Air pollution consists of chemicals resulting from many human activities and natural resources, which can cause gene mutations.
It is long known that urban air is polluted by gaseous and some solid particles, and long or short term exposure to these pollutants leads to various disease and mortality. Many of these solid or gas compounds are mutagenic and carcinogenic substances, which can lead to various types of cancer.
Several studies have shown that exposure to air pollution is considered as a factor associated with breast cancer.Women living in areas that experience high levels of pollution could be at a higher risk of breast cancer, according to a new study.
Research has suggested that increased exposure to soot particles could lead to denser breast tissue, which is one of the strongest risk factors linked to breast cancer.Therefore, increasing the knowledge about the consequence of air pollutants on public health is necessary for the development of practical policies to lessen the negative effect of air pollution.
Those with dense breast tissue are up to six times more likely to develop some form of breast cancer. This suggests that those in city areas could be at high risk of the disease, whether there is a family history of breast cancer or not.
Here are some studies which show the relationship between breast cancer and air pollution.
Hystad et al. (2014)
In a case–control study (N=cases 619 pre- menopausal and N=1140 postmenopausal) and (N=controls 611 premenopausal and N=1261 postmenopausal), a positive link was found between breast cancer occurrence and long-term exposure to ambient NO2. This study hypothesized that traffic pollution may have connection with the progress of breast cancer, with a larger relations in pre-menopausal women.
Reding et al. (2015)
The results of a sister study on 47,591 women showed that no connection exists between invasive breast cancer and PM2.5, PM10, or NO2; however, associated was found between NO2 and a growing risk of ER+/PR+ breast cancer. They reported that for a differential role of air pollution, there is biological plausibility by hormone receptor status.
White et al. (2016)
Moreover, the results of a study on the relationship between breast cancer incidence and exposure to multiple long-term PAH (polycyclic aromatic hydrocarbon) sources showed that PAH exposure is ubiquitous. Humans are exposed to PAHs during their life from variety of sources, such as diet, environmental tobacco smoke (ETS), cigarette smoking, and indoor and outdoor air pollution. In this population-based case-control study (1508 breast cancer cases/ 1556 controls), they found that the incidence of breast cancer rises about 30-50% in groups who are exposed to PAH sources.
In 2017 researchers from the University of Florida, US, looked at 279,967 women to discover if there was a link between pollution and breast cancer. This is the first study to assess the correlation between air pollution and breast density.
They discovered that women who have dense breast tissue were around 19 per cent more likely to live in areas that experience high levels of fine particle air pollution. Fine particle pollution – called PM2.5 – is able to penetrate into people’s systems more deeply, which can cause a number of health concerns.
The study revealed that each one unit rise in PM2.5 increased the chance of a woman having dense breast tissue by four per cent. This could also be an indication of the reason behind geographic breast cancer patterns, according to the researchers.
It is thought that increases in PM2.5 impact the body’s hormone levels, which can trigger different tissue types in the breast to start growing. Dense breast tissue tends to contain less fat, but more glandular tissue, which increases the chance of cells becoming cancerous.
Seventeen studies had been identified in 2018 evaluating the risk of breast cancer associated with air pollution. A higher risk of breast cancer has been associated with nitrogen dioxide (NO2) and nitrogen oxides (NOx) levels, both of which are proxies for traffic exposure.
Hazardous air toxic levels and sources of indoor air pollution may also contribute to breast cancer risk.
In 2018, another research was conducted which focused on the case of one unnamed woman who worked for 20 years at the Ambassador Bridge between Detroit, Michigan and Windsor, Ontario.
Doctors Michael Gilbertson and Jim Brophy, from the University of Stirling in Scotland, believe chemicals in the traffic fumes caused the cancer.
They say the BRCA1 and BRCA2 genes, which try to stop tumours growing, can be shut down by vehicle exhaust fumes.
Dr. Gilbertson said ” these outbreaks of breast cancer represent a new occupational disease”.
The woman in the case study developed breast cancer when she was 44, and then again at the age 51.
Her diagnosis came within 30 months of five other women working at the same border crossing.
And at the Detroit-Windsor tunnel, four miles away, another seven women were developing the same disease alongside them.
Dr. Gilbertson added: ‘This new research indicates the role of traffic-related air pollution in … increasing [the] incidence of breast cancer in the general population.’
The Stirling researchers say chemicals in traffic pollution can shut down the genes in the same way.
Dioxins, polycyclic aromatic hydrocarbons and aldehydes – all of which are found in exhaust fumes – are believed to stop the genes working.
Past research has confirmed this and the woman in the study did not have functioning BRCA genes but hadn’t inherited the defect.
BRCA1 and BRCA2 are genes – the breast cancer genes – which play a big role in preventing breast cancer by repairing DNA to stop defects leading to uncontrolled tumours.
Dr Gilbertson said: ‘We now have plausible mechanisms for inferring how the BRCA1/2 tumour suppressors in this highly-exposed border guard became dysfunctional and likely contributed to the ongoing epidemic of sporadic, early onset, premenopausal breast cancer among her colleagues.’
And shift work could make the pollution-cancer link worse, as past research on rats has shown those constantly exposed to daylight developed 60 per cent more tumours and the tumours grew 36 per cent faster.
In the multiethnic cohort study (2019), air pollutant exposures of particulate matter and oxides of nitrogen were estimated by kriging (NOx, NO2, PM10, PM2.5), land use regression (LUR, NOx, NO2) and California Line Source Dispersion model (CALINE4, NOx, PM2.5) for 57,589 females from the Multiethnic Cohort, residing largely in Los Angeles County from recruitment (1993–1996) through 2010. Cox proportional hazards models were used to examine the associations between time-varying air pollution and breast cancer incidence adjusting for confounding factors. Stratified analyses were conducted by race/ethnicity and distance to major roads.
Among all women, breast cancer risk was positively but not significantly associated with NOx (per 50 parts per billion [ppb]) and NO2 (per 20 ppb) determined by kriging and LUR and with PM2.5 and PM10 (per 10 µg/m3) determined by kriging. However, among women who lived within 500?m of major roads, significantly increased risks were observed with NOx, NO2, PM10 and PM2.5 determined by kriging and NOx and NO2 determined by LUR.
Subgroup analyses suggested stronger associations of NOx and NO2 among African Americans and Japanese Americans.
Further studies to confirm the effects of air pollution, particularly near-roadway exposures, on the risk of breast cancer is warranted.