Air pollution and liver cancer: A systematic review

Air pollution and its impact on cancer incidence, cancer care and cancer outcomes

Air pollution is an under-recognised global health threat linked to an increased risk of cancers and is due primarily to the burning of fossil fuels. This review provides a high-level overview of the associations between outdoor and indoor air pollution and cancer risk and outcomes. Outdoor air pollutants are largely due to the burning of fossil fuels from human activities, although there is growing data implicating outdoor pollution from wildfire smoke. Indoor air pollution is primarily caused by burning solid fuel sources such as wood, coal and charcoal for household cooking and heating. There is a growing number of pieces of evidence linking exposure to pollution and the risk of developing cancers. The strongest evidence is seen on the positive association of air pollution, particularly particulate matter 2.5 with lung cancer. Emerging data implicate exposure to pollutants in the development of breast, gastrointestinal and other cancers. The mechanisms underlying these associations include oxidative stress, inflammation and direct DNA damage facilitated by pollutant absorption and distribution in the body. References were identified through a PubMed search for articles published in 2000 to October 2024 using the terms 'air pollution' or 'pollutants' and 'carcinoma' or ''cancer'. Air pollution poses significant risks to health. Its health impacts, including cancer risks, are often underestimated. Hazardous pollutants have been studied in several epidemiological cohort studies. Despite the mounting evidence, air pollution is often overlooked in predictive cancer risk models and public health intervention.

Mediating effect of diabetes in the association between long-term PM2.5 exposure and cancer risk in CHARLS

Long-term exposure to air pollutants and diabetes are both linked to cancer development. However, their combined effect remains unclear. This study examined the relationship between air pollutants and cancer incidence, with diabetes as a potential mediator. Data from 10,590 participants in the 2015 China Health and Retirement Longitudinal Study (CHARLS) were analyzed. Participants were grouped based on cancer diagnosis, and air pollutant exposure levels were estimated using satellite-based spatiotemporal models. Generalized linear regression and restricted cubic spline (RCS) analysis were used to assess the impact of air pollutants and diabetes in covariates-adjusted models. Further analyses, including conditional independence test, mediation effect and sensitivity analysis based on Bayesian networks, were performed to further analyze specific air pollutants. After adjusting for covariates, particulate matter (PM) (PM ≤ 1 μm in aerodynamic diameter [PM1], PM2.5, ammonium (NH4), nitrate (NO3) and diabetes showed significant associations with cancer incidence. RCS analysis confirmed significant direct effects of PM2.5 and PM10 on cancer and the mediated effects of diabetes. The interaction between diabetes and both PM2.5 and PM10 was further supported by conditional independence tests, highlighting diabetes as a significant mediator in the PM2.5-cancer relationship. This study offers a novel perspective by identifying diabetes as a key intermediary in the association between PM2.5 exposure and cancer risk, providing evidence that diabetes plays a significant mediating role in air pollutant-related cancer development.

Effects of air pollution on the development and progression of digestive diseases: an umbrella review of systematic reviews and meta-analyses

Air pollution, especially particulate matter (PM), is one of the most common risk factors for global burden of disease. However, its effect on the risk of digestive diseases is unclear. Herein, we attempt to explore this issue by reviewing the existing evidence from published meta-analyses. We conducted a systematic literature search to identify all relevant meta-analyses regarding the association of air pollution with digestive diseases, and summarize their major findings. We assessed the methodological quality and evidence quality of the included meta-analyses using the AMSTAR-2 and GRADE tools, respectively, and the overlap of primary studies was assessed by the GROOVE tool. Nine meta-analyses were included in our analysis, containing 43 primary studies with high overlap. In the included meta-analyses, the methodological quality was from critically low to moderate, and the evidence quality was from very low to moderate. The exposure was primarily PM2.5. Seven, four, and one meta-analysis investigated the effect of air pollution on liver diseases, gastrointestinal diseases, and pancreatic diseases, respectively. PM2.5 exposure was significantly associated with liver dysfunction, chronic liver diseases, liver cancer, and colorectal cancer, but not oesophagus cancer, gastric cancer, or pancreatic cancer. Based on very low to moderate quality evidence from meta-analyses, PM2.5 exposure may contribute to the development of some digestive diseases, especially liver diseases.

Exploring the association between air pollution and the incidence of liver cancers

Liver cancer, namely hepatocellular carcinoma (HCC), is a major global health concern deeply influenced by environmental factors. Air pollutants emerged as significant contributors to its incidence. This review explores the association between air pollution-specifically particulate matter (PM2.5), industrial chemicals like vinyl chloride, and benzene-and the increased risk of liver cancer. Mechanistically, air pollutants may cause liver damage by inducing oxidative stress, inflammation, and genetic mutations, contributing to cancer development. Epidemiological evidence from cohort and geographic studies highlights a positive correlation between long-term exposure to air pollutants and elevated incidence and mortality of liver cancer. Furthermore, air pollution has been shown to worsen survival outcomes in liver cancer patients, particularly those diagnosed at early stages. The review emphasizes the need for stricter air quality regulations and relevant research for underlying mechanisms exposed to air pollution. Addressing air pollution exposure could be crucial for reducing liver cancer risks and improving public health outcomes.

Association of Socio-Environmental Burden and Inequality With Cancer Screening and Mortality

BACKGROUND AND OBJECTIVES

Social and environmental injustice may influence accessibility and utilization of health resources, affecting outcomes of patients with cancer. We sought to assess the impact of socio-environmental inequalities on cancer screening and mortality rates for breast, colon, and cervical cancer.

METHODS

Data on cancer screening and environmental justice index social and environmental ranking (SER) was extracted from the CDC PLACES and ATSDR, respectively. Mortality rates were extracted using CDC WONDER. Screening targets were defined by Healthy People 2030.

RESULTS

Among census tracts, 14 659 were classified as "low," 29 534 as "moderate," and 15 474 as "high" SER (high SER denoting greater socioenvironmental injustice). Screening targets were achieved by 31.1%, 16.2%, and 88.6% of tracts for colon, breast, and cervical cancers, respectively. High SER tracts were much less likely to reach screening targets compared with low SER tracts for colon (OR: 0.06), breast (OR: 0.24), and cervical cancer (OR: 0.05) (all p < 0.001). Median mortality rates for low and high SER were 16.7, and 21.0, respectively, for colon, 13.4, 14.75, respectively, for breast, and 1.0, 1.6, respectively, for cervical cancer (all p < 0.05).

CONCLUSION

Socioenvironmental disparities negatively influence cancer screening and mortality, underscoring the need to reduce environmental injustices through measures like equitable cancer screening services.

Association Between Environmental Air Pollution and Thyroid Cancer and Nodules: A Systematic Review

Background: The global incidence of thyroid cancer has increased over the past several decades. While this increase is partially due to increased detection, environmental pollutants have also emerged as a possible contributing factor. Our goal was to perform a systematic review to assess the relationship between environmental air pollution and thyroid cancer. Methods: Systematic literature search was performed using PubMed, EMBASE, Cochrane Library, Web of Science, and Scopus databases for original articles published prior to March 2024, investigating outdoor air pollution and thyroid cancer/nodules (PROSPERO CRD42024517624). Inclusion criteria included quantitative reporting of pollutant levels and effect size. Specific pollutants included ozone (O3), particulate matter less than 2.5 (PM2.5) or 10 microns in diameter (PM10), sulfur dioxide (SO2), nitric oxides (NOx), carbon monoxide (CO), and polyaromatic hydrocarbons (PAHs). Study design, sample size, pollution assessment method, covariates, and strength/direction of associations between pollutants and thyroid cancer/nodule detection were extracted, and descriptive synthesis was utilized to summarize pertinent findings. Risk of bias was assessed using the National Heart, Lung, and Blood Institute quality assessment tool. Results: Of 1294 identified studies, 11 met inclusion criteria. Over 6 million patients from diverse regions were represented across studies. Pollutants studied included O3 in 5 studies; PM2.5, PM10, SO2, and NOx in 3 studies; unspecified PM and CO in 2 studies; and PAHs in 1 study. Primary outcome was thyroid cancer diagnosis among 9 studies and thyroid nodule detection in 2. All studies examining NOx and O3 reported increased risks ranging from 1.03 to 1.5-fold and 1.1 to 1.3-fold, respectively. Both studies assessing PM2.5 reported 1.18 to 1.23-fold increased odds of thyroid cancer diagnosis, and the magnitude of association increased with increasing duration or concentration of PM2.5 Inconsistent results were observed for levels of CO, PM10, and SO2. Conclusion: While an emerging body of literature suggests a potential association between air pollution and thyroid cancer, the quality of evidence is limited by study design constraints, variability in exposure assessment, and inconsistent adjustment for potential confounding factors. The heterogeneity in study designs and methodologies present challenges in interpreting results, underscoring the need for standardized approaches in future research.

Air pollutants and primary liver cancer mortality: a cohort study in crop-burning activities and forest fires area

Introduction

Northern Thailand experiences high levels of air pollution in the dry season due to agricultural waste burning and forest fires. Some air pollutants can enter the bloodstream, and the liver has the role of detoxifying these along with other harmful substances. In this study, we assessed the effects of long-term exposure to air pollutants on liver cancer mortality in this area.

Methods

A cohort of 10,859 primary liver cancer patients diagnosed between 2003 and 2018 and followed up to the end of 2020 were included in the study. Extended time-varying covariates of the annually averaged pollutant concentrations updated each year were utilized. The associations between air pollutants and mortality risk were examined by using a Cox proportional hazard model.

Results

Metastatic cancer stage had the highest adjusted hazard ratio (aHR) of 3.57 (95% confidence interval (CI):3.23-3.95). Being male (aHR = 1.10; 95% CI: 1.04-1.15), over 60 years old (aHR = 1.16; 95% CI: 1.11-1.21), having a history of smoking (aHR = 1.16; 95%CI: 1.11-1.22), and being exposed to a time-updated local concentration of PM2.5 of 40 μg/m3 (aHR = 1.10; 95% CI: 1.05-1.15) increased the mortality risk.

Conclusion

We found that air pollution is one of several detrimental factors on the mortality risk of liver cancer.

Long-Term Effect of Temperature Increase on Liver Cancer in Australia: A Bayesian Spatial Analysis

BACKGROUND

While some evidence has potentially linked climate change to carcinogenic factors, the long-term effect of climate change on liver cancer risk largely remains unclear.

OBJECTIVES

Our objective is to evaluate the long-term relationship between temperature increase and liver cancer incidence in Australia.

METHODS

We mapped the spatial distribution of liver cancer incidence from 2001 to 2019 in Australia. A Bayesian spatial conditional autoregressive (CAR) model was used to estimate the relationships between the increase in temperature at different lags and liver cancer incidence in Australia, after controlling for chronic hepatitis B prevalence, chronic hepatitis C prevalence, and the Index of Relative Socio-economic Disadvantage. Spatial random effects obtained from the Bayesian CAR model were also mapped.

RESULTS

The research showed that the distribution of liver cancer in Australia is spatially clustered, most areas in Northern Territory and Northern Queensland have higher incidence and relative risk. The increase in temperature at the lag of 30 years was found to correlate with the increase in liver cancer incidence in Australia, with a posterior mean of 30.57 [95% Bayesian credible interval (CrI): 0.17, 58.88] for the univariate model and 29.50 (95% CrI: 1.27, 58.95) after controlling for confounders, respectively. The results were not highly credible for other lags.

DISCUSSION

Our Bayesian spatial analysis suggested a potential relationship between temperature increase and liver cancer. To our knowledge, this research marks the first attempt to assess the long-term effect of global warming on liver cancer. If the relationship is confirmed by other studies, these findings may inform the development of prevention and mitigation strategies based on climate change projections. https://doi.org/10.1289/EHP14574.

The Association of Socio-Environmental Inequality and Outcomes Among Patients Undergoing Major Surgery

INTRODUCTION

Environmental hazards may influence health outcomes and be a driver of health inequalities. We sought to characterize the extent to which social-environmental inequalities were associated with surgical outcomes following a complex operation.

METHODS

In this cross-sectional study, patients who underwent abdominal aortic aneurysm repair, coronary artery bypass grafting, colectomy, pneumonectomy, or pancreatectomy between 2016 and 2021 were identified from Medicare claims data. Patient data were linked with social-environmental data sourced from Centers for Disease Control and Agency for Toxic Substances and Disease Registry data based on county of residence. The Environmental Justice Index social-environmental ranking (SER) was used as a measure of environmental injustice. Multivariable regression analysis was performed to assess the relationship between SER and surgical outcomes.

RESULTS

Among 1,052,040 Medicare beneficiaries, 346,410 (32.9%) individuals lived in counties with low SER, while 357,564 (33.9%) lived in counties with high SER. Patients experiencing greater social-environmental injustice were less likely to achieve textbook outcome (odds ratio 0.95, 95% confidence interval 0.94-0.96, P < 0.001) and to be discharged to an intermediate care facility or home with a health agency (odds ratio 0.97, 95% confidence interval 0.96-0.98, P < 0.001).

CONCLUSIONS

Cumulative social and environmental inequalities, as captured by the Environmental Justice Index SER, were associated with postoperative outcomes among Medicare beneficiaries undergoing a range of surgical procedures. Policy makers should focus on environmental, as well as socioeconomic injustice to address preventable health disparities.

In-Utero exposure to potential sources of indoor air pollution and umbilical cord blood leukocyte telomere length

Indoor air pollution (IAP) has been associated with various adverse health effects. However, the evidence regarding such an association with leukocyte telomere length (LTL) in cord blood samples is still scarce. Therefore, the present study aimed to assess the relationship between exposure to indicators of IAP and LTL in umbilical cord blood samples. This cross-sectional study was based on 188 mother-newborn pairs who participated in our study between 2020 and 2022 in Isfahan, Iran. Umbilical LTL was measured by quantitative real-time polymerase chain reaction (qRT-PCR) technique. Linear mixed-effect models were used to assess the relationship between IAP indicators and umbilical LTL, adjusted for relevant covariates. The median (interquartile range (IQR)) of umbilical LTL was 0.92 (0.47). In fully adjusted models, frequency of using degreasing spray during pregnancy (times per month) (β = -0.047, 95% CI:0.09, -0.05, P-value = 0.02), using air freshener spray during pregnancy (β = -0.26, 95% CI: -0.5, -0.02, P-value = 0.03) and frequency of using insecticides during pregnancy (times per month) (β = -0.025, 95% CI: -0.047, -0.003, P-value = 0.02) were significantly associated with shorter umbilical LTL. There was a positive significant relationship between the frequency of using cleaning spray during pregnancy (times per month) with umbilical LTL (β = 0.019, 95% CI: 0.005, 0.033, P-value = 0.01). Furthermore, the direct connection of the parking with home and the frequency of using barbecue (times per week) were marginally associated with shorter umbilical LTL. For other indicators of IAP, we did not observe any statistically significant associations. Overall, this study suggested a negative association between prenatal exposure to IAP during pregnancy and umbilical LTL.