Exposure to second-hand smoke and breast cancer risk in non-smoking women: a comprehensive systematic review and meta-analysis.

Through the use of an innovative method to identify original publications, we conducted a meta-analysis of all epidemiological studies evaluating the association between second-hand smoke (SHS) exposure and breast cancer risk among female non-smokers published in English up to October 2022. Pooled relative risks (RR) were obtained through the use of random-effects models. Dose-response relationships were derived using log-linear functions. Out of 73 identified eligible studies, 63 original articles were included in the meta-analysis. The pooled RR for breast cancer for overall exposure to SHS was 1.24 (95% confidence interval, CI, 1.15-1.34, number of articles, n = 52). Regarding the setting of exposure, RRs were 1.17 (95% CI 1.08-1.27, n = 37) for SHS exposure at home, 1.03 (95% CI 0.98-1.08, n = 15) at the workplace, 1.24 (95% CI 1.11-1.37, n = 16) at home or workplace, and 1.45 (95% CI 1.16-1.80, n = 13) for non-specified settings. The risk of breast cancer increased linearly with higher duration (RR 1.29; 95% CI 1.04-1.59 for 40 years of SHS exposure, n = 12), intensity (RR 1.38; 95% CI 1.14-1.67 for 20 cigarettes of SHS exposure per day, n = 6), and pack-years (RR 1.50; 95% CI 0.92-2.45 for 40 SHS pack-years, n = 6) of SHS exposure. This meta-analysis shows a statistically significant excess risk of breast cancer in women exposed to SHS.

Second-hand smoke exposure and cervical cancer: a systematic review and meta-analysis.

PURPOSE: The association between second-hand smoke (SHS) exposure and cervical cancer (CC) risk is still unclear. The aim of this study is to provide an accurate and updated estimate of this association. METHODS: Through an original methodology to identify original publications, we conducted a systematic review and meta-analysis of all epidemiological studies published up to October 2022 evaluating the association between SHS exposure and CC risk among female non-smokers. Meta-analytic estimates were obtained using random-effects models and dose-response relationships were derived using log-linear functions. RESULTS: Out of 25 eligible studies, 21 were included in the meta-analysis, providing a pooled relative risk (RR) of cervical intraepithelial neoplasia (CIN) of grade 2 or higher of 1.52 (95% confidence interval, CI 1.30-1.78, 21 studies) for overall SHS exposure versus non-exposure. When restricting the analysis to invasive CC, the pooled RR was 1.42 (95% CI 1.17-1.71, 13 studies), whereas the pooled RR for CIN was 1.50 (95% CI 1.22-1.84, 6 studies). Analyzing RR by setting or source of SHS exposure resulted in significant associations with CC risk for SHS exposure at home (RR for CIN2+ 1.49, 95% CI 1.21-1.84, 14 studies), in non-specified settings (RR for CIN2+ 1.64, 95% CI 1.20-2.23, 8 studies) and from partner (RR for CIN2+ 1.55, 95% CI 1.25-1.94, 10 studies). The risk of CIN2+ significantly increased linearly with the intensity and pack-years of SHS exposure. CONCLUSION: This comprehensive review and meta-analysis confirmed the association of SHS exposure with CC, further suggesting the need to raise concern about SHS exposure in the population.