Doctor warns PM2.5 pollution can trigger lung cancer risk, including among non-smokers

Assoc Prof Dr Thanika Ketphueak, an oncologist in the Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, said Chiang Mai and many northern provinces have faced air pollution for more than a decade, with conditions worsening—particularly over the past three to five years.

She said severe pollution, often reflected by red or purple readings on the Air Quality Index (AQI), has clear health impacts, including respiratory disease, stroke and heart disease—and lung cancer.

PM2.5 refers to particulate matter smaller than 2.5 microns—about a thousand times smaller than a millimetre—which allows it to penetrate deep into the lungs, she said.

Thanika said lung cancer is widely understood to be linked to smoking, and that is correct: the more and longer people smoke, the higher the risk.

However, she said lung cancer can also occur in non-smokers, and not rarely—especially among younger people, women, and those of East Asian background.

She said studies dating back to 2009 found that patients with these characteristics are often linked to a gene mutation known as EGFR. Lung cancer in this group can be influenced by multiple contributing factors, including genetics, ethnicity, exposure to carcinogens, and air pollution.

Thanika said research has found that for every 1 microgram increase in PM2.5, the incidence of lung cancer associated with the EGFR mutation increases, with findings reported in populations in the United Kingdom, South Korea and Taiwan. She said people exposed to high air pollution for three years had 1.08 times higher incidence of EGFR-mutated lung cancer than those exposed to lower levels—suggesting three years of high exposure may be enough to trigger this type of cancer.

She also cited animal studies showing PM can act as a trigger for lung cancer in mice that already carry EGFR and KRAS mutations, stimulating the growth of mutated cells in both normal lung tissue and lesions that may later develop into cancer. This is thought to occur through inflammation and inflammatory cytokines, including IL-1β.

In another study examining normal lung tissue from 295 patients—both those with cancer and those with small suspected tumours—Thanika said researchers found 18% of normal lung tissue carried an EGFR mutation, and 53% carried a KRAS mutation.

Based on these findings, she said PM2.5 can act as a trigger for lung cancer, particularly in people who already have EGFR or KRAS mutations.

She stressed, however, that PM2.5 is a trigger rather than a single direct cause, and it is not possible to definitively attribute an individual lung cancer case to one factor alone, as cancer development is complex and can be driven by multiple influences.

Thanika said people should avoid areas with high air pollution where possible. If avoidance is not possible, she recommended wearing masks that protect against PM2.5—such as N95 masks or higher—to filter fine particles. She also advised limiting outdoor activities, staying indoors, and using air purifiers.