Ambient air pollution and urological cancer risk: A systematic review and meta-analysis of epidemiological evidence

Abstract

Exposure to ambient air pollution has significant adverse health effects; however, whether air pollution is associated with urological cancer is largely unknown. We conduct a systematic review and meta-analysis with epidemiological studies, showing that a 5 μg/m³ increase in PM_2.5 exposure is associated with a 6%, 7%, and 9%, increased risk of overall urological, bladder, and kidney cancer, respectively; and a 10 μg/m³ increase in NO₂ is linked to a 3%, 4%, and 4% higher risk of overall urological, bladder, and prostate cancer, respectively. Were these associations to reflect causal relationships, lowering PM_2.5 levels to 5.8 μg/m³ could reduce the age-standardized rate of urological cancer by 1.5 ~ 27/100,000 across the 15 countries with the highest PM_2.5 level from the top 30 countries with the highest urological cancer burden. Implementing global health policies that can improve air quality could potentially reduce the risk of urologic cancer and alleviate its burden.

Fig. 1. PRISMA flow diagram.

Flow diagram summarises the search strategy and number of studies excluded at each stage. Abbreviations: CINAHL, Cumulative Index to Nursing and Applied Health Literature; CNKI, China National Knowledge Infrastructure.

Fig. 2. Forest plot of studies reporting PM_2.5 exposure and urological cancer risk.

Meta-analysis of evidence on the association between a 5 μg/m³ increase in PM_2.5 and risk of individual urological cancers using random effects meta-analysis. The square represents the relative risk and the bar represents the 95% confidence interval (CI) from each study (n = 41 association estimates which are independent for each cancer type). All statistical tests are two-sided.

Fig. 3. Forest plot of studies reporting NO₂ exposure and urological cancer risk.

Meta-analysis of evidence on the association between a 10 μg/m³ increase in NO₂ and risk of individual urological cancers using random effects meta-analysis. The square represents the relative risk and the bar represents the 95% confidence interval (CI) from each study (n = 28 association estimates which are independent for each cancer type). All statistical tests are two-sided.

Fig. 4. Funnel plots to assess publication bias.

Publication bias in the pooled associations of (left) NO₂ and (right) PM_2.5 air pollution with overall urological cancer risk.

Fig. 5. Reduction in urological cancer burden from decreased PM_2.5 exposure globally.

Annual average PM_2.5 levels (X-axis) and estimated impact of a reduction in PM_2.5 to a target level (5.8 μg/m³, below which it is challenging to predict the harmful health effects of PM_2.5) on age-standard rate (ASR) of individual urological cancer (Y-axis) for top 15 countries with the highest PM_2.5 level from 30 countries with highest urological cancer burden. A. Reduction in ASR of prostate and testicular cancer; B. Reduction in ASR of kidney and bladder cancer.