Environmental risk factors for lung cancer in Iran: a case–control study

Background Lung cancer remains the leading cause of cancer death in the world. In Iran, lung cancer is one of the five leading tumours and its incidence has been increasing steadily in both men and women. There is a paucity of data from Iran on risk factors for lung cancer. We evaluated environmental risk factors for lung cancer in a case–control study in five hospitals of Tehran. Methods Between October 2002 and October 2005, 242 (178 male, 64 female) patients with histologically confirmed lung cancer and two controls for each patient (242 hospital controls and 242 visiting healthy controls) matched for age, sex and place of residence were interviewed using a structured questionnaire on potential risk factors for lung cancer, including environmental and occupational exposures. Associations between risk factors and lung cancer were assessed using conditional logistic regression. Results Smokers were 66.5% of all cases (85.4% of men and 14.1% of women) and smoking was the strongest correlate of lung cancer in multivariate analysis [odds ratio (OR) 5.4, 95% confidence interval (CI) 3.2–8.9]. Occupational exposures to inorganic dusts (OR 4.2, 95% CI 2.8–6.7), chemical compounds (OR = 3.4, 95% CI 2.1–5.6) and heavy metals (OR 3.0, 95% CI 1.3–7.0) were also independent risk factors for lung cancer. Conclusions In our study, smoking was the principal risk factor for lung cancer. However, preventable exposures in the environment, including occupational settings, should not be ignored.