Associations between air pollutants and cancer incidence rates in Japan: An ecological study

We investigated the associations between the incidence rates of the five most common cancer types and five air pollutants in 317 Japanese municipalities in 2017. We obtained the concentrations of the five air pollutants, i.e., sulfur dioxide (SO₂), nitric oxide (NO), nitric dioxide (NO₂), photochemical oxidants (O_x), and fine particulate matter (PM_2.5) from Japan's National Institute for Environmental Studies and calculated the yearly mean of each. We identified patients of both genders with the five most common cancers in Japan's National Cancer Registry, which covers all of the cancer patients in the country. For the males, we included prostate, stomach, colon, lung, and liver cancers. For the females, we included breast, colon, lung, stomach, and uterine cancers. We calculated the Spearman rank correlation coefficients between 25 pairs of air-pollutant concentrations and the age-standardized incidence rate of the cancer types for each gender. We used a Poisson regression to examine the dose-response relationships. We identified 11 positive correlation coefficients at the Bonferroni-corrected alpha level for the five pollutants for the five cancers in both genders. We observed positive dose-response relationships between NO₂ and colon cancer and PM_2.5 and lung cancer for both genders. We also observed dose-response relationships between SO₂ and PM_2.5 and liver cancer for the males, and between NO and lung cancer and NO₂ and breast cancer for the females. As an example of a dose-response relationship, with the first quartile of PM_2.5 concentrations as the reference, the relative risks for lung cancer among the males were 1.01 (95%CI: 0.97–1.06) in the second quartile, 1.05 (95%CI: 1.00–1.10) in the third quartile, and 1.12 (95%CI: 1.07–1.17) in the fourth quartile. We did not observe significant associations with prostate, stomach, and uterine cancer. Our findings support the concept that exposure to air pollutants increases cancer incidence rates.