Air pollution and Cancer: Evidence from BMJ Oncology
Air pollution has long been recognized as a major risk factor for cardiovascular and respiratory diseases. Increasingly, however, scientific evidence indicates that air pollution is also an important and underappreciated risk factor for cancer. A narrative review published in BMJ Oncology synthesizes current evidence on the relationship between air pollution and cancer incidence, cancer care and cancer outcomes, highlighting the scale and complexity of this global health challenge.
Air pollution as a complex mixture of pollutants
Air pollution is not a single exposure but a complex and heterogeneous mixture of particulate matter and gaseous pollutants. Key components discussed in the review include particulate matter (PM10 and PM2.5), nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs) and heavy metals.
Outdoor air pollution primarily arises from the combustion of fossil fuels associated with transportation, industrial activity and power generation. In addition, wildfire smoke is increasingly recognized as a significant source of air pollution. Indoor air pollution is largely driven by the combustion of solid fuels, such as wood, coal and biomass, for cooking and heating, particularly in low- and middle-income countries.
Strongest evidence: lung cancer
The International Agency for Research on Cancer (IARC) has classified outdoor air pollution, particulate matter and diesel exhaust as Group 1 carcinogens, indicating sufficient evidence of carcinogenicity in humans. The review highlights consistent epidemiological evidence linking long-term exposure to PM2.5 with increased lung cancer incidence and mortality, including among never-smokers.
Mechanistically, exposure to air pollution is associated with oxidative stress and chronic inflammation. Fine and ultrafine particles can penetrate deep into the lungs, generating reactive oxygen species that damage DNA, proteins and lipids. Sustained inflammatory responses may promote tumor initiation and progression. The review also discusses emerging evidence suggesting that PM2.5 exposure may contribute to lung cancer development in individuals with specific molecular characteristics, including EGFR-mutated lung cancer in never-smokers.
Associations with other cancer types
Beyond lung cancer, the review summarizes growing evidence that air pollution may be associated with several other malignancies, reflecting the ability of inhaled pollutants to enter systemic circulation or reach the gastrointestinal tract.
Breast cancer
Epidemiological studies reviewed suggest associations between exposure to particulate matter and nitrogen dioxide and an increased risk of breast cancer, particularly hormone receptor–positive tumors. Air pollution exposure has been linked to increased mammographic breast density, a known risk factor for breast cancer, as well as inflammatory and oxidative pathways that may influence tumor development.
Gastrointestinal cancers
After inhalation, particulate matter can be cleared from the respiratory tract and swallowed or translocate via the bloodstream to other organs. Meta-analyses cited in the review report associations between particulate matter exposure and colorectal and liver cancers. In addition, exposure to indoor air pollution from the use of biomass and kerosene fuels has been associated with cancers of the esophagus and stomach.
Brain cancer, ovarian cancer and childhood cancers
The review also describes evidence linking exposure to traffic-related air pollutants, including PM2.5, NO2 and black carbon, with brain tumors and cancers of the central nervous system. These associations may be mediated through systemic inflammation and potential effects on the blood–brain barrier. Furthermore, air pollution exposure has been associated with ovarian cancer and with childhood leukemia, particularly when exposure occurs during pregnancy or early life.
Implications for cancer care and outcomes
Importantly, the review emphasizes that air pollution may influence not only cancer incidence but also cancer care and cancer outcomes. Exposure to air pollution can exacerbate underlying health conditions, potentially affecting treatment tolerance, recovery and survival. Some studies suggest higher mortality among patients with cancer who are exposed to elevated levels of air pollution, although this area remains less extensively studied than cancer incidence.
Despite mounting evidence, air pollution is often underrepresented in cancer risk models and public health strategies, particularly in low- and middle-income countries where exposure levels are frequently highest. Given the long latency period between exposure and cancer development, the review cautions that the burden of air pollution–related cancers may continue to rise in the coming decades, including among younger populations and individuals without traditional risk factors such as smoking.
Improving air quality as a strategy for cancer prevention
Based on the available evidence, the authors conclude that air pollution represents one of the most widespread environmental carcinogenic exposures worldwide. Efforts to improve ambient and indoor air quality have the potential not only to reduce cardiovascular and respiratory disease but also to play a meaningful role in cancer prevention and improved cancer outcomes. Addressing air pollution therefore constitutes a critical component of long-term strategies to protect population health.
Source: BMJ Oncology