Lung cancer in "never smokers": the most frequent cause is second hand smoke!

‘Never-smoker’ generally refers to patients who have smoked less than the equivalent of 100 cigarettes in their lifetime.4 Lung cancers in never-smokers can be partly attributed to environmental pathogens; however, identifying the cause of cancer in individual patients is difficult due to the overlapping and ubiquitous nature of risk factors and exposures. Current estimates of the major contributors to lung cancers in never-smokers in the UK are: second-hand smoke (15%); occupational carcinogen exposure (20.5% men, 4.3% in women); outdoor pollution (8%); X-ray radiation (0.8%); and radon exposure (0.5%).4,5 Additionally, several risk factors potentiate the risk of lung cancer in smokers; for example, 2.9% of lung cancers are caused by radon exposure and smoking, in which case avoiding either exposure would have prevented cancer from occurring.9 A higher proportion of lung cancers in women occur among never-smokers, as compared to men, reflecting historically lower smoking prevalence and industrial exposures. Although hormonal factors have been an area of interest, data from the UK based Million Women Study do not support increased lung cancers in never-smokers risk with use of hormone replacement therapy.10 Globally, the use of solid fuels for indoor cooking and second-hand smoke exposure are important contributions to lung cancers in never-smokers and disproportionately affect women.4 There appears to be a higher incidence of lung cancers in never-smokers in  Asia with a younger age at presentation and distinct genotypes which can be targeted with specific therapies.11 A number of other risk factors have been suggested, including previous lung disease, dietary intake, alcohol intake, family history, hormonal factors, infectious diseases (including previous tuberculosis infection, human papillomavirus infection and pneumonia) and diabetes mellitus.5


Journal of the Royal Society of Medicine; 0(0) 1–3 DOI: 10.1177/0141076819843654