Pre-diagnosis and post-treatment exposures to PM, PM, and PM and breast cancer survival: A cohort study.

Ambient PM exposure is associated with poorer breast cancer survival, yet prior work rarely distinguished exposure timing or assessed multiple PM fractions. This study examined PM, PM, and PM in relation to cancer-specific survival in Liaoning, China, using Mostofsky's residual models to isolate independent associations with breast cancer survival. We conducted a retrospective cohort study of 3975 breast cancer patients (2015-2020) in Liaoning, China. Pre- and post-diagnosis exposures to PM, PM, and PM were estimated from high-resolution CHAP datasets. Pre-diagnosis exposure was defined as the average PM concentration during the 5 years preceding breast cancer diagnosis, whereas post-diagnosis exposure was treated as a time-varying exposure during follow-up. Time-stratified Cox proportional hazards models, adjusted for age, stage, estrogen/progesterone receptor status, NDVI, artificial light at night, and other covariates, assessed risks via Mostofsky's residual and remaining mass models. Subgroup, exploratory, and sensitivity analyses evaluated robustness. Post-treatment exposures were associated with poorer survival, with fully adjusted hazard ratios (HRs) per 1 μg/m increase of 1.459 (95% CI: 1.376-1.546) for PM, 1.215 (1.180-1.252) for PM, and 1.144 (1.120-1.169) for PM. Pre-diagnosis exposures showed limited associations, with only modest for PM (1.038; 1.008-1.069). Independent associations via Mostofsky's residual models confirmed finer fractions' roles: PM adjusted for PM (HR: 1.132; 1.049-1.223), PM adjusted for PM (HR: 1.100; 1.018-1.187). Subgroups showed stronger associations in older patients (≥65 years) and early-stage disease (I/II). Exploratory analyses revealed escalating HRs over time and key PM constituents: sulfate, nitrate, and ammonium in remaining mass models. Findings were robust across alternative buffers, exposure cutoffs, and stratification. In conclusion, post-treatment PM exposures, especially finer fractions, independently predict poorer breast cancer survival, emphasizing the necessity for air quality interventions to enhance outcomes in polluted regions.