Long-term air pollution exposure and mortality outcomes in colorectal cancer patients: Evidence from a multicenter...

Limited evidence exists regarding the relationship between air pollution and all-cause mortality in colorectal cancer stratified by clinical stages.

In this retrospective cohort study, initiated in 2010, we included patients with pathologically confirmed colorectal carcinoma. Each participant's address was geocoded to the corresponding village/borough or township, for accurate matching with estimated air pollution concentrations. The risk of all-cause mortality was assessed using Kaplan-Meier analysis and Cox proportional hazards regression models.

Our study enrolled 5126 colorectal cancer patients, with a median survival time of 72.0 months. Higher exposures were associated with greater all-cause mortality: PM_2.5₅ tertile 3 vs tertile 1-HR 1.32 (95 % CI 1.14-1.52) and SO₂ tertile 3 vs tertile 1-HR 1.22 (95 % CI 1.06-1.40). Stage-stratified results showed PM_2.5 remained significant in stages 0-I (HR 1.62, 95 % CI 1.01-2.58) and III (HR 1.39, 95 % CI 1.11-1.73), whereas SO₂ was significant in stages II (HR 1.62, 95 % CI 1.03-2.53) and III (HR 1.34, 95 % CI 1.07-1.67). In multiplicative interactions, each unit increase in PM_2.5 was linked to a 1 % higher hazard (HR = 1.01; 95 % CI, 1.01-1.02), and each unit increase in SO₂ to a 5 % higher hazard (HR = 1.05; 95 % CI, 1.04-1.05). When stage was included additively, the per-unit effects were larger-7 % for PM_2.5 (HR = 1.07; 95 % CI, 1.05-1.10) and 14 % for SO₂ (HR = 1.14; 95 % CI, 1.11-1.17). Overall, pollutant levels and clinical stage jointly heightened all-cause mortality.

Elevated PM_2.5 and SO₂ exposures were significantly associated with higher all-cause mortality, with effect sizes varying by stage and generally stronger in stages 0-I and II-III. Clinical stage interacted both associations, and joint exposure-stage categories showed higher risks, underscoring the need to reduce pollution exposure in high-risk patients.