In Utero and Early-Life Exposure to Ambient Air Toxics and Childhood Brain Tumors: A Population-Based Case-Control Study in California, USA

Insights into Targeted and Stimulus-Responsive Nanocarriers for Brain Cancer Treatment

Brain cancers, especially glioblastoma multiforme, are associated with poor prognosis due to the limited efficacy of current therapies. Nanomedicine has emerged as a versatile technology to treat various diseases, including cancers, and has played an indispensable role in combatting the COVID-19 pandemic as evidenced by the role that lipid nanocarrier-based vaccines have played. The tunability of nanocarrier physicochemical properties -including size, shape, surface chemistry, and drug release kinetics- has resulted in the development of a wide range of nanocarriers for brain cancer treatment. These nanocarriers can improve the pharmacokinetics of drugs, increase blood-brain barrier transfer efficiency, and specifically target brain cancer cells. These unique features would potentially allow for more efficient treatment of brain cancer with fewer side effects and better therapeutic outcomes. This review provides an overview of brain cancers, current therapeutic options, and challenges to efficient brain cancer treatment. The latest advances in nanomedicine strategies are investigated with an emphasis on targeted and stimulus-responsive nanocarriers and their potential for clinical translation.

Species profile of volatile organic compounds emission and health risk assessment from typical indoor events in daycare centers

Daycare centers (DCCs) play an instrumental role in early childhood development, making them a significant indoor environment for a large number of children globally. Amidst routine DCC activities, young children are exposed to a myriad of volatile organic compounds (VOCs), potentially impacting their health. Therefore, this study aims to investigate the VOC emissions during typical DCCs activities and evaluate respective health risk assessments. Employing a full-scale experimental setup within a well-controlled climate chamber, research was conducted into VOC emissions during three typical DCC events: arts-and-crafts (painting, gluing, modeling), cleaning, and sleeping activities tied to mattresses. The research identified 96 distinct VOCs, grouped into twelve categories, from 20 different events examined. Each event exhibited a unique VOC fingerprint, pinpointing potential source tracers. Also, significant variations in VOC emissions from different events were demonstrated. For instance, under cool & dry conditions, acrylic painting recorded high total VOC concentrations of 808 μg/m3, whereas poster painting showed only 58 μg/m3. Given these disparities, the study emphasizes the critical need for carefully selecting arts-and-crafts materials and cleaning agents in DCCs to effectively reduce VOC exposure. It suggests ventilating new mattresses before use and regular mattress check-ups to mitigate VOCs exposure during naps. Importantly, it revealed that certain events resulted in VOC levels exceeding the 10-5 cancer risk thresholds for younger children. Specifically, tetrachloroethylene and styrene from used mattresses in cool & dry conditions, ethylene oxide from new mattresses in warm & humid conditions, and styrene, during sand modeling in both conditions, were the key compounds contributing to this risk. These findings highlight the critical need for age-specific health risk assessments in DCCs. This study highlights the significance of understanding the profiles of VOC emissions from indoor events in DCCs, emphasizing potential health implications and laying a solid foundation for future investigations in this field.

Risk factors for childhood brain tumours: A systematic review and meta-analysis of observational studies from 1976 to 2022

BACKGROUND

Childhood brain tumours (CBTs) are the leading cause of cancer death in children under the age of 20 years globally. Though the aetiology of CBT remains poorly understood, it is thought to be multifactorial. We aimed to synthesize potential risk factors for CBT to inform primary prevention.

METHODS

We conducted a systematic review and meta-analysis of epidemiological studies indexed in the PubMed, Web of Science, and Embase databases from the start of those resources through 27 July 2023. We included data from case-control or cohort studies that reported effect estimates for each risk factor around the time of conception, during pregnancy and/or during post-natal period. Random effects meta-analysis was used to estimate summary effect sizes (ES) and 95% confidence intervals (CIs). We also quantified heterogeneity (I2) across studies.

FINDINGS

A total of 4040 studies were identified, of which 181 studies (85 case-control and 96 cohort studies) met our criteria for inclusion. Of all eligible studies, 50% (n = 91) were conducted in Europe, 32% (n = 57) in North America, 9% (n = 16) in Australia, 8% (n = 15) in Asia, 1% (n = 2) in South America, and none in Africa. We found associations for some modifiable risk factors including childhood domestic exposures to insecticides (ES 1.44, 95% CI 1.20-1.73) and herbicides (ES 2.38, 95% CI 1.31-4.33). Maternal domestic exposure to insecticides (ES 1.45, 95% CI 1.09-1.94), maternal consumption of cured meat (ES 1.51, 95% CI 1.05-2.17) and coffee ≥ 2 cups/day (ES 1.45, 95% 95% CI 1.07-1.95) during pregnancy, and maternal exposure to benzene (ES 2.22; 95% CI 1.01-4.88) before conception were associated with CBTs in case-control studies. Also, paternal occupational exposure to pesticides (ES 1.48, 95% CI 1.23-1.77) and benzene (ES 1.74, 95% CI 1.10-2.76) before conception and during pregnancy were associated in case-control studies and in combined analysis. On the other hand, assisted reproductive technology (ART) (ES 1.32, 95% CI 1.05-1.67), caesarean section (CS) (ES 1.12, 95% CI 1.01-1.25), paternal occupational exposure to paint before conception (ES 1.56, 95% CI 1.02-2.40) and maternal smoking > 10 cigarettes per day during pregnancy (ES 1.18, 95% CI 1.00-1.40) were associated with CBT in cohort studies. Maternal intake of vitamins and folic acid during pregnancy was inversely associated in cohort studies. Hormonal/infertility treatment, breastfeeding, child day-care attendance, maternal exposure to electric heated waterbed, tea and alcohol consumption during pregnancy were among those not associated with CBT in both case-control and cohort studies.

CONCLUSION

Our results should be interpreted with caution, especially as most associations between risk factors and CBT were discordant between cohort and case-control studies. At present, it is premature for any CBT to define specific primary prevention guidelines.

Environmental, social and behavioral risk factors in association with spatial clustering of childhood cancer incidence

Childhood cancer incidence is known to vary by age, sex, and race/ethnicity, but evidence is limited regarding external risk factors. We aim to identify harmful combinations of air pollutants and other environmental and social risk factors in association with the incidence of childhood cancer based on 2003-2017 data from the Georgia Cancer Registry. We calculated the standardized incidence ratios (SIR) of Central Nervous System (CNS) tumors, leukemia and lymphomas based on age, gender and ethnic composition in each of the 159 counties in Georgia, USA. County-level information on air pollution, socioeconomic status (SES), tobacco smoking, alcohol drinking and obesity were derived from US EPA and other public data sources. We applied two unsupervised learning tools (self-organizing map [SOM] and exposure-continuum mapping [ECM]) to identify pertinent types of multi-exposure combinations. Spatial Bayesian Poisson models (Leroux-CAR) were fit with indicators for each multi-exposure category as exposure and SIR of childhood cancers as outcomes. We identified consistent associations of environmental (pesticide exposure) and social/behavioral stressors (low socioeconomic status, alcohol) with spatial clustering of pediatric cancer class II (lymphomas and reticuloendothelial neoplasms), but not for other cancer classes. More research is needed to identify the causal risk factors for these associations.

Long-term exposure to airborne metals and risk of cancer in the French cohort Gazel

BACKGROUND

The specific compounds that make ambient fine particulate matter (PM_2.5) carcinogen remain poorly identified. Some metals contribute to ambient PM_2.5 and possibly to its adverse effects. But the challenge of assessing exposure to airborne metals limits epidemiological studies.

OBJECTIVE

To analyze the relationships between several airborne metals and risk of cancer in a large population.

METHODS

We estimated the individual exposure to 12 airborne metals of ∼ 12,000 semi-urban and rural participants of the French population-based Gazel cohort using moss biomonitoring data from a 20-year national program. We used principal component analyses (PCA) to derive groups of metals, and focused on six single carcinogenic or toxic metals (arsenic, cadmium, chromium, lead, nickel, and vanadium). We used extended Cox models with attained age as time-scale and time-varying weighted average exposures, adjusted for individual and area-level covariables, to analyze the association between each exposure and all-site combined, bladder, lung, breast, and prostate cancer incidence.

RESULTS

We identified 2,401 cases of all-site cancer between 2001 and 2015. Over the follow-up, median exposures varied from 0.22 (interquartile range (IQR): 0.18-0.28) to 8.68 (IQR: 6.62-11.79) µg.g^-1 of dried moss for cadmium and lead, respectively. The PCA yielded three groups identified as "anthropogenic", "crustal", and "marine". Models yielded positive associations between most single and groups of metal and all-site cancer, with e.g. hazard ratios of 1.08 (95% CI: 1.03, 1.13) for cadmium or 1.06 (95% CI: 1.02,1.10) for lead, per interquartile range increase. These findings were consistent across supplementary analyses, albeit attenuated when accounting for total PM_2.5. Regarding specific site cancers, we estimated positive associations mostly for bladder, and generally with large confidence intervals.

CONCLUSION

Most single and groups of airborne metals, except vanadium, were associated with risk of cancer. These findings may help identify sources or components of PM_2.5 that may be involved in its carcinogenicity.

Impacts of Environmental Pollution on Brain Tumorigenesis

Pollutants consist of several components, known as direct or indirect mutagens, that can be associated with the risk of tumorigenesis. The increased incidence of brain tumors, observed more frequently in industrialized countries, has generated a deeper interest in examining different pollutants that could be found in food, air, or water supply. These compounds, due to their chemical nature, alter the activity of biological molecules naturally found in the body. The bioaccumulation leads to harmful effects for humans, increasing the risk of the onset of several pathologies, including cancer. Environmental components often combine with other risk factors, such as the individual genetic component, which increases the chance of developing cancer. The objective of this review is to discuss the impact of environmental carcinogens on modulating the risk of brain tumorigenesis, focusing our attention on certain categories of pollutants and their sources.

Childhood cancer and traffic-related air pollution in Switzerland: A nationwide census-based cohort study

Motor vehicle exhaust is a major contributor to air pollution, and exposure to benzene or other carcinogenic components may increase cancer risks. We aimed to investigate the association between traffic-related air pollution and risk of childhood cancer in a nationwide cohort study in Switzerland. We identified incident cases from the Swiss Childhood Cancer Registry diagnosed < 16 years of age between 1990 and 2015 and linked them probabilistically with the census-based Swiss National Cohort study. We developed land use regression models to estimate annual mean ambient levels of nitrogen dioxide (NO2) and benzene outside 1.4 million children's homes. We used risk-set sampling to facilitate the analysis of time-varying exposure and fitted conditional logistic regression models adjusting for neighborhood socio-economic position, level of urbanization, and background ionizing radiation. We included 2,960 cancer cases in the analyses. The adjusted hazard ratios (HR) and 95% confidence intervals for exposure to NO2 per 10 μg/m3 were 1.00 (95%-CI 0.88-1.13) for acute lymphoblastic leukemia (ALL) and 1.31 (95%-CI 1.00-1.71) for acute myeloid leukemia (AML). Using exposure lagged by 1 to 5 years instead of current exposure attenuated the effect for AML. The adjusted HR for exposure to benzene per 1 μg/m3 was 1.03 (95%-CI 0.86-1.23) for ALL and 1.29 (95%-CI 0.86-1.95) for AML. We also observed increased HRs for other diagnostic groups, notably non-Hodgkin lymphoma. Our study adds to the existing evidence that exposure to traffic-related air pollution is associated with an increased risk of childhood leukemia, particularly AML.

Childhood cancer and residential proximity to petrol stations: a nationwide registry-based case-control study in Switzerland and an updated meta-analysis

PURPOSE

Benzene is a known carcinogen for adult leukemia. Exposure to benzene through parental occupation and the use of household products has been associated with childhood leukemia (CL). Ambient benzene has also been associated with CL and central nervous system (CNS) tumors. We aimed to investigate whether the higher ambient levels of benzene in proximity of petrol stations are associated with a greater risk of childhood cancers, leukemia, and CNS tumors.

METHODS

We identified children diagnosed with cancer at age 0-15 years during 1985-2015 from the Swiss Childhood Cancer Registry and selected 10 age and sex-matched controls per case from national censuses. We calculated the distance from children's home to the nearest petrol station using precise geocodes. We estimated odds ratios using conditional logistic regression adjusting for ambient levels of NO₂, distance to highways, level of urbanization, and presence of a cantonal cancer registry. In addition, we ran a meta-analysis pooling current results for CL with those of previous studies.

RESULTS

We identified 6129 cases, of which 1880 were leukemias and 1290 CNS tumors. 24 cases lived within 50 m from a petrol station. The adjusted odds ratio of a cancer diagnosis for children thus exposed compared to unexposed children (> 500 m) was 1.29 (0.84-1.98) for all cancers combined, 1.08 (0.46-2.51) for leukemia, and 1.30 (0.51-3.35) for CNS tumors. During 2000-2015, when exposure assessment was more precise, the adjusted odds ratio for any cancer diagnosis was 1.77 (1.05-2.98). The summary relative risk estimate for CL in the meta-analysis including four studies was 2.01 (1.25-3.22).

CONCLUSIONS

Our study provides weak support for an increased risk of childhood cancers among children living close to petrol stations. A meta-analysis including our study suggests an increased risk for CL.

Association between long-term exposure to particulate matter and childhood cancer: A retrospective cohort study

BACKGROUND

Although particulate matter is a known carcinogen, its association with childhood cancer is inconclusive. The present study aimed to examine the association between long-term exposure to particulate matter and childhood cancer.

METHODS

A retrospective cohort was constructed from the claims database of the Korea National Health Insurance Service, including children born in seven metropolitan cities in Korea between 2002 and 2012. Monthly mean concentrations of particulate matter with aerodynamic diameter <10 μm (PM₁₀) and other air pollutants (NO₂, SO₂, CO, and O₃) were calculated using data from the AirKorea. Monthly mean concentrations of particulate matter with aerodynamic diameter <2.5 μm (PM_2.5) were estimated based on a data fusion approach. Cumulative exposure was assessed by averaging the monthly concentrations accounting for the residential mobility of the children. The occurrence of cancer was identified by the appearance of diagnosis codes in the claims database. Hazard ratios (HR) and 95% confidence intervals (95% CI) were calculated using Cox proportional regression, adjusting for potential confounders and O₃ concentrations.

RESULTS

During the study period, 1,725 patients were newly diagnosed with cancer among 1,261,855 children. HR of all cancers per 10 μg/m³ increment in annual mean concentrations of PM_2.5 and PM₁₀ were 3.02 (95% CI: 1.63, 5.59) and 1.04 (0.74, 1.45), respectively.

CONCLUSION

PM_2.5 exposure was positively associated with childhood cancer in a large retrospective cohort with exposure assessment accounting for residential mobility.

1,3-Butadiene: a ubiquitous environmental mutagen and its associations with diseases

1,3-Butadiene (BD) is a petrochemical manufactured in high volumes. It is a human carcinogen and can induce lymphohematopoietic cancers, particularly leukemia, in occupationally-exposed workers. BD is an air pollutant with the major environmental sources being automobile exhaust and tobacco smoke. It is one of the major constituents and is considered the most carcinogenic compound in cigarette smoke. The BD concentrations in urban areas usually vary between 0.01 and 3.3 μg/m³ but can be significantly higher in some microenvironments. For BD exposure of the general population, microenvironments, particularly indoor microenvironments, are the primary determinant and environmental tobacco smoke is the main contributor. BD has high cancer risk and has been ranked the second or the third in the environmental pollutants monitored in most urban areas, with the cancer risks exceeding 10^-5. Mutagenicity/carcinogenicity of BD is mediated by its genotoxic metabolites but the specific metabolite(s) responsible for the effects in humans have not been determined. BD can be bioactivated to yield three mutagenic epoxide metabolites by cytochrome P450 enzymes, or potentially be biotransformed into a mutagenic chlorohydrin by myeloperoxidase, a peroxidase almost specifically present in neutrophils and monocytes. Several urinary BD biomarkers have been developed, among which N-acetyl-S-(4-hydroxy-2-buten-1-yl)-L-cysteine is the most sensitive and is suitable for biomonitoring BD exposure in the general population. Exposure to BD has been associated with leukemia, cardiovascular disease, and possibly reproductive effects, and may be associated with several cancers, autism, and asthma in children. Collectively, BD is a ubiquitous pollutant that has been associated with a range of adverse health effects and diseases with children being a subpopulation with potentially greater susceptibility. Its adverse effects on human health may have been underestimated and more studies are needed.

Interpreting a standardized and normalized measure of neighborhood socioeconomic status for a better understanding of health differences

BACKGROUND

Standardization and normalization of continuous covariates are used to ease the interpretation of regression coefficients. Although these scaling techniques serve different purposes, they are sometimes used interchangeably or confused for one another. Therefore, the objective of this study is to demonstrate how these scaling techniques lead to different interpretations of the regression coefficient in multilevel logistic regression analyses.

METHODS

Area-based socioeconomic data at the census tract level were obtained from the 2015-2019 American Community Survey for creating two measures of neighborhood socioeconomic status (SES), and a hypothetical data on health condition (favorable versus unfavorable) was constructed to represent 3000 individuals living across 300 census tracts (i.e., neighborhoods). Two measures of neighborhood SES were standardized by subtracting its mean and dividing by its standard deviation (SD) or by dividing by its interquartile range (IQR), and were normalized into a range between 0 and 1. Then, four separate multilevel logistic regression analyses were conducted to assess the association between neighborhood SES and health condition.

RESULTS

Based on standardized measures, the odds of having unfavorable health condition was roughly 1.34 times higher for a one-SD change or a one-IQR change in neighborhood SES; these reflect a health difference of individuals living in relatively high SES (relatively affluent) neighborhoods and those living in relatively low SES (relatively deprived) neighborhoods. On the other hand, when these standardized measures were replaced by its respective normalized measures, the odds of having unfavorable health condition was roughly 3.48 times higher for a full unit change in neighborhood SES; these reflect a health difference of individuals living in highest SES (most affluent) neighborhoods and those living in lowest SES (most deprived) neighborhoods.

CONCLUSION

Multilevel logistic regression analyses using standardized and normalized measures of neighborhood SES lead to different interpretations of the effect of neighborhood SES on health. Since both measures are valuable in their own right, interpreting a standardized and normalized measure of neighborhood SES will allow us to gain a more rounded view of the health differences of individuals along the gradient of neighborhood SES in a certain geographic location as well as across different geographic locations.

Inequalities in Exposure to Ambient Air Neurotoxicants and Disparities in Markers of Neurodevelopment in Children by Maternal Nativity Status

Exposure levels to environmental pollutants vary significantly among different populations. These inequities in exposure to hazardous air pollutants (HAP) among different populations can contribute to disparities in neurodevelopmental outcomes. The aim of this study was to determine if exposure to HAP varies by maternal nativity status, a demographic marker often overlooked in the study of health disparities. We also assessed if those inequalities in exposure levels are associated with neurodevelopmental measures in young children. To do this, we obtained data from the Early Childhood Longitudinal Study-Birth cohort (ECLS-B), a nationally representative sample of children born in the U.S. in the year 2001 (n = 4750). Bayley’s Short Form-Research Edition (BSF-R) was used to measure cognitive development at 2 years of age. Using residential location at nine months of age, participants were assigned exposures to ten HAPs identified as potentially neurotoxic. Linear regression models were used to assess the joint effect of maternal nativity status and HAP exposure on neurodevelopment. Results showed inequities in exposure levels to ten different HAPs among the populations, as approximately 32% of children of foreign-born mothers were exposed to high levels of HAPs, compared to 21% of children born to U.S.-born mothers. Adjusting for socioeconomic factors, both isophorone exposure (a marker of industrial pollution) (−0.04, 95% CI, −0.12, 0.04) and maternal nativity status (−0.17, 95% CI, −0.27, −0.06) were independently associated with lower standardized BSF-R mental scores in children. Interaction between nativity status and isophorone was not statistically significant, but the change in mental scores associated with isophorone exposure was greater in children of foreign-born mothers compared to children of U.S.-born mothers (−0.12, vs. −0.03, p = 0.2). In conclusion, exposure to HAPs within the highest quartile was more commonly found among children of foreign-born mothers as compared to children of US-born mothers, indicating inequities in pollutant exposure by nativity status within urban populations. Exposures associated with nativity status may negatively contribute to children’s neurodevelopment.

Individual and neighbourhood socioeconomic measures and the risk of non-central nervous system solid tumours in children: A nationwide register-based case-control study in Denmark

BACKGROUND

The aetiology for most solid tumours in childhood is largely unknown. The lack of evidence concerns also the relationship between socioeconomic position (SEP) and risk of childhood solid tumours other than in the central nervous system (CNS). We sought to access the association between individual and neighbourhood SEP measures and risk of childhood non-CNS solid tumours in Denmark and to evaluate whether associations varied by measure of SEP, time point of SEP assessment (during pregnancy versus before diagnosis) and tumour type.

METHODS

We conducted a nationwide case-control study based on Danish registry data. We identified all children born in 1980-2013 and diagnosed with a non-CNS solid tumour at ages 0-19 years (N = 1961) from the Danish Cancer Registry and sampled four individually matched controls per case using the Population Registry. We fitted conditional logistic regression models to estimate associations with register-based individual-level and neighbourhood-level SEP measures.

RESULTS

We observed a tendency of increased odd ratios (OR) in association with medium and high maternal income for most tumour types (e.g. OR for the highest income quintile and malignant bone tumours = 2.11; 95 % CI: 1.01, 4.38) and for parental education in association with higher education for some tumour types. For malignant epithelial neoplasms, higher parental education and income level were overall associated with an increased risk, e.g. OR = 1.63 (95 % CI: 1.00, 2.65) for the fourth group of maternal income during pregnancy. We found no risk pattern for neighbourhood SEP.

CONCLUSION

This large register-study with minimal risk of bias found a tendency of slightly to moderately increased risks for most childhood non-CNS solid tumours in association with higher maternal income and parental education. Future research examining the underlying mechanisms of these socioeconomic differences in non-CNS solid tumours as well as other childhood cancer types are warranted.

Ambient ultrafine particle concentrations and incidence of childhood cancers

BACKGROUND

Ambient air pollution has been associated with childhood cancer. However, little is known about the possible impact of ambient ultrafine particles (<0.1 μm) (UFPs) on childhood cancer incidence.

OBJECTIVE

This study aimed to evaluate the association between prenatal and childhood exposure to UFPs and development of childhood cancer.

METHODS

We conducted a population-based cohort study of within-city spatiotemporal variations in ambient UFPs across the City of Toronto, Canada using 653,702 singleton live births occurring between April 1, 1998 and March 31, 2017. Incident cases of 13 subtypes of paediatric cancers among children up to age 14 were ascertained using a cancer registry. Associations between ambient air pollutant concentrations and childhood cancer incidence were estimated using random-effects Cox proportional hazards models. We investigated both single- and multi-pollutant models accounting for co-exposures to PM_2.5 and NO₂.

RESULTS

A total of 1,066 childhood cancers were identified. We found that first trimester exposure to UFPs (Hazard Ratio (HR) per 10,000/cm³ increase = 1.13, 95% CI: 1.03-1.22) was associated with overall cancer incidence diagnosed before 6 years of age after adjusting for PM_2.5, NO₂, and for personal and neighborhood-level covariates. Association between UFPs and overall cancer incidence exhibited a linear shape. No statistically significant associations were found for specific cancer subtypes.

CONCLUSION

Ambient UFPs may represent a previously unrecognized risk factor in the aetiology of cancers in children. Our findings reinforce the importance of conducting further research on the effects of UFPs given their high prevalence of exposure in urban areas.

Outdoor air pollution and cancer: An overview of the current evidence and public health recommendations

Outdoor air pollution is a major contributor to the burden of disease worldwide. Most of the global population resides in places where air pollution levels, because of emissions from industry, power generation, transportation, and domestic burning, considerably exceed the World Health Organization's health-based air-quality guidelines. Outdoor air pollution poses an urgent worldwide public health challenge because it is ubiquitous and has numerous serious adverse human health effects, including cancer. Currently, there is substantial evidence from studies of humans and experimental animals as well as mechanistic evidence to support a causal link between outdoor (ambient) air pollution, and especially particulate matter (PM) in outdoor air, with lung cancer incidence and mortality. It is estimated that hundreds of thousands of lung cancer deaths annually worldwide are attributable to PM air pollution. Epidemiological evidence on outdoor air pollution and the risk of other types of cancer, such as bladder cancer or breast cancer, is more limited. Outdoor air pollution may also be associated with poorer cancer survival, although further research is needed. This report presents an overview of outdoor air pollutants, sources, and global levels, as well as a description of epidemiological evidence linking outdoor air pollution with cancer incidence and mortality. Biological mechanisms of air pollution-derived carcinogenesis are also described. This report concludes by summarizing public health/policy recommendations, including multilevel interventions aimed at individual, community, and regional scales. Specific roles for medical and health care communities with regard to prevention and advocacy and recommendations for further research are also described.

Socioeconomic differences in the risk of childhood central nervous system tumors in Denmark: a nationwide register-based case-control study

PURPOSE

Differences in the risk of childhood central nervous system (CNS) tumors by socioeconomic status (SES) may enhance etiologic insights. We conducted a nationwide register-based case-control study to evaluate socioeconomic differences in the risk of childhood CNS tumors in Denmark and examined whether associations varied by different SES measures, time points of assessment, specific tumor types, and age at diagnosis.

METHODS

We identified all children born between 1981 and 2013 and diagnosed with a CNS tumor at ages 0-19 years (n = 1,273) from the Danish Cancer Registry and sampled four individually matched controls per case (n  = 5,086). We used conditional logistic regression models to estimate associations with individual-level and neighborhood-level socioeconomic measures.

RESULTS

We observed elevated risks of ependymoma and embryonal CNS tumors in association with higher parental education (odds ratios (ORs) of 1.6-2.1 for maternal or paternal high education and ependymoma) and higher risk of all tumor types in association with higher maternal income, e.g., OR  1.93; 95% CI 1.05-3.52 for high versus low income for astrocytoma and other gliomas. Associations were often stronger in children diagnosed at ages 5-19 years. We found little evidence for an association with neighborhood SES.

CONCLUSION

This large nationwide register study with minimal risk of bias showed that having parents with higher educational level and a mother with higher income was associated with a higher risk of childhood CNS tumors. Bias or under-ascertainment of cases among families with low income or basic education is unlikely to explain our findings.

Exposure to lead increases the risk of meningioma and brain cancer: A meta-analysis

OBJECTIVE

To analyze the relationship between environmental lead exposure and various types of brain tumors.

METHODS

Search databases PubMed, Web of Science, Embase and Chinese National Knowledge Infrastructure (CNKI) as of July 1, 2019. Stata 15.0 software was used for analysis.

RESULTS

In the case control, lead exposure was associated with gliomas and meningiomas 0.82 (95 % CI: 0.69, 0.95) and 1.06 (95 % CI: 0.65, 1.46). In the cohort study, lead exposure was associated with brain cancer and meningiomas 1.07 (95 % CI: 0.95, 1.19) and 1.06 (95 % CI: 0.94, 1.17). The risk of childhood brain tumors associated with parental lead exposure was 1.17 (95 % CI: 0.99, 1.34).

CONCLUSIONS

Lead may be a risk factor for meningiomas and brain cancers. However, the glioma results suggest that lead may be a protective factor, which needs to be further studied.

Birth seasonality of childhood central nervous system tumors: Analysis of primary data from 16 Southern-Eastern European population-based registries

Season of birth, a surrogate of seasonal variation of environmental exposures, has been associated with increased risk of several cancers. In the context of a Southern-Eastern Europe (SEE) consortium, we explored the potential association of birth seasonality with childhood (0-14 years) central nervous system (CNS) tumors. Primary CNS tumor cases (n = 6,014) were retrieved from 16 population-based SEE registries (1983-2015). Poisson regression and meta-analyses on birth season were performed in nine countries with available live birth data (n = 4,987). Subanalyses by birth month, age, gender and principal histology were also conducted. Children born during winter were at a slightly increased risk of developing a CNS tumor overall [incidence rate ratio (IRR): 1.06, 95% confidence intervals (CI): 0.99-1.14], and of embryonal histology specifically (IRR: 1.13, 95% CI: 1.01-1.27). The winter peak of embryonal tumors was higher among boys (IRR: 1.24, 95% CI: 1.05-1.46), especially during the first 4 years of life (IRR: 1.33, 95% CI: 1.03-1.71). In contrast, boys <5 years born during summer seemed to be at a lower risk of embryonal tumors (IRR: 0.73, 95% CI: 0.54-0.99). A clustering of astrocytomas was also found among girls (0-14 years) born during spring (IRR: 1.23, 95% CI: 1.03-1.46). Although the present exploratory results are by no means definitive, they provide some indications for age-, gender- and histology-related seasonal variations of CNS tumors. Expansion of registration and linkage with cytogenetic reports could refine if birth seasonality is causally associated with CNS tumors and shed light into the complex pathophysiology of this lethal disease.

Association Between Outdoor Air Pollution and Risk of Malignant and Benign Brain Tumors: The Multiethnic Cohort Study

Background

There are increasing concerns about the potential impact of air pollution on chronic brain inflammation and microglia cell activation, but evidence of its carcinogenic effects is limited.

Methods

We used kriging interpolation and land use regression models to estimate long-term air pollutant exposures of oxides of nitrogen (NO_x, NO₂), kriging interpolation for ozone (O₃), carbon monoxide, and particulate matter (PM_2.5, PM₁₀), and nearest monitoring station measurements for benzene for 103 308 men and women from the Multiethnic Cohort, residing largely in Los Angeles County from recruitment (1993–1996) through 2013. We used Cox proportional hazards models to examine the associations between time-varying pollutants and risk of malignant brain cancer (94 men, 116 women) and meningioma (130 men, 425 women) with adjustment for sex, race and ethnicity, neighborhood socioeconomic status, smoking, occupation, and other covariates. Stratified analyses were conducted by sex and race and ethnicity.

Results

Brain cancer risk in men increased in association with exposure to benzene (hazard ratio [HR] = 3.52, 95% confidence interval [CI] = 1.55 to 7.55) and PM₁₀ (HR = 1.80, 95% CI = 1.00 to 3.23). Stronger associations with PM₁₀ (HR = 3.02, 95% CI = 1.26 to 7.23), O₃ (HR = 2.93, 95% CI = 1.09 to 7.88), and benzene (HR = 4.06, 95% CI = 1.17 to 18.2) were observed among Latino men. Air pollution was unrelated to risk of meningioma except that O₃ exposure was associated with risk in men (HR = 1.77, 95% CI = 1.02 to 3.06). Brain cancer risk in women was unrelated to air pollution exposures.

Conclusions

Confirmation of these sex differences in air pollution–brain cancer associations and the stronger findings in Latino men in additional diverse populations is warranted.

Residential mobility in early childhood and the impact on misclassification in pesticide exposures

Studies of environmental exposures and childhood cancers that rely on records often only use maternal address at birth or address at cancer diagnosis to assess exposures in early childhood, possibly leading to exposure misclassification and questionable validity due to residential mobility during early childhood. Our objective was to assess patterns and identify factors that may predict residential mobility in early childhood, and examine the impact of mobility on early childhood exposure assessment for agriculturally applied pesticides and childhood cancers in California. We obtained the addresses at diagnosis of all childhood cancer cases born in 1998-2011 and diagnosed at 0-5 years of age (n = 6478) from the California Cancer Registry (CCR), and their birth addresses from linked birth certificates. Controls were randomly selected from California birth records and frequency matched (20:1) to all cases by year of birth. We obtained residential histories from a public-record database LexisNexis for both case (n = 3877 with age at diagnosis 1-5 years) and control (n = 99,262) families. Logistic regression analyses were conducted to assess the socio-demographic factors in relation to residential mobility in early childhood. We employed a Geographic Information System (GIS)-based system to estimate children's first year of life exposures to agriculturally applied pesticides based on birth vs diagnosis address or residential histories based upon Lexis-Nexis Public Records and assessed agreement between exposure measures using Spearman correlations and kappa statistics. Over 20% of case and control children moved in their first year of life, and 55% of children with cancer moved between birth and diagnosis. Older age at diagnosis, younger maternal age, lower maternal education, not having a Hispanic ethnic background, use of public health insurance, and non-metropolitan residence at birth were predictors of higher residential mobility. There was moderate to strong correlation (Spearman correlation = 0.76-0.83) and good agreement (kappa = 0.75-0.81) between the first year of life exposure estimates for agricultural pesticides applied within 2 km of a residence relying on an address at birth or at diagnosis or LexisNexis addresses; this did not differ by outcome status, but agreement decreased with decreasing buffer size, and increasing distance moved or age at diagnosis. These findings suggest that residential addresses collected at one point in time may represent residential history in early childhood to a reasonable extent; nevertheless, they exposure misclassification in the first year of life remains an issue. Also, the highest proportion of women not captured by LexisNexis were Hispanic women born in Mexico and those living in the lowest SES neighborhoods, i.e. possibly those with the higher environmental exposures, as well as younger women and those with less than high school education. Though LexisNexis only captures a sub-population, its data may be useful for augmenting address information and assessing the extent of exposure misclassification when estimating environmental exposures in large record linkage studies. Future research should investigate how to correct for exposure misclassification introduced by residential mobility that is not being captured by records.

Prenatal Exposure to Air Toxics and Malignant Germ Cell Tumors in Young Children

OBJECTIVE

To assess prenatal air toxics exposure and risk for childhood germ cell tumors (GCTs) by histological subtype (yolk sac tumor and teratoma).

METHODS

In this case-control study, GCT cases less than 6 years (n = 243) identified from California Cancer Registry records were matched by birth year to cancer-free population controls (n = 147,100), 1984 to 2013. Routinely monitored air toxic exposures were linked to subjects' birth address. Logistic regression estimated GCT risks per interquartile range increase in exposure.

RESULTS

Prenatal exposure to various highly-correlated, traffic-related air toxics during the second trimester increased GCT risk, particularly 1,3-butadiene (odds ratio [OR] = 1.51; 95% confidence interval [CI] = 1.01, 2.26) and meta/para-xylene (OR = 1.56; 95% CI = 1.10, 2.21). Analyses by subtype indicated elevated ORs for yolk sac tumors but not teratomas.

CONCLUSION

Our estimated ORs are consistent with positive associations between some prenatal traffic-related air toxics and GCT risk, notably yolk sac tumors.

Transplacental exposure to carcinogens and risks to children: evidence from biomarker studies and the utility of omic profiling

The factors underlying the increasing rates and the geographic variation of childhood cancers are largely unknown. Epidemiological studies provide limited evidence for a possible role in the etiology of certain types of childhood cancer of the exposure of pregnant women to environmental carcinogens (e.g., tobacco smoke and pesticides); however, such evidence is inadequate to allow definitive conclusions. Complementary evidence can be obtained from biomarker-based population studies. Such studies have demonstrated that, following exposure of pregnant mothers, most environmental carcinogens reach the fetus and, in many cases, induce therein genotoxic damage which in adults is known to be associated with increased cancer risk, implying that environmental carcinogens may contribute to the etiology of childhood cancer. During recent years, intermediate disease biomarkers, obtained via omic profiling, have provided additional insights into the impact of transplacental exposures on fetal tissues which, in some cases, are also compatible with a precarcinogenic role of certain in utero exposures. Here we review the epidemiological and biomarker evidence and discuss how further research, especially utilizing high-density profiling, may allow a better evaluation of the links between in utero environmental exposures and cancer in children.

Exposure to ambient air pollution and risk of childhood cancers: A population-based study in Tehran, Iran

The relationship between air pollution and childhood cancer is inconclusive. We investigated the associations between exposure to ambient air pollution and childhood cancers in Tehran, Iran. This project included children between 1 and 15 years-of-age with a cancer diagnosis by the Center for the Control of Non Communicable Disease (n = 161) during 2007 to 2009. Controls were selected randomly within the city using a Geographic Information System (GIS) (n = 761). The cases were geocoded based on exact home addresses. Air pollution exposure of cases and random controls were estimated by a previously developed Land Use Regression (LUR) model for the 2010 calendar year. The annual mean concentrations of Particulate Matter ≤ 10 μm (PM₁₀), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) in the locations of cancer cases were 101.97 μg/m³, 49.42 ppb and 38.92 ppb respectively, while in the random control group, respective mean exposures were 98.63 μg/m³, 45.98 ppb and 38.95 ppb. A logistic regression model was used to find the probability of childhood cancer per unit increase in PM₁₀, NO₂ and SO₂. We observed a positive association between exposures to PM₁₀ with childhood cancers. We did, however, observe a positive, but not statistically significant association between NO₂ exposure and childhood cancer. Our study is the first to highlight an association between air pollution exposure and childhood cancer risk in Iran, however these findings require replication through future studies.

A reverse metabolic approach to weaning: in silico identification of immune-beneficial infant gut bacteria, mining their metabolism for prebiotic feeds and sourcing these feeds in the natural product space

BACKGROUND

Weaning is a period of marked physiological change. The introduction of solid foods and the changes in milk consumption are accompanied by significant gastrointestinal, immune, developmental, and microbial adaptations. Defining a reduced number of infections as the desired health benefit for infants around weaning, we identified in silico (i.e., by advanced public domain mining) infant gut microbes as potential deliverers of this benefit. We then investigated the requirements of these bacteria for exogenous metabolites as potential prebiotic feeds that were subsequently searched for in the natural product space.

RESULTS

Using public domain literature mining and an in silico reverse metabolic approach, we constructed probiotic-prebiotic-food associations, which can guide targeted feeding of immune health-beneficial microbes by weaning food; analyzed competition and synergy for (prebiotic) nutrients between selected microbes; and translated this information into designing an experimental complementary feed for infants enrolled in a pilot clinical trial ( http://www.nourishtoflourish.auckland.ac.nz/ ).

CONCLUSIONS

In this study, we applied a benefit-oriented microbiome research strategy for enhanced early-life immune health. We extended from "classical" to molecular nutrition aiming to identify nutrients, bacteria, and mechanisms that point towards targeted feeding to improve immune health in infants around weaning. Here, we present the systems biology-based approach we used to inform us on the most promising prebiotic combinations known to support growth of beneficial gut bacteria ("probiotics") in the infant gut, thereby favorably promoting development of the immune system.

Medulloblastoma in association with sacral agenesis; a case report

Medulloblastoma is a congenital brain tumor which can be associated with different congenital anomalies. However, coincidence of cerebellar medulloblastoma with sacral agenesis has not been reported so far. A variety of genetic and/or environmental predisposing factors have been proposed for both diseases. Herein, an unprecedented coincidence of these two conditions is presented. A neonate was born with lumbosacral agenesis, paraplegia, and atrophic legs, and he developed medulloblastoma with three ventricular hydrocephalus 3 years later. Different aspects regarding the embryology and etiology of both ailments are discussed, assuming the possibility that the same genetic and/or environmental risk factors may have played a part in both conditions.

Ambient benzene at the residence and risk for subtypes of childhood leukemia, lymphoma and CNS tumor

Exposure to benzene increases the risk for acute myeloid leukemia and possibly other types of cancer in adults. For children, only limited evidence about benzene and cancer exists. A few studies have indicated that benzene may increase risk for some subtypes of childhood cancer but not for others. We aimed to investigate if outdoor levels of benzene at the residence increase the risk for subtypes of leukemia, lymphoma and CNS tumor in children. We identified 1,989 children diagnosed with leukemia, lymphoma or CNS tumor during 1968-1991 in the Danish Cancer Registry and randomly selected 5,506 control children from the Danish population, matched on sex, age and calendar time. We traced residential history of all children from 9 months before birth to time of diagnosis, calculated outdoor benzene concentration at all addresses and summarized cumulative exposure over fetal and childhood periods separately. We used conditional logistic regression for the statistical analyses. Benzene exposure during childhood above the 90th percentile was associated with relative risks for acute lymphocytic leukemia (ALL) and acute myeloid leukemia (AML) of 1.0 (95% confidence intervals (CI): 0.6-1.7) and 1.9 (95% CI: 0.3-11.1), respectively, when compared with exposure levels below the median. For CNS tumors, there was a tendency of lower risk for ependymoma and higher risk for medulloblastoma in association with higher exposure. In conclusion, benzene was associated with higher risk for childhood AML, but not ALL, which is consistent with the few previous studies.

Maternal exposure to ambient air pollution and risk of early childhood cancers: A population-based study in Ontario, Canada

BACKGROUND

There are increasing concerns regarding the role of exposure to ambient air pollution during pregnancy in the development of early childhood cancers.

OBJECTIVE

This population based study examined whether prenatal and early life (<1year of age) exposures to ambient air pollutants, including nitrogen dioxide (NO₂) and particulate matter with aerodynamic diameters ≤2.5μm (PM_2.5), were associated with selected common early childhood cancers in Canada.

METHODS

2,350,898 singleton live births occurring between 1988 and 2012 were identified in the province of Ontario, Canada. We assigned temporally varying satellite-derived estimates of PM_2.5 and land-use regression model estimates of NO₂ to maternal residences during pregnancy. Incident cases of 13 subtypes of pediatric cancers among children up to age 6 until 2013 were ascertained through administrative health data linkages. Associations of trimester-specific, overall pregnancy and first year of life exposures were evaluated using Cox proportional hazards models, adjusting for potential confounders.

RESULTS

A total of 2044 childhood cancers were identified. Exposure to PM_2.5, per interquartile range increase, over the entire pregnancy, and during the first trimester was associated with an increased risk of astrocytoma (hazard ratio (HR) per 3.9μg/m3=1.38 (95% CI: 1.01, 1.88) and, HR per 4.0μg/m³=1.40 (95% CI: 1.05-1.86), respectively). We also found a positive association between first trimester NO₂ and acute lymphoblastic leukemia (ALL) (HR=1.20 (95% CI: 1.02-1.41) per IQR (13.3ppb)).

CONCLUSIONS

In this population-based study in the largest province of Canada, results suggest an association between exposure to ambient air pollution during pregnancy, especially in the first trimester and an increased risk of astrocytoma and ALL. Further studies are required to replicate the findings of this study with adjustment for important individual-level confounders.