Jason D. Wright

Objective To investigate associations between air particulate matter of ≤2.5 μm in diameter (PM 2.5 ) and ovarian cancer. Design County‐level ecological study. Setting Surveillance, epidemiology, and end results from a collection of state‐level cancer registries across 744 counties. Data from the Environmental Protection Agency's network for PM 2.5 monitoring was used to calculate trailing 5‐ and 10‐year PM 2.5 county‐level values. County‐level data on demographic characteristics were obtained from the American Community Survey. Population A total of 98 751 patients with histologically confirmed ovarian cancer as a primary malignancy from 2000 to 2016. Methods Generalised linear regression models were developed to estimate the association between PM 2.5 and PM 10 levels, over 5‐ and 10‐year periods of exposure, and ovarian cancer risk, after accounting for county‐level covariates. Main outcome measures Risk ratios for associations between ovarian cancer (both overall and specifically epithelial ovarian cancer) and PM 2.5 levels. Results For the 744 counties included, the average PM 2.5 level from 1990 through 2018 was 11.75 μg/m 3 (SD = 3.7) and the average PM 10 level was 22.7 μg/m 3 (SD = 5.7). After adjusting for county‐level covariates, the overall annualised ovarian cancer incidence was significantly associated with increases in 5‐year PM 2.5 (RR = 1.11 per 10 units (μg/m 3 ) increase, 95% CI 1.06–1.16). Similarly, when the analysis was limited to epithelial cell tumours and adjusted for county‐level covariates there was a significant association with trailing 5‐year PM 2.5 exposure models (RR = 1.12 per 10 units increase, 95% CI 1.08–1.17). Likewise, 10‐year PM 2.5 exposure was associated with ovarian cancer overall and with epithelial ovarian cancer. Conclusions Higher county‐level ambient PM 2.5 levels are associated with 5‐ and 10‐year incidences of ovarian cancer, as measurable in an ecological study.