Abstract
BACKGROUND: Although cigarette smoking is a major risk factor for lung cancer, the incidence rate of lung cancer among non-smokers is notable. The etiology and potential mechanism of non-smoker lung cancer are worthy of further research. This study was designed to explore the collective effects of environmental factors and the relationship between environmental exposure index (EEI) and lung cancer among non-smokers by evaluating the joint effects among lung disease history, environmental factors, and family history of lung cancer without smoking confounders. METHODS: A total of 767 never-smoked lung cancer cases and 767 sex- and age-matched controls were selected from the department of Thoracic Surgery and Respiratory Medicine of three hospitals in Fujian, China. We used two methods to develop the EEI according to 12 statistically significant environmental risk factors. Restricted cubic spline (RCS) was applied to analyze the non-linear relationship between EEI and lung cancer in non-smokers. Combined effects, additive interaction, and multiplicative interaction were assessed among lung disease history, EEI, and family history of lung cancer to estimate susceptibility to develop lung cancer. RESULTS: Lung disease history, especially asthma, was significantly associated with an increased risk of lung cancer with an odds ratio (OR) for asthma history of 14.720 (95% CI: 1.877-115.449). Family history of lung cancer was related to susceptibility of lung cancer (OR = 3.347, 95% CI: 1.930-5.806). According to type of relatives and cancer, a parental or children's history and a sibling's history of lung cancer were significantly associated with an increased risk of lung cancer. The positive association between EEI and lung cancer was apparently stronger in those with lung disease history or family lung cancer history. Furthermore, there was a addictive interaction between EEI and lung disease history, and a possibly addictive interaction between EEI and family lung cancer history on development of lung cancer. CONCLUSIONS: There were combined effects among lung disease history, environmental exposures, and family history of lung cancer toward susceptibility to lung cancer in Chinese non-smokers. Non-smokers who had a family history of lung cancer were at higher risk of lung cancer than non-smokers who had lung disease history. Non-smokers with family cancer history may obtain benefits from removal of environmental exposures and active treatment of lung disease.