Secondhand smoke and lung cancer risk in never-smoking women: A cohort and meta-analysis study.

[BACKGROUND] Most existing evidence on secondhand smoke (SHS) exposure and lung cancer in never-smoking women comes from case-control studies, while findings from prospective cohort studies remain inconsistent. Regional variation in SHS-associated risk is poorly understood, and the potential impact of reducing SHS exposure in never-smoking women has not been quantified.

[METHODS] We analyzed data from 20,401 never-smoking women in the Wenling lung cancer screening cohort (Zhejiang, China), applying Cox proportional hazards regression models to evaluate the association between SHS exposure and lung cancer risk. We further conducted a meta-analysis of published studies to examine regional variation and estimated the population attributable fraction (PAF) of SHS exposure for lung cancer incidence in never-smoking women.

[RESULTS] SHS exposure was associated with an increased lung cancer risk (HR=1.52, 95% CI: 1.19-1.95). Lung cancer risk tended to increase with higher smoking intensity, with a linear trend observed for cigarettes per day, years of smoking, and pack-years of co-residents and colleagues (P<0.05; P>0.05). In meta-analysis, the pooled relative risk was higher in Asia than in Europe and America [RR= 1.31 (95% CI: 1.20-1.43) vs 1.13 (95% CI: 1.04-1.23); P = 0.039]. The PAF suggested that 16.9% (95% CI: 11.6%-22.0%) of lung cancer cases among never-smoking women could be attributed to SHS exposure.

[CONCLUSIONS] SHS exposure is a risk factor for lung cancer in never-smoking women, with stronger effects observed in Asian populations. Reducing SHS exposure could prevent a substantial proportion of lung cancer cases, underscoring the urgent need for strengthened tobacco control policies.