; 95% confidence interval = 1.42 to 4.27; P = 0.001; 4 studies).

CONCLUSION

These findings provide evidence of increased myeloid leukemia risk with exposure to formaldehyde.

Formaldehyde and leukemia: epidemiology, potential mechanisms, and implications for risk assessment

Formaldehyde is widely used in the United States and other countries. Occupational and environmental exposures to formaldehyde may be associated with an increased risk of leukemia in exposed individuals. However, risk assessment of formaldehyde and leukemia has been challenging due to inconsistencies in human and animal studies and the lack of a known mechanism for leukemia induction. Here, we provide a summary of the symposium at the Environmental Mutagen Society Meeting in 2008, which focused on the epidemiology of formaldehyde and leukemia, potential mechanisms, and implication for risk assessment, with emphasis on future directions in multidisciplinary formaldehyde research. Updated results of two of the three largest industrial cohort studies of formaldehyde-exposed workers have shown positive associations with leukemia, particularly myeloid leukemia, and a recent meta-analysis of studies to date supports this association. Recent mechanistic studies have shown the formation of formaldehyde-induced DNA adducts and characterized the essential DNA repair pathways that mitigate formaldehyde toxicity. The implications of the updated findings for the design of future studies to more effectively assess the risk of leukemia arising from formaldehyde exposure were discussed and specific recommendations were made. A toxicogenomic approach in experimental models and human exposure studies, together with the measurement of biomarkers of internal exposure, such as formaldehyde-DNA and protein adducts, should prove fruitful. It was recognized that increased communication among scientists who perform epidemiology, toxicology, biology, and risk assessment could enhance the design of future studies, which could ultimately reduce uncertainty in the risk assessment of formaldehyde and leukemia.

Epidemiological studies of formaldehyde exposure and risk of leukemia and nasopharyngeal cancer: a meta-analysis

The authors conducted meta-analyses of the epidemiological literature on formaldehyde exposure and risk of leukemia and risk of nasopharyngeal cancer. The authors abstracted study results and confounder information from cohort and case-control studies, and used quantile plots and regression models to evaluate heterogeneity and possible publication bias. No evidence of serious heterogeneity or publication bias was seen. For leukemias, the summary relative risk (RR) was 1.05 (95% confidence interval [CI]: 0.93, 1.20) for cohort studies, and the summary odds ratio (OR) was 0.99 (95% CI: 0.71, 1.37) for case-control studies. Based on cohort and case-control studies, no significant differences were seen by leukemia subtype, job type, publication period, or region. Summary estimates for nasopharyngeal cancers were not elevated after excluding a single plant with an unexplained cluster of nasopharyngeal cancers (cohort RR = 0.72, 95% CI: 0.40, 1.28). The summary estimate was increased for case-control studies overall, but the summary OR for smoking-adjusted studies was 1.10 (95% CI: 0.80, 1.50). Previous meta-analyses showed elevated summary estimates for leukemia; however, these analyses included results from proportionate mortality studies and did not explore other factors that could influence or confound results. By limiting analyses to stronger case-control and cohort study designs, considering the effects of smoking and ignoring anomalous results from a single plant, our meta-analyses provide little support for a causal relationship between formaldehyde exposure and leukemia or nasopharyngeal cancer.

Occupational exposure to solvents and risk of non-Hodgkin lymphoma in Connecticut women

A population-based case-control study involving 601 incident cases of non-Hodgkin lymphoma (NHL) and 717 controls was conducted in 1996-2000 among Connecticut women to examine associations with exposure to organic solvents. A job-exposure matrix was used to assess occupational exposures. Increased risk of NHL was associated with occupational exposure to chlorinated solvents (odds ratio (OR) = 1.4, 95% confidence interval (CI): 1.1, 1.8) and carbon tetrachloride (OR = 2.3, 95% CI: 1.3, 4.0). Those ever exposed to any organic solvent in work settings had a borderline increased risk of NHL (OR = 1.3, 95% CI: 1.0, 1.6); moreover, a significantly increased risk was observed for those with average probability of exposure to any organic solvent at medium-high level (OR = 1.5, 95% CI: 1.1, 1.9). A borderline increased risk was also found for ever exposure to formaldehyde (OR = 1.3, 95% CI: 1.0, 1.7) in work settings. Risk of NHL increased with increasing average intensity (P = 0.01), average probability (P < 0.01), cumulative intensity (P = 0.01), and cumulative probability (P < 0.01) level of organic solvent and with average probability level (P = 0.02) and cumulative intensity level of chlorinated solvent (P = 0.02). Analyses by NHL subtype showed a risk pattern for diffuse large B-cell lymphoma similar to that for overall NHL, with stronger evidence of an association with benzene exposure. Results suggest an increased risk of NHL associated with occupational exposure to organic solvents for women.

The non-Hodgkin lymphomas: a review of the epidemiologic literature

The non-Hodgkin lymphomas (NHL) are a heterogeneous group of B-cell and T-cell neoplasms that arise primarily in the lymph nodes. NHL incidence rates in the US doubled between about 1970 and 1990, and stabilized during the 1990s. NHL accounts for approximately 3.4% of cancer deaths in the US. Although some of the observed patterns in NHL have been related to HIV/AIDS, these conditions cannot fully explain the magnitude of the changes; neither do changes in classification systems nor improved diagnostic capabilities. Studies of occupational and environmental exposures (e.g., pesticides, solvents) have produced no consistent pattern of significant positive associations. Inverse associations with ultraviolet radiation exposure and alcohol and fish intake, and positive associations with meat and saturated fat intake have been reported in several studies; additional studies are needed to confirm or refute these associations. Family history of NHL or other hematolympho-proliferative cancers and personal history of several autoimmune disorders are associated with increased risk of NHL, but are not likely to account for a large proportion of cases. HIV and other infectious agents, such as human herpesvirus 8 and Epstein-Barr, appear to be associated with differing types of NHL, such as some B-cell lymphomas. Future epidemiologic studies should evaluate associations by NHL type, enhance exposure information collected, and elucidate factors that may identify susceptible (or resistant) subpopulations because of genetic, immunologic or other characteristics. The extent to which the etiology of NHL types may differ is important to resolve in ongoing and future studies.

Non-Hodgkin's lymphoma risk derived from exposure to organic solvents: a review of epidemiologic studies

The rate of non-Hodgkin's lymphomas (NHL) has increased around the world during the last decades. Apart from the role of the human immunodeficiency virus (HIV) infection in the development of NHL, exposure to chemical agents like phenoxyacetic pesticides, hair dyes, metal fumes and organic solvents are suspected to be involved. The present review evaluates the results of studies that directly or indirectly searched for an association between solvent exposure and NHL. The selected studies comprised those published from 1979 to 1997, designed to investigate risk factors for NHL, whether specifically looking for solvent exposure or for general risks in which solvent exposure could be included. In 25 of the 45 reviewed studies (55.5%), fifty-four statistically significant associations between NHL and solvent exposure related occupations or industries were reported. Statistical significance was more frequently shown in studies where solvent exposure was more accurately defined. In eighteen of such studies, 13 (72.2%) defined or suggested organic solvents as possible risk factors for NHL.

Respiratory symptoms and pulmonary function among wood dust-exposed joss stick workers

Health hazards associated with wood dust exposure have been investigated in various industries. This study surveyed wood dust exposure levels and pulmonary effects among joss stick workers. Greater dust concentrations, as measured by six-stage cascade impactors, were observed in work areas where joss sticks were produced and incense was mixed than in other work areas. Total dust concentrations for these two high dust activities ranged from 9.9 to 42.7 mg/m3, and respirable proportions were between 2.0% and 54.6%. Higher dust levels were observed for dry joss stick production methods than for wet production methods. Dust levels for all other performance areas were lower than the permissible exposure level of 10 mg/m3. Although symptoms of cough and phlegm were higher in smoking workers than in nonsmoking workers, the prevalence of respiratory symptoms for exposed workers was not significantly higher than for the controls. The prevalence of pulmonary function deficits and the values of FEF25% and FEF75% in the exposed workers were significantly worse than those in the controls. But no difference was found between the male controls and the male exposed workers, the high-exposure group. Respiratory symptoms and pulmonary function also did not show a dose-response trend with the exposure levels estimated by correlation with worker job titles and duration of employment. No suspected case of pneumoconiosis was found from the chest radiographs. These results suggest that wood dust exposure in the joss stick industries might not lead to significant pulmonary damage.