Association between previous lung diseases and lung cancer risk: a systematic review and meta-analysis.

Previous lung diseases (PLD) are known risk factors for lung cancer. However, it remains unclear how the association varies by lung cancer subtype and socio-demographic characteristics. We conducted a systematic literature search in three electronic databases from the inception of each database up until 13 January 2021. A total of 73 studies (18 cohort and 55 case-control studies) consisting of 97,322 cases and 7,761,702 controls were included. Heterogeneity was assessed using the I 2 statistic. Based on the heterogeneity, either the fixed-effects or random-effects model was used to estimate the pooled summary estimate (PSE) and 95% confidence interval (CI) for the association between PLD and lung cancer risk. A history of asthma, chronic bronchitis, emphysema, pneumonia, tuberculosis, and COPD was associated with higher lung cancer risk, with a history of COPD and emphysema having at least two-fold relative risk. A history of hay fever was associated with lower lung cancer risk (PSE= 0.66, 95% CI= 0.54-0.81), even among ever-smokers (PSE= 0.55, 95% CI= 0.41-0.73). Older individuals with a history of asthma, chronic bronchitis, emphysema, COPD, or tuberculosis were associated with higher lung cancer risk. Individuals with a diagnosis of asthma, emphysema, or pneumonia within 1 to 10 years prior to lung cancer diagnosis were associated with higher lung cancer risk. Among ever-smokers, a history of COPD or emphysema have at least two-fold relative risk of lung cancer. PLD was associated with higher risk of lung cancer. Individuals with PLD should be closely monitored and prioritised for lung cancer screening.