Ambient air pollution and incident bladder cancer risk: Updated analysis of the Spanish Bladder Cancer Study

Although outdoor air pollution and particulate matter in outdoor air have been consistently linked with increased lung cancer risk, the evidence for associations at other cancer sites is limited. Bladder cancer shares several risk factors with lung cancer and some positive associations of ambient air pollution and bladder cancer risk have been observed. This study examined associations of ambient air pollution and bladder cancer risk in the large-scale Spanish Bladder Cancer Study. Estimates of ambient fine particulate matter (PM_2.5 ) and nitrogen dioxide (NO₂ ) concentrations were assigned to the geocoded participant residence of 938 incident bladder cancer cases and 973 hospital controls based on European multicity land-use regression models. Adjusted odds ratios (ORs) and 95% confidence intervals (CI) for associations of ambient air pollution and bladder cancer risk were estimated using unconditional logistic regression models. Overall, there was no clear association between either ambient PM_2.5 (OR per 5.9 μg/m³  = 1.06, 95% CI 0.71-1.60) or NO₂ (OR per 14.2 μg/m³  = 0.97, 95% CI 0.84-1.13) concentrations and incident bladder cancer risk. There was no clear evidence for effect modification according to age group, sex, region, education, cigarette smoking status, or pack-years. Results were also similar among more residentially stable participants and in two-pollutant models. Overall, there was no clear evidence for associations of ambient PM_2.5 and NO₂ concentrations and incident bladder cancer risk. Further research in other large-scale population studies is needed with detailed information on measured or modeled estimates of ambient air pollution concentrations and individual level risk factors.