Atmospheric fine particulate matter and breast cancer mortality: a population-based cohort study

Atmospheric fine particulate matter (PM_2.5) has multiple adverse effects on human health. Global atmospheric levels of PM_2.5 increased by 0.55 μg/m³/year (2.1%/year) from 1998 through 2012. There is evidence of a causal relationship between atmospheric PM_2.5 and breast cancer (BC) incidence, but few studies have investigated BC mortality and atmospheric PM_2.5. We investigated BC mortality in relation to atmospheric PM_2.5 levels among patients living in Varese Province, northern Italy.

We selected female BC cases, archived in the local population-based cancer registry, diagnosed at age 50-69 years, between 2003 and 2009. The geographic coordinates of each woman's place of residence were identified, and individual PM_2.5 exposures were assessed from satellite data. Grade, stage, age at diagnosis, period of diagnosis and participation in BC screening were potential confounders. Kaplan-Meir and Nelson-Aalen methods were used to test for mortality differences in relation to PM_2.5 quartiles. Multivariable Cox proportional hazards modelling estimated HRs and 95% CIs of BC death in relation to PM_2.5 exposure.

Of 2021 BC cases, 325 died during follow-up to 31 December 2013, 246 for BC. Risk of BC death was significantly higher for all three upper quartiles of PM_2.5 exposure compared to the lowest, with HRs of death: 1.82 (95% CI 1.15 to 2.89), 1.73 (95% CI 1.12 to 2.67) and 1.72 (95% CI 1.08 to 2.75).

Our study indicates that the risk of BC mortality increases with PM_2.5 exposure. Although additional research is required to confirm these findings, they are further evidence that PM_2.5 exposure is harmful and indicate an urgent need to improve global air quality.