Particulate matter air pollution and liver cancer survival

Particulate matter (PM) air pollution exposure has been associated with cancer incidence and mortality especially with lung cancer. The liver is another organ possibly affected by PM due to its role in detoxifying xenobiotics absorbed from PM. Various studies have investigated the mechanistic pathways between inhaled pollutants and liver damage, cancer incidence, and tumor progression. However, little is known about the effects of PM on liver cancer survival. Twenty thousand, two hundred and twenty-one California Cancer Registry patients with hepatocellular carcinoma (HCC) diagnosed between 2000 and 2009 were used to examine the effect of exposure to ambient PM with diameter <2.5 microm (PM_2.5 ) on HCC survival. Cox proportional hazards models were used to estimate hazard ratios (HRs) relating PM_2.5 to all-cause and liver cancer-specific mortality linearly and nonlinearly-overall and stratified by stage at diagnosis (local, regional and distant)-adjusting for potential individual and geospatial confounders.PM_2.5 exposure after diagnosis was statistically significantly associated with HCC survival. After adjustment for potential confounders, the all-cause mortality HR associated with a 1 standard deviation (5.0 µg/m³ ) increase in PM_2.5 was 1.18 (95% CI: 1.16-1.20); 1.31 (95% CI:1.26-1.35) for local stage, 1.19 (95% CI:1.14-1.23) for regional stage, and 1.05 (95% CI:1.01-1.10) for distant stage. These associations were nonlinear, with substantially larger HRs at higher exposures. The associations between liver cancer-specific mortality and PM_2.5 were slightly attenuated compared to all-cause mortality, but with the same patterns.Exposure to elevated PM_2.5 after the diagnosis of HCC may shorten survival, with larger effects at higher concentrations.