Everyone knows that tobacco smoking can cause lung cancer. But whoever thought air pollution could lead to lung cancer with equal severity?
Lung Care Foundation, a not-for-profit organization that works on improving lung health in India, did a study of lung cancer patients at Sir Ganga Ram Hospital, New Delhi. It found that nearly half of those patients had never smoked [i].
About Lung Cancer
Lung cancer is the biggest killer among various cancers. It has a survival rate of fewer than 5 years.
The prime cause of lung cancer, as has been the conventional understanding over decades, is tobacco smoking.
The damage due to tobacco is at the cellular DNA level and takes many years of abuse to result in cancer. As a result, lung cancer mainly afflicts older people, with the incidence rising steeply after 45-49 years of age [ii].
There are various types of lung cancers.
The most common is Squamous Cell Carcinoma, which is seen in smokers. Another type of lung cancer, Adenocarcinoma, is more common in non-smokers.
Air Pollution and PM2.5
Air pollution has many ingredients, one of which is PM2.5, or particulate matter of size less than 2.5 micrometers.
These particles are so small that they can penetrate deep into your lungs and even into your bloodstream, causing disease and even death.
In 2013, outdoor air pollution was classified as a cancer-causing agent by the International Agency for Research on Cancer (IARC), a part of WHO[iii].
Besides lung cancer, PM2.5 is also known to cause stroke, heart, and respiratory diseases.
The Study Results
The Lung Care Foundation study found the incidence of lung cancer in younger patients is rising.
According to a study done 70 years ago in India, 2.5 percent of the lung cancer patients were below 30 years of age. In the current study, this proportion was increased to 3.3 percent.
Nearly 21 percent of the patients were young (under 50 years old). Overall, 50 percent of the patients studied had never smoked in their life. Among the younger patients, this proportion rose to 70 percent.
This increase in the proportion of younger lung cancer patients was not due to increased smoking among them.
The percentage of women among lung cancer patients is increasing. From 1958-85, the male to female ratio of lung cancer patients was 6.7:1, which nearly halved to 3.8:1 between 2012-18.
However, this increase is not due to increased smoking among women. This increase is also not coming from work-related air pollution since women are less likely to be exposed to mines and construction sites.
A 2016 paper in the European Respiratory Journal mentioned that among non-smokers, adenocarcinoma is the most common form of lung cancer.
Increasing levels of ambient PM2.5 levels have proven to be associated with increasing evidence of adenocarcinoma [iv].
The Lung Care Foundation study found an increase in the numbers of women and younger people with mostly adenocarcinoma, and not squamous cell carcinoma.
This shows that the lung cancer cases in women and younger people are not related to smoking, but to air pollution, specifically PM2.5 levels.