Ambient ultrafine particulate matter (UFP) exposure has a modest association with lung cancer and may increase the risk for adenocarcinoma of the lung, according to a study in the American Journal of Respiratory and Critical Care Medicine.
The Los Angeles Ultrafines Study evaluated the relationship between long-term outdoor UFP exposure and lung cancer risk in individuals residing in Southern California in 1995 to 1996.
During a median of 22 years of follow-up, 1770 primary lung cancer cases were newly diagnosed. The patients were followed from enrollment until lung cancer diagnosis, relocation from the registry areas, death, or December 31, 2017.
The investigators measured outdoor UFP in the region in 2016 and developed land use regression models to predict average levels at residential addresses. In the current analysis, they back-extrapolated UFP exposures annually to 1980 with use of PM2.5 (1980-2016) and NO2 (1990-2016) residential-level estimates from validated spatiotemporal models.
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Conducted among older adults residing in one of the most heavily polluted areas of the US historically, this study represents the first evaluation of estimated long-term outdoor UFP exposure and lung cancer risk by histologic subtype.
Continuous UFP exposure was associated with an overall increased risk for lung cancer (hazard ratio [HR], 1.03; 95% CI, 0.99-1.08 per 10,000 particles/cm3). An increased risk was observed in the 3rd exposure quartile (HRQ3vsQ1 =1.15; 95% CI, 1.01-1.31), particularly in men (HRQ3vsQ1 =1.18; 95% CI, 0.99-1.40).
The risk for adenocarcinoma had a similar increase in Q3 (HRQ3vsQ1 =1.29; 95% CI, 1.07-1.56) with no monotonic trend among the quartiles. A marginally increased risk was found in men for adenocarcinoma (HR, 1.09; 95% CI, 1.00-1.18 per 10,000 particles/cm3), although it was not observed in women (HR, 0.93; 95% CI, 0.82-1.05; P-interaction =.03). The risk of adenocarcinoma in men also increased across UFP exposure quartiles (P-trend =.01), and categorical analyses in women were null.
In analysis of independent exposures in models co-adjusted for UFP, an association was found between continuous PM2.5 and lung cancer in men (HR, 1.35; 95% CI, 1.06-1.73 per 10 µg/m3) but not in women (HR, 0.88; 95% CI, 0.68-1.15; P-interaction =.01). Increased risks for the small cell carcinoma subtype were observed in men (HR, 2.51; 95% CI, 1.12-5.61) and not women (HR, 0.99; 95% CI, 0.37-2.62; respectively; P-interaction =.04).
The strongest associations with UFP according to smoking status occurred in men who never smoked, for lung cancer overall and for adenocarcinoma subtype. In those who formerly smoked, the risk for adenocarcinoma was increased in men but not women, and the association was weakest for those who currently smoked.
For men in the oldest birth cohort (aged ≥65 years at enrollment), an increased risk for lung cancer associated with UFP was suggested (HR, 1.06; 95% CI, 0.97-1.16 per 10,000 particles/cm3) but not in other birth cohorts (P-interaction =.72). The risk was increased for adenocarcinomas only in this group of older men (HR, 1.13; 95% CI, 1.02-1.26; P-interaction =.38). No lung cancer associations, overall or by subtype, were found in women across birth cohorts (P-interaction >.6).
Limitations include exposure misclassification, lack of available information on potential confounders such as occupation or environmental tobacco smoke, suboptimal power in some stratified analyses, and lack of residence history information for all participants.
“Conducted among older adults residing in one of the most heavily polluted areas of the US historically, this study represents the first evaluation of estimated long-term outdoor UFP exposure and lung cancer risk by histologic subtype,” the study authors noted. “UFP exposure was modestly associated with lung cancer overall, with stronger associations observed for adenocarcinoma of the lung,” the researchers concluded.
