Ambient air pollution and laryngeal cancer: A systematic review

Ambient air pollution is a major global health concern, yet its association with laryngeal cancer remains poorly defined. This systematic review aimed to evaluate the relationship between long-term exposure to outdoor air pollutants and incidence of laryngeal cancer. Comprehensive searches of MEDLINE, EMBASE, CENTRAL, and SCOPUS were conducted from inception to 01/06/2024. Eligible studies included observational and ecological designs reporting quantitative associations between ambient pollutants and laryngeal cancer incidence. Study quality, risk of bias, and evidence certainty graded were appraised using the NIH tool, National Toxicology Program framework and GRADE approach respectively. A total of nine studies (4 ecological, 5 cohort) comprising over 7.4 million participants were included. Each pollutant was analysed by a maximum of 3 studies. Nitrogen dioxide (NO₂) demonstrated the most consistent association with laryngeal cancer, with hazard ratios between 1.18 and 1.24 per 10 μg/m³ increase. One large cohort reported a significant relationship between particulate matter ≤ 2.5 μm (PM₂.₅) and laryngeal cancer (HR 1.85; 95 % CI: 1.2-2.85), while findings across other pollutants, including PM₁₀, SO₂, O₃, CO, and NOₓ, were inconsistent. Although data remain limited, emerging evidence suggests that chronic exposure to ambient NO₂ and PM₂.₅ may increase laryngeal cancer risk. Future large-scale prospective cohort studies with standardized exposure metrics and robust confounding control are needed to better characterise this relationship. Natural experiments in regions undergoing major air-quality policy changes can provide valuable evidence on the impact of reducing exposure on laryngeal cancer incidence at a population level.