Air Pollution And Breast Cancer: Is There A Link?

Air pollution is a complex mixture of various gaseous pollutants and solid particles. According to the World Health Organization, more than 80% of populations living in urban areas with air monitoring devices are exposed to air quality levels exceeding WHO thresholds. A study by the US Department of Health and Human Services found that living in an area with high levels of particulate air pollution was associated with an increased incidence of breast cancer. Another study found that an increase of 10 μg/m3 in ethylbenzene, o-xylene, m-xylene, and 10 ppb of NO in the adjusted model corresponded to an increase in the odds of stage I BC in comparison to non-invasive BC. Benzene and o-xylene were also associated with an increased odds of BC (stages III & IV) compared to non-aggressive stages.

Air pollution and breast cancer: a review

Air pollution is a complex mixture of various gaseous pollutants and solid particles. According to the World Health Organization (WHO), more than 80% of people living in urban areas with air monitoring are exposed to poor air quality. A recent study has shown that air pollution caused 4.2 million premature deaths globally in 2019.

Breast cancer has now become the most prevalent cancer worldwide, surpassing lung cancer. By the end of 2020, there were 7.8 million women diagnosed with breast cancer in the previous five years, making it the world's most common cancer. It is predicted that by 2040, the burden of breast cancer will increase to over 3 million new cases and 1 million deaths annually.

Although breast cancer is a complex multifactorial disease with several known risk factors, almost half of diagnosed breast cancers in women have no detectable risk factor, suggesting a need to identify still unknown risk factors. There is growing evidence that air pollution can be a risk factor for breast cancer. Ecological studies propose that breast cancer risk is higher in urban areas with higher air pollution compared to rural areas. Air pollution contains many carcinogens that may perform as endocrine disruptors and cause oxidative DNA-damage, which may affect breast cancer risk. However, studies have shown inconsistent results about the impact of air pollution on breast cancer.

Methods

This review aims to examine the impacts of single and multiple air pollutants on the severity of breast cancer. Data on 1148 diagnosed breast cancer cases between 2008 and 2016 were obtained from the Cancer Research Center and private oncologist offices in Tehran, Iran. Ambient air pollution data were obtained from previously developed land use regression models. Associations between pollutants and stage of breast cancer were assessed by multinomial logistic regression models.

Results

An increase of 10 μg/m3 in ethylbenzene, o-xylene, m-xylene, and 10 ppb of NO in the adjusted model corresponded to a significant increase in the odds of stage I breast cancer in comparison to non-invasive breast cancer. Benzene and o-xylene were associated with increased odds of stages III & IV breast cancer compared to non-aggressive stages. The highest multiple-air-pollutants quartile was associated with a higher odds of stage I breast cancer in patients under 50 years old.

This study provides evidence that exposure to air pollutants is associated with increased breast cancer stage at diagnosis, especially under premenopause age.

Outdoor air pollution and breast cancer: a meta-analysis of epidemiological evidence

Outdoor air pollution is a major contributor to the global disease burden, with most people living in areas where air pollution levels exceed the World Health Organization's air quality guidelines. Fine particulate matter (PM2.5) is of particular concern as it can be inhaled deep into the lungs and has been linked to various adverse health effects, including cancer. While the link between outdoor air pollution and lung cancer is well-established, the evidence for other types of cancer, such as breast cancer, is more limited. This meta-analysis aims to examine the epidemiological evidence on the association between outdoor air pollution and breast cancer risk.

Methods

The meta-analysis included studies that assessed the relationship between outdoor air pollution and breast cancer incidence or mortality. A systematic literature search was performed using databases such as Medline and reference lists of relevant studies. The studies were assessed for eligibility based on predefined criteria, and data on study design, exposure assessment, outcome definition, and effect estimates were extracted.

Results

The meta-analysis included 14 studies that investigated the association between outdoor air pollution and breast cancer. The studies were conducted in North America, Europe, and Asia, with a total of over 400,000 participants. The majority of the studies used fixed-site monitoring or model-based indicators of outdoor air pollution exposure. The air pollutants of interest included particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), and ozone (O3).

The meta-analysis found a positive association between outdoor air pollution and breast cancer risk. The increase in risk ranged from 8% to 14% per 10 μg/m3 increase in PM2.5 concentrations. Similar results were observed for PM10, with an 8% increase in risk per 10 μg/m3. Studies also reported significant adverse associations between NO2 exposure and lung cancer mortality, particularly in North America and Europe. However, the evidence for other types of cancer, such as breast cancer, is more limited, and further research is needed.

Public Health Implications

The findings of this meta-analysis have important public health implications. As outdoor air pollution is a widespread issue affecting a large portion of the global population, reducing air pollution levels can potentially reduce the burden of cancer, including breast cancer. Policy interventions and regulations aimed at reducing emissions from major sources, such as industry, power generation, transportation, and domestic burning, are crucial to mitigate the health risks associated with outdoor air pollution.

Vehicular traffic-related air pollution and breast cancer risk: a systematic review and meta-analysis of observational studies

The study, published in the *Journal of the National Cancer Institute*, is one of the largest studies to date that looks at the relationship between outdoor air pollution, specifically fine particulate matter, and breast cancer incidence. The research was conducted by scientists at the National Institute of Environmental Health Sciences (NIEHS) and the National Cancer Institute (NCI).

Methods

The researchers combined historical air quality data with breast cancer data from a large U.S. study, the NIH-AARP Diet and Health Study. They found that living in an area with high levels of particulate air pollution was associated with an increased incidence of breast cancer. The largest increases in breast cancer incidence were among women who, on average, had higher particulate matter levels (PM2.5) near their homes prior to enrolling in the study, compared to those who lived in areas with lower levels of PM2.5.

Results

The researchers saw an 8% increase in breast cancer incidence for women living in areas with higher PM2.5 exposure. Although this is a relatively modest increase, the findings are significant given that air pollution is a ubiquitous exposure that impacts almost everyone. The study provides further support for the growing body of literature suggesting that air pollution is related to breast cancer.

Discussion

The ability to consider historical air pollution levels is an important strength of this research. It can take many years for breast cancer to develop, and in the past, air pollution levels tended to be higher, which may make previous exposure levels particularly relevant for cancer development. The study also evaluated estrogen receptor-positive (ER+) and -negative (ER-) tumors separately and found that PM2.5 was associated with a higher incidence of ER+ breast cancer but not ER- tumors. This suggests that PM2.5 may affect breast cancer through an underlying biologic pathway of endocrine disruption.

The study concludes that high levels of particulate air pollution are associated with an increased incidence of breast cancer. The findings provide further evidence of the carcinogenicity of air pollution and have important implications for public health and policy. Further research is needed to confirm the conclusions and to better understand the underlying biological mechanisms.

Exposure to ambient air pollution and the incidence of lung cancer and breast cancer in the Ontario Population Health and Environment Cohort

Lung and breast cancers are highly prevalent worldwide. While the link between exposure to ambient fine particulate matter (PM2.5) and lung cancer is well-established, the association between PM2.5 and breast cancer is less clear.

Li Bai et al. conducted a population-based cohort study using the Ontario Population Health and Environment Cohort (ONPHEC) to investigate the associations between chronic exposure to PM2.5, nitrogen dioxide (NO2), ozone (O3), and redox-weighted average of NO2 and O3 (Ox) with incident lung and breast cancer. The cohort included all long-term residents aged 35-85 years living in Ontario, Canada, from 2001 to 2015, totaling approximately 4.9 million individuals and 2.5 million women, respectively. Incident lung and breast cancers were identified using the Ontario Cancer Registry, and annual exposure estimates were assigned based on the residential postal codes of the subjects.

The results showed positive associations between lung cancer incidence and PM2.5 and NO2, with hazard ratios (HR) of 1.02 (95% CI: 1.01-1.05) per 5.3 μg/m3 and 1.05 (95% CI: 1.03-1.07) per 14 ppb, respectively. However, no significant associations were found between air pollution and breast cancer incidence.

While this particular study did not find compelling evidence of a link between air pollution and breast cancer, other studies have suggested potential associations, especially with specific subtypes of breast cancer. Further research is needed to fully understand the relationship between air pollution and breast cancer incidence.

Long-term exposure to fine particulate matter and breast cancer incidence in the Danish Nurse Cohort Study

The study "Long-term Exposure to Fine Particulate Matter and Breast Cancer Incidence in the Danish Nurse Cohort Study" by Zorana Jovanovic Andersen and colleagues investigated the potential link between air pollution and breast cancer risk. The study included 22,877 female nurses from the Danish Nurse Cohort who were recruited in 1993 or 1999, with a mean follow-up of 16 years. During this period, 1,145 nurses developed breast cancer. The researchers estimated annual mean concentrations of particulate matter (PM2.5 and PM10) and nitrogen dioxide (NO2) at the nurses' residences since 1990 using an atmospheric chemistry transport model. They examined the association between the 3-year running mean of each pollutant and breast cancer incidence using a time-varying Cox regression analysis.

The results of the study showed no association between breast cancer incidence and exposure to PM2.5, PM10, or NO2. The hazard ratios (HR) and 95% confidence intervals (CI) were as follows: HR 0.99 (0.94-1.10) for PM2.5, HR 1.02 (0.94-1.10) for PM10, and HR 0.99 (0.93-1.05) for NO2. These findings suggest that exposure to air pollution in adulthood does not increase the risk of breast cancer. However, the researchers noted that more data is needed to understand the effects of early exposure to air pollution, before the first birth, on breast cancer risk.

The study had several strengths, including a large cohort of female nurses, significant air pollution exposure contrasts, detailed information on breast cancer risk factors, and a high-resolution air pollution model. However, a limitation of the study was the lack of data on air pollution levels during puberty and early adulthood, which may also be relevant exposure windows for breast cancer development.

In conclusion, the "Long-term Exposure to Fine Particulate Matter and Breast Cancer Incidence in the Danish Nurse Cohort Study" found no association between air pollution and breast cancer risk in adulthood. However, more research is needed to understand the potential effects of early exposure to air pollution on breast cancer development.

Frequently asked questions