Air pollution and risk of Lung Cancer

By Dr. Bhuvan Chugh in Cancer Care / Oncology

Nov 08 , 2021 | 3 min read

No cancer kills more than lung cancer and no other cancer has its causes more clearly identified. It is the most common cancer in men worldwide and the second most common when considering the number of new cases in both sexes combined. Lung cancer accounts for 18% of all cancer deaths, which is worrying considering it accounts for 11% of the entire new cancer burden each year. Put it simply, it is one type of cancer that has poor outcomes and our best bet lies in prevention. 

The primary risk factor is smoking, which accounts for up to 90% of cases of all lung cancers. Smoking increases the risk of lung cancer by 10-30-fold and cessation brings down the risk by 20-90% and is evident within 5 years of cessation. The risk reduces by 80-90% after 15 years of stopping. Not only cessation but the reduction in smoking has also been found to be beneficial, especially in heavy smokers, reducing the risk by almost one-third.

Air pollution, the bane of our modern world, has numerous adverse health effects and lung cancer is among one them. Air pollution consists of gaseous pollutants such as sulfur dioxide, nitrogen dioxide, carbon monoxide, volatile organic compounds, and particulate matter (PM). These pollutants are predominant components of the measured Air Quality Index (AQI) as defined in the Clean Air Act. Among the pollutants, PM is a major concern as they lead to prolonged low-grade inflammation and oxidative stress, which further causes genetic mutation and gives rise to cancer. Particulate Matter (PM) is broadly characterized by its size. PM >10 µm size are usually unable to go beyond the nose or windpipe and are not deposited in the lung. Those that are less than 10 µm, called PM10, are the largest inhalable particles. PM10 also includes fine particulate matter - those with a size less than 2.5 µm (PM2.5) and nanoparticles (size <0.1 µm). The mass concentration (µg/m3) is a common metric used to measure and regulate PM pollution. The WHO-based air quality guidelines recommend PM2.5 <10µg/m3. 

In India average annual PM2.5 exposure is 83.2 µg/m3. International Agency for Research on Cancer (IARC) has classified outdoor pollution and PM as a group 1 human carcinogen for lung cancer. PM2.5 air pollution contributes to more than 250,000 cases of lung cancer worldwide in a year and is second only to smoking as a cause of lung cancer-related deaths. Data suggests a spine chilling 8% and 9% increase in the lung cancer incidence and deaths, for each 10µg/m3 increase in PM2.5 and PM10 concentration respectively over the WHO based air quality guidelines. What is even scary is recent data suggests that the risk maybe even as high as 14%. Children, the elderly, diabetics, those with heart & lung disease, and those who work, or exercise outdoors are at a particularly higher risk of being affected. 

Measures to reduce air pollution-associated cancers are challenging due to numerous sources of production and poor understanding of the risk. Measures to reduce air pollution need to be considered. Indian Government launched National Clean Air Programme (NCAP) to tackle the air pollution problem across the country. It plans to achieve a 20% to 30% reduction in Particulate Matter concentrations by 2024 keeping 2017 as the base year. It is a comprehensive, city-specific plan to reduce vehicular and industrial pollution among other things. Individual-level interventions include the use of respirators and avoidance behavior such as avoiding outdoor work or exercise during peak PM2.5 times. 

Lung cancer is a particularly challenging health problem. It is associated with high morbidity and mortality. Air pollution represents a growing public health emergency that needs immediate attention both at the public health level and policy interventions. It is time we give that attention; prevention is always better than cure.