Background: Although pneumonia has been suggested as a risk factor for lung cancer, previous studies have not evaluated the influence of number of pneumonia diagnoses in relation to lung cancer risk.
Methods: The Environment And Genetics in Lung cancer Etiology (EAGLE) population-based study of 2,100 cases and 2,120 controls collected information on pneumonia more than 1 year before enrollment from 1,890 cases and 2,078 controls.
Results: After adjusting for study design variables, smoking, and chronic bronchitis, pneumonia was associated with decreased risk of lung cancer [odds ratio (OR), 0.79; 95% confidence interval (CI), 0.64-0.97], especially among individuals with three or more diagnoses versus none (OR, 0.35; 95% CI, 0.16-0.75). Adjustment for chronic bronchitis contributed to this inverse association. In comparison, pulmonary tuberculosis was not associated with lung cancer (OR, 0.96; 95% CI, 0.62-1.48).
Conclusions: The apparent protective effect of pneumonia among individuals with multiple pneumonia diagnoses may reflect an underlying difference in immune response and requires further investigation and confirmation. Therefore, careful evaluation of the number of pneumonia episodes may shed light on lung cancer etiology.