How air pollution contributes to lung cancer

Particulate matter, a combination of extremely small solid particles and liquid droplets that are found in the air, increase the risk of lung cancer


Photo: Arun Sharma/Hindustan Times
Photo: Arun Sharma/Hindustan Times

Smoking is the biggest known cause of lung cancer, but over the past few years, exposure to air pollution is also being recognized as a prominent risk factor. It’s actually a myth that only smokers get lung cancer, says Gagan Saini, senior consultant (radiation oncology), Fortis Hospital, Noida, near Delhi. “While it is true that smoking increases the risk of lung cancer the most, there are many non-smokers who also get lung cancer. The culprit could be second-hand smoke, pollution, radiation exposure or genetic propensity.” 

There’s another myth about lung cancer that women don’t get this disease. According to a report published in the Indian Journal Of Medical Research last year, lung cancer constitutes 6.9% of all new cancer cases and 9.3% of all cancer-related deaths in both sexes.

“Lung cancer is the No.1 killer cancer in women, more than breast cancer,” says Dr Saini.

The pollution connection

Researchers across the world are pointing out that smoking alone cannot explain the relatively high rates of lung cancer that are observed among non-smokers and never-smokers. The World Health Organization (WHO) estimates that in 2012, 14% of outdoor air pollution-related deaths were due to lung cancer. In a 2015 report, published in the Lancet journal, Jennifer King of the Lung Cancer Alliance in the US, says that up to 20% of lung cancers occur among never-smokers, and a large population of young women with lung cancer are in the never-smoker group.

In 2013, WHO’s International Agency for Research on Cancer, after evaluating over 1,000 scientific papers and studies from five continents, classified outdoor air pollution as a carcinogen (cancer-causing agent) to look out for, particularly for lung and bladder cancers.  

The threat

When it comes to cancer risk, it is the tiny dust-like particles called particulate matter (PM), a combination of extremely small solid particles and liquid droplets that are found in the air, which are the most risky.

“In particular, the smallest particles, known as PM2.5, are the most risky for lung cancers as they are extremely permeable to lung tissue linings. These are chiefly found in emissions from diesel engines. And the scary part is that one third of the population in India lives in towns with PM10 levels classified as critical,” says Dr Saini. “Things may get worse as it gets colder due to the formation of smog which makes the delivery of pollutants to the end of lung airways even easier,” he adds.

Our body has defence mechanisms to keep pollutants out of the respiratory system, such as nasal hair, mucus and macrophage, which is a type of white blood cell that destroys foreign substances and microbes. But these defence mechanisms fail if the pollution level is very high.

Take precaution

Majority of the patients get diagnosed at an advanced stage of the disease. Cough that does not go away, chest pain, blood-tinged sputum or blood in the sputum are the common symptoms, often associated with generalized weakness, weight loss, muscle aches, says Sundeep Salvi, director, Chest Research Foundation, Pune. “X-ray of the chest, CT scan or MRI scan of the lungs. Bronchoscopy and lung biopsy are the common ways used to diagnose the disease,” he adds.

Sachin Almel, consultant (medical oncology), Hinduja Healthcare Surgical, Mumbai lists a few ways in which we can help prevent it. “Choosing ‘active travel’ options where possible, like walking and cycling, can help reduce pollution levels from transport in the long term and is also a great way to be more active, which is linked to a reduced risk of cancer and other diseases,” he says. For exercising outdoors, suggests Dr Almel, one could choose less polluted times like the afternoons.

Dr Salvi says surgical masks are useless as the particles that cause lung cancer are small enough to pass through them. “Only sophisticated masks like the N95 are the ones which can prevent the entry of these tiny particles into the lung,” he adds. He also says that mosquito coil smoke contains carcinogens, which when inhaled over a long period of time can increase the risk of developing lung cancer.

“Air purifiers are an option one can try, and one must also avoid going to places that have poor air quality. Tapzo (formerly Helpchat), Safar, and Plume Air Report are some of the apps that will tell you which areas are unsafe,” says Dr Almel. 

We need governments and local authorities to work together to develop a comprehensive strategy to reduce air pollution, says Dr Salvi. “Meanwhile, we need to consciously reduce our exposure to pollution as far as possible to hedge the risks,” he adds. 

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