New York, Aug 5: Air pollution may shorten survival chances in patients with lung cancer detected at an early stage of the disease, particularly adenocarcinoma, according to a study.

Adenocarcinoma is the most common type of non-small cell lung cancer, which accounts for 80 percent of lung cancer cases.

Air pollution has been linked to a higher incidence of lung cancer and death, but little is known about its potential impact on an individual’s chances of survival after diagnosis.

To clarify this, the researchers tracked the health outcomes of more than 3,52,000 people newly diagnosed with lung cancer with an average age of 69.

More than half (53 percent) of the cancers were diagnosed at an advanced stage (distant spread) and the average survival time for early stage disease was 3.6 years.

For patients with early stage disease, average survival time was shortest for those with small and large cell cancers (around 1.5 years) and longest for those with adenocarcinoma (around 5 years).

Participants’ average exposure to nitrogen dioxide (NO2), ozone (O3), particulate matter of less than 10 um (micrometre) and less than 2.5 um, in diameter (PM10 and PM2.5) was calculated using data from air quality monitoring stations, mapped to an area of residence.

Almost half of the study participants (45.4 percent) lived more than 1,500 metres away from a major interstate motorway while less than 10 percent lived within a 300-metre radius of one.

Their risk of death from any cause was then estimated, based on disease stage and tumour cell type.

“After taking account of these, and other potentially influential factors, the calculations showed that higher exposures to each of the four pollutants were associated with a correspondingly heightened risk of death and shorter average and five-year survivals,” said Jaime E. Hart, researcher at the Harvard Medical School in the study published in the journal Thorax.

But the magnitude of heightened risk was greatest for patients with early stage disease, among whom average survival was 2.4 years for those with high PM2.5 exposure (at least 16 ug/m3) and 5.7 years for those with low exposure (less than 10 ug/m3).

Overall, for patients with early stage disease, the risk of death from any cause was 30 per cent greater for NO2; 26 percent greater for PM10, and 38 percent greater for PM2.5. The impact of exposure to O3 was small (4 percent).

These trends were particularly evident among patients with early stage adenocarcinoma.

“This study provides compelling initial evidence that air pollution may be a potential target for future prevention and intervention studies to increase cancer survival,” she writes.