Abstract Background Lung cancer is commonly associated with older age and exposure to tobacco; recent evidence shows a small but significant increase among young adults (less than 54 years of age) who have never smoked. Recent case reports and epidemiological studies have highlighted changing patterns in histology, molecular biology, and environmental risk factors. Objective To summarise current evidence on the prevalence, clinical features and potential risk factors of lung cancer in young non-smokers (54 years old). Methods We accessed databases including PubMed, MedLine, Embase, Cochrane, ProQuest and Prospero. We included English language studies and excluded studies which involved active and passive smoking. We looked at case reports, case series, single-centre reviews and epidemiological studies. Results Twenty-one studies were identified that specifically looked at lung cancer in young non-smokers. Global data indicate that cases in individuals aged ≤ 54 years have increased by more than 50% since 1990, despite a decline in age-adjusted rates. Adenocarcinoma is the commonest histological pattern, often caused by molecular changes such as EGFR, ROS1, or ALK mutations. Environmental exposures, including cooking oil fumes, radon exposure and air pollution, are particularly prevalent among women, especially in low- to middle-income regions. Studies highlight histological subtypes like small cell, sarcomatoid, basaloid squamous, and micropapillary adenocarcinoma in young adults without tobacco exposure. Population data from Iran indicates that roughly one-third of lung cancer cases occur in non-smokers, with onset reported as early as the mid-20s. In active lifestyle cohorts, like long-distance skiers, there was a reduced overall incidence but not complete protection, emphasising that lung cancer can still occur in non-smoking, healthy individuals. Conclusion Lung cancer in young non-smokers is rare but is increasing. It is characteristically seen with a histological pattern of adenocarcinoma and oncogenic driver mutations. It has strong associations with air pollution, radon exposure, and other environmental or genetic factors rather than smoking. Despite a low prevalence, case numbers are increasing, particularly among non-smoking younger women in Asia and the Middle East. Implications Clinicians should be vigilant and consider lung cancer even in younger non-smokers presenting with persistent respiratory symptoms or atypical imaging findings. Public health strategies should address modifiable non-tobacco exposures such as indoor air pollution and cooking fumes and environmental risk factors. Routine molecular profiling and region-specific surveillance are needed to improve early detection and refine treatment for this emerging subgroup. This abstract is funded by: None
Aravind et al. (Fri,) studied this question.