Residential greenspace exposure and prognosis of nasopharyngeal carcinoma in a large cohort: the role of PM2.5

Environmental exposures may influence cancer prognosis. While fine particulate matter (PM 2.5 ) is a recognized risk factor for nasopharyngeal carcinoma (NPC), the role of residential greenspace and its interplay with PM 2.5 remains unclear. Based on a hospital-based cohort at Sun Yat-sen University Cancer Center, we included 7780 NPC patients. Residential greenspace was assessed using the normalized difference vegetation index (NDVI). Cox and multi-state models evaluated associations of NDVI and PM 2.5 with NPC-specific death, recurrence, metastasis across five exposure windows. Four-way decomposition and stratified analyses explored the role of PM 2.5 in the NDVI-NPC prognosis relationship. Higher NDVI was associated with reduced risks of recurrence and metastasis (12-month HRs=0.92, 95% CI: 0.89–0.96 and 0.92, 95% CI: 0.87–0.97), but not NPC-specific death. In contrast, PM 2.5 exposure was consistently associated with increased risks of all NPC outcomes (12-month HRs=1.49(1.33–1.66) for death; 1.95(1.82–2.08) for recurrence; 2.13(1.94–2.33) for metastasis). Multi-state models indicated that PM 2.5 was associated with transitions from diagnosis to progression (HR = 1.33, 95% CI: 1.25–1.43) and from progression to death (HR = 1.34, 95% CI: 1.17–1.52) at 12 months. Four-way decomposition analyses further indicated that PM 2.5 partially mediated the association between NDVI and disease progression for metastasis across the 3, 6, 12, and 36-month windows and for recurrence at the 12 and 36-month windows. Stratified analyses revealed that the inverse associations were evident under lower PM 2.5 exposure but attenuated in higher pollution. Residential greenspace was inversely associated with NPC progression, whereas PM 2.5 exposure worsened prognosis. PM 2.5 may act as both a mediator and effect modifier in the relationship between greenspace and NPC outcomes.