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 I2 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 chronic obstructive pulmonary disease (COPD) was associated with higher lung cancer risk, with a history of COPD and emphysema having at least twofold relative risk. A history of hay fever was associated with lower lung cancer risk (PSE= 0.66, 95% CI= 0.54-0.81), particularly among ever-smokers (PSE= 0.55, 95% CI= 0.41-0.73). Individuals with a diagnosis of asthma, emphysema, or pneumonia within 1-10 years prior to lung cancer diagnosis were observed to have a higher lung cancer risk as compared to those who were diagnosed more than 10 years prior to lung cancer diagnosis. Ever-smokers with a history of COPD or emphysema were observed to have at least twofold relative risk of lung cancer compared to those without this history. Due to the observed association between PLD with higher risk of lung cancer, it is advisable that individuals with PLD should be closely monitored and prioritised for lung cancer screening.