Cluster Analysis Evaluating PM2.5, Occupation Risk and Mode of Transportation as Surrogates for Air-pollution and the Impact on Lung Cancer Diagnosis and 1-Year Mortality

OBJECTIVE: Epidemiological studies have reported the close relationship between risk for lung cancers and air pollution in particular, for non-smoking related lung cancers. However, most studies used residential address as proxies which may not estimate accurately an individual’s air pollution exposure. Therefore, the aim of this study was to identify risk factors such as occupation and mode of transportation associated with lung cancer diagnosis and death. METHODS: Subjects with lung cancer (n=514) were evaluated both by chart reviews for clinical data and interviews to determine residential address for ten years, main occupation and main mode of transportation. Annual particulate matter with diameter size less than 2.5 micrometre (PM2.5) concentration were calculated based on particulate matter with diameter size less than 10 micrometre (PM10) data recorded by Malaysian Department of Environment. Logistic regression analysis, cluster analysis and the Cox regression analysis were performed to the studied variables. RESULTS: This study concurred with previous studies that lung adenocarcinoma were diagnosed in predominantly younger, female non-smokers compared to the other types of lung cancers. Lung adenocarcinoma subjects had annual PM2.5 that was almost twice higher than squamous cell carcinoma, small cell carcinoma and other histological subtypes (p=0.024). Independent of smoking, the κ -means cluster analysis revealed two clusters in which the high risk cluster involves occupation risk with air pollution of more than four hours per day, main transportation involving motorcycle and trucks and mean annual PM2.5 concentration of more than 30 based on residential address for more than ten years. The increased risk for the high-risk cluster was more than five times for the diagnosis of lung adenocarcinoma (OR=5.69, 95% CI=3.14-7.21, p<0.001). The hazard ratio for the high-risk cluster was 3.89 (95% CI=2.12-4.56, p=0.02) for lung adenocarcinoma mortality at 1 year. CONCLUSION: High-risk cluster including PM2.5, occupation risk and mode of transportation as surrogates for air-pollution exposure was identified and highly associated with lung adenocarcinoma diagnosis and 1-year mortality.