Air Pollution and the Risk of Liver Cancer Incidence and Mortality: A Systematic Review and Meta-Analysis.

BACKGROUND AND AIM: Liver cancer (LC) is a leading cause of global cancer mortality, with established risk factors including viral hepatitis, alcohol use and metabolic disorders. Emerging evidence suggests air pollution may contribute to hepatocarcinogenesis, but a comprehensive synthesis of this association is lacking. This systematic review and meta-analysis evaluates the relationship between long-term air pollution exposure and LC incidence and mortality.

METHODS

Following PRISMA guidelines, we searched PubMed/MEDLINE, Embase, Web of Science and Scopus through July 2025. Observational studies reporting adjusted effect estimates (HR/RR/OR) for LC outcomes associated with PM2.5, PM10, NO2 or other pollutants were included. Random-effects meta-analyses assessed pollutant-specific risks per standardised increments (1 μg/m3 for PM2.5; 10 μg/m3 for NO2, etc.). Heterogeneity (I2) assessment, subgroup (geography, study design) and sensitivity analyses were performed. The protocol for this study was registered on PROSPERO (CRD420251082568).

RESULTS

Among 23 included studies (11 incidence, 12 mortality), PM2.5 exposure (per 1 μg/m3) was significantly associated with increased LC incidence (HR = 1.020, 95% CI: 1.01-1.03) and mortality (HR = 1.02, 95% CI: 1.01-1.04). NO2 (per 10 μg/m3) showed stronger incidence risks (HR = 1.16, 95% CI: 1.04-1.28) but non-significant mortality associations (HR = 1.06, 95% CI: 0.91-1.22). Subgroup analyses revealed higher PM2.5-associated risks in studies with prospective design and those with higher median follow-up.

CONCLUSIONS

Long-term exposure to PM2.5 and NO2 is associated with elevated LC risk, independent of traditional etiologies. These findings underscore air pollution as an environmental carcinogen for LC and advocate for stricter air quality controls. Regional variations highlight the need for targeted interventions.