Air pollution and incident bladder cancer: A risk assessment

I have read with interest the article entitled “Ambient air pollution and incident bladder cancer risk: Updated analysis of the Spanish Bladder Cancer Study” by Turner et al.1 that evaluated the association between ambient particulate matter within a diameter of 2.5 (PM2.5), nitrogen dioxide (NO2) and bladder cancer incidence. Although there were no significant associations of ambient PM2.5 and NO2 concentrations with incident bladder cancer, some cautions should be paid to the methodology of their research. First, the authors adopted single pollutant and two pollutant models by using estimation data from residential areas and a dependent variable was personal information on incident bladder cancer. As there is a variation of ambient PM2.5 and NO2 within the same study area, individual exposure levels of ambient PM2.5 and NO2 should be used instead of estimated values, although there are difficulties of measuring individual data. Second, the authors adopted unconditional logistic regression models for the analysis. I suppose that case–control matching data were canceled and conservative results would be derived by their statistical procedure.2 Although there are some stronger factors than air pollutions for incident bladder cancer, conditional logistic regression models can be applied to case–control matching data. Finally, the authors cited a meta-analysis of cohort studies, presenting no significant association between air pollution and incident bladder cancer. The air pollution data were gathered by the same method, and I speculate that personal lifestyle factors would greatly contribute to the risk of bladder cancer.3, 4 Yours sincerely Tomoyuki Kawada