Lung cancer among patients with secondhand smoke exposure: A systematic review.
Authors: Qasim Hana , Sardesai Krish , Alghizzawi Mohd , Ponvilawan Ben , Bunte B.S Kailee , Gorjala Vedvignesh , Phatak Simrin , Daggumati Lasya , Ali Ayra , Miran Muhammad Shah 
Published: June 2024

e22506 Background: Smoking tobacco is recognized as the leading cause of lung cancer. However, it is imperative to note that 10–15% of lung cancer patients have no history of smoking, and that lung cancer remains the leading cause of cancer deaths among non-smokers. Since passive smokers are exposed to many carcinogenic compounds in the exhaled smoke, it is naturally plausible that secondhand smoking (SHS) is a risk factor for lung cancer. However, current USPSTF screening guidelines for lung cancer with low dose CT (LDCT) do not include patients exposed to SHS. We performed a systematic review to highlight SHS as an etiology of lung cancer and insights for inclusion in cancer screening criteria. Methods: We utilized the PubMed, Medline, Science Direct, and ClinicalTrials.gov databases to search for relevant literature using keywords ('low Dose CT,' 'secondhand smoke,' 'lung cancer'). The search strategy was designed to ensure a comprehensive retrieval of pertinent literature, minimizing the possibility of omitting articles due to insignificant spelling and/or semantic variations. Eligible studies had to be published between 2010 and 2023 and focused on examining the effect of SHS in populations at risk of lung cancer or those undergoing lung cancer screening. Articles not available in English were excluded from this systematic review. In total, 239 relevant articles were retrieved from all databases, narrowing down to 14 articles after the initial screening and further reducing to 4 articles after the second round of screening. Results: Three of the four articles included in our systemic review were conducted in Asia. A study by He et al. showed a substantial increase in the relative risk of lung cancer among SHS (RR 2.00; 95% CI, 0.62-6.40), with significant dose-response relationships between cumulative SHS exposure at home and work and the increased risk of cause-specific and total mortality. Another observational study on the use of LDCT in Japan has interestingly shown a shifting landscape of lung cancer demographics, with 49.6% of patients identified as never-smokers and 70.0% of the never-smoker lung cancer patients having SHS exposure. Secondhand smoking has also been reported to increase the risk of pulmonary nodules (HR 1.17; 95% CI, 1.01-1.35) and pulmonary emphysema (OR 13.6; 95% CI, 1.70-106.1) in those with moderate-to-high SHS exposure, which was the population where lung cancer was more prevalent. Conclusions: Our findings suggest a critical gap in current healthcare recommendations, specifically addressing the absence of guidelines for LDCT screening in individuals with moderate-to-high SHS exposure despite established evidence linking SHS to a significant increase in the risk of lung cancer development. More studies are needed to formulate evidence-based guidelines for lung cancer screening and detection in this population, given the expected mortality reduction benefit.