There is a growing body of evidence to show that air pollution is a major risk factor for lung cancer among never-smokers, although there is less certainty about the duration of exposure to fine particulate matter in ambient air as it relates to risk for lung cancer.
But as Canadian researchers now report, even 20 years of data on cumulative exposure to air pollution may underestimate the magnitude of the effect, especially among people diagnosed with lung cancer who have migrated from regions where heavy air pollution is the norm.
In a study of Canadian women with newly diagnosed lung cancer who never smoked, Renelle Myers, MD, FRCPC, from the University of British Columbia in Vancouver and colleagues found that shorter-term assessment of cumulative exposure to ambient air particles smaller than 2.5 microns (PM2.5) may underestimate the health effects of chronic exposure to pollution, especially among those patients who had migrated to Canada after living in areas of high PM2.5 exposure for long periods of time.
“Our study points to the importance of incorporating this long-term cumulative exposure to air pollutants in the assessment of individual lung cancer risk, of course in combination with traditional risk factors, and depending on the country of residence, I think that even a 20-year cumulative exposure may underestimate the effects of PM2.5, as we’re not capturing childhood or adolescent exposure when the lung is developing, and what effect that will have,” she said in an oral abstract presented at the World Conference on Lung Cancer.
Satellite data on local pollution
With the objective of comparing cumulative 3-year vs. 20-year exposure to PM2.5 in women who had never smoked and had a new diagnosis of lung cancer, Dr. Myers and colleagues conducted a cross-sectional study.
They recruited a total of 236 women and had them fill out a detailed residential history questionnaire, and demographic details including age, race, country of birth, arrival in Canada for those born out of the country, occupations, family history of lung cancer, and exposure to second-hand smoke.
The investigators linked local addresses or postal to satellite-derived data on local PM2.5 levels, which first became available in 1996.
The median age of participants was 66.1 years. Of the 236 participants, 190 (80.5%) were born outside of Canada, and came to the country at the median age of 45. About half of all participants came from mainland China or Hong Kong, and another one-third came from elsewhere in Asia.
Tumor histologies included adenocarcinomas in 219 patients, squamous cell carcinoma in 1, and other types in 16 patients. Slightly more than half of the patients (55.%) had stage III or IV disease at diagnosis. In all, 106 of 227 evaluable patients had EGFR mutations.
3 years not enough
Among the foreign-born patients, only 4 (2%) had 3-year cumulative PM2.5 exposure greater than 10 mcg/m3, but 38 (20%) had 20-year cumulative exposure greater than 10 mcg/m3 (P < .0001).
All of the patients had cumulative PM2.5 exposures greater than 5 mcg/m3.
Comparing patients with and without EGFR mutations, the investigators found that higher 3-year cumulative PM2.5 exposure was significantly associated with EGFR mutations compared with nonmutated cancers (P = .049), but there was no significant association with higher 20-year cumulative exposures.
“The significance of this study really captures that short term or at least less than 3-year cumulative exposure risk for PM2.5 will probably underestimate the adverse effects that chronic exposure to air pollution has, especially among patients who lived elsewhere that may have had higher exposure throughout their lifetime than where you actually meet them,” Dr. Myers said in a media briefing held prior to her presentation.