New Delhi: Exposure to fine particulate matter (PM) 2.5 — inhalable particulate pollutants with a diameter of 2.5 micrometers present in the air — may cause lung cancer even in people with no history of smoking, researchers at the Francis Crick Institute in London have found. The study, which was released on 10 September, looked at a cohort of 40,000 people and has been hailed as a “breakthrough” in scientific circles.
While cigarette smoking is the biggest risk factor for lung cancer, responsible for more than 70 per cent of cases, the Francis Crick Institute in a statement issued about the study said that in 2019, over three lakh lung cancer deaths around the world were attributable to air pollution.
The study investigated the hypothesis that PM 2.5 causes inflammation in the lungs that causes usually dormant cells carrying cancerous mutations to become active. Proliferation of these cells, it said, along with the inflammation caused by PM 2.5 can lead to the formation of tumours, with a propensity to grow uncontrollably — cancer.
The study also found that in areas where PM 2.5 is high, the rates of other kinds of cancer are also higher.
The findings were presented by Professor Charles Swanton, lead researcher and an authority on cancer medicine, last week at the European Society of Medical Oncology (ESMO) congress. ESMO is a leading professional organisation of oncologists.
The Lancet Oncology in an article on the Francis Crick study published Thursday, described it as a “breakthrough”, and quoted Swanton as saying: “Our study has fundamentally changed how we view lung cancer in people who have never smoked.”
Swanton added: “Cells with cancer-causing mutations accumulate naturally as we age, but they are normally inactive. We’ve demonstrated that air pollution wakes these cells up in the lungs, encouraging them to grow and potentially form tumours.”
Several Indian cities, particularly those in the Gangetic flood plains, including Delhi, have been grappling with high levels of air pollution for many years now. In 2020, an analysis published in The Lancet Planetary Health estimated that in 2019, 1.67 million deaths in India were attributable to air pollution. This was about 17.8 per cent of all deaths in the country.
‘Air pollution causes 1 in 10 lung cancer cases in UK’
According to the Francis Crick Institute’s statement on the study, “Although smoking remains the biggest risk factor for lung cancer, outdoor air pollution causes roughly 1 in 10 cases of lung cancer in the UK.”
The statement added: “An estimated 6,000 people who have never smoked die of lung cancer every year in the UK, some of which may be due to air pollution exposure. Globally, around 300,000 lung cancer deaths in 2019 were attributed to exposure to PM2.5.”
Even small changes in air pollution may have a devastating effect on human health, revealed the study.
“According to our analysis, increasing air pollution levels increases the risk of lung cancer, mesothelioma and cancers of the mouth and throat,” said co-first author Dr Emilia Lim in a statement.
She added: “This finding suggests a broader role for cancers caused by inflammation triggered by a carcinogen like air pollution. Even small changes in air pollution levels can affect human health. Ninety-nine per cent of the world’s population lives in areas which exceed annual WHO (World Health Organization) limits for PM2.5, underlining the public health challenges posed by air pollution across the globe.”
The 2020 Lancet Planetary Health article on deaths caused by air pollution in India had claimed the majority of such deaths were caused from ambient particulate matter pollution (0.98 million) and household air pollution (0.61 million).
“The death rate due to household air pollution decreased by 64.2% from 1990 to 2019, while that due to ambient particulate matter pollution increased by 115.3% and that due to ambient ozone pollution increased by 139.2%,” the authors had written.
(Edited by Poulomi Banerjee)