title: A meta-analysis of asthma and risk of lung cancer (United States).
abstract: OBJECTIVE
  To review epidemiologic evidence that asthma is a risk factor for lung cancer, with particular attention to the role of smoking on this association.
  
  
  METHODS
  Through MEDLINE computer searches (January 1966 to April 2002) and a review of references, we identified studies with quantitative data on the relation of asthma to lung cancer. Summary estimates of relative risks (RR) were calculated using the fixed-effects model or the random-effects model as appropriate.
  
  
  RESULTS
  The combined results from five case-control studies--that presented data limited to individuals who had never smoked--showed a 1.8-fold increase in lung cancer risk among asthmatics (95% confidence interval (CI) = 1.3-2.3). The results from six case-control and four cohort studies, which controlled for smoking history also were significant (RR = 1.7; 95% CI = 1.3-2.2). Finally, to illustrate the potential confounding by tobacco, we combined data from seven cohort studies that did not control for smoking history and found an overall RR of 1.4 (95% CI = 1.2-1.6).
  
  
  CONCLUSIONS
  The increased risk of lung cancer among never smoking individuals with asthma supports a direct relation between asthma and lung cancer. There is biological evidence to support this association.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA.
authors.forename: Alfredo A
authors.initials: AA
authors.lastname: Santillan
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Camargo
authors.forename: Graham A
authors.initials: GA
authors.lastname: Colditz
mesh_terms: D001249:Asthma / Q000150:complications* / Q000453:epidemiology; D016022:Case-Control Studies; D006801:Humans; D008175:Lung Neoplasms / Q000453:epidemiology / Q000209:etiology* / Q000473:pathology; D018570:Risk Assessment; D012907:Smoking / Q000009:adverse effects; D014481:United States / Q000453:epidemiology