Occupational exposure to solvents and risk of breast cancer

Evaluation of mortality among Marines, Navy personnel, and civilian workers exposed to contaminated drinking water at USMC base Camp Lejeune: a cohort study

BACKGROUND

Drinking water at U.S. Marine Corps Base (MCB) Camp Lejeune, North Carolina was contaminated with trichloroethylene and other industrial solvents from 1953 to 1985.

METHODS

A cohort mortality study was conducted of Marines/Navy personnel who, between 1975 and 1985, began service and were stationed at Camp Lejeune (N = 159,128) or MCB Camp Pendleton, California (N = 168,406), and civilian workers employed at Camp Lejeune (N = 7,332) or Camp Pendleton (N = 6,677) between October 1972 and December 1985. Camp Pendleton's drinking water was not contaminated with industrial solvents. Mortality follow-up was between 1979 and 2018. Proportional hazards regression was used to calculate adjusted hazard ratios (aHRs) comparing mortality rates between Camp Lejeune and Camp Pendleton cohorts. The ratio of upper and lower 95% confidence interval (CI) limits, or CIR, was used to evaluate the precision of aHRs. The study focused on underlying causes of death with aHRs ≥ 1.20 and CIRs ≤ 3.

RESULTS

Deaths among Camp Lejeune and Camp Pendleton Marines/Navy personnel totaled 19,250 and 21,134, respectively. Deaths among Camp Lejeune and Camp Pendleton civilian workers totaled 3,055 and 3,280, respectively. Compared to Camp Pendleton Marines/Navy personnel, Camp Lejeune had aHRs ≥ 1.20 with CIRs ≤ 3 for cancers of the kidney (aHR = 1.21, 95% CI: 0.95, 1.54), esophagus (aHR = 1.24, 95% CI: 1.00, 1.54) and female breast (aHR = 1.20, 95% CI: 0.73, 1.98). Causes of death with aHRs ≥ 1.20 and CIR > 3, included Parkinson disease, myelodysplastic syndrome and cancers of the testes, cervix and ovary. Compared to Camp Pendleton civilian workers, Camp Lejeune had aHRs ≥ 1.20 with CIRs ≤ 3 for chronic kidney disease (aHR = 1.88, 95% CI: 1.13, 3.11) and Parkinson disease (aHR = 1.21, 95% CI: 0.72, 2.04). Female breast cancer had an aHR of 1.19 (95% CI: 0.76, 1.88), and aHRs ≥ 1.20 with CIRs > 3 were observed for kidney and pharyngeal cancers, melanoma, Hodgkin lymphoma, and chronic myeloid leukemia. Quantitative bias analyses indicated that confounding due to smoking and alcohol consumption would not appreciably impact the findings.

CONCLUSION

Marines/Navy personnel and civilian workers likely exposed to contaminated drinking water at Camp Lejeune had increased hazard ratios for several causes of death compared to Camp Pendleton.

Exposure to outdoor ambient air toxics and risk of breast cancer: The multiethnic cohort

BACKGROUND

A growing literature has reported associations between traffic-related air pollution and breast cancer, however there are fewer investigations into specific ambient agents and any putative risk of breast cancer development, particularly studies occurring in populations residing in higher pollution areas such as Los Angeles.

OBJECTIVES

To estimate breast cancer risks related to ambient air toxics exposure at residential addresses.

METHODS

We examined the relationships between ambient air toxics and breast cancer risk in the Multiethnic Cohort among 48,665 California female participants followed for cancer from 2003 through 2013. We obtained exposure data on chemicals acting as endocrine disruptors or mammary gland carcinogens from the National-Scale Air Toxics Assessment. Cox proportional hazards models were used to estimate breast cancer risk per one interquartile range (IQR) increase in air toxics exposure lagged by 5-years. Stratified analyses were conducted by race, ethnicity, and hormone receptor types.

RESULTS

Among all women, increased risks of invasive breast cancer were observed with toxicants related to industries [1,1,2,2-tetrachloroethane (hazard ratio [HR] = 4.22, 95% confidence interval [95% CI] 3.18-5.60), ethylene dichloride (HR = 2.81, 95% CI 2.20-3.59), and vinyl chloride (HR = 2.27, 95% CI 1.81, 2.85); these 3 agents were correlated (r2 = 0.45-0.77)]. Agents related to gasoline production or combustion were related to increased breast cancer risk [benzene (HR = 1.32, 95% CI 1.24, 1.41), ethylbenzene (HR = 1.20, 95% CI 1.13-1.28), toluene (HR = 1.29, 95% CI 1.20-1.38), naphthalene (HR = 1.11, 95% CI 1.02-2.22), acrolein (HR = 2.26, 95% CI 1.92, 2.65)]. Higher hazard ratios were observed in African Americans and Whites compared to other racial and ethnic groups (p-heterogeneity <0.05 for traffic-related air toxics, acrolein, and vinyl acetate).

CONCLUSIONS

Our findings suggest that specific toxic air pollutants may be associated with increase breast cancer risk.

Reproductive outcomes among female health care workers

OBJECTIVE

Occupational exposures may be associated with reproductive health and pregnancy outcomes. This study investigated the association between occupational exposures and reproductive health, pregnancy outcomes, and the lactation period among hospital staff.

MATERIALS AND METHODS

Seven hundred thirty-three female healthcare workers from hospitals affiliated with the Tehran University of Medical Sciences were invited to participate in this cross-sectional study. The measurement method for fertility consequences was self-report. Demographic characteristics, occupational data, medical history, and reproductive history were collected via data collection form. Finally, reproductive outcomes were evaluated in different occupational hazard categories.

RESULT

Chemical exposures (solvents) were a risk factor for stillbirth. Prolonged working hours were associated with spontaneous abortion and breastfeeding periods. Shift workers did not have a higher frequency of reproductive and pregnancy outcomes, but the breastfeeding period was significantly decreased in shift workers. Psychiatric disorders were associated with preterm labour, low birth weight, and stillbirth in sequence with nervousness, depression, and mood disturbance. Furthermore, depression affects the breastfeeding period. Moreover, we found a link between job titles and infertility. In addition, socioeconomic status was related to stillbirth and infertility.

CONCLUSION

The study revealed that chemical and ergonomic exposures have associations with some reproductive outcomes. We also conclude that shift work could adversely affect the breastfeeding period. So, implementing some organizational strategies to control adverse health effects of occupational hazards and modifying shift work and working hours for nursing mothers is recommended.

The association between the incidence of postmenopausal breast cancer and occupational exposure to selected organic solvents, Montreal, Canada, 2008-2011

BACKGROUND

Breast cancer is the most diagnosed cancer among women and recognized risk factors explain 25%-47% of cases. Organic solvents are used widely in the workplace and exposure may increase the risk of developing breast cancer, yet there are insufficient data to confirm this hypothesis. We sought to determine whether past occupational exposures to selected organic solvents were associated with the incidence of invasive breast cancer in postmenopausal women in Montréal, Canada.

METHODS

From a population-based case-control study (2008-2011), using in-depth interviews we elicited information on risk factors and lifetime occupational histories. Industrial hygienists and chemists translated job descriptions into specific chemical and physical exposures. We assessed 11 individual solvents and four solvent groups. Unconditional logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) for metrics of past exposures to selected solvents. Exposure metrics included any previous exposure, average frequency in hours per week, duration in years, and average cumulative concentration weighted by hours per workweek exposed.

RESULTS

We enrolled 695 cases and 608 controls. We found increased ORs for average cumulative concentration of exposure to mononuclear aromatic hydrocarbons (OR: 1.52, 95% CI: 1.04, 2.28), chlorinated alkanes (OR: 2.42, 95% CI: 1.23, 5.68), toluene (OR: 1.59, 95% CI: 1.02, 2.59), and a group of organic solvents with reactive metabolites (OR: 1.53, 95% CI: 1.08, 2.24). Positive associations were found across all exposure metrics and were higher among women with estrogen-positive/progesterone-negative tumors.

CONCLUSION

Our findings suggest occupational exposure to certain organic solvents may increase the risk of incident postmenopausal breast cancer.

Cancer incidence among visual artists: 45 years of follow-up in four Nordic countries

INTRODUCTION

Professional visual artists constitute a heterogeneous vocational group, including, but not limited to painters, photographers, textile artists, and sculptors who may face exposure to workplace hazardous substances and lifestyle factors that may contribute to the development of selected cancers. The objective of this registry-based cohort study was to assess the cancer incidence among Nordic visual artists.

MATERIALS AND METHODS

This study is based on data from the Nordic Occupational Cancer (NOCCA) project that combines census data of 15 million people from all Nordic countries and cancer registries from 1961 to 2005. For the present study we selected a cohort of visual artists from Finland, Iceland, Norway, and Sweden. Standardized incidence ratio (SIR) analyses were conducted with the cancer incidence rates for the entire national study populations used as reference rates.

RESULTS

In male visual artists, there were statistically significant excesses in cancers of the tongue (SIR 2.91, 95% confidence interval 1.74-4.55), oral cavity (2.09, 1.26-3.27), pharynx (2.18, 1.45--3.15), testis (1.91, 1.11-3.05), renal pelvis (2.48, 1.42-4.03) and bladder (1.33, 1.14-1.55). The risk was significantly decreased for cancers of the lip (0.45, 0.18-0.93) and stomach (0.65, 0.50-0.84). In female visual artists, the only significantly increased risk was observed for breast cancer (1.29, 1.13-1.48) and the only significantly decreased risk for stomach cancer (0.43, 0.17-0.88). The incidence of lung cancer was close to the population average in both sexes.

CONCLUSIONS

The non-elevated incidence of lung cancer suggests a similar prevalence of smoking between visual artists and the general population, while the elevated risk of cancers of mouth and pharynx among male visual artists is suggestive of more widespread alcohol drinking. The excess risk of urogenital cancers might be associated with exposure to solvents.

Comparison of agreement in asthmagen exposure assessments between rule-based automatic algorithms and a job exposure matrix in healthcare workers in Australia and Bhutan

Background:

Assessment of occupational exposures is an integral component of population-based studies investigating the epidemiology of occupational diseases. However, all the available methods for exposure assessment have been developed, tested and used in high-income countries. Except for a few studies examining pesticide exposures, there is limited research on whether these methods are appropriate for assessing exposure in LMICs. The aim of this study is to compare a task-specific algorithm-based method (OccIDEAS) to a job-specific matrix method (OAsJEM) in the assessment of asthmagen exposures among healthcare workers in a high-income country and a low- and middle- income country (LMIC) to determine an appropriate assessment method for use in LMICs for future research.

Methods:

Data were obtained from a national cross-sectional survey of occupational asthmagens exposure in Australia and a cross-sectional survey of occupational chemical exposure among Bhutanese healthcare workers. Exposure was assessed using OccIDEAS and the OAsJEM. Prevalence of exposure to asthmagens and inter-rater agreement were calculated.

Results:

In Australia, the prevalence was higher for a majority of agents when assessed by OccIDEAS than by the OAsJEM (13 versus 3). OccIDEAS identified exposures to a greater number of agents (16 versus 7). The agreement as indicated by κ (Cohen’s Kappa coefficient) for six of the seven agents assessed was poor to fair (0.02 to 0.37). In Bhutan, the prevalence of exposure assessed by OccIDEAS was higher for four of the seven agents and κ was poor for all the four agents assessed (-0.06 to 0.13). The OAsJEM overestimated exposures to high-level disinfectants by assigning exposures to all participants from 10 (Bhutan) and 12 (Australia) ISCO-88 codes; whereas OccIDEAS assigned exposures to varying proportions of participants from these ISCO-codes.

Conclusion:

There was poor to fair agreement in the assessment of asthmagen exposure in healthcare workers between the two methods. The OAsJEM overestimated the prevalence of certain exposures. As compared to the OAsJEM, OccIDEAS appeared to be more appropriate for evaluating cross-country exposures to asthmagens in healthcare workers due to its inherent quality of assessing task-based determinants and its versatility in being adaptable for use in different countries with different exposure circumstances.

Breast cancer incidence in a national cohort of female workers exposed to special health hazards in Taiwan: a retrospective case-cohort study of ~ 300,000 occupational records spanning 20 years

OBJECTIVE

Breast cancer is the most common cancer among women worldwide. In Taiwan, workers exposed to any of 31 hazardous chemicals or carcinogens in the work environment are designated as especially exposed workers (EEWs) by Taiwan's Ministry of Labor. We assessed the risk of breast cancer in this nationwide female EEW cohort.

METHODS

We conducted a nationwide retrospective study of 4,774,295 workers combining data collected from Taiwan's Ministry of Labor's EEW database between 1997 and 2018 and Taiwan's Cancer Registry between 1997 and 2016. Standardized incidence ratios (SIRs) for women exposed to different hazards and breast cancer incidence rate ratios (IRRs) were calculated by Poisson regression, adjusting for age and duration of exposure.

RESULTS

3248 female workers with breast cancer and 331,967 without breast cancer were included. The SIRs and adjusted IRRs were 1.27 (95% CI 1.18-1.35) and 1.31 (95% CI 1.21-1.42) for lead, 1.74 (95% CI 1.23-2.24) and 1.52 (95% CI 1.13-2.04) for 1,1,2,2-tetrachloroethane, 1.47 (95% CI 1.12-1.82) and 1.42 (95% CI 1.12-1.81) for trichloroethylene/tetrachloroethylene), 1.40 (95% CI 1.23-1.57) and 1.38 (95% CI 1.22-1.57) for benzene, and 2.07 (95% CI 1.06-3.09) and 1.80 (95% CI 1.10-2.94) for asbestos. The results remained similar when factoring in a 2- or 5-year latency period.

CONCLUSION

This study found possible correlations between occupational exposure to lead, chlorinated solvents (such as 1,1,2,2-tetrachloroethane, trichloroethylene, and tetrachloroethylene), benzene, and asbestos with breast cancer risk among female EEW, suggesting a need for regular screening for breast cancer for employees exposed to these special workplace hazards.

Risk of breast cancer in Danish women occupationally exposed to organic solvents, including ethanol

BACKGROUND

Organic solvents have been suggested to increase the risk of breast cancer although the epidemiologic evidence is limited. This study explored the association between organic solvents and breast cancer.

METHODS

This nested population-based case-control study comprised 845 women with primary breast cancer initially identified in the Danish Cancer Registry between 2000 and 2003, and 1500 controls matched on year of birth who were randomly selected from the Danish Civil Registration System. Information on occupational exposure to organic solvents, and specifically ethanol, as well as risk factors for breast cancer was collected through structured interviews.

RESULTS

For organic solvents, an increased risk was indicated for ever-exposure (odds ratio = 3.20, 95% confidence interval: 2.27-4.52), however, no noteworthy risk patterns were detected when exploring duration of exposure and cumulative exposure. Ever-exposure to organic solvents was associated with an increased risk of estrogen receptor negative and positive tumors as well as pre- and postmenopausal breast cancer. No associations were detected between occupational exposure to ethanol and breast cancer.

CONCLUSIONS

This study indicates a positive association between organic solvents and breast cancer.

Employment and risk of female breast cancer in Denmark

BACKGROUND

Occupational exposures may play a role in breast cancer etiology, and research focusing on identifying high-risk workplaces is important to advance the understanding and prevention of breast cancer.

METHODS

We undertook a population-based nested case-control study among women who were less than 70 years of age and born in Denmark, based on registry data including 38,375 breast cancer cases and 191,875 controls matched on year of birth, with information on lifetime work history. Odds ratios for women ever employed in a job branch were adjusted for socioeconomic status and reproductive variables.

RESULTS

Adjusted odds ratios of less than 0.75 were observed for several occupations in agriculture, hunting, forestry, and fishing, while increased risk patterns (odds ratios greater than 1.50) were noted for a number of production occupations, including employment in graphics and printing, and metal and machinery production. In services, several military professions were also associated with a high increased breast cancer risk.

CONCLUSIONS

The study shows a variation in the risk of female breast cancer by employment in different industrial and occupational sectors, and suggests that certain occupational exposures, for example, outdoor work, organic solvents, polycyclic aromatic hydrocarbons (PAHs), and night-shift work may play a role in the risk of breast cancer. Further hypothesis-testing studies focusing on these employments with a detailed assessment of specific occupational exposures are warranted.

Occupational exposure to organic solvents and breast cancer risk: a systematic review and meta-analysis

Breast cancer is the most common cancer worldwide. Recent studies suggest that organic solvent exposure could be closely related to breast cancer, although the evidence remains controversial. Thus, we evaluated existing epidemiological evidence for the association between occupational solvent exposure and breast cancer. PubMed, Embase, and Cochrane Library were searched to identify published case-control and cohort studies that addressed occupational exposure to organic solvents and breast cancer, up to April, 2021. Meta-analyses using random-effects models were conducted to obtain the pooled odds ratios (OR) and 95% confidence intervals (CI) on the incidence of breast cancer in relation to occupational exposure. The pooled OR of breast cancer among workers exposed to organic solvents overall was 1.18 (95%CI, 1.11 ~ 1.25; I² = 76.3%; 24 studies), compared to those with no exposure. After stratification by menopause and study location, it was revealed that the association between occupational exposure to organic solvents and the risk of breast cancer in postmenopausal women (OR, 1.35; 95% CI, 1.09 ~ 1.67; I² = 73.4%; 7 studies) was significant, and there was also a clear association in workers in Europe (OR, 1.21; 95% CI, 1.12 ~ 1.32; I² = 82.9%; 13 studies). We observed a significant association between occupational exposure to organic solvents and breast cancer in both cohort and case-control studies.

Breast cancer and occupational exposures: an integrative review of the literature

Occupational factors can lead to breast cancer, though the relationship between these variables is not well established. The objective of this study was to search the relevant literature for information on the association between breast cancer and exposure to occupational risk factors. For that purpose, electronic databases were searched using the following keywords: breast cancer and occupational exposures. A total of 40 articles published in the 10-year period from 2009 to 2019 were included in this review. Workers exposed to metals such as cadmium, chemical products, radiation and night work were more susceptible to breast cancer. The findings showed significant evidence to support an association between breast cancer and some chemical products, ionizing radiation and night work. However, most studies have difficulty establishing a causal relationship between these variables, pointing to the need for further investigation of these issues.

Occupational exposure to specific organic solvents and risk of subtypes of breast cancer in a large population of Danish women, 1964-2016

OBJECTIVE

To explore associations between occupational exposure to four specific organic solvents, respectively, and female breast cancer, including subtypes.

METHODS

Using the Danish Cancer Registry, we identified 38 375 women under age 70 years with primary breast cancer. Five randomly selected breast-cancer-free controls per case matched on year of birth were retrieved from the Danish Civil Registration System . A nationwide pension fund was used to retrieve full employment history, and exposure to 1,1,1-trichloroethane, trichloroethylene (TCE), benzene and toluene was assessed using a job exposure matrix. ORs were estimated using conditional logistic regression with adjustment for reproductive factors and socioeconomic status.

RESULTS

Overall results indicated no noteworthy associations between the specific organic solvents and breast cancer before and after age 50 years, except for a small increased risk after age 50 in women exposed to TCE (OR=1.15, 95% CI: 0.97-1.36). After age 50 years, exposure to TCE was associated with a small increased risk in women with over 20 years of latency (OR=1.26, 95% CI: 1.02-1.56). Further, an increased risk of oestrogen receptor positive (ER+) tumours was also observed (OR=1.21, 95% CI: 1.01-1.47), and high cumulative exposure and longer latency also increased the risk of this subtype.

CONCLUSION

This study provides limited evidence supporting the association between occupational exposure to each of the four organic solvents and breast cancer. The risk of ER+ breast tumours after age 50 years may be increased in women with TCE exposure, and this possible association therefore needs further attention in future studies.

Environmental exposures and breast cancer risk in the context of underlying susceptibility: A systematic review of the epidemiological literature

BACKGROUND

The evidence evaluating environmental chemical exposures (ECE) and breast cancer (BC) risk is heterogeneous which may stem in part as few studies measure ECE during key BC windows of susceptibility (WOS). Another possibility may be that most BC studies are skewed towards individuals at average risk, which may limit the ability to detect signals from ECE.

OBJECTIVES

We reviewed the literature on ECE and BC focusing on three types of studies or subgroup analyses based on higher absolute BC risk: BC family history (Type 1); early onset BC (Type 2); and/or genetic susceptibility (Type 3).

METHODS

We systematically searched the PubMed database to identify epidemiologic studies examining ECE and BC risk published through June 1, 2019.

RESULTS

We identified 100 publications in 56 unique epidemiologic studies. Of these 56 studies, only 2 (3.6%) were enriched with BC family history and only 11% of studies (6/56) were specifically enriched with early onset cases. 80% of the publications from these 8 enriched studies (Type 1: 8/10 publications; Type 2: 8/10 publications) supported a statistically significant association between ECE and BC risk including studies of PAH, indoor cooking, NO₂, DDT; PCBs, PFOSA; metals; personal care products; and occupational exposure to industrial dyes. 74% of Type 3 publications (20/27) supported statistically significant associations for PAHs, traffic-related air pollution, PCBs, phthalates, and PFOSAs in subgroups of women with greater genetic susceptibility due to variants in carcinogen metabolism, DNA repair, oxidative stress, cellular apoptosis and tumor suppressor genes.

DISCUSSION

Studies enriched for women at higher BC risk through family history, younger age of onset and/or genetic susceptibility consistently support an association between an ECE and BC risk. In addition to measuring exposures during WOS, designing studies that are enriched with women at higher absolute risk are necessary to robustly measure the role of ECE on BC risk.

Occupational Chemical Exposure and Breast Cancer Risk According to Hormone Receptor Status: A Systematic Review

Breast cancers include a heterogeneous group of diseases with clinical behaviors that may vary according to the hormonal receptor status. However, limited knowledge is available on the role of breast cancer environmental and occupational risk factors in the onset of specific molecular disease phenotypes. Therefore, the aim of this review was to provide an overview on the possible correlation between occupational chemical exposures and breast cancers with a specific receptor pattern. Pubmed, Scopus, and ISI Web of Science databases were systematically reviewed to identify all the studies addressing chemical exposure in workplaces and risk of breast cancer classified according to the presence of estrogen and/or progesterone receptors. Some positive associations were reported between solvent, polycyclic aromatic hydrocarbon, organophosphoric insecticide, and synthetic fiber exposure and estrogen receptor-positive cases, while other investigations demonstrated a relationship with receptor-negative tumors or failed to detect any significant effect. Overall, further investigation should overcome limitations due to the self-reported information on work histories, the chemical classification in general categories, and the lack of environmental or biological monitoring exposure data. This may support the development of suitable and individually "tailored" occupational risk assessment and management strategies to protect the health of exposed workers, particularly those with hypersusceptibility conditions.

Using Decision Rules to Assess Occupational Exposure in Population-Based Studies

PURPOSE OF REVIEW

Population-based studies increasingly link task-based occupational questionnaire responses collected from subjects to exposure estimates via transparent, programmable decision rules. We reviewed recent applications and methodological developments of rule-based approaches.

RECENT FINDINGS

Agent-specific decision rules require interviews incorporating work-task-based questions. Some studies have developed rules before the interviews took place, while others developed rules after the interviews were completed. Agreement between rule-based estimates and exposures assigned using job-by-job expert review were generally moderate to good (Kappa = 0.4-0.8). Rules providing quantitative intensity levels using measurement data or that integrate multiple independent exposure sources for the same job represent further advances to improve the characterization of occupational exposures in population studies. Decision rules have provided transparent and reproducible assessments, reduce job-by-job review, and facilitate sensitivity analyses in epidemiologic studies. Future studies should consider the development of decision rules concurrent with the questionnaire design to facilitate occupational exposure assessment efforts.

Work and Female Breast Cancer: The State of the Evidence, 2002-2017

The authors undertook a scoping review to assess the literature from 2002 to 2017 on the relationship between occupation and female breast cancer. Case-control, cohort, and meta-analytic studies suggest that women working as flight attendants, in medical professions, some production positions, sales and retail, and scientific technical staff are likely to have elevated risk of breast cancer. In addition, occupational exposures to night-shift work, ionizing radiation, some chemicals, job stress, and sedentary work may increase risk of breast cancer. Occupational physical activity appears to decrease risk. Workplace exposures to passive smoke and occupational exposure to nonionizing radiation do not appear to affect breast cancer risk. Some studies of occupational categories and workplace exposures indicate that risk may be modified by duration of exposure, timing of exposure, dose, hormone-receptor subtypes, and menopausal status at diagnosis. The compelling data from this review reveal a substantial need for further research on occupation and breast cancer.

Occupational exposure to endocrine disrupting substances and the risk of breast Cancer: the Singapore Chinese health study

Background

Evidence from basic research links exposure to endocrine disrupting chemicals (EDCs) with a higher risk for breast cancer. However, there is less evidence from observational epidemiological research and the results are equivocal. Therefore, we examined the association between occupational exposure to substances where exposure to EDCs is likely and the risk of breast cancer.

Methods

A prospective study consisting of a population-based cohort of 33,458 Singaporean Chinese women aged 45–74 years enrolled in the Singapore Chinese Health Study (SCHS) from 1993 to 98 and followed through 2014. Subjects’ self-reported occupational exposure and duration to industries, job titles, and substance types were garnered at baseline, and cases of incident breast cancer (N = 988) were determined by linkage with the Singapore Cancer Registry. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated for exposure to substances, job titles, and industries.

Results

There was no association between cumulative exposure to substances via occupation where EDC exposure is likely and risk of breast cancer. These results were consistent for hypothesized high (HR 0.94, 95% CI: 0.66–1.35), medium (HR 1.03 95% CI: 0.77–1.38) and low (HR 0.74, 95% CI 0.48–1.13) combined substance exposure groups when compared with those who were not exposed via occupation. Similar null associations were observed when examining job titles and industry categories.

Conclusions

There was no association between EDC related occupational exposures and breast cancer risk in working women of the Singaporean Chinese Health Study. Future studies that employ rigorous methods with regard to exposure assessment of EDCs are needed.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-5862-2) contains supplementary material, which is available to authorized users.

Environmental chemicals and breast cancer: An updated review of epidemiological literature informed by biological mechanisms

BACKGROUND

Many common environmental chemicals are mammary gland carcinogens in animal studies, activate relevant hormonal pathways, or enhance mammary gland susceptibility to carcinogenesis. Breast cancer's long latency and multifactorial etiology make evaluation of these chemicals in humans challenging.

OBJECTIVE

For chemicals previously identified as mammary gland toxicants, we evaluated epidemiologic studies published since our 2007 review. We assessed whether study designs captured relevant exposures and disease features suggested by toxicological and biological evidence of genotoxicity, endocrine disruption, tumor promotion, or disruption of mammary gland development.

METHODS

We systematically searched the PubMed database for articles with breast cancer outcomes published in 2006-2016 using terms for 134 environmental chemicals, sources, or biomarkers of exposure. We critically reviewed the articles.

RESULTS

We identified 158 articles. Consistent with experimental evidence, a few key studies suggested higher risk for exposures during breast development to dichlorodiphenyltrichloroethane (DDT), dioxins, perfluorooctane-sulfonamide (PFOSA), and air pollution (risk estimates ranged from 2.14 to 5.0), and for occupational exposure to solvents and other mammary carcinogens, such as gasoline components (risk estimates ranged from 1.42 to 3.31). Notably, one 50-year cohort study captured exposure to DDT during several critical windows for breast development (in utero, adolescence, pregnancy) and when this chemical was still in use. Most other studies did not assess exposure during a biologically relevant window or specify the timing of exposure. Few studies considered genetic variation, but the Long Island Breast Cancer Study Project reported higher breast cancer risk for polycyclic aromatic hydrocarbons (PAHs) in women with certain genetic variations, especially in DNA repair genes.

CONCLUSIONS

New studies that targeted toxicologically relevant chemicals and captured biological hypotheses about genetic variants or windows of breast susceptibility added to evidence of links between environmental chemicals and breast cancer. However, many biologically relevant chemicals, including current-use consumer product chemicals, have not been adequately studied in humans. Studies are challenged to reconstruct exposures that occurred decades before diagnosis or access biological samples stored that long. Other problems include measuring rapidly metabolized chemicals and evaluating exposure to mixtures.

Occupation and mammographic density: A population-based study (DDM-Occup)

INTRODUCTION

High mammographic density is one of the main risk factors for breast cancer. Although several occupations have been associated with breast cancer, there are no previous occupational studies exploring the association with mammographic density. Our objective was to identify occupations associated with high mammographic density in Spanish female workers.

METHODS

We conducted a population-based cross-sectional study of occupational determinants of high mammographic density in Spain, based on 1476 women, aged 45-68 years, recruited from seven screening centers within the Spanish Breast Cancer Screening Program network. Reproductive, family, personal, and occupational history data were collected. The latest occupation of each woman was collected and coded according to the 1994 National Classification of Occupations. Mammographic density was assessed from the cranio-caudal mammogram of the left breast using a semi-automated computer-assisted tool. Association between mammographic density and occupation was evaluated by using mixed linear regression models, using log-transformed percentage of mammographic density as dependent variable. Models were adjusted for age, body mass index, menopausal status, parity, smoking, alcohol intake, educational level, type of mammography, first-degree relative with breast cancer, and hormonal replacement therapy use. Screening center and professional reader were included as random effects terms.

RESULTS

Mammographic density was higher, although non-statistically significant, among secondary school teachers (e^β = 1.41; 95%CI = 0.98-2.03) and nurses (e^β = 1.23; 95%CI = 0.96-1.59), whereas workers engaged in the care of people (e^β = 0.81; 95%CI = 0.66-1.00) and housewives (e^β = 0.87; 95%CI = 0.79-0.95) showed an inverse association with mammographic density. A positive trend for every 5 years working as secondary school teachers was also detected (p-value = 0.035).

CONCLUSIONS

Nurses and secondary school teachers were the occupations with the highest mammographic density in our study, showing the latter a positive trend with duration of employment. Future studies are necessary to confirm if these results are due to chance or are the result of a true association whose causal hypothesis is, for the moment, unknown.

Occupational exposures and mammographic density in Spanish women

OBJECTIVES

The association between occupational exposures and mammographic density (MD), a marker of breast cancer risk, has not been previously explored. Our objective was to investigate the influence of occupational exposure to chemical, physical and microbiological agents on MD in adult women.

METHODS

This is a population-based cross-sectional study based on 1476 female workers aged 45-65 years from seven Spanish breast cancer screening programmes. Occupational history was surveyed by trained staff. Exposure to occupational agents was assessed using the Spanish job-exposure matrix MatEmESp. Percentage of MD was measured by two radiologists using a semiautomatic computer tool. The association was estimated using mixed log-linear regression models adjusting for age, education, body mass index, menopausal status, parity, smoking, alcohol intake, type of mammography, family history of breast cancer and hormonal therapy use, and including screening centre and professional reader as random effects terms.

RESULTS

Although no association was found with most of the agents, women occupationally exposed to perchloroethylene (e^β=1.51; 95% CI 1.04 to 2.19), ionising radiation (e^β=1.23; 95% CI 0.99 to 1.52) and mould spores (e^β=1.44; 95% CI 1.01 to 2.04) tended to have higher MD. The percentage of density increased 12% for every 5 years exposure to perchloroethylene or mould spores, 11% for every 5 years exposure to aliphatic/alicyclic hydrocarbon solvents and 3% for each 5 years exposure to ionising radiation.

CONCLUSIONS

Exposure to perchloroethylene, ionising radiation, mould spores or aliphatic/alicyclic hydrocarbon solvents in occupational settings could be associated with higher MD. Further studies are needed to clarify the accuracy and the reasons for these findings.